Self-penetration--a structural compromise between single networks and interpenetration: magnetic properties and crystal structures of

PubMed

Jensen; Price; Batten; Moubaraki; Murray

2000-09-01

The three-dimensional coordination polymers [Mn(dca)2(H2O)] (1) and [M(dca)(tcm)], M =Co (2), Ni (3), Cu (4), dca =dicyanamide, N(CN)2-, tcm = tricyanomethanide, C(CN)3-, have isomorphous structures. In 1 half the dca ligands coordinate directly (through all three nitrogen atoms) to three Mn atoms (all metal atoms are six-coordinate), while the other half coordinate to two Mn atoms (through the nitrile nitrogens) and hydrogen bond to water molecules coordinated to a third Mn atom (through the amide nitrogen). This dca. H2O structural moiety is disordered over a mirror plane, and is replaced by the structurally equivalent tcm ligand in compounds 2-4. The resulting structures display a new self-penetrating 3,6-connected (2:1) network topology that can be related to, but is different from, the rutile net. The self-penetrating [M(dca)(tcm)] network can be viewed as a structural compromise between the two interpenetrating rutile-like networks of [M(tcm)2] and the single rutile-like network of alpha-[M(dca)2]. The temperature and field dependence of the DC and AC magnetic susceptibilities and magnetisations has been measured for complexes 1-4. Compounds 1-3 exhibit long-range magnetic order with critical temperatures of 6.3 K for 1, 3.5 K for 2 and 8.0 K for 3. The Cu11 compound 4 does not order and is essentially a paramagnet. Hysteresis measurements of coercive field and remnant magnetisation show that 1, 2 and 3 are soft magnets, 1 being a canted-spin antiferromagnet (weak ferromagnet), while 2 and 3 are ferromagnets that display some unusual features in their high-field magnetisation isotherms in comparison to their related alpha-[M(dca)2] phases.

Structure and magnetism of a Mn(III)-Mn(II)-Mn(II)-Mn(III) chain complex.

PubMed

Uhrecký, Róbert; Moncoľ, Ján; Koman, Marian; Titiš, Ján; Boča, Roman

2013-07-14

A novel tetranuclear manganese(II/III) complex with anions of pyridine-2,6-dicarboxylic acid (dipicolinic acid) has been synthesised and magneto-structurally characterised. The crystal structure of [Mn(II)2Mn(III)2(dipic)6(H2O)4]·2CH3OH·4H2O has been determined by single-crystal X-ray diffraction. The tetranuclear complex molecule [Mn(II)2Mn(III)2(dipic)6(H2O)4] is centrosymmetric and two manganese(II) and two manganese(III) atoms are bridged by four dipicolinate ligands. The complex molecules and uncoordinated water and methanol molecules are connected through hydrogen bonds and they form a 3D supramolecular hydrogen-bonding network.

Magnetic field dependent electronic transport of Mn4 single-molecule magnet.

NASA Astrophysics Data System (ADS)

Haque, F.; Langhirt, M.; Henderson, J. J.; Del Barco, E.; Taguchi, T.; Christou, G.

2010-03-01

We have performed single-electron transport measurements on a Mn4 single-molecule magnet (SMM) in where amino groups were added to electrically protect the magnetic core and to increase the stability of the molecule when deposited on the single-electron transistor (SET) chip. A three-terminal SET with nano-gap electro-migrated gold electrodes and a naturally oxidized Aluminum back gate. Experiments were conducted at temperatures down to 230mK in the presence of high magnetic fields generated by a superconducting vector magnet. Mn4 molecules were deposited from solution to form a mono-layer. The optimum deposition time was determined by AFM analysis on atomically flat gold surfaces. We have observed Coulomb blockade an electronic excitations that curve with the magnetic field and present zero-field splitting, which represents evidence of magnetic anisotropy. Level anticrossings and large excitations slopes are associated with the behavior of molecular states with high spin values (S ˜ 9), as expected from Mn4.

Crystal structure of the ternary silicide Gd2Re3Si5.

PubMed

Fedyna, Vitaliia; Kozak, Roksolana; Gladyshevskii, Roman

2014-12-01

A single crystal of the title compound, the ternary silicide digadolinium trirhenium penta-silicide, Gd2Re3Si5, was isolated from an alloy of nominal composition Gd20Re30Si50 synthesized by arc melting and investigated by X-ray single-crystal diffraction. Its crystal structure belongs to the U2Mn3Si5 structure type. All atoms in the asymmetric lie on special positions. The Gd site has site symmetry m..; the two Mn atoms have site symmetries m.. and 2.22; the three Si atoms have site symmetries m.., ..2 and 4.. . The coordination polyhedra of the Gd atoms have 21 vertices, while those of the Re atoms are cubo-octa-hedra and 13-vertex polyhedra. The Si atoms are arranged as tricapped trigonal prisms, bicapped square anti-prisms, or 11-vertex polyhedra. The crystal structure of the title compound is also related to the structure types CaBe2Ge2 and W5Si3. It can be represented as a stacking of Gd-centred polyhedra of composition [GdSi9]. The Re atoms form infinite chains with an Re-Re distance of 2.78163 (5) Å and isolated squares with an Re-Re distance of 2.9683 (6) Å.

Crystal structure of the ternary silicide Gd2Re3Si5

PubMed Central

Fedyna, Vitaliia; Kozak, Roksolana; Gladyshevskii, Roman

2014-01-01

A single crystal of the title compound, the ternary silicide digadolinium trirhenium penta­silicide, Gd2Re3Si5, was isolated from an alloy of nominal composition Gd20Re30Si50 synthesized by arc melting and investigated by X-ray single-crystal diffraction. Its crystal structure belongs to the U2Mn3Si5 structure type. All atoms in the asymmetric lie on special positions. The Gd site has site symmetry m..; the two Mn atoms have site symmetries m.. and 2.22; the three Si atoms have site symmetries m.., ..2 and 4.. . The coordination polyhedra of the Gd atoms have 21 vertices, while those of the Re atoms are cubo­octa­hedra and 13-vertex polyhedra. The Si atoms are arranged as tricapped trigonal prisms, bicapped square anti­prisms, or 11-vertex polyhedra. The crystal structure of the title compound is also related to the structure types CaBe2Ge2 and W5Si3. It can be represented as a stacking of Gd-centred polyhedra of composition [GdSi9]. The Re atoms form infinite chains with an Re—Re distance of 2.78163 (5) Å and isolated squares with an Re—Re distance of 2.9683 (6) Å. PMID:25552967

Monoatomic and dimer Mn adsorption on the Au(111) surface from first principles

NASA Astrophysics Data System (ADS)

Muñoz, Francisco; Romero, Aldo H.; Mejía-López, Jose; Morán-López, J. L.

2011-05-01

A theoretical study based on the density functional theory of the adsorption of Mn monomers and dimers on a Au-(111) surface is presented. As necessary preliminary steps, the bulk and clean surface electronic structure are calculated, which agree well with previous reports. Then, the electronic structure of the Mn adatom, chemisorbed on four different surface geometries, is analyzed. It is found that the most stable geometry is when the Mn atom is chemisorbed on threefold coordinated sites. Using this geometry for a single adatom a second Mn atom is chemisorbed and the most stable dimer geometrical structure is calculated. The lowest-energy configuration corresponds to the molecule lying parallel to the surface, adsorbed on two topological equivalent threefold coordinated sites. It is also found that the lowest-energy magnetic configuration corresponds to the antiferromagnetic arrangement with individual magnetic moments of 4.64μB. Finally, it is concluded that the dimer is not stable and should fragment at the surface.

Polarized Neutron Study of Ni-Mn-Ga Alloys: Site-Specific Spin Density Affected by Martensitic Transformation.

PubMed

Lázpita, P; Barandiarán, J M; Gutiérrez, J; Mondelli, C; Sozinov, A; Chernenko, V A

2017-10-13

Polarized neutron scattering has been used to obtain the magnetic moment at specific crystallographic sites of the austenitic and martensitic phases of two nonstoichiometric Ni-Mn-Ga single crystals with close composition. These alloys have been chosen because they exhibit different structures in the paramagnetic state and inverse positions of the respective martensitic transformation and Curie temperature. The diffraction analysis revealed a remarkable result: Despite the similar alloy composition, the magnetic moments of Mn are quite different for the two alloys at the same crystallographic position. Furthermore, such a difference enabled us to assess that the exchange coupling between Mn atoms switches from ferro- to antiferromagnetic at a distance between 2.92 and 3.32 Å in the martensite. These results are of great importance to guide first principles calculations that, up to now, have not been contrasted with experiments at the atomic level.

Polarized Neutron Study of Ni-Mn-Ga Alloys: Site-Specific Spin Density Affected by Martensitic Transformation

NASA Astrophysics Data System (ADS)

Lázpita, P.; Barandiarán, J. M.; Gutiérrez, J.; Mondelli, C.; Sozinov, A.; Chernenko, V. A.

2017-10-01

Polarized neutron scattering has been used to obtain the magnetic moment at specific crystallographic sites of the austenitic and martensitic phases of two nonstoichiometric Ni-Mn-Ga single crystals with close composition. These alloys have been chosen because they exhibit different structures in the paramagnetic state and inverse positions of the respective martensitic transformation and Curie temperature. The diffraction analysis revealed a remarkable result: Despite the similar alloy composition, the magnetic moments of Mn are quite different for the two alloys at the same crystallographic position. Furthermore, such a difference enabled us to assess that the exchange coupling between Mn atoms switches from ferro- to antiferromagnetic at a distance between 2.92 and 3.32 Å in the martensite. These results are of great importance to guide first principles calculations that, up to now, have not been contrasted with experiments at the atomic level.

An observation of nanotwin lamellae in Cd 0.6Mn 0.4Te crystal by atomic force microscopy

NASA Astrophysics Data System (ADS)

George, M. A.; Azoulay, M.; Collins, W. E.; Burger, A.; Silberman, E.

1993-05-01

Atomic force microscopy (AFM) is used to examine the structure of freshly cleaved Cd 0.6Mn 0.4Te surfaces. The present report complements previous results obtained with X-ray diffraction and optical microscopy which showed the existence of microtwins. The AFM analysis was performed under ambient conditions and yielded nanometer scale resolution images of single twin lamellae that ranged between 20 and 100 nm in width. This is a first observation using AFM of such a substructure, which we interpret as evidence for the presence of nonotwins.

Defect propagation in one-, two-, and three-dimensional compounds doped by magnetic atoms

DOE PAGES

Furrer, A.; Podlesnyak, A.; Krämer, K. W.; ...

2014-10-29

Inelastic neutron scattering experiments were performed to study manganese(II) dimer excitations in the diluted one-, two-, and three-dimensional compounds CsMn xMg 1-xBr 3, K 2Mn xZn 1-xF 4, and KMn xZn 1-xF 3 (x≤0.10), respectively. The transitions from the ground-state singlet to the excited triplet, split into a doublet and a singlet due to the single-ion anisotropy, exhibit remarkable fine structures. These unusual features are attributed to local structural inhomogeneities induced by the dopant Mn atoms which act like lattice defects. Statistical models support the theoretically predicted decay of atomic displacements according to 1/r 2, 1/r, and constant (for three-,more » two-, and one-dimensional compounds, respectively) where r denotes the distance of the displaced atoms from the defect. In conclusion, the observed fine structures allow a direct determination of the local exchange interactions J, and the local intradimer distances R can be derived through the linear law dJ/dR.« less

Mixing of MnPc electronic states at the MnPc/Au(110) interface

NASA Astrophysics Data System (ADS)

Gargiani, Pierluigi; Lisi, Simone; Avvisati, Giulia; Mondelli, Pierluigi; Fatale, Sara; Betti, Maria Grazia

2017-10-01

Manganese-phthalocyanines form assembled chains with a variety of ordered super-structures, flat lying along the Au(110) reconstructed channels. The chains first give rise to a ×5 symmetry reconstruction, while further deposition of MnPc leads to a ×7 periodicity at the completion of the first single layer. A net polarization with the formation of an interface dipole is mainly due to the molecular π-states located on the macrocycles pyrrole rings, while the central metal ion induces a reduction in the polarization, whose amount is related to the Mn-Au interaction. The adsorption-induced interface polarization is compared to other 3d-metal phthalocyanines, to unravel the role of the central metal atom configuration in the interaction process of the d-states. The MnPc adsorption on Au(110) induces the re-hybridization of the electronic states localized on the central metal atom, promoting a charge redistribution of the molecular orbitals of the MnPc molecules. The molecule-substrate interaction is controlled by a symmetry-determined mixing between the electronic states, involving also the molecular empty orbitals with d character hybridized with the nitrogen atoms of the pyrrole ring, as deduced by photoemission and X-ray absorption spectroscopy exploiting light polarization. The symmetry-determined mixing between the electronic states of the Mn metal center and of the Au substrate induces a density of states close to the Fermi level for the ×5 phase.

Electrical properties of Pb{sub 1-x}Mn{sub x}Te single crystals with an excess of tellurium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bagieva, G. Z., E-mail: bagieva-gjulandam@rambler.ru; Abdinova, G. D.; Mustafayev, N. B.

2013-03-15

The effect of excess Te atoms (as high as 0.5 at %) and thermal treatment at 473 K for 120 h on the electrical conductivity {sigma}, the thermopower coefficient {alpha}, and the Hall coefficient R of Pb{sub 0.96}Mn{sub 0.04}Te single crystals in the temperature range {approx}77-300 K is investigated. It is shown that excess atoms of tellurium predominantly act as acceptor impurity centers at low concentrations in unannealed samples and form antisite defects at relatively high concentrations (0.05 at % or higher) being located mainly in vacancies of the lead sublattice, and decrease the hole concentration. As a result ofmore » annealing, certain lattice defects (for example, deformational) are healed, and the accommodation process for Te atoms at lead-sublattice vacancies is intensified. These processes substantially affect the values of the electrical parameters, their temperature dependences, as well as the sign of the thermopower and Hall coefficients of the samples.« less

Making Mn substitutional impurities in InAs using a scanning tunneling microscope.

PubMed

Song, Young Jae; Erwin, Steven C; Rutter, Gregory M; First, Phillip N; Zhitenev, Nikolai B; Stroscio, Joseph A

2009-12-01

We describe in detail an atom-by-atom exchange manipulation technique using a scanning tunneling microscope probe. As-deposited Mn adatoms (Mn(ad)) are exchanged one-by-one with surface In atoms (In(su)) to create a Mn surface-substitutional (Mn(In)) and an exchanged In adatom (In(ad)) by an electron tunneling induced reaction Mn(ad) + In(su) --> Mn(In) + In(ad) on the InAs(110) surface. In combination with density-functional theory and high resolution scanning tunneling microscopy imaging, we have identified the reaction pathway for the Mn and In atom exchange.

Attractive interaction between Mn atoms on the GaAs(110) surface observed by scanning tunneling microscopy.

PubMed

Taninaka, Atsushi; Yoshida, Shoji; Kanazawa, Ken; Hayaki, Eiko; Takeuchi, Osamu; Shigekawa, Hidemi

2016-06-16

Scanning tunneling microscopy/spectroscopy (STM/STS) was carried out to investigate the structures of Mn atoms deposited on a GaAs(110) surface at room temperature to directly observe the characteristics of interactions between Mn atoms in GaAs. Mn atoms were paired with a probability higher than the random distribution, indicating an attractive interaction between them. In fact, re-pairing of unpaired Mn atoms was observed during STS measurement. The pair initially had a new structure, which was transformed during STS measurement into one of those formed by atom manipulation at 4 K. Mn atoms in pairs and trimers were aligned in the <110> direction, which is theoretically predicted to produce a high Curie temperature.

Mechanisms of radiation-induced segregation in CrFeCoNi-based single-phase concentrated solid solution alloys

DOE PAGES

He, Mo-Rigen; Wang, Shuai; Shi, Shi; ...

2016-12-31

Single-phase concentrated solid solution alloys have attracted wide interest due to their superior mechanical properties and enhanced radiation tolerance, which make them promising candidates for the structural applications in next-generation nuclear reactors. However, little has been understood about the intrinsic stability of their as-synthesized, high-entropy configurations against radiation damage. In this paper, we report the element segregation in CrFeCoNi, CrFeCoNiMn, and CrFeCoNiPd equiatomic alloys when subjected to 1250 kV electron irradiations at 400 °C up to a damage level of 1 displacement per atom. Cr/Fe/Mn/Pd can deplete and Co/Ni can accumulate at radiation-induced dislocation loops, while the actively segregating elementsmore » are alloy-specific. Moreover, electron-irradiated matrix of CrFeCoNiMn and CrFeCoNiPd shows L1 0 (NiMn)-type ordering decomposition and <001>-oriented spinodal decomposition between Co/Ni and Pd, respectively. Finally, these findings are rationalized based on the atomic size difference and enthalpy of mixing between the alloying elements, and identify a new important requirement to the design of radiation-tolerant alloys through modification of the composition.« less

Strong Inhibition of O-Atom Transfer Reactivity for Mn(IV)(O)(π-Radical-Cation)(Lewis Acid) versus Mn(V)(O) Porphyrinoid Complexes.

PubMed

Zaragoza, Jan Paulo T; Baglia, Regina A; Siegler, Maxime A; Goldberg, David P

2015-05-27

The oxygen atom transfer (OAT) reactivity of two valence tautomers of a Mn(V)(O) porphyrinoid complex was compared. The OAT kinetics of Mn(V)(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl)corrolazinato(3-)) reacting with a series of triarylphosphine (PAr3) substrates were monitored by stopped-flow UV-vis spectroscopy, and revealed second-order rate constants ranging from 16(1) to 1.43(6) × 10(4) M(-1) s(-1). Characterization of the OAT transition state analogues Mn(III)(OPPh3)(TBP8Cz) and Mn(III)(OP(o-tolyl)3)(TBP8Cz) was carried out by single-crystal X-ray diffraction (XRD). A valence tautomer of the closed-shell Mn(V)(O)(TBP8Cz) can be stabilized by the addition of Lewis and Brønsted acids, resulting in the open-shell Mn(IV)(O)(TBP8Cz(•+)):LA (LA = Zn(II), B(C6F5)3, H(+)) complexes. These Mn(IV)(O)(π-radical-cation) derivatives exhibit dramatically inhibited rates of OAT with the PAr3 substrates (k = 8.5(2) × 10(-3) - 8.7 M(-1) s(-1)), contrasting the previously observed rate increase of H-atom transfer (HAT) for Mn(IV)(O)(TBP8Cz(•+)):LA with phenols. A Hammett analysis showed that the OAT reactivity for Mn(IV)(O)(TBP8Cz(•+)):LA is influenced by the Lewis acid strength. Spectral redox titration of Mn(IV)(O)(TBP8Cz(•+)):Zn(II) gives Ered = 0.69 V vs SCE, which is nearly +700 mV above its valence tautomer Mn(V)(O)(TBP8Cz) (Ered = -0.05 V). These data suggest that the two-electron electrophilicity of the Mn(O) valence tautomers dominate OAT reactivity and do not follow the trend in one-electron redox potentials, which appear to dominate HAT reactivity. This study provides new fundamental insights regarding the relative OAT and HAT reactivity of valence tautomers such as M(V)(O)(porph) versus M(IV)(O)(porph(•+)) (M = Mn or Fe) found in heme enzymes.

Neutron diffraction studies of some rare earth-transition metal deuterides

NASA Astrophysics Data System (ADS)

James, W. J.

1984-04-01

Neutron diffraction studies of the ternary alloy system Y6(Fel-xMnx)23 reveal that the unusual magnetic behavior upon substitution of Mn or Fe into the end members, is a consequence of atomic ordering wherein there is strong site preference of Mn for the f sub 2 sites and of Fe for the f sub 1 sites. In the Mn-rich compositions, Fe is found to have no spontaneous moments. Therefore, the long range magnetic ordering arises solely from Mn-Mn interactions. Upon substitution of Mn into the Fe-rich ternaries, the Fe moments are considerably reduced. Neutron diffraction studies of Y6Mn23D23 show that a transition occurs below 180K from a fcc structure to a primitive tetragonal structure, space group P4/mmm with the onset of antiferromagnetic ordering. The Mn moments are directed along the c-axis. The transition probably results from atomic ordering of the D atoms at low temperature which induces c axis magnetic ordering. The question of the appropriate space group of LaNi4.5Al0.5D4.5, P6/mmm or P3/m has been resolved by a careful refinement and analysis of neutron diffraction data. The preferred space group is P6/mmm. Neutron powder diffraction and thermal magnetization measurements on small single crystals of ErNi3, ErCo3, and ErFe3 (space group R3m) show that the magnetocrystalline properties are a consequence of competing local site anisotropies between the two non-equivalent crystallographic sites of Er and two of the three non-equivalent sites of the 3d-transition metal.

Crystallographic order and decomposition of [MnIII 6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

NASA Astrophysics Data System (ADS)

Gryzia, Aaron; Volkmann, Timm; Brechling, Armin; Hoeke, Veronika; Schneider, Lilli; Kuepper, Karsten; Glaser, Thorsten; Heinzmann, Ulrich

2014-02-01

Monolayers and submonolayers of [Mn III 6 Cr III ] 3+ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.

Local structure and polarization resistance of Ce doped SrMnO{sub 3} using extended x-ray fine structure analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Jiseung; Lee, Heesoo, E-mail: heesoo@pusan.ac.kr

2014-09-15

Changes to the local structure of Sr and Mn atoms in Sr{sub 1−x}Ce{sub x}MnO{sub 3} (SCM) according to increasing Ce content and the effect of the structural change on the polarization resistance of SCM were investigated. The reduction of manganese was confirmed by the absorption edge shift of the Mn K-edge toward lower energies. The noise of oscillation in extended X-ray absorption fine structure k{sup 3}χ data at Mn K-edge reveals the distortion of the local structure of Mn atoms, and the peak that indicates the bonding length of Mn-O, Sr/Ce, and -Mn decreased with the addition of Ce contentmore » in Fourier transformations of the Mn K-edge. The distortion of the local structure at Mn atoms was affected by the reduced manganese ions having larger ionic radii than Mn{sup 4+}. Meanwhile, few distortions of local atomic structures of Sr atoms occurred, and the average nearest neighboring distances of Sr-O and Sr-Mn are ∼2.13 Å and ∼2.95 Å, respectively. The average bonding lengths of the Ce-O and Ce-Mn increased because the ionic radius of substituted Ce ion with 12 coordination number is smaller than that of Sr ion, which leads the reduction of Mn ions and the distortion of local structure at the substituted A-site. Therefore, we reasoned that the distortion of the local atomic structure at Mn atoms in MnO{sub 6} and Ce atoms in A-site is one of the causes for interrupting oxygen ion transfers as a geometric factor, which results in an increase in the polarization resistance of SCM within the Ce composition range from 10 mol. % to 30 mol. %.« less

Local moment formation and magnetic coupling of Mn dopants in Bi2Se3: A low-temperature ferromagnetic resonance study

NASA Astrophysics Data System (ADS)

Savchenko, D.; Tarasenko, R.; Vališka, M.; Kopeček, J.; Fekete, L.; Carva, K.; Holý, V.; Springholz, G.; Sechovský, V.; Honolka, J.

2018-05-01

We compare the magnetic and electronic configuration of single Mn atoms in molecular beam epitaxy (MBE) grown Bi2Se3 thin films, focusing on electron paramagnetic (ferromagnetic) resonance (EPR and FMR, respectively) and superconducting quantum interference device (SQUID) techniques. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) reveal the expected increase of disorder with increasing concentration of magnetic guest atoms, however, Kikuchi patterns show that disorder consists majorly of μm-scale 60° twin domains in the hexagonal Bi2Se3 structure, which are promoted by the presence of single unclustered Mn impurities. Ferromagnetism below TC (5.4±0.3) K can be well described by critical scaling laws M (T) (1 - T /TC) β with a critical exponent β = (0.34 ± 0.2) , suggesting 3D Heisenberg class magnetism instead of e.g. 2D-type coupling between Mn-spins in van der Waals gap sites. From EPR hyperfine structure data we determine a Mn2+ (d5, S = 5/2) electronic configuration with a g-factor of 2.002 for -1/2 → +1/2 transitions. In addition, from the strong dependence of the low temperature FMR fields and linewidth on the field strength and orientation with respect to the Bi2Se3 (0001) plane, we derive magnetic anisotropy energies of up to K1 = -3720 erg/cm3 in MBE-grown Mn-doped Bi2Se3, reflecting the first order magneto-crystalline anisotropy of an in-plane magnetic easy plane in a hexagonal (0001) crystal symmetry. We observe an increase of K1 with increasing Mn concentration, which we interpret to be correlated to a Mn-induced in-plane lattice contraction. Across the ferromagnetic-paramagnetic transition the FMR intensity is suppressed and resonance fields converge the paramagnetic limit of Mn2+ (d5, S = 5/2).

Isolation and reconstitution of iron- and manganese-containing superoxide dismutases from Bacteroides thetaiotaomicron.

PubMed Central

Pennington, C D; Gregory, E M

1986-01-01

Superoxide dismutase (SOD) from extracts of anaerobically maintained Bacteroides thetaiotaomicron was a dimer of equally sized 23,000-molecular-weight monomers joined noncovalently. A preparation with a specific activity of 1,200 U/mg contained 1.1 g-atom of Fe, 0.6 g-atom of Zn, and less than 0.05 g-atom of Mn per mol of dimer. The apoprotein, prepared by dialysis of iron-SOD in 5 M guanidinium chloride-20 mM 8-hydroxyquinoline, had no superoxide-scavenging activity when renatured without exogenous metal. Enzymatic activity was restored to the denatured apoprotein by dialysis against either 1 mM Fe(NH4)2 or 1 mM MnCl2 in 20 mM Tris (pH 7.0). The Fe-reconstituted enzyme and the native enzyme were inhibited approximately 50% by 0.2 mM NaN3, whereas the Mn-reconstituted enzyme was inhibited 60% by 10 mM NaN3. Aeration of the anaerobic cells resulted in a fourfold induction of an azide-resistant SOD. The enzyme (43,000 molecular weight) isolated from aerated cells was a dimer of equally sized subunits. The metal content was 1.0 g-atom of Mn, 0.55 g-atom of Fe, and 0.3 g-atom of Zn per mol of dimer. Enzymatic activity of the denatured apoprotein from this enzyme was also restored on addition of either iron or manganese. The constitutive Fe-SOD and the O2-induced Mn-SOD, tested alone and in combination, migrated identically on acrylamide gels, had similar amino acid compositions, and had alanine as the sole N-terminal amino acid. These data are consistent with the synthesis of a single apoprotein in either anaerobically maintained or oxygenated cells. We have observed a similar phenomenon with SOD from Bacteroides fragilis (E. M. Gregory, Arch. Biochem. Biophys. 238:83-89, 1985). PMID:3700336

Atom-atom interactions around the band edge of a photonic crystal waveguide

NASA Astrophysics Data System (ADS)

Hood, Jonathan D.; Goban, Akihisa; Asenjo-Garcia, Ana; Lu, Mingwu; Yu, Su-Peng; Chang, Darrick E.; Kimble, H. J.

2016-09-01

Tailoring the interactions between quantum emitters and single photons constitutes one of the cornerstones of quantum optics. Coupling a quantum emitter to the band edge of a photonic crystal waveguide (PCW) provides a unique platform for tuning these interactions. In particular, the cross-over from propagating fields E(x)∝e±ikxxE(x)∝e±ikxx outside the bandgap to localized fields E(x)∝e-κx|x|E(x)∝e-κx|x| within the bandgap should be accompanied by a transition from largely dissipative atom-atom interactions to a regime where dispersive atom-atom interactions are dominant. Here, we experimentally observe this transition by shifting the band edge frequency of the PCW relative to the D1D1 line of atomic cesium for N¯=3.0±0.5N¯=3.0±0.5 atoms trapped along the PCW. Our results are the initial demonstration of this paradigm for coherent atom-atom interactions with low dissipation into the guided mode.

Anisotropic compressibility of the coordination polymer emim[Mn(btc)].

PubMed

Madsen, Solveig R; Moggach, Stephen A; Overgaard, Jacob; Brummerstedt Iversen, Bo

2016-06-01

The effect of pressure on the crystal structure of a coordination polymer, emim[Mn(II)(btc)] (emim = 1-ethyl,3-methyl imidazolium cation, btc = 1,3,5-benzene-tricarboxylate), was investigated with single-crystal X-ray diffraction. At 4.3 GPa the unit-cell volume had decreased by 14% compared with ambient conditions. The unit-cell contraction is highly anisotropic, with the a- and b-axes decreasing by 5.5 and 9.5%, respectively, and the c-axis compressing a mere 0.25% up to 1.7 GPa followed by a 0.2% expansion between 1.7 and 4.3 GPa. The 0.2% increase in length of the c-axis in this interval happens above the quasi-hydrostatic limit of the pressure-transmitting medium and therefore it might be a consequence of strain gradients. Under ambient conditions, two MnO6 units are connected by two carboxylate ligands to form dimeric units. On increasing pressure, a non-bonded O atom from a bridging carboxylate group approaches the Mn atom, with the Mn-O distance decreasing from 2.866 (1) Å at 0.3 GPa to 2.482 (6) Å at 4.3 GPa, increasing the coordination environment of the Mn ion from six- to seven-coordinated.

Transformation twinning of Ni-Mn-Ga characterized with temperature-controlled atomic force microscopy.

PubMed

Reinhold, Matthew; Watson, Chad; Knowlton, William B; Müllner, Peter

2010-06-01

The magnetomechanical properties of ferromagnetic shape memory alloy Ni-Mn-Ga single crystals depend strongly on the twin microstructure, which can be modified through thermomagnetomechanical training. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) were used to characterize the evolution of twin microstructures during thermomechanical training of a Ni-Mn-Ga single crystal. Experiments were performed in the martensite phase at 25 degrees C and in the austenite phase at 55 degrees C. Two distinct twinning surface reliefs were observed at room temperature. At elevated temperature (55 degrees C), the surface relief of one twinning mode disappeared while the other relief remained unchanged. When cooled back to 25 degrees C, the twin surface relief recovered. The relief persisting at elevated temperature specifies the positions of twin boundaries that were present when the sample was polished prior to surface characterization. AFM and MFM following thermomechanical treatment provide a nondestructive method to identify the crystallographic orientation of each twin and of each twin boundary plane. Temperature dependent AFM and MFM experiments reveal the twinning history thereby establishing the technique as a unique predictive tool for revealing the path of the martensitic and reverse transformations of magnetic shape memory alloys.

Set-up of a high-resolution 300 mK atomic force microscope in an ultra-high vacuum compatible (3)He/10 T cryostat.

PubMed

von Allwörden, H; Ruschmeier, K; Köhler, A; Eelbo, T; Schwarz, A; Wiesendanger, R

2016-07-01

The design of an atomic force microscope with an all-fiber interferometric detection scheme capable of atomic resolution at about 500 mK is presented. The microscope body is connected to a small pumped (3)He reservoir with a base temperature of about 300 mK. The bakeable insert with the cooling stage can be moved from its measurement position inside the bore of a superconducting 10 T magnet into an ultra-high vacuum chamber, where the tip and sample can be exchanged in situ. Moreover, single atoms or molecules can be evaporated onto a cold substrate located inside the microscope. Two side chambers are equipped with standard surface preparation and surface analysis tools. The performance of the microscope at low temperatures is demonstrated by resolving single Co atoms on Mn/W(110) and by showing atomic resolution on NaCl(001).

Atomic-scale inversion of spin polarization at an organic-antiferromagnetic interface

NASA Astrophysics Data System (ADS)

Caffrey, Nuala M.; Ferriani, Paolo; Marocchi, Simone; Heinze, Stefan

2013-10-01

Using first-principles calculations, we show that the magnetic properties of a two-dimensional antiferromagnetic transition-metal surface are modified on the atomic scale by the adsorption of small organic molecules. We consider benzene (C6H6), cyclooctatetraene (C8H8), and a small transition-metal-benzene complex (BzV) adsorbed on a single atomic layer of Mn deposited on the W(110) surface—a surface which exhibits a nearly antiferromagnetic alignment of the magnetic moments in adjacent Mn rows. Due to the spin dependent hybridization of the molecular pz orbitals with the d states of the Mn monolayer, there is a significant reduction of the magnetic moments in the Mn film. Furthermore, the spin polarization at this organic-antiferromagnetic interface is found to be modulated on the atomic scale, both enhanced and inverted, as a result of the molecular adsorption. We show that this effect can be resolved by spin-polarized scanning tunneling microscopy (SP-STM). Our simulated SP-STM images display a spatially dependent spin resolved vacuum charge density above an adsorbed molecule—i.e., different regions above the molecule sustain different signs of spin polarization. While states with s and p symmetry dominate the vacuum charge density in the vicinity of the Fermi energy for the clean magnetic surface, we demonstrate that after a molecule is adsorbed those d states, which are normally suppressed due to their symmetry, can play a crucial role in the vacuum due to their interaction with the molecular orbitals. We also model the effect of small deviations from perfect antiferromagnetic ordering, induced by the slight canting of magnetic moments due to the spin spiral ground state of Mn/W(110).

Ruddlesden-Popper interface in correlated manganite heterostructures induces magnetic decoupling and dead layer reduction

NASA Astrophysics Data System (ADS)

Belenchuk, A.; Shapoval, O.; Roddatis, V.; Bruchmann-Bamberg, V.; Samwer, K.; Moshnyaga, V.

2016-12-01

We report on the interface engineering in correlated manganite heterostructures by octahedral decoupling using embedded stacks of atomic layers that form the Ruddlesden-Popper structure. A room temperature magnetic decoupling was achieved through deposition of a (SrO)2-TiO2-(SrO)2 sequence of atomic layers at the interface between La0.7Sr0.3MnO3 and La0.7Sr0.3Mn0.9Ru0.1O3 films. Moreover, the narrowing of the interfacial dead layer in ultrathin La0.7Sr0.3MnO3 films was demonstrated by insertion of a single (SrO)2 rock-salt layer at the interface with the SrTiO3(100) substrate. The obtained results are discussed based on the symmetry breaking and disconnection of the MnO6 octahedra network at the interface that may lead to the improved performance of all-oxide magnetic tunnel junctions. We suggest that octahedral decoupling realized by formation of Ruddlesden-Popper interfaces is an effective structural mechanism to control functionalities of correlated perovskite heterostructures.

Metal-semiconductor transition at a comparable resistivity level and positive magnetoresistance in Mn3Mn1-x Pd x N thin films

NASA Astrophysics Data System (ADS)

Xu, T.; Ji, G. P.; Cao, Z. X.; Ji, A. L.

2018-02-01

Thin films of antiperovskite Mn3Mn1-x Pd x N with x up to 0.36 were grown by reactive magnetron co-sputtering method. All the deposits exhibit a [1 0 0] preferential orientation, with the lattice constant slightly enlarged in samples with ever more Pd atoms partially substituting the MnI atoms in Mn3MnN matrix. The replacement of MnI atoms in antiperovskite structure by Pd atoms, besides reducing the saturation magnetization, also invokes a metal-semiconductor transition which occurs remarkably at a comparable resistivity level. Moreover, a positive magnetoresistance was observed in samples of a high Pd content. These tunable electrical and magnetic properties of ternary antiperovskite compounds might promise some ingenious applications in electronic industry.

Mn-silicide nanostructures aligned on massively parallel silicon nano-ribbons

NASA Astrophysics Data System (ADS)

De Padova, Paola; Ottaviani, Carlo; Ronci, Fabio; Colonna, Stefano; Olivieri, Bruno; Quaresima, Claudio; Cricenti, Antonio; Dávila, Maria E.; Hennies, Franz; Pietzsch, Annette; Shariati, Nina; Le Lay, Guy

2013-01-01

The growth of Mn nanostructures on a 1D grating of silicon nano-ribbons is investigated at atomic scale by means of scanning tunneling microscopy, low energy electron diffraction and core level photoelectron spectroscopy. The grating of silicon nano-ribbons represents an atomic scale template that can be used in a surface-driven route to control the combination of Si with Mn in the development of novel materials for spintronics devices. The Mn atoms show a preferential adsorption site on silicon atoms, forming one-dimensional nanostructures. They are parallel oriented with respect to the surface Si array, which probably predetermines the diffusion pathways of the Mn atoms during the process of nanostructure formation.

Mn-silicide nanostructures aligned on massively parallel silicon nano-ribbons.

PubMed

De Padova, Paola; Ottaviani, Carlo; Ronci, Fabio; Colonna, Stefano; Olivieri, Bruno; Quaresima, Claudio; Cricenti, Antonio; Dávila, Maria E; Hennies, Franz; Pietzsch, Annette; Shariati, Nina; Le Lay, Guy

2013-01-09

The growth of Mn nanostructures on a 1D grating of silicon nano-ribbons is investigated at atomic scale by means of scanning tunneling microscopy, low energy electron diffraction and core level photoelectron spectroscopy. The grating of silicon nano-ribbons represents an atomic scale template that can be used in a surface-driven route to control the combination of Si with Mn in the development of novel materials for spintronics devices. The Mn atoms show a preferential adsorption site on silicon atoms, forming one-dimensional nanostructures. They are parallel oriented with respect to the surface Si array, which probably predetermines the diffusion pathways of the Mn atoms during the process of nanostructure formation.

Mechanism of γ-irradiation induced phase transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jagadeesha Angadi, V.; Anupama, A.V.; Choudhary, Harish K.

The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-irradiation were investigated in this work and a mechanism of phase transformation/decomposition is provided based on the metastable nature of the Mn-atoms in the spinel lattice. The nano-powder sample was prepared by solution combustion route and the pellets of the sample were exposed to γ-radiation. Up to a dose of 25 kGy of γ-radiation, the sample retained the single phase cubic spinel (Fd-3m) structure, but the disorder in the sample increased. On irradiatingmore » the sample with 50 kGy γ-radiation, the spinel phase decomposed into new stable phases such as α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases along with amorphous MnO phase, leading to a change in the surface morphology of the sample. Along with the structural transformations the magnetic properties deteriorated due to breakage of the ferrimagnetic order with higher doses of γ-irradiation. Our results are important for the understanding of the stability, durability and performance of the Mn-Zn ferrite based devices used in space applications. - Graphical abstract: The nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramic sample transforms to crystalline α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases (and amorphous MnO phase) at a γ-irradiation dose of 50 kGy, as MnO goes out of the spinel lattice. The high energy γ-irradiation causes structural damage to the nanomaterials leading to change in morphology of the sample as seen in the SEM images. - Highlights: • Mn atoms are more unstable in the Mn-Zn ferrite spinel lattice than Zn-atoms. • Displacement of Mn atoms by γ-radiation from the lattice renders phase transformation. • In Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4}, Mn-ferrite cell transforms to crystalline α-Fe{sub 2}O{sub 3} and amorphous MnO. • The stable ZnFe{sub 2}O{sub 4} phase retains its structure even after 50 KGy γ-irradiation. • The γ-irradiation degrades the magnetic properties of Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics.« less

Synthesis and crystal structure of the coordination compound of pyridoxine with manganese sulfate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furmanova, N. G., E-mail: furm@ns.crys.ras.ru; Verin, I. A.; Shyityeva, N.

2011-11-15

The reaction of pyridoxine with manganese sulfate in an aqueous solution gave the coordination compound MnSO{sub 4} {center_dot} 2C{sub 8}H{sub 11}O{sub 3}N {center_dot} 2H{sub 2}O (I). The structure of I was determined from single-crystal X-ray diffraction data. In the centrosymmetric complex (sp. gr. P1-bar, Z = 1), the Mn atom is coordinated by two pyridoxine molecules and two water molecules, thus adopting an octahedral coordination. The sulfate anion is also at a center of symmetry and, consequently, is disordered. The pyridoxine molecules are coordinated to the metal atom through the oxygen atoms of the deprotonated hydroxyl group and the CH{submore » 2}OH group that retains the hydrogen atom. The nitrogen atom is protonated in such a way that the heterocycle assumes a pyridinium character. The crystal structure also contains six water molecules of crystallization. A thermogravimetric study showed that the decomposition of I occurs in several successive steps, such as dehydration, the combustion of organic ligands, and the formation of an inorganic residue.« less

2-tert-Butyl-5-(2-pyridyl)-2H-tetrazole as a chelating ligand in the direct synthesis of novel Cu(II) and heterobimetallic Cu(II)/Mn(II) complexes.

PubMed

Mosalkova, Anastasiya P; Voitekhovich, Sergei V; Lyakhov, Alexander S; Ivashkevich, Ludmila S; Lach, Jochen; Kersting, Berthold; Gaponik, Pavel N; Ivashkevich, Oleg A

2013-02-28

For the first time, a representative of the 2,5-disubstituted tetrazoles, namely, 2-tert-butyl-5-(2-pyridyl)-2H-tetrazole (L), has been found to participate in oxidative dissolution of copper powder in homometalic systems Cu0–L–NH4X–DMSO (X = Cl, SCN, ClO4) and heterobimetallic ones Cu0–Mn(OAc)2–L–NH4OAc–Solv (Solv = DMSO, DMF), providing the formation of molecular homometallic complexes [CuL2Cl2] (1), [CuL2(SCN)2] (2), and [CuL2(H2O)](ClO4)2 (3), heterobimetallic complex [Cu2MnL2(OAc)6] (4) from DMF solution and its mixture with complex [Cu2MnL2(OAc)6]·2DMSO (5) from DMSO solution. Free ligand L and complexes 1–4 were characterized by elemental analysis, IR spectroscopy, thermal and X-ray single crystal analyses, whereas complex 5 was characterized by X-ray analysis only. Compounds 1–3 are mononuclear complexes, with chelating coordination mode of L via the tetrazole ring N4 and pyridine ring N7 atoms. Heterobimetallic complexes 4 and 5 possess trinuclear structures, with a linear Cu–Mn–Cu arrangement of the metal atoms, linked by the acetate anions; each copper(II) atom is decorated by a chelating unit of L via the tetrazole ring N1 and pyridine ring N7 atoms in complex 4, and via the N4, N7 atoms in complex 5. Temperature-dependent magnetic susceptibility measurements of complex 4 revealed a weak antiferromagnetic coupling between the paramagnetic copper(II) and manganese(II) ions (J = −2.5 cm(−1), g(Cu) = 2.25 and g(Mn) = 2.01), with magnetic exchange through the acetato bridges.

EPR and optical investigation of Mn2+ doped L-histidine-4-nitrophenolate 4-nitrophenol single crystal

NASA Astrophysics Data System (ADS)

Prabakaran, R.; Subramanian, P.

2018-04-01

Single crystals of L-histidine-4-nitrophenolate 4-nitrophenol[LHFNP] complex doped with Mn2+ were grown by the slow evaporation method at room temperature. The EPR spectrum reveals the entry of one Mn2+ ion in the lattice. The angular variation plot was drawn between the angles and the magnetic field position. The spin Hamiltonian parameters were obtained by EPR-NMR program. The D and E values show the rhombic field around the ion and is an interstitial one. The g value obtained here suggests that the Mn2+ ion experiences a strong field and there is a transfer of electron from the metal ion to the ligand atom. The optical absorption study shows various bands and are assigned to the transition from the ground state 6A1g(S). The Racah and crystal field parameters have also been evaluated and fitted to the experimental values. The Racah parameter shows the covalent bonding between the metal ion to the ligand.

Giant increase of critical current density and vortex pinning in Mn doped K{sub x}Fe{sub 2−y}Se{sub 2} single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Mingtao; Zhang, Jincang, E-mail: jczhang@staff.shu.edu.cn; Materials Genome Institute, Shanghai University, Shanghai 200444

2014-11-10

We report a comparative study of the critical current density (J{sub c}) and vortex pinning among pure and Mn doped K{sub x}Fe{sub 2−y}Se{sub 2} single crystals. It is found that the J{sub c} values can be greatly improved by Mn doping and post-quenching treatment when comparing to pristine pure sample. In contrast to pure samples, an anomalous second magnetization peak (SMP) effect is observed in both 1% and 2% Mn doped samples at T = 3 K for H∥ab but not for H∥c. Referring to Dew-Hughes and Kramer's model, we performed scaling analyses of the vortex pinning force density vs magnetic field inmore » 1% Mn doped and quenched pristine crystals. The results show that the normal point defects are the dominant pinning sources, which probably originate from the variations of intercalated K atoms. We propose that the large nonsuperconducting K-Mn-Se inclusions may contribute to the partial normal surface pinning and give rise to the anomalous SMP effect for H∥ab in Mn doped crystals. These results may facilitate further understanding of the superconductivity and vortex pinning in intercalated iron-selenides superconductors.« less

Oxygen-atom transfer reactivity of axially ligated Mn(V)-oxo complexes: evidence for enhanced electrophilic and nucleophilic pathways.

PubMed

Neu, Heather M; Yang, Tzuhsiung; Baglia, Regina A; Yosca, Timothy H; Green, Michael T; Quesne, Matthew G; de Visser, Sam P; Goldberg, David P

2014-10-01

Addition of anionic donors to the manganese(V)-oxo corrolazine complex Mn(V)(O)(TBP8Cz) has a dramatic influence on oxygen-atom transfer (OAT) reactivity with thioether substrates. The six-coordinate anionic [Mn(V)(O)(TBP8Cz)(X)](-) complexes (X = F(-), N3(-), OCN(-)) exhibit a ∼5 cm(-1) downshift of the Mn-O vibrational mode relative to the parent Mn(V)(O)(TBP8Cz) complex as seen by resonance Raman spectroscopy. Product analysis shows that the oxidation of thioether substrates gives sulfoxide product, consistent with single OAT. A wide range of OAT reactivity is seen for the different axial ligands, with the following trend determined from a comparison of their second-order rate constants for sulfoxidation: five-coordinate ≈ thiocyanate ≈ nitrate < cyanate < azide < fluoride ≪ cyanide. This trend correlates with DFT calculations on the binding of the axial donors to the parent Mn(V)(O)(TBP8Cz) complex. A Hammett study was performed with p-X-C6H4SCH3 derivatives and [Mn(V)(O)(TBP8Cz)(X)](-) (X = CN(-) or F(-)) as the oxidant, and unusual "V-shaped" Hammett plots were obtained. These results are rationalized based upon a change in mechanism that hinges on the ability of the [Mn(V)(O)(TBP8Cz)(X)](-) complexes to function as either an electrophilic or weak nucleophilic oxidant depending upon the nature of the para-X substituents. For comparison, the one-electron-oxidized cationic Mn(V)(O)(TBP8Cz(•+)) complex yielded a linear Hammett relationship for all substrates (ρ = -1.40), consistent with a straightforward electrophilic mechanism. This study provides new, fundamental insights regarding the influence of axial donors on high-valent Mn(V)(O) porphyrinoid complexes.

An all-electron density functional theory study of the structure and properties of the neutral and singly charged M12 and M13 clusters: M = Sc-Zn.

PubMed

Gutsev, G L; Weatherford, C W; Belay, K G; Ramachandran, B R; Jena, P

2013-04-28

The electronic and geometrical structures of the M12 and M13 clusters where M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn along with their singly negatively and positively charged ions are studied using all-electron density functional theory within the generalized gradient approximation. The geometries corresponding to the lowest total energy states of singly and negatively charged ions of V13, Mn12, Co12, Ni13, Cu13, Zn12, and Zn13 are found to be different from the geometries of the corresponding neutral parents. The computed ionization energies of the neutrals, vertical electron detachment energies from the anions, and energies required to remove a single atom from the M13 and M13(+) clusters are in good agreement with experiment. The change in a total spin magnetic moment of the cation or anion with respect to a total spin magnetic moment of the corresponding neutral is consistent with the one-electron model in most cases, i.e., they differ by ±1.0 μ(B). Exceptions are found only for Sc12(-), Ti12(+), Mn12(-), Mn12(+), Fe12(-), Fe13(+), and Co12(+).

The structure of [MnIII6 CrIII]3+ single-molecule magnets deposited in submono-layers and monolayers on surfaces studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin Probe Force Microscopy in UHV

NASA Astrophysics Data System (ADS)

Heinzmann, U.; Gryzia, A.; Volkmann, T.; Brechling, A.; Hoeke, V.; Glaser, T.

2014-04-01

Single molecule magnets (SMM) deposited in submonolayers and monolayers have been analyzed with respect to their structures by means of non-contact AFM (topographic as well as damping mode) and Kelvin Probe Force Microscopy with molecular resolution.

Electron paramagnetic resonance spectral study of [Mn(acs){sub 2}(2–pic){sub 2}(H{sub 2}O){sub 2}] single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocakoç, Mehpeyker, E-mail: mkocakoc@cu.edu.tr; Tapramaz, Recep, E-mail: recept@omu.edu.tr

Acesulfame potassium salt is a synthetic and non-caloric sweetener. It is also important chemically for its capability of being ligand in coordination compounds, because it can bind over Nitrogen and Oxygen atoms of carbonyl and sulfonyl groups and ring oxygen. Some acesulfame containing transition metal ion complexes with mixed ligands exhibit solvato and thermo chromic properties and these properties make them physically important. In this work single crystals of Mn{sup +2} ion complex with mixed ligand, [Mn(acs){sub 2}(2-pic){sub 2}(H{sub 2}O){sub 2}], was studied with electron paramagnetic resonance (EPR) spectroscopy. EPR parameters were determined. Zero field splitting parameters indicated that themore » complex was highly symmetric. Variable temperature studies showed no detectable chance in spectra.« less

Graphene-Composite Carbon Nanofiber-Based Electrodes for Energy Storage Devices

DTIC Science & Technology

2014-04-18

electrochemical supercapacitors . 1. Development of highly conductive graphene composite CNF webs Graphene, a single-atom-thick sheet of sp 2 bonded...electrochemical supercapacitors and evaluated their performance. The capacitance increased with an increase in the amount of MnO2 NWs (duration of the deposition

Mn doped InSb studied at the atomic scale by cross-sectional scanning tunneling microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mauger, S. J. C.; Bocquel, J.; Koenraad, P. M., E-mail: p.m.koenraad@tue.nl

2015-11-30

We present an atomically resolved study of metal-organic vapor epitaxy grown Mn doped InSb. Both topographic and spectroscopic measurements have been performed by cross-sectional scanning tunneling microscopy (STM). The measurements on the Mn doped InSb samples show a perfect crystal structure without any precipitates and reveal that Mn acts as a shallow acceptor. The Mn concentration of the order of ∼10{sup 20 }cm{sup −3} obtained from the cross-sectional STM data compare well with the intended doping concentration. While the pair correlation function of the Mn atoms showed that their local distribution is uncorrelated beyond the STM resolution for observing individual dopants,more » disorder in the Mn ion location giving rise to percolation pathways is clearly noted. The amount of clustering that we see is thus as expected for a fully randomly disordered distribution of the Mn atoms and no enhanced clustering or second phase material was observed.« less

ENDOR/ESR of Mn atoms and MnH molecules in solid argon

NASA Astrophysics Data System (ADS)

van Zee, R. J.; Garland, D. A.; Weltner, W., Jr.

1986-09-01

Mn atoms and MnH molecules, the latter formed by reaction between metal and hydrogen atoms, were trapped in solid argon and their ESR/ENDOR spectra measured at 4 K. At each pumping magnetic field two ENDOR lines were observed for 55Mn(I=5/2) atoms, corresponding to hyperfine transitions within the MS =±1/2 levels. Values of the hyperfine interaction constant and nuclear moment of 55Mn were derived from the six sets of data. For MnH, three sets of signals were detected: a proton ``matrix ENDOR'' line, transitions in the MS =0,±1 levels involving MI (55Mn)=1/2, 3/2, 5/2 levels, and proton transitions corresponding to νH and νH±aH. Analysis yielded the hyperfine constant aH =6.8(1) MHz and the nuclear quadrupole coupling constant Q'(55Mn)=-11.81(2) MHz. The latter compared favorably with a theoretical value derived earlier by Bagus and Schaefer. A higher term in the spin Hamiltonian appeared to be necessary to fit the proton hyperfine data.

Set-up of a high-resolution 300 mK atomic force microscope in an ultra-high vacuum compatible {sup 3}He/10 T cryostat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allwörden, H. von; Ruschmeier, K.; Köhler, A.

The design of an atomic force microscope with an all-fiber interferometric detection scheme capable of atomic resolution at about 500 mK is presented. The microscope body is connected to a small pumped {sup 3}He reservoir with a base temperature of about 300 mK. The bakeable insert with the cooling stage can be moved from its measurement position inside the bore of a superconducting 10 T magnet into an ultra-high vacuum chamber, where the tip and sample can be exchanged in situ. Moreover, single atoms or molecules can be evaporated onto a cold substrate located inside the microscope. Two side chambersmore » are equipped with standard surface preparation and surface analysis tools. The performance of the microscope at low temperatures is demonstrated by resolving single Co atoms on Mn/W(110) and by showing atomic resolution on NaCl(001).« less

Zinc-blende MnN bilayer formation on the GaN(111) surface

NASA Astrophysics Data System (ADS)

Gutierrez-Ojeda, S. J.; Guerrero-Sánchez, J.; Garcia-Diaz, R.; Ramirez-Torres, A.; Takeuchi, Noboru; H. Cocoletzi, Gregorio

2017-07-01

Atomic layers of manganese nitride, deposited on the cubic gallium nitride (111) surface, are investigated using spin polarized periodic density functional theory calculations. The adsorption of a manganese atom has been evaluated at different high symmetry sites. Incorporation into the GaN substrate by replacing gallium atoms drives the formation of a site in which the displaced Ga atom forms bonds with Ga atoms at the surface. This energetically favorable configuration shows a ferromagnetic alignment. Surface formation energy calculations demonstrate that when a full Mn ML is incorporated into the GaN structure, a Ga ML on top of a MnN bilayer may be formed for very Ga-rich conditions. On the other hand, when a full Mn ML is deposited on top of the nitrogen terminated surface, an epitaxial MnN bilayer is formed with antiferromagnetic characteristics. Density of states and partial density of states are reported to show the antiferromagnetic alignment in both structures. This behavior is mainly induced by the Mn-d orbitals.

Single d-metal atoms on F(s) and F(s+) defects of MgO(001): a theoretical study across the periodic table.

PubMed

Neyman, Konstantin M; Inntam, Chan; Matveev, Alexei V; Nasluzov, Vladimir A; Rösch, Notker

2005-08-24

Single d-metal atoms on oxygen defects F(s) and F(s+) of the MgO(001) surface were studied theoretically. We employed an accurate density functional method combined with cluster models, embedded in an elastic polarizable environment, and we applied two gradient-corrected exchange-correlation functionals. In this way, we quantified how 17 metal atoms from groups 6-11 of the periodic table (Cu, Ag, Au; Ni, Pd, Pt; Co, Rh, Ir; Fe, Ru, Os; Mn, Re; and Cr, Mo, W) interact with terrace sites of MgO. We found bonding with F(s) and F(s+) defects to be in general stronger than that with O2- sites, except for Mn-, Re-, and Fe/F(s) complexes. In M/F(s) systems, electron density is accumulated on the metal center in a notable fashion. The binding energy on both kinds of O defects increases from 3d- to 4d- to 5d-atoms of a given group, at variance with the binding energy trend established earlier for the M/O2- complexes, 4d < 3d < 5d. Regarding the evolution of the binding energy along a period, group 7 atoms are slightly destabilized compared to their group 6 congeners in both the F(s) and F(s+) complexes; for later transition elements, the binding energy increases gradually up to group 10 and finally decreases again in group 11, most strongly on the F(s) site. This trend is governed by the negative charge on the adsorbed atoms. We discuss implications for an experimental detection of metal atoms on oxide supports based on computed core-level energies.

Synthesis and characterization of electron doped La{sub 0.85}Te{sub 0.15}MnO{sub 3} thin film grown on LaAlO{sub 3} substrate by pulsed laser deposition technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhat, Irshad, E-mail: bhat.amu85@gmail.com; Husain, Shahid; Patil, S. I.

2015-06-24

We report the structural, morphological and magneto-transport properties of electron doped La{sub 0.85}Te{sub 0.15}MnO{sub 3} (LTMO) thin film grown on (001) LaAlO{sub 3} single crystal substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD) results confirm that the film has good crystalline quality, single phase, and c-axis orientation. The atomic force microscopy (AFM) results have revealed that the film consists of grains with the average size in a range of 20–30 nm and root-mean square (rms) roughness of 0.27nm. The resistivity versus temperature measurement exhibits an insulator to metal transition (MIT). We have noticed a huge value of magnetoresistance (∼93%)more » close to MIT in presence of 8T field. X-ray photoemission spectroscopy confirms the electron doping and suggests that Te ions could be in the Te{sup 4+} state, while the Mn ions stay in the Mn{sup 2+} and Mn{sup 3+} valence state.« less

Dioxygen Activation and O–O Bond Formation Reactions by Manganese Corroles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Mian; Lee, Yong-Min; Gupta, Ranjana

Activation of dioxygen (O 2) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O–O bond formation, which is the reverse of the O 2-activation reaction, has been the focus of current research. Herein, we report the O 2-activation and O–O bond formation reactions by manganese corrole complexes. In the O 2-activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O 2 in the presence of base (e.g., OH –) and hydrogen atom (H atom) donor (e.g., THF or cyclic olefins); the O 2-activation reaction did not occurmore » in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O 2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O–O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O–O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O–O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present paper reports the first example of using the same manganese complex in both O 2-activation and O–O bond formation reactions.« less

Dioxygen Activation and O–O Bond Formation Reactions by Manganese Corroles

DOE PAGES

Guo, Mian; Lee, Yong-Min; Gupta, Ranjana; ...

2017-10-22

Activation of dioxygen (O 2) in enzymatic and biomimetic reactions has been intensively investigated over the past several decades. More recently, O–O bond formation, which is the reverse of the O 2-activation reaction, has been the focus of current research. Herein, we report the O 2-activation and O–O bond formation reactions by manganese corrole complexes. In the O 2-activation reaction, Mn(V)-oxo and Mn(IV)-peroxo intermediates were formed when Mn(III) corroles were exposed to O 2 in the presence of base (e.g., OH –) and hydrogen atom (H atom) donor (e.g., THF or cyclic olefins); the O 2-activation reaction did not occurmore » in the absence of base and H atom donor. Moreover, formation of the Mn(V)-oxo and Mn(IV)-peroxo species was dependent on the amounts of base present in the reaction solution. The role of the base was proposed to lower the oxidation potential of the Mn(III) corroles, thereby facilitating the binding of O 2 and forming a Mn(IV)-superoxo species. The putative Mn(IV)-superoxo species was then converted to the corresponding Mn(IV)-hydroperoxo species by abstracting a H atom from H atom donor, followed by the O–O bond cleavage of the putative Mn(IV)-hydroperoxo species to form a Mn(V)-oxo species. We have also shown that addition of hydroxide ion to the Mn(V)-oxo species afforded the Mn(IV)-peroxo species via O–O bond formation and the resulting Mn(IV)-peroxo species reverted to the Mn(V)-oxo species upon addition of proton, indicating that the O–O bond formation and cleavage reactions between the Mn(V)-oxo and Mn(IV)-peroxo complexes are reversible. The present paper reports the first example of using the same manganese complex in both O 2-activation and O–O bond formation reactions.« less

The exchange interactions and the state of manganese atoms in the solid solutions in Bi{sub 3}NbO{sub 7} of cubic and tetragonal modifications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chezhina, N.V., E-mail: chezhina@nc2490.spb.edu; Zhuk, N.A.; Korolev, D.A.

2016-01-15

The comparative analysis of magnetic behavior of manganese-containing solid solutions Bi{sub 3}Nb{sub 1−x}Mn{sub x}O{sub 7−δ} (x=0.01−0.10) of cubic and tetragonal modifications was performed. Based on the results of magnetic susceptibility studies paramagnetic manganese atoms in solid solutions of cubic and tetragonal modifications were found to be in the form of Mn(III), Mn(IV) monomers and exchange-coupled dimers of Mn(III)–O–Mn(III), Mn(IV)–O–Mn(IV), Mn(III)–O–Mn(IV). The exchange parameters and the distribution of monomers and dimers in solid solutions as a function of the content of paramagnetic atoms were calculated. - Graphical abstract: Structural transition of cubic to tetragonal Bi{sub 3}NbO{sub 7−δ}.

Periodic table of 3d-metal dimers and their ions.

PubMed

Gutsev, G L; Mochena, M D; Jena, P; Bauschlicher, C W; Partridge, H

2004-10-08

The ground states of the mixed 3d-metal dimers TiV, TiCr, TiMn, TiFe, TiCo, TiNi, TiCu, TiZn, VCr, VMn, VFe, VCo, VNi, VCu, VZn, CrMn, CrFe, CrCo, CrNi, CrCu, CrZn, MnFe, MnCo, MnNi, MnCu, MnZn, FeCo, FeNi, FeCu, FeZn, CoNi, CoCu, CoZn, NiCu, NiZn, and CuZn along with their singly negatively and positively charged ions are assigned based on the results of computations using density functional theory with generalized gradient approximation for the exchange-correlation functional. Except for TiCo and CrMn, our assignment agrees with experiment. Computed spectroscopic constants (r(e),omega(e),D(o)) are in fair agreement with experiment. The ground-state spin multiplicities of all the ions are found to differ from the spin multiplicities of the corresponding neutral parents by +/-1. Except for TiV, MnFe, and MnCu, the number of unpaired electrons, N, in a neutral ground-state dimer is either N(1)+N(2) or mid R:N(1)-N(2)mid R:, where N(1) and N(2) are the numbers of unpaired 3d electrons in the 3d(n)4s(1) occupation of the constituent atoms. Combining the present and previous results obtained at the same level of theory for homonuclear 3d-metal and ScX (X=Ti-Zn) dimers allows one to construct "periodic" tables of all 3d-metal dimers along with their singly charged ions.

Crystal growth and crystal structures of six novel phases in the Mn/As/O/Cl(Br) system, as well as magnetic properties of α-Mn3(AsO4)2

NASA Astrophysics Data System (ADS)

Weil, Matthias; Kremer, Reinhard K.

2017-01-01

Chemical vapour transport reactions (900 °C → 820 °C, Cl2 or Br2 as transport agent) of in situ formed Mn3(AsO4)2 yielded the orthoarsenates(V) α-Mn3(AsO4)2 and β-Mn3(AsO4)2 as well as the oxoarsenate(V) halide compounds Mn7(AsO4)4Cl2, Mn11(AsO4)7Cl, Mn11(AsO4)7Br and Mn5(AsO4)3Cl. The crystal structures of all six phases were determined from single crystal X-ray diffraction data. The crystal structures of α-and β-Mn3(AsO4)2 are isotypic with the corresponding phosphate phases γ- and α-Mn3(PO4)2, respectively, and are reported here for the first time. A comparative discussion with other structures of general composition M3(AsO4)2 (M = Mg; divalent first-row transition metal) is given. The unique crystal structures of Mn7(AsO4)4Cl2 and that of the two isotypic Mn11(AsO4)7X (X = Cl, Br) structures are composed of two [MnO5] polyhedra, two [MnO4Cl2] polyhedra (one with site symmetry 1 bar), two AsO4 tetrahedra, and one [MnO5] polyhedron, three [MnO6] octahedra (one with site symmetry.m.), one [MnO4X], one [MnO5X] polyhedron and four AsO4 tetrahedra, respectively. The various polyhedra of the three arsenate(V) halides are condensed into three-dimensional framework structures by corner- and edge-sharing. Mn5(AsO4)3Cl adopts the chloroapatite structure. The magnetic and thermal properties of pure polycrystalline samples of a-Mn3(AsO4)2 were investigated in more detail. The magnetic susceptibility proves all Mn atoms to be in the oxidation state +2 yielding an effective magnetic moment per Mn atom of 5.9 μB. Long-range antiferromagnetic ordering is observed below 8.2 K consistent with the negative Curie-Weiss temperature of -50 K derived from the high temperature susceptibility data.

Single molecule magnets with protective ligand shells on gold and titanium dioxide surfaces: In situ electrospray deposition and x-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Handrup, Karsten; Richards, Victoria J.; Weston, Matthew; Champness, Neil R.; O'Shea, James N.

2013-10-01

Two single molecule magnets based on the dodecamanganese (III, IV) cluster with either benzoate or terphenyl-4-carboxylate ligands, have been studied on the Au(111) and rutile TiO2(110) surfaces. We have used in situ electrospray deposition to produce a series of surface coverages from a fraction of a monolayer to multilayer films in both cases. X-ray absorption spectroscopy measured at the Mn L-edge (Mn 2p) has been used to study the effect of adsorption on the oxidation states of the manganese atoms in the core. In the case of the benzoate-functionalised complex reduction of the manganese metal centres is observed due to the interaction of the manganese core with the underlying surface. In the case of terphenyl-4-carboxylate, the presence of this much larger ligand prevents the magnetic core from interacting with either the gold or the titanium dioxide surfaces and the characteristic Mn3+ and Mn4+ oxidation states necessary for magnetic behaviour are preserved.

Oxygen-atom transfer chemistry and thermolytic properties of a di-tert-butylphosphate-ligated Mn4O4 cubane.

PubMed

Van Allsburg, Kurt M; Anzenberg, Eitan; Drisdell, Walter S; Yano, Junko; Tilley, T Don

2015-03-16

[Mn4O4{O2P(OtBu)2}6] (1), an Mn4O4 cubane complex combining the structural inspiration of the photosystem II oxygen-evolving complex with thermolytic precursor ligands, was synthesized and fully characterized. Core oxygen atoms within complex 1 are transferred upon reaction with an oxygen-atom acceptor (PEt3), to give the butterfly complex [Mn4O2{O2P(OtBu)2}6(OPEt3)2]. The cubane structure is restored by reaction of the latter complex with the O-atom donor PhIO. Complex 1 was investigated as a precursor to inorganic Mn metaphosphate/pyrophosphate materials, which were studied by X-ray absorption spectroscopy to determine the fate of the Mn4O4 unit. Under the conditions employed, thermolyses of 1 result in reduction of the manganese to Mn(II) species. Finally, the related butterfly complex [Mn4O2{O2P(pin)}6(bpy)2] (pin = pinacolate) is described. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Charge versus orbital-occupancy ordering in manganites

NASA Astrophysics Data System (ADS)

Luo, Weidong; Varela, Maria; Tao, Jing; Pennycook, Stephen J.; Pantelides, Sokrates T.

2006-03-01

It is generally assumed that density-functional theory (DFT) in the local-spin-density approximation (LSDA) or the generalized- gradient approximation (GGA) is not adequate to describe mixed- valence manganites. Here we report benchmark DFT/GGA calculations for the ground-state structural, electronic and magnetic properties for both undoped and doped CaMnO3 and find the results to be in excellent agreement with available data, including new atomic-resolution Z-contrast imaging and electron-energy loss spectra. More specifically, we found that the DFT results predict two inequivalent Mn atoms in both 0.33 and 0.5 electron-doped CaMnO3, in agreement with experimental evidence of Mn^+3/Mn^+4 oxidation state ordering. The inequivalent Mn atoms are marked by their distinctive orbital occupancies, dissimilar local Jahn-Teller distortion and different magnetic moments from DFT calculations. We also show that the spherically integrated charges associated with the two inequivalent Mn atoms are the same, and they are actually the same as in the Mn metal. This charge neutrality with different orbital occupancies is the result of self-consistency and atomic relaxations in the crystal. We conclude that DFT without additional correlations can account for the observed properties of oxidation-state ordering in this system. The impact of the results on other mixed-valence systems will be discussed.

Crystal structure of tetra­wickmanite, Mn2+Sn4+(OH)6

PubMed Central

Lafuente, Barbara; Yang, Hexiong; Downs, Robert T.

2015-01-01

The crystal structure of tetra­wickmanite, ideally Mn2+Sn4+(OH)6 [mangan­ese(II) tin(IV) hexa­hydroxide], has been determined based on single-crystal X-ray diffraction data collected from a natural sample from Långban, Sweden. Tetra­wickmanite belongs to the octa­hedral-framework group of hydroxide-perovskite minerals, described by the general formula BB’(OH)6 with a perovskite derivative structure. The structure differs from that of an ABO3 perovskite in that the A site is empty while each O atom is bonded to an H atom. The perovskite B-type cations split into ordered B and B′ sites, which are occupied by Mn2+ and Sn4+, respectively. Tetra­wickmanite exhibits tetra­gonal symmetry and is topologically similar to its cubic polymorph, wickmanite. The tetra­wickmanite structure is characterized by a framework of alternating corner-linked [Mn2+(OH)6] and [Sn4+(OH)6] octa­hedra, both with point-group symmetry -1. Four of the five distinct H atoms in the structure are statistically disordered. The vacant A site is in a cavity in the centre of a distorted cube formed by eight octa­hedra at the corners. However, the hydrogen-atom positions and their hydrogen bonds are not equivalent in every cavity, resulting in two distinct environments. One of the cavities contains a ring of four hydrogen bonds, similar to that found in wickmanite, while the other cavity is more distorted and forms crankshaft-type chains of hydrogen bonds, as previously proposed for tetra­gonal stottite, Fe2+Ge4+(OH)6. PMID:25878828

Atomic moments in Mn 2CoAl thin films analyzed by X-ray magnetic circular dichroism

DOE PAGES

Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; ...

2014-12-05

Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn 2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

Poly[tetra­aqua­(μ6-9,10-dioxo-9,10-dihydro­anthracene-1,4,5,8-tetra­carboxyl­ato)dimanganese(II)

PubMed Central

Xu, Rui; Liu, Jian-Lan

2012-01-01

The title complex, [Mn2(C18H4O10)(H2O)4]n, was synthesized from manganese(II) chloride tetra­hydrate and 9,10-dioxo-9,10-dihydro­anthracene-1,4,5,8-tetra­carb­oxy­lic acid (H4AQTC) in water. The anthraquinone unit is located about a crystallographic center of inversion. Each asymmetric unit therefore contains one MnII atom, two water ligands and one half AQTC4− anion. The MnII atom is coordinated in a distorted octa­hedral geometry by four O atoms from three AQTC4− ligands and two water O atoms. Two of the carboxyl­ate groups coordinate one MnII atom in a chelating mode, whereas the others each coordinate two MnII atoms. Each AQTC4− tetra-anion therefore coordinates six different MnII ions and, as a result, a three-dimensional coordination polymer is formed. O—H⋯O hydrogen bonds, some of them bifurcated, between water ligands and neighboring water or anthraquinone ligands are observed in the crystal structure. PMID:22807779

Synthesis and Structural Characterization of a Series of Mn(III)-OR Complexes, Including a Water-Soluble Mn(III)-OH that Promotes Aerobic Hydrogen Atom Transfer

PubMed Central

Coggins, Michael K.; Brines, Lisa M.; Kovacs, Julie A.

2013-01-01

Hydrogen atom transfer reactions (HAT) are a class of proton-coupled electron transfer (PCET) reactions used in biology to promote substrate oxidation. The driving force for such reactions depend on both the oxidation potential of the catalyst and the pKa of the proton acceptor site. Both high-valent transition-metal oxo M(IV)=O (M= Fe, Mn) and lower-valent transition-metal hydroxo compounds M(III)–OH (M= Fe, Mn) have been shown to promote these reactions. Herein we describe the synthesis, structure and reactivity properties of a series of Mn(III)-OR compounds (R= pNO2Ph(5), Ph(6), Me(7), H(8)), some of which abstract H-atoms. The Mn(III)-OH complex 8 is water-soluble and represents a rare example of a stable mononuclear Mn(III)-OH. In water, the redox potential of 8 was found to be pH-dependent and the Pourbaix (Ep,c vs pH) diagram has a slope (52 mV/pH) that is indicative of the transfer a single proton with each electron (ie, PCET). The two compounds with the lowest oxidation potential, hydroxide and methoxide-bound 7 and 8 are found to oxidize TEMPOH, whereas the compounds with the highest oxidation potential, phenol-ligated 5 and 6, are shown to be unreactive. Hydroxide-bound 8 reacts with TEMPOH an order of magnitude faster than methoxide-bound 7. Kinetic data (kH/kD= 3.1 (8), kH/kD= 2.1 (7)) are consistent with concerted H-atom abstraction. The reactive species 8 can be aerobically regenerated in H2O, and at least 10 turnovers can be achieved without significant degradation of the “catalyst”. The linear correlation between redox potential and pH, obtained from the Pourbaix diagram, was used to calculate the BDFE= 74.0±0.5 kcal/mol for Mn(II)-OH2 in water, and in MeCN its BDFE was estimated to be (70.1 kcal/mol). The reduced protonated derivative of 8, [MnII(SMe2N4(tren))(H2O)]+ (9), was estimated to have a pKa of 21.2 in MeCN. The ability (7) and inability (5 and 6) of the other members of the series to abstract a H-atom from TEMPOH was used to estimate either an upper or lower limit to the Mn(II)-O(H)R pKa based on their experimentally determined redox potentials. The trend in pKa (21.2(R=H) > 16.2(R=Me) > 13.5(R=Ph) > 12.2(R=pNO2Ph)) is shown to oppose that of oxidation potential Ep,c (−220(R= pNO2Ph) > −300(R= Ph) > −410(R= Me) > −600(R= H) mV vs Fc+/0) for this particular series. PMID:24156315

Ferromagnetic properties of manganese doped iron silicide

NASA Astrophysics Data System (ADS)

Ruiz-Reyes, Angel; Fonseca, Luis F.; Sabirianov, Renat

We report the synthesis of high quality Iron silicide (FeSi) nanowires via Chemical Vapor Deposition (CVD). The materials exhibits excellent magnetic response at room temperature, especially when doped with manganese showing values of 2.0 X 10-04 emu for the FexMnySi nanowires. SEM and TEM characterization indicates that the synthesized nanowires have a diameter of approximately 80nm. MFM measurements present a clear description of the magnetic domains when the nanowires are doped with manganese. Electron Diffraction and XRD measurements confirms that the nanowires are single crystal forming a simple cubic structure with space group P213. First-principle calculations were performed on (111) FeSi surface using the Vienna ab initio simulation package (VASP). The exchange correlations were treated under the Ceperley-Alder (CA) local density approximation (LDA). The Brillouin Zone was sampled with 8x8x1 k-point grid. A total magnetic moment of about 10 μB was obtained for three different surface configuration in which the Iron atom nearest to the surface present the higher magnetization. To study the effect of Mn doping, Fe atom was replaced for a Mn. Stronger magnetization is presented when the Mn atom is close to the surface. The exchange coupling constant have been evaluated calculating the energy difference between the ferromagnetic and anti-ferromagnetic configurations.

Magnetic states of Mn and Co atoms at Co2MnGe/MgO interfaces seen via soft x-ray magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Asakura, D.; Koide, T.; Yamamoto, S.; Tsuchiya, K.; Shioya, T.; Amemiya, K.; Singh, V. R.; Kataoka, T.; Yamazaki, Y.; Sakamoto, Y.; Fujimori, A.; Taira, T.; Yamamoto, M.

2010-11-01

The magnetic states of Mn and Co atoms in Co-rich Co2MnGe Heusler alloy thin films facing an MgO barrier were studied by means of soft x-ray magnetic circular dichroism (XMCD). In particular, the Co2MnGe film-thickness dependence of the Mn and Co magnetic moments was investigated. With a decrease in the Co2MnGe film thickness to 1-2 monolayers (MLs), the spin magnetic moment of Mn decreased and the MnL2,3 -edge x-ray absorption spectra (XAS) showed a Mn2+ -like multiplet structure in MnO, in contrast to samples thicker than 4 ML, indicating that the Mn atoms of the 1 and 2 ML samples were oxidized. The Co spin magnetic moment increased slightly with decreasing thickness. A Co2+ -like multiplet structure in CoO was not observed in all the CoL2,3 -edge XAS and XMCD, indicating that, even in the ultrathin samples, the Co atoms were not oxidized, and were more strongly spin polarized than those in the thicker samples. Co spin magnetic moments of 1.40-1.77μB larger than the theoretical value for ideal stoichiometric Co2MnGe (˜1μB) and the Co-rich film composition imply the presence of Co antisites that would lower the spin polarization.

Investigation of Y6Mn23 and YMn12 intermetallic alloys under high hydrogen pressure

NASA Astrophysics Data System (ADS)

Filipek, S. M.; Sato, R.; Kuriyama, N.; Tanaka, H.; Takeichi, N.

2010-03-01

Among three intermetallic compounds existing in Y-Mn system the YMn2 and Y6Mn23 can easily form interstitial hydrides while for YMn12 existence of hydride has never been reported. At moderate hydrogen pressure YMn2 and Y6Mn23 transform into YMn2H4.5 and Y6Mn23H25 respectively. At high hydrogen pressure the YMn2 (C15 or C14 parent structure) forms a unique YMn2H6 (s.g. Fm3m) complex hydride of fluorite structure in which one Mn atom Mn(1) and Y randomly occupy the 8c sites while second manganese (Mn2) in position 4a forms complex anion with 6 hydrogen atoms located in positions 24e. Formation of YMn2H6 independently of the structure of parent phase (C14 or C15) as well as occupation of the same site (8c) by Y and Mn(1) atoms suggested that also Y6Mn23 and YMn12 could transform into YMn2H6 - type hydride in which suitable number of Y atoms will be substituted by Mn(1) in the 8c positions. This assumption was confirmed by exposing R6Mn23 and RMn12 to 1 GPa of hydrogen pressure at 1000C. Formation of (RxMn2-x)MnH6 (where x = 18/29 or 3/13 for R6Mn23 and RMn12 hydrides respectively) was confirmed by XRD. Hydrogen concentration in both R6Mn23 and RMn12 based hydrides reached H/Me = 2 thus value two times higher than in R6Mn23H25.

Spin polarized first principles study of Mn doped gallium nitride monolayer nanosheet

NASA Astrophysics Data System (ADS)

Sharma, Venus; Kaur, Sumandeep; Srivastava, Sunita; Kumar, Tankeshwar

2017-05-01

The structural, electronic and magnetic properties of gallium nitride nanosheet (GaNs) doped with Mn atoms have been studied using spin polarized density functional theory. The binding energy per atom, Energy Band gap, Fermi energy, magnetic moment, electric dipole moment have been found. The doped nanosheet is found to be more stable than pure GaN monolayer nanosheet. Adsorption of Mn atom has been done at four different sites on GaNs which affects the fermi level position. It is found that depending on the doping site, Mn can behave both like p-type semiconductor and also as n-type semiconductor. Also, it is ascertained that Mn doped GaNs (GaNs-Mn) exhibits ferromagnetic behavior.

The Intrinsic Ferromagnetism in a MnO2 Monolayer.

PubMed

Kan, M; Zhou, J; Sun, Q; Kawazoe, Y; Jena, P

2013-10-17

The Mn atom, because of its special electronic configuration of 3d(5)4s(2), has been widely used as a dopant in various two-dimensional (2D) monolayers such as graphene, BN, silicene and transition metal dichalcogenides (TMDs). The distributions of doped Mn atoms in these systems are highly sensitive to the synthesis process and conditions, thus suffering from problems of low solubility and surface clustering. Here we show for the first time that the MnO2 monolayer, synthetized 10 years ago, where Mn ions are individually held at specific sites, exhibits intrinsic ferromagnetism with a Curie temperature of 140 K, comparable to the highest TC value achieved experimentally for Mn-doped GaAs. The well-defined atomic configuration and the intrinsic ferromagnetism of the MnO2 monolayer suggest that it is superior to other magnetic monolayer materials.

Oxygen-storage behavior and local structure in Ti-substituted YMnO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, I., E-mail: igor.levin@nist.gov; Krayzman, V.; Vanderah, T.A.

Hexagonal manganates RMnO{sub 3} (R=Y, Ho, Dy) have been recently shown to exhibit oxygen-storage capacities promising for three-way catalysts, air-separation, and related technologies. Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygen-breathing properties of these materials towards practical applications. Specifically, Y(Mn{sub 1−x}Ti{sub x})O{sub 3} solid solutions exhibit facile oxygen absorption/desorption via reversible Ti{sup 3+}↔Ti{sup 4+} and Mn{sup 3+}↔Mn{sup 4+} reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn{sup 3+}{sub 1−x-y}Mn{sup 4+}{sub y}Ti{sup 4+}{sub x}O{submore » 3+δ}. The presence of Ti promotes the oxidation of Mn{sup 3+} to Mn{sup 4+}, which is almost negligible for YMnO{sub 3} in air, thereby increasing the uptake of oxygen beyond that required for a given Ti{sup 4+} concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO{sub 5}] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO{sub 3} structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO{sub 5}] bipyramids. The tensile bond strain around the 5-fold coordinated Mn site and the strong preference of Ti{sup 4+}(and Mn{sup 4+}) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere. - Graphical abstract: Concurrent redox reactions involving Ti and Mn yield facile absorption/desorption of excess oxygen. - Highlights: • Concurrent redox reactions involving Ti and Mn yield oxygen absorption/desorption. • Excess oxygen is accommodated as interstitials via correlated atomic shifts. • Oxygen breathing is facilitated by the under-bonding of host Mn and O atoms.« less

Mn induced 1 × 2 reconstruction in the τ-MnAl(0 0 1) surface

NASA Astrophysics Data System (ADS)

Guerrero-Sánchez, J.; Takeuchi, Noboru

2018-05-01

We report on first principles total energy calculations to describe the structural, electronic and magnetic properties of MnAl(0 0 1) surfaces. We have concentrated in structural models having 1 × 1 and 1 × 2 periodicities, since recent experiments of the similar MnGa(0 0 1) surface have found 1 × 1 and 1 × 2 reconstructions. Our calculations show the existence of two stable structures for different ranges of chemical potential. A 1 × 1 surface is stable for Al-rich conditions, whereas a Mn-induced 1 × 2 reconstruction appears after increasing the Mn chemical potential up to Mn-rich conditions. It is important to notice that experimentally, Mn rich conditions are important for improved magnetic properties. The Mn layers in both structures have ferromagnetic arrangements, but they are aligned antiferromagnetically with the almost no magnetic Al atoms. Moreover, the on top Mn atoms, which produce the 1 × 2 reconstruction, align antiferromagnetically with the second layer Mn atoms. These findings are similar to those obtained experimentally in MnGa thin films grown by molecular beam epitaxy. Therefore, this method could also be used to grow the proposed MnAl films.

Orbital Picture of Yu-Shiba-Rusinov Multiplets

NASA Astrophysics Data System (ADS)

Heinrich, Benjamin W.; Ruby, Michael; Franke, Katharina J.; Peng, Yang; von Oppen, Felix

Magnetic impurities on an s-wave superconductor induce Yu-Shiba-Rusinov (YSR) bound states within the excitation gap of the superconductor. Here, we investigate single manganese (Mn) atoms adsorbed on different surface orientations of superconducting lead (Pb) and the nature of their YSR states. Depending on the adsorption site and surface, we detect a distinct number and characteristic patterns of YSR states around the Mn atoms. We show that the YSR states inherit their properties from the Mn d levels, which are split by the surrounding crystal field. The periodicity of the long-range YSR oscillations allows us to identify a dominant coupling of the d states to the outer Fermi sheet of the two-band superconductor Pb. The long-range and directional nature of the states are promising for the design of coupled adatom structures, which could bear topological phases. We acknowledge funding by the Deutsche Forschungsgemeinschaft through Grant No. FR2726/4 and through collaborative research Grants No. Sfb 658, No. CRC 183, and No. SPP 1666, as well as by the European Research Council through Consolidator Grant NanoSpin.

Defect formation energy and magnetic structure of shape memory alloys Ni-X-Ga (X=Mn, Fe, Co) by first principle calculation

NASA Astrophysics Data System (ADS)

Bai, J.; Raulot, J. M.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.

2010-09-01

The crystallographic and magnetic structures of the Ni2XGa (X=Mn, Fe, Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The formation energies of several kinds of defects (atomic exchange, antisite, vacancy) are estimated. The Ga atoms stabilize the cubic structure, and the effect of X atoms on the structural stability is opposite. For most cases of the site occupation, the excess atoms of the rich component directly occupy the site(s) of the deficient one(s), except for Ga-rich Ni-deficient type. The magnitude of the variation in Ni moments is much larger than that of Mn in defective Ni2XGa. The value of Ni magnetic moment sensitively depends on the distance between Ni and X. Excess Mn could be ferromagnetic or antiferromagnetic, depending on the distance between the neighboring Mn atoms.

Effect of L1{sub 2} ordering in antiferromagnetic Ir-Mn epitaxial layer on exchange bias of FePd films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Y. C.; Duh, J. G., E-mail: pmami.hsiao@gmail.com, E-mail: lin.yg@nsrrc.org.tw, E-mail: jgd@mx.nthu.edu.tw; Hsiao, S. N., E-mail: pmami.hsiao@gmail.com, E-mail: lin.yg@nsrrc.org.tw, E-mail: jgd@mx.nthu.edu.tw

2015-05-07

Two series of samples of single-layer IrMn and IrMn/FePd bilayer films, deposited on a single-crystal MgO substrate at different IrMn deposition temperatures (T{sub s} = 300–700 °C), were investigated using magnetron sputtering. L1{sub 2} ordering was revealed for the 30 nm-thick IrMn epitaxial (001) films with T{sub s} ≥ 400 °C, determined by synchrotron radiation x-ray diffractometry (XRD). XRD results also provide evidence of the epitaxial growth of the IrMn films on MgO substrate. Increasing T{sub s} from 400 to 700 °C monotonically increases the ordering parameter of L1{sub 2} phases from 0.17 to 0.81. An in-plane exchange bias field (H{sub eb}) of 22 Oe is obtained in amore » 10 nm-thick FePd film that is deposited on the disordered IrMn films. As the L1{sub 2} ordering of the IrMn layers increases, the H{sub eb} gradually decreases to 0 Oe, meaning that the exchange bias behavior vanishes. The increased surface roughness, revealed by atomic force microscopy, of the epitaxial IrMn layers with increasing T{sub s} cannot be the main cause of the decrease in H{sub eb} due to the compensated surface spins regardless of the disordered and ordered (001) IrMn layers. The change of antiferromagnetic structure from the A1 to the L1{sub 2} phase was correlated with the evolution of H{sub eb}.« less

Manganese-Oxygen Intermediates in O-O Bond Activation and Hydrogen-Atom Transfer Reactions.

PubMed

Rice, Derek B; Massie, Allyssa A; Jackson, Timothy A

2017-11-21

Biological systems capitalize on the redox versatility of manganese to perform reactions involving dioxygen and its derivatives superoxide, hydrogen peroxide, and water. The reactions of manganese enzymes influence both human health and the global energy cycle. Important examples include the detoxification of reactive oxygen species by manganese superoxide dismutase, biosynthesis by manganese ribonucleotide reductase and manganese lipoxygenase, and water splitting by the oxygen-evolving complex of photosystem II. Although these enzymes perform very different reactions and employ structurally distinct active sites, manganese intermediates with peroxo, hydroxo, and oxo ligation are commonly proposed in catalytic mechanisms. These intermediates are also postulated in mechanisms of synthetic manganese oxidation catalysts, which are of interest due to the earth abundance of manganese. In this Account, we describe our recent efforts toward understanding O-O bond activation pathways of Mn III -peroxo adducts and hydrogen-atom transfer reactivity of Mn IV -oxo and Mn III -hydroxo complexes. In biological and synthetic catalysts, peroxomanganese intermediates are commonly proposed to decay by either Mn-O or O-O cleavage pathways, although it is often unclear how the local coordination environment influences the decay mechanism. To address this matter, we generated a variety of Mn III -peroxo adducts with varied ligand environments. Using parallel-mode EPR and Mn K-edge X-ray absorption techniques, the decay pathway of one Mn III -peroxo complex bearing a bulky macrocylic ligand was investigated. Unlike many Mn III -peroxo model complexes that decay to oxo-bridged-Mn III Mn IV dimers, decay of this Mn III -peroxo adduct yielded mononuclear Mn III -hydroxo and Mn IV -oxo products, potentially resulting from O-O bond activation of the Mn III -peroxo unit. These results highlight the role of ligand sterics in promoting the formation of mononuclear products and mark an important step in designing Mn III -peroxo complexes that convert cleanly to high-valent Mn-oxo species. Although some synthetic Mn IV -oxo complexes show great potential for oxidizing substrates with strong C-H bonds, most Mn IV -oxo species are sluggish oxidants. Both two-state reactivity and thermodynamic arguments have been put forth to explain these observations. To address these issues, we generated a series of Mn IV -oxo complexes supported by neutral, pentadentate ligands with systematically perturbed equatorial donation. Kinetic investigations of these complexes revealed a correlation between equatorial ligand-field strength and hydrogen-atom and oxygen-atom transfer reactivity. While this trend can be understood on the basis of the two-state reactivity model, the reactivity trend also correlates with variations in Mn III/IV reduction potential caused by changes in the ligand field. This work demonstrates the dramatic influence simple ligand perturbations can have on reactivity but also illustrates the difficulties in understanding the precise basis for a change in reactivity. In the enzyme manganese lipoxygenase, an active-site Mn III -hydroxo adduct initiates substrate oxidation by abstracting a hydrogen atom from a C-H bond. Precedent for this chemistry from synthetic Mn III -hydroxo centers is rare. To better understand hydrogen-atom transfer by Mn III centers, we developed a pair of Mn III -hydroxo complexes, formed in high yield from dioxygen oxidation of Mn II precursors, capable of attacking weak O-H and C-H bonds. Kinetic and computational studies show a delicate interplay between thermodynamic and steric influences in hydrogen-atom transfer reactivity, underscoring the potential of Mn III -hydroxo units as mild oxidants.

Self-assembled growth of MnSi~1.7 nanowires with a single orientation and a large aspect ratio on Si(110) surfaces

PubMed Central

2013-01-01

MnSi~1.7 nanowires (NWs) with a single orientation and a large aspect ratio have been formed on a Si(110) surface with the molecular beam epitaxy method by a delicate control of growth parameters, such as temperature, deposition rate, and deposition time. Scanning tunneling microscopy (STM) was employed to study the influence of these parameters on the growth of NWs. The supply of free Si atoms per unit time during the silicide reaction plays a critical role in the growth kinetics of the NWs. High growth temperature and low deposition rate are favorable for the formation of NWs with a large aspect ratio. The orientation relationship between the NWs and the reconstruction rows of the Si(110) surface suggests that the NWs grow along the 11¯0 direction of the silicon substrate. High-resolution STM and backscattered electron scanning electron microscopy images indicate that the NWs are composed of MnSi~1.7. PMID:23339353

Synthesis, crystal structure, spectroscopic characterization and nonlinear optical properties of manganese (II) complex of picolinate: A combined experimental and computational study

NASA Astrophysics Data System (ADS)

Tamer, Ömer; Avcı, Davut; Atalay, Yusuf; Çoşut, Bünyemin; Zorlu, Yunus; Erkovan, Mustafa; Yerli, Yusuf

2016-02-01

A novel manganese (II) complex with picolinic acid (pyridine 2-carboxylic acid, Hpic), namely, [Mn(pic)2(H2O)2] was prepared and its crystal structure was fully characterized by using single crystal X-ray diffraction. Picolinate (pic) ligands were coordinated to the central manganese(II) ion as bidentate N,O-donors through the nitrogen atoms of pyridine rings and the oxygen atoms of carboxylate groups forming five-membered chelate rings. The spectroscopic characterization of Mn(II) complex was performed by the applications of FT-IR, Raman, UV-vis and EPR techniques. In order to support these studies, density functional theory (DFT) calculations were carried out by using B3LYP level. IR and Raman spectra were simulated at B3LYP level, and obtained results indicated that DFT calculations generally give compatible results to the experimental ones. The electronic structure of the Mn(II) complex was predicted using time dependent DFT (TD-DFT) method with polarizable continuum model (PCM). Molecular stability, hyperconjugative interactions, intramolecular charge transfer (ICT) and bond strength were investigated by applying natural bond orbital (NBO) analysis. Nonlinear optical properties of Mn(II) complex were investigated by the determining of molecular polarizability (α) and hyperpolarizability (β) parameters.

Li-adsorption on doped Mo2C monolayer: A novel electrode material for Li-ion batteries

NASA Astrophysics Data System (ADS)

Mehta, Veenu; Tankeshwar, K.; Saini, Hardev S.

2018-04-01

A first principle calculation has been used to study the electronic and magnetic properties of pristine and N/Mn-doped Mo2C with and without Li-adsorption. The pseudopotential method implemented in SIESTA code based on density functional theory with generalized gradient approximation (GGA) as exchange-correlation (XC) potential has been employed. Our calculated results revealed that the Li gets favorably adsorbed on the hexagonal centre in pristine Mo2C and at the top of C-atom in case of N/Mn-doped Mo2C. The doping of Mn and N atom increases the adsorption of Li in Mo2C monolayer which may results in enhancement of storage capacity in Li-ion batteries. The metallic nature of Li-adsorbed pristine and N/Mn-doped Mo2C monolayer implies a good electronic conduction which is crucial for anode materials for its applications in rechargeable batteries. Also, the open circuit voltage for single Li-adsorption in doped Mo2C monolayer comes in the range of 0.4-1.0 eV which is the optimal range for any material to be used as an anode material. Our result emphasized the enhanced performance of doped Mo2C as an anode material in Li-ion batteries.

Observation of martensitic transformation in Ni50Mn41Cu4Sn5 Heusler alloy prepared by mechanical alloying

NASA Astrophysics Data System (ADS)

Saini, Dinesh; Singh, Satyavir; Banerjee, M. K.; Sachdev, K.

2017-05-01

Mechanical alloying route has been employed for preparation of a single phase Ni50Mn41Cu4Sn5 (atomic %) Heusler alloy. Use of high energy planetary ball mill enables successful preparation of the same as authenticated by detailed X-ray diffraction (XRD) study. Microstructural study is carried out by optical and scanning electron microscopic techniques. XRD results reveal that increasing milling time leads to reduction in crystallite size and concurrent increase in lattice strain. Microstructural results indicate formation of self-assembled martensite twins.

From single magnetic adatoms on superconductors to coupled spin chains

NASA Astrophysics Data System (ADS)

Franke, Katharina J.

Magnetic adsorbates on conventional s-wave superconductors lead to exchange interactions that induce Yu-Shiba-Rusinov (YSR) states inside the superconducting energy gap. Here, we employ tunneling spectroscopy at 1.1 K to investigate magnetic atoms and chains on superconducting Pb surfaces. We show that individual Manganese (Mn) atoms give rise to a distinct number of YSR-states. The single-atom junctions are stable over several orders of magnitude in conductance. We identify single-electron tunneling as well as Andreev processes. When the atoms are brought into sufficiently close distance, the Shiba states hybridize, thus giving rise to states with bonding and anti-bonding character. It has been shown that the Pb(110) surface supports the self-assembly of Fe chains, which exhibit fingerprints of Majorana bound states. Using superconducting tips, we resolve a rich subgap structure including peaks at zero energy and low-energy resonances, which overlap with the putative Majorana states. We gratefully acknowledge funding by the Deutsche Forschungsgemeinschaft through collaborative research Grant Sfb 658, and through Grant FR2726/4, as well by the European Research Council through Consolidator Grant NanoSpin.

First-principles studies on 3d transition metal atom adsorbed twin graphene

NASA Astrophysics Data System (ADS)

Li, Lele; Zhang, Hong; Cheng, Xinlu; Miyamoto, Yoshiyuki

2018-05-01

Twin graphene is a new two-dimensional semiconducting carbon allotrope which is proposed recently. The structural, magnetic and electronic properties are investigated for 3d transition metal (TM) atom adsorbed twin graphene by means of GGA+U calculations. The results show most of single 3d transition metal atom except Zn can make twin graphene magnetization. The adsorption of single TM atom can also make the twin graphene systems turn to half metal (V adsorption), half-semiconductor (Fe adsorption) or metal (Sc, Cr, Mn, Co and Cu adsorption). The semiconducting nature still exists for Ti, Ni and Zn adsorption. All the 3d TM adatoms belong to n-type doping for transferring charge to the neighboring C atoms and have strong covalent bond with these C atoms. The influence of Hubbard U value on half-metallic V adsorbed system is also considered. As the U increases, the system can gradually transform from metal to half metal and metal. The effect of the coverage is investigated for two TM atoms (Sc-Fe) adsorption, too. We can know TM atoms adsorbed twin graphene have potentials to be spintronic device and nanomagnets from the results.

Oxygen-storage behavior and local structure in Ti-substituted YMnO3

NASA Astrophysics Data System (ADS)

Levin, I.; Krayzman, V.; Vanderah, T. A.; Tomczyk, M.; Wu, H.; Tucker, M. G.; Playford, H. Y.; Woicik, J. C.; Dennis, C. L.; Vilarinho, P. M.

2017-02-01

Hexagonal manganates RMnO3 (R=Y, Ho, Dy) have been recently shown to exhibit oxygen-storage capacities promising for three-way catalysts, air-separation, and related technologies. Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygen-breathing properties of these materials towards practical applications. Specifically, Y(Mn1-xTix)O3 solid solutions exhibit facile oxygen absorption/desorption via reversible Ti3+↔Ti4+ and Mn3+↔Mn4+ reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn3+1-x-yMn4+yTi4+xO3+δ. The presence of Ti promotes the oxidation of Mn3+ to Mn4+, which is almost negligible for YMnO3 in air, thereby increasing the uptake of oxygen beyond that required for a given Ti4+ concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO5] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO3 structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO5] bipyramids. The tensile bond strain around the 5-fold coordinated Mn site and the strong preference of Ti4+(and Mn4+) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere.

Oxygen-storage behavior and local structure in Ti-substituted YMnO 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, I.; Krayzman, V.; Vanderah, T. A.

Hexagonal manganates RMnO3 (R=Y, Ho, Dy) have been recently shown to exhibit oxygen-storage capacities promising for three-way catalysts, air-separation, and related technologies. Here, we demonstrate that Ti substitution for Mn can be used to chemically tune the oxygen-breathing properties of these materials towards practical applications. Specifically, Y(Mn1-xTix)O3 solid solutions exhibit facile oxygen absorption/desorption via reversible Ti3+↔Ti4+ and Mn3+↔Mn4+ reactions already in ambient air at ≈400 °C and ≈250 °C, respectively. On cooling, the oxidation of both cations is accompanied by oxygen uptake yielding a formula YMn3+1-x-yMn4+yTi4+xO3+δ. The presence of Ti promotes the oxidation of Mn3+ to Mn4+, which is almostmore » negligible for YMnO3 in air, thereby increasing the uptake of oxygen beyond that required for a given Ti4+ concentration. The reversibility of the redox reactions is limited by sluggish kinetics; however, the oxidation process continues, if slowly, even at room temperature. The extra oxygen atoms are accommodated by the large interstices within a triangular lattice formed by the [MnO5] trigonal bipyramids. According to bond distances from Rietveld refinements using the neutron diffraction data, the YMnO3 structure features under-bonded Mn and even more severely under-bonded oxygen atoms that form the trigonal bases of the [MnO5] bipyramids. The tensile bond strain around the 5-fold coordinated Mn site and the strong preference of Ti4+(and Mn4+) for higher coordination numbers likely provide driving forces for the oxidation reaction. Reverse Monte Carlo refinements of the local atomic displacements using neutron total scattering revealed how the excess oxygen atoms are accommodated in the structure by correlated local displacements of the host atoms. Large displacements of the under-bonded host oxygen atoms play a key part in this lattice-relaxation process, facilitating reversible exchange of significant amounts of oxygen with atmosphere.« less

Spin-polarized electron emitter: Mn-doped GaN nanotubes and their arrays

NASA Astrophysics Data System (ADS)

Hao, Shaogang; Zhou, Gang; Wu, Jian; Duan, Wenhui; Gu, Bing-Lin

2004-03-01

The influences from the doping magnetic atom, Mn, on the geometry, electronic properties, and spin-polarization characteristics are demonstrated for open armchair gallium nitrogen (GaN) nanotubes and arrays by use of the first-principles calculations. The interaction between dangling bonds of Ga (Mn) and N atoms at the open-end promotes the self-close of the tube mouth and formation of a more stable open semicone top. Primarily owing to hybridization of Mn 3d and N 2p orbitals, one Mn atom introduces several impurity energy levels into the original energy gap, and the calculated magnetic moment is 4μB. The electron spin polarizations in the field emission are theoretically evaluated. We suggest that armchair open GaN nanotube arrays doped with a finite number of magnetic atoms may have application potential as the electron source of spintronic devices in the future.

Accelerated Oxygen Atom Transfer and C-H Bond Oxygenation by Remote Redox Changes in Fe3 Mn-Iodosobenzene Adducts.

PubMed

de Ruiter, Graham; Carsch, Kurtis M; Gul, Sheraz; Chatterjee, Ruchira; Thompson, Niklas B; Takase, Michael K; Yano, Junko; Agapie, Theodor

2017-04-18

We report the synthesis, characterization, and reactivity of [LFe 3 (PhPz) 3 OMn( s PhIO)][OTf] x (3: x=2; 4: x=3), where 4 is one of very few examples of iodosobenzene-metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57 Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (Fe III 2 Fe II Mn II vs. Fe III 3 Mn II ) influence oxygen atom transfer in tetranuclear Fe 3 Mn clusters. In particular, a one-electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

An intramolecular antiferromagnetically coupled pentanuclear Mn(II) cluster containing acetate and tetracarboxylate linkers: Synthesis, structure and magnetism

NASA Astrophysics Data System (ADS)

Wu, Jian; Liu, Wei-Cong; Wu, Xi-Ren; Liu, Jian-Qiang; Sakiyama, Hiroshi; Yadav, Reena; Kumar, Abhinav

2016-06-01

A new Mn(II) complex {[Mn5(CH3COO)2(L)2(DMF)8](DMF)}n (1), (H4L = 3,5-bis(3‧,5‧-dicarboxylphenyl)-1H-1,2,3-triazole), has been synthesized and structurally characterized. The complex 1 have pentanuclear Mn(II) core, where the two sides of metal centers (Mn2 and Mn3) have trigonal bipyramidal arrangement and the middle metal center (Mn1) have octahedral environment utilizing two O atoms from adjacent bridging bidentate carboxylate groups and four O atoms from four coordinated DMF molecules. The planar arrangement of pentanuclear Mn(II) atoms are linked by L linkage to generate two dimensional sheet. The magnetic property of the compound indicates χMT value for the five Mn(II) unit to be 21.3 cm3 K mol-1 at 300 K, which is close to the spin-only value (21.9 cm3 K mol-1) for the pentamer having S = 5/2. Also, the Hirshfeld surface analyses have been performed which indicated the absence of weak Mn···Mn interaction thereby corroborating the results of observed magnetic properties.

Atomization from a tantalum surface in graphite furnace atomic absorption spectrometry

NASA Astrophysics Data System (ADS)

Gregoire, D. C.; Chakrabarti, C. L.

The mechanism of atom formation of U, V, Mo, Ni, Mn, Cu and Mg atomized from pyrolytic graphite and tantalum metal surfaces has been studied. The mechanism of atom formation for U from a graphite tube atomizer is reported for the first time. The peak absorbance for U and Cu is increased by factors of 59.7 and 2.0, respectively, whereas that of V, Mo and Ni is reduced by several orders of magnitude when they are atomized from a tantalum metal surface. The peak absorbance of Mn and Mg is not appreciably affected by the material of the atomization surface. Interaction of Mn and Mg with the graphite surface and formation of their refractory carbides was found to be negligible. Uranium forms a refractory carbide when heated from a graphite surface.

Highly atom-economic synthesis of graphene/Mn3O4 hybrid composites for electrochemical supercapacitors

NASA Astrophysics Data System (ADS)

Jiangying, Qu; Feng, Gao; Quan, Zhou; Zhiyu, Wang; Han, Hu; Beibei, Li; Wubo, Wan; Xuzhen, Wang; Jieshan, Qiu

2013-03-01

A highly atom-economic procedure for the preparation of reduced graphene oxide/Mn3O4 (rGO/Mn3O4) composites is reported. Pristine graphene oxide/manganese sulfate (GO/MnSO4) suspension produced by modified Hummers method is utilized with high efficiency, which has been in situ converted into GO/Mn3O4 hybrid composite by air oxidation, then into rGO/Mn3O4 composite by means of dielectric barrier discharge (DBD) plasma-assisted deoxygenation. The Mn3O4 content of the rGO/Mn3O4 composites can be readily tailored. It is observed that Mn3O4 nanoparticles of 15-24 nm are well-dispersed on graphene sheets with Mn3O4 loading as high as 90%. The specific capacitance of the as-prepared rGO/Mn3O4 hybrids with 90% Mn3O4 reaches 193 F g-1 when employed as the electrode material in neutral Na2SO4 electrolyte solutions (76 F g-1 for pristine graphene and 95 F g-1 for pure Mn3O4), which indicates the positive synergetic effects from both graphene and attached Mn3O4. The method developed in this study should offer a new technique for the large scale and highly atom-economic production of graphene/MnOx composites for many applications.

XANES, EXAFS and Kbeta spectroscopic studies of the oxygen-evolving complex in Photosystem II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robblee, John Henry

A key question for the understanding of photosynthetic water oxidation is whether the four oxidizing equivalents necessary to oxidize water to dioxygen are accumulated on the four Mn ions of the oxygen evolving complex (OEC), or whether some ligand-centered oxidations take place before the formation and release of dioxygen during the S 3 → [S 4] → S 0 transition. Progress in instrumentation and flash sample preparation allowed us to apply Mn Kβ X-ray emission spectroscopy (Kb XES) to this problem for the first time. The Kβ XES results, in combination with Mn X-ray absorption near-edge structure (XANES) and electronmore » paramagnetic resonance (EPR) data obtained from the same set of samples, show that the S 2 → S 3 transition, in contrast to the S 0 → S 1 and S 1 → S 2 transitions, does not involve a Mn-centered oxidation. This is rationalized by manganese μ-oxo bridge radical formation during the S 2 → S 3 transition. Using extended X-ray absorption fine structure (EXAFS) spectroscopy, the local environment of the Mn atoms in the S 0 state has been structurally characterized. These results show that the Mn-Mn distance in one of the di-μ-oxo-bridged Mn-Mn moieties increases from 2.7 Å in the S 1} state to 2.85 Å in the S 0 state. Furthermore, evidence is presented that shows three di-μ-oxo binuclear Mn 2 clusters may be present in the OEC, which is contrary to the widely held theory that two such clusters are present in the OEC. The EPR properties of the S 0 state have been investigated and a characteristic ''multiline'' signal in the S 0 state has been discovered in the presence of methanol. This provides the first direct confirmation that the native S 0 state is paramagnetic. In addition, this signal was simulated using parameters derived from three possible oxidation states of Mn in the S 0 state. The dichroic nature of X-rays from synchrotron radiation and single-crystal Mn complexes have been exploited to selectively probe Mn-ligand bonds using XANES and EXAFS spectroscopy. The results from single-crystal Mn complexes show that dramatic dichroism exists in these complexes, and are suggestive of a promising future for single-crystal studies of PS II.« less

Nuclearity controlled cyanide-bridged bimetallic CrIII-MnII compounds: synthesis, crystal structures, magnetic properties and theoretical calculations.

PubMed

Toma, Luminita; Lescouëzec, Rodrigue; Vaissermann, Jacqueline; Delgado, Fernando S; Ruiz-Pérez, Catalina; Carrasco, Rosa; Cano, Juan; Lloret, Francesc; Julve, Miguel

2004-11-19

The preparation, X-ray crystallography and magnetic investigation of the compounds PPh4[Cr(bipy)(CN)4].2 CH3CN.H2O (1) (mononuclear), [[Cr(bipy)(CN)4]2Mn-(H2O)4].4H2O (2) (trinuclear), [[Cr(bipy)(CN)4]2Mn(H2O)2] (3) (chain) and [[Cr(bipy)(CN)4]2Mn(H2O)].H2O.CH3CN (4) (double chain) [bipy=2,2'-bipyridine; PPh4 (+)=tetraphenylphosphonium] are described herein. The [Cr(bipy)(CN)4]- unit act either as a monodentate (2) or bis-monodentate (3) ligand toward the manganese atom through one (2) or two (3) of its four cyanide groups. The manganese atom is six-coordinate with two (2) or four (3) cyanide nitrogens and four (2) or two (3) water molecules building a distorted octahedral environment. In 4, two chains of 3 are pillared through interchain Mn-N-C-Cr links which replace one of the two trans-coordinated water molecules at the manganese atom to afford a double chain structure where bis- and tris-monodenate coordination modes of [Cr(bipy)(CN)4]- coexist. The magnetic properties of 1-4 were investigated in the temperature range 1.9-300 K. A Curie law behaviour for a magnetically isolated spin quartet is observed for 1. A significant antiferromagnetic interaction between CrIII and MnII through the single cyanide bridge [J=-6.2 cm(-1), the Hamiltonian being defined as H=-J(SCr1.SMn+SCr2.SMn] occurs in 2 leading to a low-lying spin doublet which is fully populated at T <5 K. A metamagnetic behaviour is observed for 3 and 4 [the values of the critical field Hc being ca. 3000 (3) and 1500 Oe (4)] which is associated to the occurrence of weak interchain antiferromagnetic interactions between ferrimagnetic Cr2III MnII chains. The analysis of the exchange pathways in 2-4 through DFT type calculations together with the magnetic bevaviour simulation using the quantum Monte Carlo methodology provided a good understanding of their magnetic properties.

A new SOD mimic, Mn(III) ortho N-butoxyethylpyridylporphyrin combines superb potency and lipophilicity with low toxicity

PubMed Central

Rajic, Zrinka; Tovmasyan, Artak; Spasojevic, Ivan; Sheng, Huaxin; Lu, Miaomiao; Li, Alice M.; Gralla, Edith B.; Warner, David S.; Benov, Ludmil; Batinic-Haberle, Ines

2012-01-01

The Mn porphyrins of kcat(O2˙−) as high as that of a superoxide dismutase enzyme, and of optimized lipophilicity have already been synthesized. Their exceptional in vivo potency is at least in part due to their ability to mimic site and location of mitochondrial superoxide dismutase, MnSOD. MnTnHex-2-PyP5+ is the most studied among lipophilic Mn porphyrins. It is of remarkable efficacy in animal models of oxidative stress injuries and particularly in central nervous system diseases. However, when used at high single and multiple doses it becomes toxic. The toxicity of MnTnHex-2-PyP5+ has been in part attributed to its micellar properties, i.e. the presence of polar cationic nitrogens and hydrophobic alkyl chains. The replacement of a CH2 group by oxygen atom in each of the four alkyl chains was meant to disrupt the porphyrin micellar character. When such modification occurs at the end of long alkyl chains, the oxygens become heavily solvated, which leads to a significant drop in the lipophilicity of porphyrin. However, when the oxygen atoms are buried deeper within the long heptyl chains, their excessive solvation is precluded and the lipophilicity preserved. The presence of oxygens and the high lipophilicity bestow the exceptional chemical and physical properties to Mn(III) meso-tetrakis(N-n-butoxyethylpyridinium-2-yl)porphyrin, MnTnBuOE-2-PyP5+. The high SOD-like activity is fully preserved and somewhat enhanced: log kcat(O2˙−) = 7.83 vs 7.48 and 7.65 for MnTnHex-2-PyP5+ and MnTnHep-2-PyP5+, respectively. MnTnBuOE-2-PyP5+ was tested in an O2˙− - specific in vivo assay – aerobic growth of SOD-deficient yeast, Saccharomyces cerevisiae, where it was fully protective in the range of 5 – 30 µM. MnTnHep-2-PyP5+ was already toxic at 5 µM, and MnTnHex-2-PyP5+ became toxic at 30 µM. In a mouse toxicity study, MnTnBuOE-2-PyP5+ was several-fold less toxic than either MnTnHex-2-PyP5+ or MnTnHep-2-PyP5+. PMID:22336516

First-principles calculations of the magnetic properties of (Cd,Mn)Te nanocrystals

NASA Astrophysics Data System (ADS)

Echeverría-Arrondo, C.; Pérez-Conde, J.; Ayuela, A.

2009-04-01

We investigate the electronic and magnetic properties of Mn-doped CdTe nanocrystals (NCs) with ˜2nm in diameter which can be experimentally synthesized with Mn atoms inside. Using the density-functional theory, we consider two doping cases: NCs containing one or two Mn impurities. Although the Mnd peaks carry five up electrons in the dot, the local magnetic moment on the Mn site is 4.65μB . It is smaller than 5μB because of the sp-d hybridization between the localized 3d electrons of the Mn atoms and the s - and p -type valence states of the host compound. The sp-d hybridization induces small magnetic moments on the Mn-nearest-neighbor Te sites, antiparallel to the Mn moment affecting the p -type valence states of the undoped dot, as usual for a kinetic-mediated exchange magnetic coupling. Furthermore, we calculate the parameters standing for the sp-d exchange interactions. Conduction N0α and valence N0β are close to the experimental bulk values when the Mn impurities occupy bulklike NCs’ central positions, and they tend to zero close to the surface. This behavior is further explained by an analysis of valence-band-edge states showing that symmetry breaking splits the states and in consequence reduces the exchange. For two Mn atoms in several positions, the valence edge states show a further departure from an interpretation based in a perturbative treatment. We also calculate the d-d exchange interactions |Jdd| between Mn spins. The largest |Jdd| value is also for Mn atoms on bulklike central sites; in comparison with the experimental d-d exchange constant in bulk Cd0.95Mn0.05Te , it is four times smaller.

Half-metallic Co-based quaternary Heusler alloys for spintronics: Defect- and pressure-induced transitions and properties

DOE PAGES

Enamullah, .; Johnson, D. D.; Suresh, K. G.; ...

2016-11-07

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L2 1) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range.more » Antisite disorder between Cr-Al pair in CoMnCrAl alloy is energetically the most favorable, and retains half-metallic character in Cr-excess regime. However, Co-deficient samples in both alloys undergo a transition from half-metallic to metallic, with a discontinuity in the saturation magnetization. For binary swaps, configurations that compete with the ground state are identified and show no loss of half-metallicity; however, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. For single binary swaps, there is a significant energy cost in CoMnCrAl but with no loss of half-metallicity. Although a few configurations in CoFeCrGe energetically compete with the ground state, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. Furthermore, this information should help in controlling these potential spintronic materials.« less

Half-metallic Co-based quaternary Heusler alloys for spintronics: Defect- and pressure-induced transitions and properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enamullah, .; Johnson, D. D.; Suresh, K. G.

Heusler compounds offer potential as spintronic devices due to their spin polarization and half-metallicity properties, where electron spin-majority (minority) manifold exhibits states (band gap) at the electronic chemical potential, yielding full spin polarization in a single manifold. Yet, Heuslers often exhibit intrinsic disorder that degrades its half-metallicity and spin polarization. Using density-functional theory, we analyze the electronic and magnetic properties of equiatomic Heusler (L2 1) CoMnCrAl and CoFeCrGe alloys for effects of hydrostatic pressure and intrinsic disorder (thermal antisites, binary swaps, and vacancies). Under pressure, CoMnCrAl undergoes a metallic transition, while half-metallicity in CoFeCrGe is retained for a limited range.more » Antisite disorder between Cr-Al pair in CoMnCrAl alloy is energetically the most favorable, and retains half-metallic character in Cr-excess regime. However, Co-deficient samples in both alloys undergo a transition from half-metallic to metallic, with a discontinuity in the saturation magnetization. For binary swaps, configurations that compete with the ground state are identified and show no loss of half-metallicity; however, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. For single binary swaps, there is a significant energy cost in CoMnCrAl but with no loss of half-metallicity. Although a few configurations in CoFeCrGe energetically compete with the ground state, the minority-spin band gap and magnetic moments vary depending on the atoms swapped. Furthermore, this information should help in controlling these potential spintronic materials.« less

Surface atomic structure of alloyed Mn 5Ge 3(0 0 0 1) by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Kim, Howon; Jung, Goo-Eun; Yoon, Jong Keon; Chung, Kyung Hoon; Kahng, Se-Jong

Surface atomic structure of Mn 5Ge 3(0 0 0 1) is studied by scanning tunneling microscopy. Hexagonal honeycomb ordering is observed at high energy levels, ∣ E - EF∣ ˜ 1.2 eV, on the flat regions of three-dimensional Mn 5Ge 3 islands. At low energy levels, ∣ E - EF∣ ˜ 0.5 eV, however, atomic images exhibit dot-array and ring-array structures, which show complete and partial contrast inversion, compared to the honeycomb ordering. Experimental observations are discussed on the basis of possible atomic models.

Slip and Twinning in the [ 1 ¯ $ /line{mathbf{1}} $ 49]-Oriented Single Crystals of a High-Entropy Alloy

NASA Astrophysics Data System (ADS)

Kireeva, I. V.; Chumlyakov, Yu. I.; Pobedennaya, Z. V.; Platonova, Yu. N.; Kuksgauzen, I. V.; Kuksgauzen, D. A.; Poklonov, V. V.; Karaman, I.; Sehitoglu, H.

2016-12-01

Using [ overline{1} 49] - oriented single crystals of an FCC Fe20Ni20Mn20Cr20Co20 (at.%) high-entropy alloy subjected to tensile deformation, the temperature dependence of critical resolved shear stresses τcr(T) and the deformation mechanism of slip and twinning are investigated in the early stages of deformation at ɛ ≤ 5% within the temperature interval T = 77-573 K. It is shown that τcr increases with decreasing the testing temperature and the τcr(T) temperature dependence is controlled by the slip of perfect dislocations a/2<110>. The early deformation stages ɛ ≤ 5% are associated with the development of planar slip by pileups of perfect dislocations a/2<110>, stacking faults and mechanical twins, which is observed in the temperature interval from 77 to 423 K. A comparison of the temperature dependence τcr(T) and the development of mechanical twinning is performed between the [ overline{1} 49] -oriented single crystals of the Fe20Ni20Mn20Cr20Co20 high-entropy alloy, the single crystals of the austenitic stainless steel, Fe - 18% Cr - 12% Ni - 2Mo (wt.%) without nitrogen atoms (Steel 316) and Hadfield steel, Fe - 13% Mn - (1-1.3)% C (wt.%).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Dan, E-mail: danzhou@is.mpg.de; Sigle, Wilfried; Wang, Yi

We studied ZrO{sub 2} − La{sub 2/3}Sr{sub 1/3}MnO{sub 3} pillar–matrix thin films which were found to show anomalous magnetic and electron transport properties. With the application of an aberration-corrected transmission electron microscope, interfacial chemistry, and atomic-arrangement of the system, especially of the pillar–matrix interface were revealed at atomic resolution. Minor amounts of Zr were found to occupy Mn positions within the matrix. The Zr concentration reaches a minimum near the pillar–matrix interface accompanied by oxygen vacancies. La and Mn diffusion into the pillar was revealed at atomic resolution and a concomitant change of the Mn valence state was observed.

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

DOE PAGES

McGuire, Michael A.; Cao, Huibo; Chakoumakos, Bryan C.; ...

2014-11-18

Here we report structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature T SR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropymore » of the atomic displacement parameters for Bi with increasing temperature above T SR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. Finally, the identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.« less

A study of QM/Langevin-MD simulation for oxygen-evolving center of photosystem II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uchida, Waka; Kimura, Yoshiro; Wakabayashi, Masamitsu

2013-12-10

We have performed three QM/Langevin-MD simulations for oxygen-evolving complex (OEC) and surrounding residues, which are different configurations of the oxidation numbers on Mn atoms in the Mn{sub 4}O{sub 5}Ca cluster. By analyzing these trajectories, we have observed sensitivity of the change to the configuration of Mn oxidation state on O atoms of carboxyl on three amino acids, Glu354, Ala344, and Glu333. The distances from Mn to O atoms in residues contacting with the Mn{sub 4}O{sub 5}Ca cluster were analyzed for the three trajectories. We found the good correlation of the distances among the simulations. However, the distances with Glu354, Ala344,more » and Glu333 have not shown the correlation. These residues can be sensitive index of the changes of Mn oxidation numbers.« less

Neutron diffraction study of a non-strichiometric Ni-Mn-Ga MSM alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ari-Gur, Pnina; Garlea, Vasile O

2013-01-01

The structure and chemical order of a Heusler alloy of non-stoichiometric composition Ni-Mn-Ga were studied using constant-wavelength (1.538 ) neutron diffraction at 363K and the diffraction pattern was refined using the FullProf software. At this temperature the structure is austenite (cubic) with Fm-3m space group and lattice constant of a = 5.83913(4) [ ]. The chemical order is of critical importance in these alloys, as Mn becomes antiferromagnetic when the atoms are closer than the radius of the 3d shell. In the studied alloy the refinement of the site occupancy showed that the 4b (Ga site) contained as much asmore » 22% Mn; that significantly alters the distances between the Mn atoms in the crystal and, as a result, also the exchange energy between some of the Mn atoms. Based on the refinement, the composition was determined to be Ni1.91Mn1.29Ga0.8« less

Control of conduction type in ferromagnetic (Zn,Sn,Mn)As2 thin films by changing Mn content and effect of annealing on thin films with n-type conduction

NASA Astrophysics Data System (ADS)

Minamizawa, Yuto; Kitazawa, Tomohiro; Hidaka, Shiro; Toyota, Hideyuki; Nakamura, Shin-ichi; Uchitomi, Naotaka

2018-04-01

The conduction type in (Zn,Sn,Mn)As2 thin films grown by molecular beam epitaxy (MBE) on InP substrates was found to be controllable from p-type to n-type as a function of Mn content. n-type (Zn,Sn,Mn)As2 thin films were obtained by Mn doping of more than approximately 11 cat.%. It is likely that Mn interstitials (MnI) incorporated by excess Mn doping are located at tetrahedral hollow spaces surrounded by Zn and Sn cation atoms and four As atoms, which are expected to act as donors in (Zn,Sn,Mn)As2, resulting in n-type conduction. The effect of annealing on the structural, electrical and magnetic properties of n-type (Zn,Sn,Mn)As2 thin films was investigated as functions of annealing temperature and time. It was revealed that even if the annealing temperature is considerably higher than the growth temperature of 320 °C, the magnetic properties of the thin films remain stable. This suggests that a MnI complex surrounded by Zn and Sn atoms is thermally stable during high-temperature annealing. The n-type (Zn,Sn,Mn)As2 thin films may be suitable for application as n-type spin-polarized injectors.

Discovery of ferromagnetism with large magnetic anisotropy in ZrMnP and HfMnP

DOE PAGES

Lamichhane, Tej N.; Taufour, Valentin; Masters, Morgan W.; ...

2016-08-29

Here, ZrMnP and HfMnP single crystals are grown by a self-flux growth technique, and structural as well as temperature dependent magnetic and transport properties are studied. Both compounds have an orthorhombic crystal structure. ZrMnP and HfMnP are ferromagnetic with Curie temperatures around 370 K and 320 K, respectively. The spontaneous magnetizations of ZrMnP and HfMnP are determined to be 1.9 μ B/f.u. and 2.1 μ B/f.u., respectively, at 50 K. The magnetocaloric effect of ZrMnP in terms of entropy change (Δ S) is estimated to be –6.7 kJ m –3 K –1 around 369 K. The easy axis of magnetizationmore » is [100] for both compounds, with a small anisotropy relative to the [010] axis. At 50 K, the anisotropy field along the [001] axis is ~4.6 T for ZrMnP and ~10 T for HfMnP. Such large magnetic anisotropy is remarkable considering the absence of rare-earth elements in these compounds. The first principle calculation correctly predicts the magnetization and hard axis orientation for both compounds, and predicts the experimental HfMnP anisotropy field within 25%. More importantly, our calculations suggest that the large magnetic anisotropy comes primarily from the Mn atoms, suggesting that similarly large anisotropies may be found in other 3d transition metal compounds.« less

1D and 3D Polymeric Manganese(II) Thiolato Complexes: Synthesis, Structure, and Properties of    ∞3[Mn4(SPh)8] and ∞1[Mn(SMes)2].

PubMed

Eichhöfer, Andreas; Lebedkin, Sergei

2018-01-16

Reactions of [Mn{N(SiMe 3 ) 2 } 2 ] 2 with 2.1 equiv of RSH, R = Ph or Mes = C 6 H 2 -2,4,6-(CH 3 ) 3 , yield compounds of the formal composition "Mn(SR) 2 ". Single-crystal X-ray diffraction reveals that ∞ 1 [Mn(SMes) 2 ] forms one-dimensional chains in the crystal via μ 2 -SMes bridges, whereas ∞ 3 [Mn 4 (SPh) 8 ] comprises a three-dimensional network in which adamantanoid cages composed of four Mn atoms and six μ 2 -bridging SPh ligands are connected in three dimensions by doubly bridging SPh ligands. Thermogravimetric analysis and powder diffractometry indicate an reversible uptake of solvent molecules (tetrahydrofuran) into the channels of ∞ 1 [Mn(SMes) 2 ]. Magnetic measurements reveal antiferromagnetic coupling for both compounds with J = -8.2 cm -1 ( ∞ 1 [Mn(SMes) 2 ]) and -10.0 cm -1 ( ∞ 3 [Mn 4 (SPh) 8 ]), respectively. Their optical absorption and photoluminescence (PL) excitation spectra display characteristic d-d bands of Mn 2+ ions in the visible spectral region. Both compounds emit bright phosphorescence at ∼800 nm at low temperatures (<100 K). However, only ∞ 1 [Mn(SMes) 2 ] retains a moderately intense emission at ambient temperature (with a quantum yield of 1.2%). Similar PL properties are also found for the related selenolate complexes ∞ 1 [Mn(SeR) 2 ] (R = Ph, Mes).

Ab initio investigation of competing antiferromagnetic structures in low Si-content FeMn(PSi) alloy

NASA Astrophysics Data System (ADS)

Li, Guijiang; Eriksson, Olle; Johansson, Börje; Vitos, Levente

2016-06-01

The antiferromagnetic structures of a low Si-content FeMn(PSi) alloy were investigated by first principles calculations. One possible antiferromagnetic structure in supercell along the c-axis was revealed in FeMnP0.75Si0.25 alloy. It was found that atomic disorder occupation between Fe atom on 3f and Mn atoms on 3g sites is responsible for the formation of antiferromagnetic structures. Furthermore the magnetic competition and the coupling between possible AFM supercells along the c and a-axis can promote a non-collinear antiferromagnetic structure. These theoretical investigations help to deeply understand the magnetic order in FeMn(PSi) alloys and benefit to explore the potential magnetocaloric materials in Fe2P-type alloys.

Doping Induced Structural Stability and Electronic Properties of GaN Nanotubes

PubMed Central

Khan, Mohammad Irfan; Tyagi, Neha; Swaroop Khare, Purnima

2014-01-01

The present paper discusses the effect of manganese doping on the structural stability and electronic band gap of chiral (2, 1), armchair (3, 3), and zigzag ((6, 0) and (10, 0)) single walled GaN nanotube by using density functional theory based Atomistix Toolkit (ATK) Virtual NanoLab (VNL). The structural stability has been analyzed in terms of minimum ground state total energy, binding, and formation energy. As an effect of Mn doping (1–4 atoms), all the GaN nanotubes taken into consideration show semiconducting to metallic transition first and after certain level of Mn doping changes its trend. PMID:24707225

Preparation of Mo-Re-C samples containing Mo7Re13C with the β-Mn-type structure by solid state reaction of planetary-ball-milled powder mixtures of Mo, Re and C, and their crystal structures and superconductivity

NASA Astrophysics Data System (ADS)

Oh-ishi, Katsuyoshi; Nagumo, Kenta; Tateishi, Kazuya; Takafumi, Ohnishi; Yoshikane, Kenta; Sugiyama, Machiko; Oka, Kengo; Kobayashi, Ryota

2017-01-01

Mo-Re-C compounds containing Mo7Re13C with the β-Mn structure were synthesized with high-melting-temperature metals Mo, Re, and C powders using a conventional solid state method with a planetary ball milling machine instead of the arc melting method. Use of the ball milling machine was necessary to obtain Mo7Re13C with the β-Mn structure using the solid state method. Almost single-phase Mo7Re13C with a trace of impurity were obtained using the synthesis method. By XRF and lattice parameter measurements on the samples, Fe element existed in the compound synthesized using the planetary ball milling machine with a pot and balls made of steel, though Fe element was not detected in the compound synthesized using a pot and balls made of tungsten carbide. The former compound containg the Fe atom did not show superconductivity but the latter compound without the Fe atom showed superconductivity at 6.1 K.

Reduced interface spin polarization by antiferromagnetically coupled Mn segregated to the C o2MnSi /GaAs (001) interface

NASA Astrophysics Data System (ADS)

Rath, Ashutosh; Sivakumar, Chockalingam; Sun, C.; Patel, Sahil J.; Jeong, Jong Seok; Feng, J.; Stecklein, G.; Crowell, Paul A.; Palmstrøm, Chris J.; Butler, William H.; Voyles, Paul M.

2018-01-01

We have investigated the interfacial structure and its correlation with the calculated spin polarization in C o2MnSi /GaAs(001) lateral spin valves. C o2MnSi (CMS) films were grown on As-terminated c(4 ×4 ) GaAs(100) by molecular beam epitaxy using different first atomic layers: MnSi, Co, and Mn. Atomically resolved Z -contrast scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) were used to develop atomic structural models of the CMS/GaAs interfaces that were used as inputs for first-principles calculations to understand the magnetic and electronic properties of the interface. First-principles structures were relaxed and then validated by comparing experimental and simulated high-resolution STEM images. STEM-EELS results show that all three films have similar six atomic layer thick, Mn- and As-rich multilayer interfaces. However, the Co-initiated interface contains a M n2As -like layer, which is antiferromagnetic, and which is not present in the other two interfaces. Density functional theory calculations show a higher degree of interface spin polarization in the Mn- and MnSi-initiated cases, compared to the Co-initiated case, although none of the interfaces are half-metallic. The loss of half-metallicity is attributed, at least in part, to the segregation of Mn at the interface, which leads to the formation of interface states. The implications for the performance of lateral spin valves based on these interfaces are discussed briefly.

Biaxial tensile strain modulates magnetic properties of the 3d transition metal doped stanene

NASA Astrophysics Data System (ADS)

Dai, Xian-Qi; Zhao, Ming-Yu; Zhao, Ru-Meng; Li, Wei

2017-06-01

Utilizing first-principle calculations, the biaxial tensile strain modulating magnetic states and electronic structures of transition metal (TM) (i.e., Mn, Fe, Sc, Ni and Ti) atoms doped in stanene are investigated. It shows that Mn and Fe doped stanene systems are magnetic, while the Sc, Ti and Ni doped stanene systems are nonmagnetic. When the biaxial tensile strain increases, a weaker antiferromagnetic coupling between the nearest neighbor (NN) Sn atoms and Mn (Fe, Ti) atom is observed. For Sc and Ni doped stanene systems, the biaxial strain doesn't introduce spin polarization for the TM atoms. In a word, the TM atoms doped stanene systems may manifest potential applications in nanoelectronics, spintronics and magnetic storage devices.

Local structure in LaMnO3 and CaMnO3 perovskites: A quantitative structural refinement of Mn K -edge XANES data

NASA Astrophysics Data System (ADS)

Monesi, C.; Meneghini, C.; Bardelli, F.; Benfatto, M.; Mobilio, S.; Manju, U.; Sarma, D. D.

2005-11-01

Hole-doped perovskites such as La1-xCaxMnO3 present special magnetic and magnetotransport properties, and it is commonly accepted that the local atomic structure around Mn ions plays a crucial role in determining these peculiar features. Therefore experimental techniques directly probing the local atomic structure, like x-ray absorption spectroscopy (XAS), have been widely exploited to deeply understand the physics of these compounds. Quantitative XAS analysis usually concerns the extended region [extended x-ray absorption fine structure (EXAFS)] of the absorption spectra. The near-edge region [x-ray absorption near-edge spectroscopy (XANES)] of XAS spectra can provide detailed complementary information on the electronic structure and local atomic topology around the absorber. However, the complexity of the XANES analysis usually prevents a quantitative understanding of the data. This work exploits the recently developed MXAN code to achieve a quantitative structural refinement of the Mn K -edge XANES of LaMnO3 and CaMnO3 compounds; they are the end compounds of the doped manganite series LaxCa1-xMnO3 . The results derived from the EXAFS and XANES analyses are in good agreement, demonstrating that a quantitative picture of the local structure can be obtained from XANES in these crystalline compounds. Moreover, the quantitative XANES analysis provides topological information not directly achievable from EXAFS data analysis. This work demonstrates that combining the analysis of extended and near-edge regions of Mn K -edge XAS spectra could provide a complete and accurate description of Mn local atomic environment in these compounds.

Elemental and lattice-parameter mapping of binary oxide superlattices of (LaNiO 3 ) 4 /(LaMnO 3 ) 2 at atomic resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, Ji-Hwan; Lu, Ping; Hoffman, Jason

2016-12-19

We construct the elemental distribution and lattice strain maps from the measured atomic column positions in a (LaNiO3)(4)/(LaMnO3)(2) superlattice over a large field of view. The correlation between the distribution of B-cations and the lattice parameter in the form of Vegard's law is validated using atomic resolution energy dispersive x-ray spectroscopy (EDS). The maps show negligible Mn intermixing in the LaNiO3 layer, while Ni intermixing in the LaMnO3 layer improves away from the substrate interface to 9.5 atomic% from the 8th period onwards, indicating that the superlattice interfacial sharpness is established as the distance from the substrate increases. The mapsmore » allow an observation of the compositional defects of the B-sites, which is not possible by Z-contrast alone. Thus, this study demonstrates a promising approach for atomic scale correlative study of lattice strain and composition, and a method for the calibration of atomic resolution EDS maps.« less

High purity polyimide analysis by solid sampling graphite furnace atomic absorption spectrometry

NASA Astrophysics Data System (ADS)

Santos, Rafael F.; Carvalho, Gabriel S.; Duarte, Fabio A.; Bolzan, Rodrigo C.; Flores, Erico M. M.

2017-03-01

In this work, Cr, Cu, Mn, Na and Ni were determined in high purity polyimides (99.5%) by solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) using Zeeman effect background correction system with variable magnetic field, making possible the simultaneous measurement at high or low sensitivity. The following analytical parameters were evaluated: pyrolysis and atomization temperatures, feasibility of calibration with aqueous solution, linear calibration range, sample mass range and the use of chemical modifier. Calibration with aqueous standard solutions was feasible for all analytes. No under or overestimated results were observed and up to 10 mg sample could be introduced on the platform for the determination of Cr, Cu, Mn, Na and Ni. The relative standard deviation ranged from 3 to 20%. The limits of detection (LODs) achieved using the high sensitivity mode were as low as 7.0, 2.5, 1.7, 17 and 0.12 ng g- 1 for Cr, Cu, Mn, Na and Ni, respectively. No addition of chemical modifier was necessary, except for Mn determination where Pd was required. The accuracy was evaluated by analyte spike and by comparison of the results with those obtained by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry after microwave-assisted digestion in a single reaction chamber system and also by neutron activation analysis. No difference among the results obtained by SS-GFAAS and those obtained by alternative analytical methods using independent techniques. SS-GFAAS method showed some advantages, such as the determination of metallic contaminants in high purity polyimides with practically no sample preparation, very low LODs, calibration with aqueous standards and determination in a wide range of concentration.

Anomalous magnetic configuration of Mn{sub 2}NiAl ribbon and the role of hybridization in the martensitic transformation of Mn{sub 50}Ni{sub 50−x}Al{sub x} ribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, R. B.; Department of Physics, Hebei Medical University, Shijiazhuang 050017; Zhao, D. W.

2014-12-08

The magnetic configuration of Mn{sub 2}NiAl ribbon has been investigated. In contrast to Ni{sub 2}MnAl, the compound Mn{sub 2}NiAl with considerable disorder does exhibit ferromagnetism and, due to exchange interaction competition, both ferromagnetic and antiferromagnetic moment orientations can coexist between nearest neighbor Mn atoms. This is unexpected in Heusler alloys. Regarding the mechanism of the martensitic transformation in Mn{sub 50}Ni{sub 50−x}Al{sub x}, it is found that increasing the Al content results in an unusual change in the lattice constant, a decrease of the transformation entropy change, and enhancement of the calculated electron localization. These results indicate that the p-d covalentmore » hybridization between Mn (or Ni) and Al atoms gradually increases at the expense of the d-d hybridization between Ni and Mn atoms. This leads to an increased stability of the austenite phase and a decrease of the martensitic transformation temperature. For 11 ≤ x ≤ 14, Mn{sub 50}Ni{sub 50−x}Al{sub x} ferromagnetic shape memory alloys are obtained.« less

Magneto-optical spectroscopy of ferromagnetic shape-memory Ni-Mn-Ga alloy

NASA Astrophysics Data System (ADS)

Veis, M.; Beran, L.; Zahradnik, M.; Antos, R.; Straka, L.; Kopecek, J.; Fekete, L.; Heczko, O.

2014-05-01

Magneto-optical properties of single crystal of Ni50.1Mn28.4Ga21.5 magnetic shape memory alloy in martensite and austenite phase were systematically studied. Crystal orientation was approximately along {100} planes of parent cubic austenite. At room temperature, the sample was in modulated 10M martensite phase and transformed to cubic austenite at 323 K. Spectral dependence of polar magneto-optical Kerr effect was obtained by generalized magneto-optical ellipsometry with rotating analyzer in the photon energy range from 1.2 to 4 eV, and from room temperature to temperature above the Curie point. The Kerr rotation spectra exhibit prominent features typical for complexes containing Mn atoms. Significant spectral changes during transformation to austenite can be explained by different optical properties caused by changes in density of states near the Fermi energy.

Crystal structure and magnetic properties of Sr 4Mn 2NiO 9

NASA Astrophysics Data System (ADS)

El Abed, Ahmed; Gaudin, Etienne; Lemaux, Sylvain; Darriet, Jacques

2001-12-01

The crystal structure of Sr 4Mn 2NiO 9 has been refined on single crystal. This phase belongs to the series A 1+ x(A 'xB 1- x)O 3 ( x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr 4Mn 2NiO 9 is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni 2+ ions in the spin state configuration S=0.

Electric Field Control of Interfacial Ferromagnetism in CaMnO3/CaRuO3 Heterostructures

NASA Astrophysics Data System (ADS)

Grutter, A. J.; Kirby, B. J.; Gray, M. T.; Flint, C. L.; Alaan, U. S.; Suzuki, Y.; Borchers, J. A.

2015-07-01

New mechanisms for achieving direct electric field control of ferromagnetism are highly desirable in the development of functional magnetic interfaces. To that end, we have probed the electric field dependence of the emergent ferromagnetic layer at CaRuO3/CaMnO3 interfaces in bilayers fabricated on SrTiO3. Using polarized neutron reflectometry, we are able to detect the ferromagnetic signal arising from a single atomic monolayer of CaMnO3, manifested as a spin asymmetry in the reflectivity. We find that the application of an electric field of 600 kV /m across the bilayer induces a significant increase in this spin asymmetry. Modeling of the reflectivity suggests that this increase corresponds to a transition from canted antiferromagnetism to full ferromagnetic alignment of the Mn4 + ions at the interface. This increase from 1 μB to 2.5 - 3.0 μB per Mn is indicative of a strong magnetoelectric coupling effect, and such direct electric field control of the magnetization at an interface has significant potential for spintronic applications.

Synthesis, crystal structure, and vibrational spectroscopic and UV-visible studies of Cs{sub 2}MnP{sub 2}O{sub 7}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaoua, Saida; Krimi, Saida; Pechev, Stanislav

2013-02-15

A new member of the A{sub 2}MP{sub 2}O{sub 7} diphosphate family, Cs{sub 2}MnP{sub 2}O{sub 7}, has been synthesized and structurally characterized. The crystal structure was determined by single crystal X-Ray diffraction. Cs{sub 2}MnP{sub 2}O{sub 7} crystallizes in the orthorhombic system, space group Pnma ( Music-Sharp-Sign 62), with the unit cell parameters a=16.3398(3), b=5.3872(1), c=9.8872(2) A, Z=4 and V=870.33(3) A{sup 3}. The structure parameters were refined to a final R{sub 1}/wR{sub 2}=0.0194/0.0441 for 1650 observed reflections. The 2D framework of Cs{sub 2}MnP{sub 2}O{sub 7} structure consists of P{sub 2}O{sub 7} and MnO{sub 5} units. The corner-shared MnO{sub 5} and P{sub 2}O{submore » 7} units are alternately arranged along the b axis to form [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains. These chains are interconnected by an oxygen atom to form sheets parallel to the (b, c) plane. The cesium atoms are located between the sheets in 9- and 10-fold coordinated sites. The infrared and Raman vibrational spectra have been investigated. A factor group analysis leads to the determination of internal modes of (P{sub 2}O{sub 7}) groups. UV-visible spectrum consists of weak bands, between 340 and 700 nm, assigned to the forbidden d-d transitions of Mn{sup 2+} ion, and of a strong band around 250 nm, attributed to the O--Mn charge transfer. - Graphical abstract: Structure of Cs{sub 2}MnP{sub 2}O{sub 7}: The 2D structure of Cs{sub 2}MnP{sub 2}O{sub 7} is built from P{sub 2}O{sub 7} diphosphate groups and MnO{sub 5} square pyramids which share corners and form [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains along b axis. These chains are interconnected by an oxygen atom to form wavy (MnP{sub 2}O{sub 7}){sup 2-} sheets parallel to the (b, c) plane. The cesium ions are located between these sheets in the inter-layers space, in zigzag positions. Highlights: Black-Right-Pointing-Pointer A new diphosphate, Cs{sub 2}MnP{sub 2}O{sub 7}, has been synthesized and structurally characterized. Black-Right-Pointing-Pointer The structure consists of a 2D framework built up from (MnP{sub 2}O{sub 7}) sheets. Black-Right-Pointing-Pointer The sheets consist of [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains formed by P{sub 2}O{sub 7} units and MnO{sub 5} square pyramids. Black-Right-Pointing-Pointer A factor group analysis leads to the determination of internal modes of (P{sub 2}O{sub 7}) groups. Black-Right-Pointing-Pointer UV-visible spectrum consists bands assigned to d-d transitions of Mn{sup 2+} ion and to O--Mn CT.« less

An x-ray absorption spectroscopy study of Ni-Mn-Ga shape memory alloys.

PubMed

Sathe, V G; Dubey, Aditi; Banik, Soma; Barman, S R; Olivi, L

2013-01-30

The austenite to martensite phase transition in Ni-Mn-Ga ferromagnetic shape memory alloys was studied by extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) spectroscopy. The spectra at all the three elements', namely, Mn, Ga and Ni, K-edges in several Ni-Mn-Ga samples (with both Ni and Mn excess) were analyzed at room temperature and low temperatures. The EXAFS analysis suggested a displacement of Mn and Ga atoms in opposite direction with respect to the Ni atoms when the compound transforms from the austenite phase to the martensite phase. The first coordination distances around the Mn and Ga atoms remained undisturbed on transition, while the second and subsequent shells showed dramatic changes indicating the presence of a modulated structure. The Mn rich compounds showed the presence of antisite disorder of Mn and Ga. The XANES results showed remarkable changes in the unoccupied partial density of states corresponding to Mn and Ni, while the electronic structure of Ga remained unperturbed across the martensite transition. The post-edge features in the Mn K-edge XANES spectra changed from a double peak like structure to a flat peak like structure upon phase transition. The study establishes strong correlation between the crystal structure and the unoccupied electronic structure in these shape memory alloys.

Highly efficient alkane oxidation catalyzed by [Mn(V)(N)(CN)4](2-). Evidence for [Mn(VII)(N)(O)(CN)4](2-) as an active intermediate.

PubMed

Ma, Li; Pan, Yi; Man, Wai-Lun; Kwong, Hoi-Ki; Lam, William W Y; Chen, Gui; Lau, Kai-Chung; Lau, Tai-Chu

2014-05-28

The oxidation of various alkanes catalyzed by [Mn(V)(N)(CN)4](2-) using various terminal oxidants at room temperature has been investigated. Excellent yields of alcohols and ketones (>95%) are obtained using H2O2 as oxidant and CF3CH2OH as solvent. Good yields (>80%) are also obtained using (NH4)2[Ce(NO3)6] in CF3CH2OH/H2O. Kinetic isotope effects (KIEs) are determined by using an equimolar mixture of cyclohexane (c-C6H12) and cyclohexane-d12 (c-C6D12) as substrate. The KIEs are 3.1 ± 0.3 and 3.6 ± 0.2 for oxidation by H2O2 and Ce(IV), respectively. On the other hand, the rate constants for the formation of products using c-C6H12 or c-C6D12 as single substrate are the same. These results are consistent with initial rate-limiting formation of an active intermediate between [Mn(N)(CN)4](2-) and H2O2 or Ce(IV), followed by H-atom abstraction from cyclohexane by the active intermediate. When PhCH2C(CH3)2OOH (MPPH) is used as oxidant for the oxidation of c-C6H12, the major products are c-C6H11OH, c-C6H10O, and PhCH2C(CH3)2OH (MPPOH), suggesting heterolytic cleavage of MPPH to generate a Mn═O intermediate. In the reaction of H2O2 with [Mn(N)(CN)4](2-) in CF3CH2OH, a peak at m/z 628.1 was observed in the electrospray ionization mass spectrometry, which is assigned to the solvated manganese nitrido oxo species, (PPh4)[Mn(N)(O)(CN)4](-)·CF3CH2OH. On the basis of the experimental results the proposed mechanism for catalytic alkane oxidation by [Mn(V)(N)(CN)4](2-)/ROOH involves initial rate-limiting O-atom transfer from ROOH to [Mn(N)(CN)4](2-) to generate a manganese(VII) nitrido oxo active species, [Mn(VII)(N)(O)(CN)4](2-), which then oxidizes alkanes (R'H) via a H-atom abstraction/O-rebound mechanism. The proposed mechanism is also supported by density functional theory calculations.

Accelerated Oxygen Atom Transfer and C-H Bond Oxygenation by Remote Redox Changes in Fe 3Mn-Iodosobenzene Adducts

DOE PAGES

de Ruiter, Graham; Carsch, Kurtis M.; Gul, Sheraz; ...

2017-03-24

In this paper, we report the synthesis, characterization, and reactivity of [LFe 3(PhPz) 3OMn( sPhIO)][OTf] x (3: x=2; 4: x=3), where 4 is one of very few examples of iodosobenzene–metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (Fe III 2Fe IIMn II vs. Fe III 3Mn II) influence oxygen atom transfer in tetranuclear Fe 3Mn clusters. Finally, in particular, a one-electron redox change atmore » a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude.« less

Correlation of martensitic transformation temperatures of Ni- Mn-Ga/Al-X alloys to non-bonding electron concentration

NASA Astrophysics Data System (ADS)

Ramudu, M.; Satish Kumar, A.; Seshubai, V.; Rajasekharan, T.

2015-02-01

The martensitic transformation TM of the alloys of Ni-Mn-Ga and Ni-Mn-Al show a general trend of increase with electron per atom ratio (e/a) calculated from the total number of electrons outside the rare gas shell of the atoms. However prediction of TM fails among iron substituted Ni-Mn-Ga alloys and those with In doped for Ga, due to the absence of a useful trend. A scheme of computing modified electron concentration is presented considering only the non-bonding electrons per atom Ne/a of the compounds, based on Pauling's ideas on the electronic structure of metallic elements. Systematic variation of TM with Ne/a is reproduced for a large number of alloys of Ni-Mn-Ga and the anomaly observed for Fe containing alloys with e/a disappears. The non-bonding electron concentration is thus demonstrated to be effective in predicting TM of shape memory alloys of Ni-Mn-Ga-X system including the isoelectronic compounds of Ni-Mn-Ga-In.

The effect of aluminium on mechanical properties and deformation mechanisms of hadfield steel single crystals

NASA Astrophysics Data System (ADS)

Zakharova, E. G.; Kireeva, I. V.; Chumlyakov, Y. I.; Shul'Mina, A. A.; Sehitoglu, H.; Karaman, I.

2004-06-01

On single crystals of Hadfield steel (Fe-13Mn-1.3C, Fe-13Mn-2.7Al-1.3C, wt.%) the systematical investigations of deformation mechanisms - slip and twinning, stages of plastic flow, strain hardening coefficient depending on orientation of tensile axis have been carried out by methods of optical and electron microscopy, x-ray analysis. Is has been shown that the combination of low stacking fault energy (γ{SF}=0.03J/m^2) with high concentration of carbon atoms in aluminium-free steel results in development of the mechanical twinning at room temperature in all crystal orientations. The new type of twinning with formation of extrinsic stacking fault has been found out in [001] single crystals. Experimentally it has been established that alloying with aluminium leads to increase of stacking fault energy of Hadfield steel and suppresses twinning in all orientations of crystals at preservation of high values of strain-hardening coefficients θ.

Programming of a Mn-coordinated 4-4‧-biphenyl dicarboxylic acid nanosystem on Au(1 1 1) and investigation of the non-covalent binding of C60 molecules

NASA Astrophysics Data System (ADS)

Zhang, Yan-Feng; Zhu, Na; Komeda, T.

The fabrication of Mn-based coordination networks on a Au(1 1 1) substrate with 4-4 '-biphenyl dicarboxylic acid (BDA) as the linker molecule was investigated by scanning tunneling microscopy. Intriguing structures of ladder and rectangular-shaped networks were obtained by controlling the ratios of deposited amount of BDA molecules and Mn atoms. These structures are well explained by models in which BDA molecules occupy the perimeter of the rectangles and a pair of two Mn atoms are placed at the lattice points. For the rectangular structure, further two phases of a rectangular and a square networks were identified in which the paired Mn atoms were directing an identical direction and 90° rotated in an alternate manner, respectively. In addition, it was revealed that the open space surrounded by rectangle BDA molecules could capture a dimer of C60 molecules which were deposited on the Mn-based BDA networks.

Mapping chemical/structural order in double perovskite Sr2-xGdxMnTiO6 by atomic resolution electron microscopy

NASA Astrophysics Data System (ADS)

Alvarez, Inmaculada; Biskup, Neven; Lopez, Maria; Garcia-Hernandez, Mar; Veiga, Luisa; Varela, Maria; UCM Collaboration; ORNL Collaboration; CSIC Collaboration

2013-03-01

We report on visualizing the chemical and structural order of double perovskite Sr2-xGdxMnTiO6. The antisite disorder of Mn and Ti is detected even at atomic scale at all x, resulting in Mn-rich and Ti-rich regions. For x ?0.75, the majority of manganese ions are in Mn3+ state and are centered in Jahn-Teller distorted MnO6octahedra. The Fourier transformation of atomic resolution images along the [110] zone axis reveals a superstructure that corresponds to the tilting of oxygen octahedra and that doubles the unit cell along [001]c. This superstructure is spatially inhomogeneous and coincides with the regions where B-site ion (Mn/Ti) is displaced along the [110] direction. We discuss these findings in the frame of possible local ferroelectricity and in the light of strong electroresistance observed in Sr1.25Gd0.75MnTiO6. Research at ORNL supported by the U.S. DOE-BES, Materials Sciences and Engineering Division, and also by ORNL's ShaRE User Program (sponsored by DOE-BES). Research at UCM supported by the ERC Starting Investigator Award and MAT2010-20117.

Tunable magnetic coupling in Mn-doped monolayer MoS2 under lattice strain

NASA Astrophysics Data System (ADS)

Miao, Yaping; Huang, Yuhong; Bao, Hongwei; Xu, Kewei; Ma, Fei; Chu, Paul K.

2018-05-01

First-principles calculations are conducted to study the electronic and magnetic states of Mn-doped monolayer MoS2 under lattice strain. Mn-doped MoS2 exhibits half-metallic and ferromagnetic (FM) characteristics in which the majority spin channel exhibits metallic features but there is a bandgap in the minority spin channel. The FM state and the total magnetic moment of 1 µ B are always maintained for the larger supercells of monolayer MoS2 with only one doped Mn, no matter under tensile or compressive strain. Furthermore, the FM state will be enhanced by the tensile strain if two Mo atoms are substituted by Mn atoms in the monolayer MoS2. The magnetic moment increases up to 0.50 µ B per unit cell at a tensile strain of 7%. However, the Mn-doped MoS2 changes to metallic and antiferromagnetic under compressive strain. The spin polarization of Mn 3d orbitals disappears gradually with increasing compressive strain, and the superexchange interaction between Mn atoms increases gradually. The results suggest that the electronic and magnetic properties of Mn-doped monolayer MoS2 can be effectively modulated by strain engineering providing insight into application to electronic and spintronic devices.

Adhesion and friction of iron-base binary alloys in contact with silicon carbide in vacuum

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1980-01-01

Single pass sliding friction experiments were conducted with various iron base binary alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a single crystal silicon carbide /0001/ surface in vacuum. Results indicate that atomic size and concentration of alloying elements play an important role in controlling adhesion and friction properties of iron base binary alloys. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases linearly as the solute to iron atomic radius ratio increases or decreases from unity. The chemical activity of the alloying elements was also an important parameter in controlling adhesion and friction of alloys, as these latter properties are highly dependent upon the d bond character of the elements.

The new Zintl phases Eu{sub 21}Cd{sub 4}Sb{sub 18} and Eu{sub 21}Mn{sub 4}Sb{sub 18}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yi; Darone, Gregory M.; Bobev, Svilen, E-mail: bobev@udel.edu

Crystals of two new Zintl compounds, Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} have been synthesized using the molten metal flux method, and their structures have been established by single-crystal X-ray diffraction. Both compounds are isotypic and crystallize in the monoclinic space group C2/m (No. 12, Z=4). The structures are based on edge- and corner-shared MnSb{sub 4} or CdSb{sub 4} tetrahedra, which make octameric [Mn{sub 8}Sb{sub 22}] or [Cd{sub 8}Sb{sub 22}] polyanions. Homoatomic Sb–Sb bonds are present in both structures. The Eu atoms take the role of Eu{sup 2+}cations with seven unpaired 4f electrons, as suggested by themore » temperature-dependent magnetization measurements. The magnetic susceptibilities of Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} indicate that both phases order anti-ferromagnetically with Néel temperatures of ca. 7 K and ca. 10 K, respectively. The unpaired 3d electrons of the Mn atoms in Eu{sub 21}Mn{sub 4}Sb{sub 18} do contribute to the magnetic response, however, the bulk magnetization measurements do not provide evidence for long-range ordering of the Mn spins down to 5 K. Electrical resistivity measurements suggest that both compounds are narrow band gap semiconductors. - Graphical abstract: Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} have complex monoclinic structures, based on MnSb{sub 4} and CdSb{sub 4} tetrahedra, both edge- and corner-shared. A perspective of the crystal structure is shown, as viewed along the b axis. Display Omitted - Highlights: • Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} are novel compounds in the respective ternary phase diagrams. • For both structures, the Zintl-Klemm rules are followed, and both are small gap semiconductors. • Eu{sub 21}Mn{sub 4}Sb{sub 18} and Eu{sub 21}Cd{sub 4}Sb{sub 18} are air-stable Zintl phases and could be new thermoelectric materials.« less

On the state of Mn in Mn{sub x}Zn{sub 1−x}O nanoparticles and their surface modification with isonipecotic acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiménez-Hernández, L.; Estévez-Hernández, O.; Instituto de Ciencia y Tecnología de Materiales

Mn-doped ZnO (Mn{sub x}Zn{sub 1−x}O) nanoparticles were synthesized by the co-precipitation method and coated with isonipecotic acid as capping ligand. The structure, composition and morphology of the resulting nanomaterial were investigated by energy disperse X-ray analysis, X-ray diffraction, and transmission electron microscopy data. Such measurements showed that the solid obtained contains 6 at% of Mn and it is formed by a highly crystalline material with 3–5 nm range of crystallite size, and only a small elongation of its cell parameter with respect to undoped ZnO wurtzite unit cell. Information on the state of manganese atom in the Mn{sub x}Zn{sub 1−x}Omore » nanostructures formed was obtained from X-ray photoelectron (XPS) and electron energy loss (EELS) spectroscopies. XPS and EELS spectra are composed of four peaks, corresponding to two species of Mn(II) and signals from Mn(III) and Mn(IV). Such spectral data on the state of Mn in the material studied is consistent with the mapping of Mn distribution observed in recorded transmission electron microscopy images, which reveal presence of clusters of Mn atoms. Only a fraction of doping Mn atoms were found forming a solid solution with the host ZnO structure. The functionalization of the nanoparticles system with Isonipecotic acid shows that this molecule remains anchored to the nanoparticles surface mainly through its N basic site. The availability of free carboxylate groups in the capping molecule was tested by conjugation to type IV horseradish peroxidase. - Graphical abstract: State of Mn atoms in Mn-doped ZnO nanostructures prepared by the precipitation method, their capping with isonipecotic acid and subsequent conjugation to peroxidase. - Highlights: • State of manganese in manganese-doped zinc oxide nanoparticles. • Isonipecotic acid as surface modifier of ZnO nanoparticles. • Peroxidase conjugation to ZnO nanoparticles modified with isonipecotic acid.« less

Two- and three-dimensional growth of Bi on i -Al-Pd-Mn studied using medium-energy ion scattering

NASA Astrophysics Data System (ADS)

Noakes, T. C. Q.; Bailey, P.; McConville, C. F.; Draxler, M.; Walker, M.; Brown, M. G.; Hentz, A.; Woodruff, D. P.; Lograsso, T. A.; Ross, A. R.; Smerdon, J. A.; Leung, L.; McGrath, R.

2010-11-01

Recent work on the growth of thin metal films on quasicrystalline substrates has indicated the formation of so-called “magic height” islands with multiples of 4 atomic layers (AL) arising as a result of quantum size effects, which lead to enhanced stability. Here the results of a study are reported of Bi deposition on i -Al-Pd-Mn using medium-energy ion scattering to characterize the island thickness and the structural arrangement of Bi atoms within the islands. In addition, data were taken from annealed surfaces after Bi cluster desorption to leave a single aperiodic monolayer of Bi at the surface. Scattered-ion energy spectra from the Bi islands are consistent with a single Bi monolayer covered with mainly 4 AL islands for both 1.8 and 3.2 monolayer equivalent coverages but with some occupation of 2 and 8 Al islands as well. The angular dependence of the scattered-ion intensity (“blocking curve”) from Bi has been compared with simulations for various models of both rhombohedral Bi and a distorted “black-phosphorus”-like structure. The data demonstrate bilayer formation within the Bi islands. In the case of the aperiodic Bi monolayer, the blocking curves from substrate scattering are found to be inconsistent with two high-symmetry sites on the quasicrystalline surface that theory indicates are energetically favorable but do not exclude the formation of pentagonal arrangements of Bi atoms as seen in other recent experimental work.

Ionization of elements in medium power capacitively coupled argon plasma torch with single and double ring electrodes.

PubMed

Ponta, Michaela; Frentiu, Maria; Frentiu, Tiberiu

2012-06-01

A medium power, low Ar consumption capacitively coupled plasma torch (275 W, 0.4 L min-1) with molybdenum tubular electrode and single or two ring electrodes in non-local thermodynamic equilibrium (LTE) was characterized with respect to its ability to achieve element ionization. Ionization degrees of Ca, Mg, Mn and Cd were determined from ionic-to-atomic emission ratio and ionization equilibrium according to Saha's equation. The ionization degrees resulted from the Saha equation were higher by 9-32% than those obtained from spectral lines intensity in LTE regime and closer to reality. A linear decrease of ionization with increase of ionization energy of elements was observed. Plasma torch with two ring electrodes provided higher ionization degrees (85 ± 7% Ca, 79 ± 7% Mn, 80 ± 7% Mg and 73 ± 8% Cd) than those in single ring arrangement (70 ± 6% Ca, 57 ± 7% Mn, 57 ± 8% Mg and 42 ± 9% Cd). The Ca ionization decreased linearly by up to 79 ± 4% and 53 ± 6% in plasma with two ring electrodes and single ring respectively in the presence of up to 400 µg mL-1 Na as interferent. The studied plasma was effective in element ionization and could be a potential ion source in mass spectrometry.

Structure and properties of Mn4Cl9: an antiferromagnetic binary hyperhalogen.

PubMed

Li, Yawei; Zhang, Shunhong; Wang, Qian; Jena, Puru

2013-02-07

Calculations based on density functional theory show that the structure of Mn(4)Cl(9) anion is that of a Mn atom at the core surrounded by three MnCl(3) moieties. Since Mn is predominantly divalent and MnCl(3) is known to be a superhalogen with a vertical detachment energy (VDE) of 5.27 eV, Mn(4)Cl(9) can be viewed as a hyperhalogen with the formula unit Mn(MnCl(3))(3). Indeed, the calculated VDE of Mn(4)Cl(9) anion, namely 6.76 eV, is larger than that of MnCl(3) anion. More importantly, unlike previously discovered hyperhalogens, Mn(4)Cl(9) is the first such hyperhalogen species composed of only two constituent atoms. We further show that Mn(4)Cl(9) can be used as a ligand to design molecules with even higher VDEs. For example, Li[Mn(MnCl(3))(3)](2) anion has a VDE of 7.26 eV. These negatively charged clusters are antiferromagnetic with most of the magnetic moments localized at the Mn sites. Our studies show new pathways for creating binary hyperhalogens.

Structure and properties of Mn4Cl9: An antiferromagnetic binary hyperhalogen

NASA Astrophysics Data System (ADS)

Li, Yawei; Zhang, Shunhong; Wang, Qian; Jena, Puru

2013-02-01

Calculations based on density functional theory show that the structure of Mn4Cl9 anion is that of a Mn atom at the core surrounded by three MnCl3 moieties. Since Mn is predominantly divalent and MnCl3 is known to be a superhalogen with a vertical detachment energy (VDE) of 5.27 eV, Mn4Cl9 can be viewed as a hyperhalogen with the formula unit Mn(MnCl3)3. Indeed, the calculated VDE of Mn4Cl9 anion, namely 6.76 eV, is larger than that of MnCl3 anion. More importantly, unlike previously discovered hyperhalogens, Mn4Cl9 is the first such hyperhalogen species composed of only two constituent atoms. We further show that Mn4Cl9 can be used as a ligand to design molecules with even higher VDEs. For example, Li[Mn(MnCl3)3]2 anion has a VDE of 7.26 eV. These negatively charged clusters are antiferromagnetic with most of the magnetic moments localized at the Mn sites. Our studies show new pathways for creating binary hyperhalogens.

First Principles Study of Adsorption of Hydrogen on Typical Alloying Elements and Inclusions in Molten 2219 Al Alloy.

PubMed

Liu, Yu; Huang, Yuanchun; Xiao, Zhengbing; Jia, Guangze

2017-07-19

To better understand the effect of the components of molten 2219 Al alloy on the hydrogen content dissolved in it, the H adsorption on various positions of alloying element clusters of Cu, Mn and Al, as well as the inclusion of Al₂O₃, MgO and Al₄C₃, were investigated by means of first principles calculation, and the thermodynamic stability of H adsorbed on each possible site was also studied on the basis of formation energy. Results show that the interaction between Al, MgO, Al₄C₃ and H atoms is mainly repulsive and energetically unfavorable; a favorable interaction between Cu, Mn, Al₂O₃ and H atoms was determined, with H being more likely to be adsorbed on the top of the third atomic layer of Cu(111), the second atomic layer of Mn(111), and the O atom in the third atomic layer of Al₂O₃, compared with other sites. It was found that alloying elements Cu and Mn and including Al₂O₃ may increase the hydrogen adsorption in the molten 2219 Al alloy with Al₂O₃ being the most sensitive component in this regard.

Structural and magnetic evolution of bimetallic MnAu clusters driven by asymmetric atomic migration.

PubMed

Wei, Xiaohui; Zhou, Rulong; Lefebvre, Williams; He, Kai; Le Roy, Damien; Skomski, Ralph; Li, Xingzhong; Shield, Jeffrey E; Kramer, Matthew J; Chen, Shuang; Zeng, Xiao Cheng; Sellmyer, David J

2014-03-12

The nanoscale structural, compositional, and magnetic properties are examined for annealed MnAu nanoclusters. The MnAu clusters order into the L1(0) structure, and monotonic size-dependences develop for the composition and lattice parameters, which are well reproduced by our density functional theory calculations. Simultaneously, Mn diffusion forms 5 Å nanoshells on larger clusters inducing significant magnetization in an otherwise antiferromagnetic system. The differing atomic mobilities yield new cluster nanostructures that can be employed generally to create novel physical properties.

Catena-poly[[bis(1H-benzotriazole-kappaN3)cobalt(II)]-di-mu-tricyanomethanido-kappa2N:N'] and catena-poly[[bis(3,5-dimethyl-1H-pyrazole-kappaN2)manganese(II)]-di-mu-tricyanomethanido-kappa2N:N'].

PubMed

Shao, Ze-Huai; Luo, Jun; Cai, Rui-Fang; Zhou, Xi-Geng; Weng, Lin-Hong; Chen, Zhen-Xia

2004-06-01

Two new one-dimensional coordination polymers, viz. the title compounds, [Co[C(CN)(3)](2)(C(6)H(5)N(3))(2)](n), (I), and [Mn[C(CN)(3)](2)(C(5)H(8)N(2))(2)](n), (II), have been synthesized and characterized by X-ray diffraction. Both complexes consist of linear chains with double 1,5-tricyanomethanide bridges between neighbouring divalent metal ions. The Co and Mn atoms are located on centres of inversion. In (I), the coordination environment of the Co(II) atom is that of an elongated octahedron. The Co(II) atom is coordinated in the equatorial plane by four nitrile N atoms of four bridging tricyanomethanide ions, with Co-N distances of 2.106 (2) and 2.110 (2) A, and in the apical positions by two N atoms from the benzotriazole ligands, with a Co-N distance of 2.149 (2) A. The [Co[C(CN)(3)](2)(C(6)H(5)N(3))(2)] units form infinite chains extending along the a axis. These chains are crosslinked via a hydrogen bond between the uncoordinated nitrile N atom of a tricyanomethanide anion and the H atom on the uncoordinated N atom of a benzotriazole ligand from an adjacent chain, thus forming a three-dimensional network structure. In (II), the Mn(II) atom also adopts a slightly distorted octahedral geometry, with four nitrile N atoms of tricyanomethanide ligands [Mn-N = 2.226 (2) and 2.227 (2) A] in equatorial positions and two N atoms of the monodentate 3,5-dimethylpyrazole ligands [Mn-N = 2.231 (2) A] in the axial sites. In (II), one-dimensional polymeric chains extending along the b axis are formed, with tricyanomethanide anions acting as bidentate bridging ligands. A hydrogen bond between the uncoordinated nitrile N atom of the tricyanomethanide ligand and the H atom on the uncoordinated N atom of a 3,5-dimethylpyrazole group from a neighbouring chain links the molecule into a two-dimensional layered structure.

General synthesis and definitive structural identification of MN 4C 4 single-atom catalysts with tunable electrocatalytic activities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fei, Huilong; Dong, Juncai; Feng, Yexin

Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MNsub>4C 4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical predictionmore » of MNsub>4C 4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni > Co > Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities.« less

General synthesis and definitive structural identification of MN 4C 4 single-atom catalysts with tunable electrocatalytic activities

DOE PAGES

Fei, Huilong; Dong, Juncai; Feng, Yexin; ...

2018-01-08

Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MNsub>4C 4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical predictionmore » of MNsub>4C 4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni > Co > Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities.« less

Structural Diversities in Heterometallic Mn-Ca Cluster Chemistry from the Use of Salicylhydroxamic Acid: {MnIII4Ca2}, {MnII/III6Ca2}, {MnIII/IV8Ca}, and {MnIII8Ca2} Complexes with Relevance to Both High- and Low-Valent States of the Oxygen-Evolving Complex.

PubMed

Alaimo, Alysha A; Koumousi, Evangelia S; Cunha-Silva, Luís; McCormick, Laura J; Teat, Simon J; Psycharis, Vassilis; Raptopoulou, Catherine P; Mukherjee, Shreya; Li, Chaoran; Gupta, Sayak Das; Escuer, Albert; Christou, George; Stamatatos, Theocharis C

2017-09-05

One-pot reactions between the [Mn 3 O(O 2 CPh) 6 (py) x ] +/0 triangular precursors and either CaBr 2 ·xH 2 O or CaCl 2 ·6H 2 O, in the presence of salicylhydroxamic acid (shaH 2 ), have afforded the heterometallic complexes [Mn III 4 Ca 2 (O 2 CPh) 4 (shi) 4 (H 2 O) 3 (Me 2 CO)] (1) and (pyH)[Mn II 2 Mn III 4 Ca 2 Cl 2 (O 2 CPh) 7 (shi) 4 (py) 4 ] (2), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO 3 ) 2 ·4H 2 O/Ca(NO 3 ) 2 ·4H 2 O and Mn(O 2 CPh) 2 ·2H 2 O/Ca(ClO 4 ) 2 ·4H 2 O "metal blends" and shaH 2 , in the presence of external base NEt 3 , led to the new complexes (NHEt 3 ) 2 [Mn III 4 Mn IV 4 Ca(OEt) 2 (shi) 10 (EtOH) 2 ] (3) and (NHEt 3 ) 4 [Mn III 8 Ca 2 (CO 3 ) 4 (shi) 8 ] (4), respectively. In all reported compounds, the anion of the tetradentate (N,O,O,O)-chelating/bridging ligand salicylhydroxime (shi 3- ), resulting from the in situ metal-ion-assisted amide-iminol tautomerism of shaH 2 , was found to bridge both Mn and Ca atoms. Complexes 1-4 exhibit a variety of different structures, metal stoichiometries, and Mn oxidation-state descriptions; 1 possesses an overall octahedral metal arrangement, 2 can be described as a Mn 4 Ca 2 octahedron bound to an additional Mn 2 unit, 3 consists of a Mn 8 "ring" surrounding a Ca II atom, and 4 adopts a rectangular cuboidal motif of eight Mn atoms accommodating two Ca II atoms. Solid-state direct-current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, leading to S = 0 spin ground-state values for all complexes. From a bioinorganic chemistry perspective, the reported compounds may demonstrate some relevance to both high-valent scheme (3) and lower-oxidation-level species (1, 2, and 4) of the catalytic cycle of the oxygen-evolving complex.

Understanding the detection of carbon in austenitic high-Mn steel using atom probe tomography.

PubMed

Marceau, R K W; Choi, P; Raabe, D

2013-09-01

A high-Mn TWIP steel having composition Fe-22Mn-0.6C (wt%) is considered in this study, where the need for accurate and quantitative analysis of clustering and short-range ordering by atom probe analysis requires a better understanding of the detection of carbon in this system. Experimental measurements reveal that a high percentage of carbon atoms are detected as molecular ion species and on multiple hit events, which is discussed with respect to issues such as optimal experimental parameters, correlated field evaporation and directional walk/migration of carbon atoms at the surface of the specimen tip during analysis. These phenomena impact the compositional and spatial accuracy of the atom probe measurement and thus require careful consideration for further cluster-finding analysis. Copyright © 2013 Elsevier B.V. All rights reserved.

Chemical complexity induced local structural distortion in NiCoFeMnCr high-entropy alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Fuxiang; Tong, Yang; Jin, Ke

In order to study chemical complexity-induced lattice distortion in high-entropy alloys, the static Debye–Waller (D-W) factor of NiCoFeMnCr solid solution alloy is measured with low temperature neutron diffraction, ambient X-ray diffraction, and total scattering methods. Here, the static atomic displacement parameter of the multi-element component alloy at 0 K is 0.035–0.041 Å, which is obvious larger than that of element Ni (~0 Å). The atomic pair distance between individual atoms in the alloy investigated with extended X-ray absorption fine structure (EXAFS) measurements indicates that Mn has a slightly larger bond distance (~0.4%) with neighbor atoms than that of others.

Chemical complexity induced local structural distortion in NiCoFeMnCr high-entropy alloy

DOE PAGES

Zhang, Fuxiang; Tong, Yang; Jin, Ke; ...

2018-06-16

In order to study chemical complexity-induced lattice distortion in high-entropy alloys, the static Debye–Waller (D-W) factor of NiCoFeMnCr solid solution alloy is measured with low temperature neutron diffraction, ambient X-ray diffraction, and total scattering methods. Here, the static atomic displacement parameter of the multi-element component alloy at 0 K is 0.035–0.041 Å, which is obvious larger than that of element Ni (~0 Å). The atomic pair distance between individual atoms in the alloy investigated with extended X-ray absorption fine structure (EXAFS) measurements indicates that Mn has a slightly larger bond distance (~0.4%) with neighbor atoms than that of others.

Interface reconstruction with emerging charge ordering in hexagonal manganite

PubMed Central

Xu, Changsong; Han, Myung-Geun; Bao, Shanyong; Nan, Cewen; Bellaiche, Laurent

2018-01-01

Multiferroic materials, which simultaneously have multiple orderings, hold promise for use in the next generation of memory devices. We report a novel self-assembled MnO double layer forming at the interface between a multiferroic YMnO3 film and a c-Al2O3 substrate. The crystal structures and the valence states of this MnO double layer were studied by atomically resolved scanning transmission electron microscopy and spectroscopy, as well as density functional theory (DFT) calculations. A new type of charge ordering has been identified within this MnO layer, which also contributes to a polarization along the [001] direction. DFT calculations further establish the occurrence of multiple couplings between charge and lattice in this novel double layer, in addition to the polarization in nearby YMnO3 single layer. The interface reconstruction reported here creates a new playground for emergent physics, such as giant ferroelectricity and strong magnetoelectric coupling, in manganite systems. PMID:29795782

Magneto-optical spectroscopy of ferromagnetic shape-memory Ni-Mn-Ga alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veis, M., E-mail: veis@karlov.mff.cuni.cz; Beran, L.; Zahradnik, M.

2014-05-07

Magneto-optical properties of single crystal of Ni{sub 50.1}Mn{sub 28.4}Ga{sub 21.5} magnetic shape memory alloy in martensite and austenite phase were systematically studied. Crystal orientation was approximately along (100) planes of parent cubic austenite. At room temperature, the sample was in modulated 10M martensite phase and transformed to cubic austenite at 323 K. Spectral dependence of polar magneto-optical Kerr effect was obtained by generalized magneto-optical ellipsometry with rotating analyzer in the photon energy range from 1.2 to 4 eV, and from room temperature to temperature above the Curie point. The Kerr rotation spectra exhibit prominent features typical for complexes containing Mn atoms. Significantmore » spectral changes during transformation to austenite can be explained by different optical properties caused by changes in density of states near the Fermi energy.« less

Only the chemical state of Indium changes in Mn-doped In3Sb1Te2 (Mn: 10 at.%) during multi-level resistance changes

NASA Astrophysics Data System (ADS)

Lee, Y. M.; Ahn, D.; Kim, J.-Y.; Kim, Y. S.; Cho, S.; Ahn, M.; Cho, M.-H.; Jung, M. S.; Choi, D. K.; Jung, M.-C.; Qi, Y. B.

2014-04-01

We fabricated and characterized the material with Mn (10 at.%: atomic percent) doped In3Sb1Te2 (MIST) using co-sputtering and synchrotron radiation, respectively. The MIST thin film showed phase-changes at 97 and 320°C, with sheet resistances of ~10 kΩsq (amorphous), ~0.2 kΩsq (first phase-change), and ~10 Ωsq (second phase-change). MIST did not exhibit any chemical separation or increased structural instability during either phase-change, as determined with high-resolution x-ray photoelectron spectroscopy. Chemical state changes were only depended for In without concomitant changes of Sb and Te. Apparently, doped Mn atoms can be induced with movement of only In atoms.

Narrowing the gap: from semiconductor to semimetal in the homologous series of rare-earth zinc arsenides RE(2-y)Zn4As4·n(REAs) and Mn-substituted derivatives RE(2-y)Mn(x)Zn(4-x)As4·n(REAs) (RE = La-Nd, Sm, Gd).

PubMed

Lin, Xinsong; Tabassum, Danisa; Mar, Arthur

2015-12-14

A homologous series of ternary rare-earth zinc arsenides, prepared by reactions of the elements at 750 °C, has been identified with the formula RE(2-y)Zn4As4·n(REAs) (n = 2, 3, 4) for various RE members. They adopt trigonal structures: RE(4-y)Zn4As6 (RE = La-Nd), space group R3̄m1, Z = 3; RE(5-y)Zn4As7 (RE = Pr, Nd, Sm, Gd), space group P3̄m1, Z = 1; RE(6-y)Zn4As8 (RE = La-Nd, Sm, Gd), space group R3̄m1, Z = 3. The Zn atoms can be partially substituted by Mn atoms, resulting in quaternary derivatives RE(2-y)Mn(x)Zn(4-x)As4·n(REAs). Single-crystal structures were determined for nine ternary and quaternary arsenides RE(2-y)M4As4·n(REAs) (M = Mn, Zn) as representative examples of these series. The structures are built by stacking close-packed nets of As atoms, sometimes in very long sequences, with RE atoms occupying octahedral sites and M atoms occupying tetrahedral sites, resulting in an intergrowth of [REAs] and [M2As2] slabs. The recurring feature of all members of the homologous series is a sandwich of [M2As2]-[REAs]-[M2As2] slabs, while rocksalt-type blocks of [REAs] increase in thickness between these sandwiches with higher n. Similar to the previously known related homologous series REM(2-x)As2·n(REAs) which is deficient in M, this new series RE(2-y)M4As4·n(REAs) exhibits deficiencies in RE to reduce the electron excess that would be present in the fully stoichiometric formulas. Enthalpic and entropic factors are considered to account for the differences in site deficiencies in these two homologous series. Band structure calculations indicate that the semiconducting behaviour of the parent n = 0 member (with CaAl2Si2-type structure) gradually evolves, through a narrowing of the gap between valence and conduction bands, to semimetallic behaviour as the number of [REAs] blocks increases, to the limit of n = ∞ for rocksalt-type REAs.

Friction and wear with a single-crystal abrasive grit of silicon carbide in contact with iron base binary alloys in oil: Effects of alloying element and its content

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1979-01-01

Sliding friction experiments were conducted with various iron-base binary alloys (alloying elements were Ti, Cr, Mn, Ni, Rh, and W) in contact with a rider of 0.025-millimeter-radius, single-crystal silicon carbide in mineral oil. Results indicate that atomic size and content of alloying element play a dominant role in controlling the abrasive-wear and -friction properties of iron-base binary alloys. The coefficient of friction and groove height (wear volume) general alloy decrease, and the contact pressure increases in solute content. There appears to be very good correlation of the solute to iron atomic radius ratio with the decreasing rate of coefficient of friction, the decreasing rate of groove height (wear volume), and the increasing rate of contact pressure with increasing solute content C. Those rates increase as the solute to iron atomic radius ratio increases from unity.

Structure disordering and thermal decomposition of manganese oxalate dihydrate, MnC2O4·2H2O

NASA Astrophysics Data System (ADS)

Puzan, Anna N.; Baumer, Vyacheslav N.; Lisovytskiy, Dmytro V.; Mateychenko, Pavel V.

2018-04-01

It is found that the known regular structures of MnC2O4·2H2O (I) do not allow to refine the powder X-ray pattern of (I) properly using the Rietveld method. Implementation of order-disorder scheme [28] via the including of appropriate displacement vector improves the refinement results. Also it is found that in the case of (I) the similar improvement may be achieved using the data on two phases of (I) obtained as result of decomposition MnC2O4·3H2O single crystal in the mother solution after growth. Thermal decomposition of (I) produce the anhydrous γ-MnC2O4 (II) the structure of which is differ from the known α- and β-modifications of VIIIb transition metal oxalates. The solved ab initio from the powder pattern structure (II) (space group Pmna, a = 7.1333 (1), b = 5.8787 (1), c = 9.0186 (2) Å, V = 378.19 (1) Å3, Z = 4 and Dx = 2.511 Mg m-3) contains seven-coordinated Mn atoms with Mn-O distances of 2.110-2.358 Å, and is not close-packed. Thermal decomposition of (II) in air flows via forming of amorphous MnO, the heating of which up to 723 K is accompanied by oxidation of MnO to Mn2O3 and further recrystallization of the latter.

Spin resolved photoelectron spectroscopy of [Mn6IIICrIII]3 + single-molecule magnets and of manganese compounds as reference layers

NASA Astrophysics Data System (ADS)

Helmstedt, Andreas; Müller, Norbert; Gryzia, Aaron; Dohmeier, Niklas; Brechling, Armin; Sacher, Marc D.; Heinzmann, Ulrich; Hoeke, Veronika; Krickemeyer, Erich; Glaser, Thorsten; Bouvron, Samuel; Fonin, Mikhail; Neumann, Manfred

2011-07-01

Properties of the manganese-based single-molecule magnet [\\mathbf {Mn}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}_{\\mathbf {6}} \\mathbf {Cr}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}]^{\\mathbf {3} \\boldsymbol {+}} are studied. It contains six MnIII ions arranged in two bowl-shaped trinuclear triplesalen building blocks linked by a hexacyanochromate and exhibits a large spin ground state of St = 21/2. The dominant structures in the electron emission spectra of [\\mathbf {Mn}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}_{\\mathbf {6}}\\mathbf {Cr}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}]^{\\mathbf {3} \\boldsymbol {+}} resonantly excited at the L3-edge are the L3M2, 3M2, 3, L3M2, 3V and L3VV Auger emission groups following the decay of the primary p3/2 core hole state. Significant differences of the Auger spectra from intact and degraded [\\mathbf {Mn}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}_{\\mathbf {6}}\\mathbf {Cr}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}]^{\\mathbf {3} \\boldsymbol {+}} show up. First measurements of the electron spin polarization in the L3M2, 3V and L3VV Auger emission peaks from the manganese constituents in [\\mathbf {Mn}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}_{\\mathbf {6}} \\mathbf {Cr}^{\\mathbf {I}\\mathbf {I}\\mathbf {I}}]^{\\mathbf {3} \\boldsymbol {+}} resonantly excited at the L3-edge near 640 eV by circularly polarized synchrotron radiation are reported. In addition spin resolved Auger electron spectra of the reference substances MnO, Mn2O3 and MnII(acetate)2·4H2O are given. The applicability of spin resolved electron spectroscopy for characterizing magnetic states of constituent atoms compared to magnetic circular dichroism (MCD) is verified: the spin polarization obtained from MnII(acetate)2·4H2O at room temperature in the paramagnetic state compares to the MCD asymmetry revealed for a star-shaped molecule with a Mn4IIO6 core at 5 K in an external magnetic field of 5 T.

Transition metal intercalated bilayer silicene

NASA Astrophysics Data System (ADS)

Pandey, Dhanshree; Kamal, C.; Chakrabarti, Aparna

2018-04-01

We investigate the electronic and magnetic properties of Mn, Fe and Co-intercalated silicene bilayer with AA and AB stacking by using spin polarized density functional theory. The intercalation of Mn increases the gap between the two layers of silicene due to the larger atomic radii of Mn as compared to Fe and Co. Bader charge analysis has been performed to understand the bonding between the TM and Si atoms. This also helps in explaining the magnetic moment possessed by the composite systems after intercalating TM in between the layers of bilayer silicene system. This study reveals that a significant net magnetic moment is observed in cases of Mn-intercalated silicene bilayers, whereas Fe has a very small moment of 0.78 µB in the case of AA stacking configuration only. Co intercalation leads to net zero magnetic moment. Further, we find that Fe and Co marginally favor the AB stacking whereas Mn has a slight preference of the AA over the AB configuration. The composite systems, specifically when intercalated with Fe and Co atoms, favor a hybridization which is far away from sp3-like hybridization along the plane of Si atoms in bilayer silicene.

Ferromagnetic germanide in Ge nanowire transistors for spintronics application.

PubMed

Tang, Jianshi; Wang, Chiu-Yen; Hung, Min-Hsiu; Jiang, Xiaowei; Chang, Li-Te; He, Liang; Liu, Pei-Hsuan; Yang, Hong-Jie; Tuan, Hsing-Yu; Chen, Lih-Juann; Wang, Kang L

2012-06-26

To explore spintronics applications for Ge nanowire heterostructures formed by thermal annealing, it is critical to develop a ferromagnetic germanide with high Curie temperature and take advantage of the high-quality interface between Ge and the formed ferromagnetic germanide. In this work, we report, for the first time, the formation and characterization of Mn(5)Ge(3)/Ge/Mn(5)Ge(3) nanowire transistors, in which the room-temperature ferromagnetic germanide was found through the solid-state reaction between a single-crystalline Ge nanowire and Mn contact pads upon thermal annealing. The atomically clean interface between Mn(5)Ge(3) and Ge with a relatively small lattice mismatch of 10.6% indicates that Mn(5)Ge(3) is a high-quality ferromagnetic contact to Ge. Temperature-dependent I-V measurements on the Mn(5)Ge(3)/Ge/Mn(5)Ge(3) nanowire heterostructure reveal a Schottky barrier height of 0.25 eV for the Mn(5)Ge(3) contact to p-type Ge. The Ge nanowire field-effect transistors built on the Mn(5)Ge(3)/Ge/Mn(5)Ge(3) heterostructure exhibit a high-performance p-type behavior with a current on/off ratio close to 10(5), and a hole mobility of 150-200 cm(2)/(V s). Temperature-dependent resistance of a fully germanided Mn(5)Ge(3) nanowire shows a clear transition behavior near the Curie temperature of Mn(5)Ge(3) at about 300 K. Our findings of the high-quality room-temperature ferromagnetic Mn(5)Ge(3) contact represent a promising step toward electrical spin injection into Ge nanowires and thus the realization of high-efficiency spintronic devices for room-temperature applications.

Spatial structure of single and interacting Mn acceptors in GaAs

NASA Astrophysics Data System (ADS)

Koenraad, Paul

2005-03-01

Ferromagnetic semiconductors such as Ga1-xMnxAs are receiving a lot of attention at the moment because of their application in spintronic devices. However, despite intense study of deep acceptors in III-V semiconductors such as MnGa, little information has been obtained on their electronic properties at the atomic scale. Yet the spatial shape of the Mn acceptor state will influence the hole-mediated Mn-Mn coupling and thus all of the magnetic properties of ferromagnetic semiconductors such as Ga1-xMnxAs. This study presents an experimental and theoretical description of the spatial symmetry of the Mn acceptor wave-function in GaAs. We present measurements of the spatial mapping of the anisotropic wavefunction of a hole localized at a Mn acceptor. To achieve this, we have used the STM tip not only to image the Mn acceptor but also to manipulate its charge state A^0/A^- at room temperature. Within an envelope function effective mass model (EFM) the anisotropy in the acceptor wave-function can be traced to the influence of the cubic symmetry of the GaAs crystal which selects specific d-states that mix into the ground state due to the spin-orbit interaction in the valence band. Comparison with calculations based on a tight-binding model (TBM) for the Mn acceptor structure supports this conclusion. Using the same experimental and theoretical approach we furthermore explored the interaction between Mn acceptors directly by analyzing close Mn-Mn pairs, which were separated by less than 2 nm. We will discuss some implications of these results for Mn delta-doped layers grown on differently oriented growth surfaces.

Atomic Layer Deposition of MnS: Phase Control and Electrochemical Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riha, Shannon C.; Koegel, Alexandra A.; Meng, Xiangbo

Manganese sulfide (MnS) thin films were synthesized via atomic layer deposition (ALD) using gaseous manganese bis(ethylcyclopentadienyl) and hydrogen sulfide as precursors. At deposition temperatures ≤150 °C phase-pure r-MnS thin films were deposited, while at temperatures >150 °C, a mixed phase, consisting of both r- and a-MnS resulted. In situ quartz crystal microbalance (QCM) studies validate the self-limiting behavior of both ALD half-reactions and, combined with quadrupole mass spectrometry (QMS) allow the derivation of a self-consistent reaction mechanism. Lastly, MnS thin films were deposited on copper foil and tested as a Li-ion battery anode. The MnS coin cells showed exceptional cyclemore » stability and near-theoretical capacity.« less

Atomic Layer Deposition of MnS: Phase Control and Electrochemical Applications

DOE PAGES

Riha, Shannon C.; Koegel, Alexandra A.; Meng, Xiangbo; ...

2016-01-19

Manganese sulfide (MnS) thin films were synthesized via atomic layer deposition (ALD) using gaseous manganese bis(ethylcyclopentadienyl) and hydrogen sulfide as precursors. At deposition temperatures ≤150 °C phase-pure r-MnS thin films were deposited, while at temperatures >150 °C, a mixed phase, consisting of both r- and a-MnS resulted. In situ quartz crystal microbalance (QCM) studies validate the self-limiting behavior of both ALD half-reactions and, combined with quadrupole mass spectrometry (QMS) allow the derivation of a self-consistent reaction mechanism. Lastly, MnS thin films were deposited on copper foil and tested as a Li-ion battery anode. The MnS coin cells showed exceptional cyclemore » stability and near-theoretical capacity.« less

Crystal structures of two new low-symmetry calcium-deficient analogs of eudialyte

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rastsvetaeva, R. K.; Rozenberg, K. A.; Pekov, I. V.

2006-03-15

The crystal structures of two new low-symmetry (sp. gr. R3) representatives of the eudialyte group from Mont Saint-Hilaire (Quebec, Canada) and the Lovozero massif (Kola Peninsula, Russia) were studied by single-crystal X-ray diffraction analysis and refined to R = 0.068 and 0.054 using 2899 reflections with F > 5{sigma}(F) and 2927 reflections with F > 3{sigma}(F), respectively. The idealized formulas of these representatives are Na{sub 13}(Ca{sub 3}Mn{sub 3})Zr{sub 3}(Fe, Mn){sub 3}({open_square})(Si)[Si{sub 3}O{sub 9}]{sub 2}[Si{sub 9}O{sub 27}]{sub 2}(O, OH, Cl){sub 3} . 2H{sub 2}O and Na{sub 15}(Ca{sub 3}Mn{sub 3})Zr{sub 3}(Fe, Zr){sub 3}(Si)(Si) . [Si{sub 3}O{sub 9}]{sub 2}[Si{sub 9}O{sub 27}]{sub 2}O{sub 2}(OH,more » F, Cl){sub 2} . 2H{sub 2}O. Both minerals are analogs of oneillite and are characterized by a low Ca content. The distinguishing features of the mineral from Quebec are that the M(4) site is essentially vacant (>50%) and Ca atoms occupy one independent site in the six-membered ring, whereas another site is occupied by Mn along with a small impurity of Na. In the mineral from the Lovozero massif, both the M(3) and M(4) sites are occupied predominantly by silicon, while Ca atoms are distributed between both octahedral sites of the six-membered ring, one of these sites being occupied predominantly by Mn.« less

First Principles Study of Adsorption of Hydrogen on Typical Alloying Elements and Inclusions in Molten 2219 Al Alloy

PubMed Central

Liu, Yu; Huang, Yuanchun; Jia, Guangze

2017-01-01

To better understand the effect of the components of molten 2219 Al alloy on the hydrogen content dissolved in it, the H adsorption on various positions of alloying element clusters of Cu, Mn and Al, as well as the inclusion of Al2O3, MgO and Al4C3, were investigated by means of first principles calculation, and the thermodynamic stability of H adsorbed on each possible site was also studied on the basis of formation energy. Results show that the interaction between Al, MgO, Al4C3 and H atoms is mainly repulsive and energetically unfavorable; a favorable interaction between Cu, Mn, Al2O3 and H atoms was determined, with H being more likely to be adsorbed on the top of the third atomic layer of Cu(111), the second atomic layer of Mn(111), and the O atom in the third atomic layer of Al2O3, compared with other sites. It was found that alloying elements Cu and Mn and including Al2O3 may increase the hydrogen adsorption in the molten 2219 Al alloy with Al2O3 being the most sensitive component in this regard. PMID:28773185

Kinetic and Thermodynamic Characterization of the Cobalt and Manganese Oxyhydroxide Cores Formed in Horse Spleen Ferritin

NASA Technical Reports Server (NTRS)

Zhang, Bo; Harb, John N.; Davis, Robert C.; Kim, Jae-Woo; Chu, Sang-Hyon; Choi, Sang; Miller, Tim; Watt, Gerald D.

2004-01-01

Horse spleen ferritin (HoSF) containing 800-1500 cobalt or 250-1200 manganese atoms as Co(O)OH and Mn(O)OH mineral cores within the HoSF interior (Co-HoSF and Mn-HoSF) was synthesized, and the chemical reactivity, kinetics of reduction, and the reduction potentials were measured. Microcoulometric and chemical reduction of HoSF containing the M(O)OH mineral core (M = Co or Mn) was rapid and quantitative with a reduction stoichiometry of 1.05+/-0.10 e/M forming a stable M(OH)2 mineral core. At pH 9.0, ascorbic acid (AH2), a two-electron reductant, effectively reduced the mineral cores; however, the reaction was incomplete and rapidly reached equilibrium. The addition of excess AH2 shifted the reaction to completion with a M(3+)/AH2 stoichiometry of 1.9-2.1, consistent with a single electron per metal atom reduction. The rate of reaction between M(0)OH and excess AH2 was measured by monitoring the decrease in mineral core absorbance with time. The reaction was first order in each reactant with second-order rate constants of 0.53 and 4.74/M/min, respectively, for Co- and Mn-HoSF at pH 9.0. From the variation of absorbance with increasing AH2 concentration, equilibrium constants at pH 9.0 of 5.0+/-1.9 for Co-HoSF and 2.9+/-0.9 for Mn-HoSF were calculated for 2M(O)OH + AH2 = 2M(OH)2 f D, where AH2 and D are ascorbic acid and dehydroascorbic acid, respectively. Consistent with these equilibrium constants, the standard potential for the reduction of Co(III)-HoSF is 42 mV more positive than that of the ascorbic acid reaction, while the standard potential of Mn(III)-HoSF is 27 mV positive relative to AH2. Fe(2+) in solution with Co- and Mn-HoSF under anaerobic conditions was oxidized to form Fe(O)OH within the HoSF interior, resulting in partial displacement of the Co or Mn by iron.

Fabrication of Mg-X-O (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn) barriers for magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Yakushiji, K.; Kitagawa, E.; Ochiai, T.; Kubota, H.; Shimomura, N.; Ito, J.; Yoda, H.; Yuasa, S.

2018-05-01

We fabricated magnetic tunnel junctions with a 3d-transition material(X)-doped MgO (Mg-X-O) barrier, and evaluated the effect of the doping on magnetoresistance (MR) and microstructure. Among the variations of X (X = Fe, Co, Ni, Cr, Mn, Ti, V, and Zn), X = Fe and Mn showed a high MR ratio of more than 100%, even at a low resistance-area product of 3 Ωμm2. The microstructure analysis revealed that (001) textured orientation formed for X = Fe and Mn despite substantial doping (about 10 at%). The elemental mappings indicated that Fe atoms in the Mg-Fe-O barrier were segregated at the interfaces, while Mn atoms were evenly involved in the Mg-Mn-O barrier. This suggests that MgO has high adaptability for Fe and Mn dopants in terms of high MR ratio.

New laboratory atomic data for neutral, singly and doubly ionised iron group elements for astrophysics applications

NASA Astrophysics Data System (ADS)

Pickering, Juliet C.; Nave, Gillian; Liggins, Florence; Clear, Christian; Ruffoni, Matthew; Sansonetti, Craig

2015-08-01

We present new laboratory spectroscopic measurements to produce atomic data for astrophysically important species: neutral, singly and doubly ionised iron group elements.We use high resolution Fourier Transform Spectrometry (FTS) (resolving power up to 2x106 at 200nm) to measure atomic spectra, giving accurate line wavelengths (to a few parts in 108), atomic energy levels, hyperfine structure splitting and log gfs (accurate to a few %) (Ruffoni et al this meeting). These data are vital for astrophysical spectral analyses for: line identification, spectrum synthesis, elemental abundance determinations [eg 1], and disentangling of blends etc. It is not possible to theoretically calculate these atomic data to the accuracy needed for modern astrophysics applications.At Imperial College we have a unique visible-VUV FT spectrometer with short wavelength cut-off of 135nm. We supplement FTS data at shorter wavelengths with spectra recorded on the NIST 10.7m grating spectrograph (with phosphor image or photographic plates) and at longer wavelengths in the IR we use the NIST IR FT spectrometer.An elemental spectrum may contain thousands of spectral lines from the IR to VUV. We use these wavelengths to correct known atomic energy levels, and search for new atomic levels. The result is a classified linelist and accurate atomic energy levels.We present progress on iron group element atomic energy levels and wavelengths for V I and V II [2,3], Co III [4], Cr I, Mn I and Mn II, and Ni II.This work is supported by STFC(UK), The Leverhulme Trust, The Royal Society and NASA.References[1] Bergemann M, Pickering JC & Gehren T,“NLTE analysis of Co I/Co II lines in spectra of cool stars with new laboratory hyperfine splitting constants",MNRAS 401(2) 1334 (2010)[2] Thorne AP, Pickering JC & Semeniuk J,“The spectrum and term analysis of V II”, ApJS 207,13 (2013)[3] Thorne AP, Pickering JC & Semeniuk J,“The spectrum and term analysis of V I",ApJS 192,11 (2011)[4] Smillie DG, Pickering JC, Nave G & Smith PL,“The Spectrum and Term Analysis of Co III Measured using Fourier Transform and Grating Spectroscopy”,ApJS submitted

Synthesis, structure, and magnetic characterization of a C3-symmetric Mn(III)3Cr(III) assembly: molecular recognition between a trinuclear Mn(III) triplesalen complex and a fac-triscyano Cr(III) complex.

PubMed

Freiherr von Richthofen, Carl-Georg; Stammler, Anja; Bögge, Hartmut; DeGroot, Marty W; Long, Jeffrey R; Glaser, Thorsten

2009-11-02

The reaction of the tris(tetradentate) triplesalen ligand H(6)talen(t-Bu(2)), which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn(II) salts under aerobic conditions, affords, in situ, the trinuclear Mn(III) triplesalen complex [(talen(t-Bu(2))){Mn(III)(solv)(n)}(3)](3+). This species then reacts with [(Me(3)tacn)Cr(CN)(3)] to form the tetranuclear complex [{(talen(t-Bu(2)))Mn(III)(3)}{(Me(3)tacn)Cr(CN)(3)}](3+) ([Mn(III)(3)Cr(III)](3+)). The regular ligand folding observed in the trinuclear triplesalen complex preorganizes the three metal ions for the reaction with three facially coordinated nitrogen atoms of [(Me(3)tacn)Cr(CN)(3)]. [{(talen(t-Bu(2)))(Mn(III)(MeOH))(3)}{(Me(3)tacn)Cr(CN)(3)}](ClO(4))(3) (1) was characterized by infrared spectroscopy, elemental analysis, mass spectrometry, electron absorption spectroscopy, and magnetic measurements. The molecular structure was established for the acetate-substituted derivative [{(talen(t-Bu(2)))(Mn(III)(MeOH))(2)(Mn(III)(OAc))}{(Me(3)tacn)Cr(CN)(3)}](ClO(4))(2) (2) by single-crystal X-ray diffraction. Variable-temperature-variable-field and mu(eff) versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction components. Satisfactory reproduction of the experimental data has been obtained for the parameters J(Mn-Cr) = -0.12 +/- 0.04 cm(-1), J(Mn-Mn) = -0.70 +/- 0.03 cm(-1), and D(Mn) = -3.0 +/- 0.4 cm(-1). These generate a triply degenerate pseudo S(t) = 7/2 spin manifold, which cannot be appropriately described by a giant spin model and which exhibits a weak easy-axis magnetic anisotropy. This is corroborated by the onset of a frequency-dependent chi'' signal at low temperatures, demonstrating a slow relaxation of the magnetization indicative of 1 being a single-molecule magnet. Comparing the properties to those of the heptanuclear analogue [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+) ([Mn(III)(6)Cr(III)](3+)) formed by the reaction of 2 equiv of [(talen(t-Bu(2))){Mn(III)(solv)(n)}(3)](3+) with 1 equiv of [Cr(CN)(6)](3-) [Glaser, T.; Heidemeier, M.; Weyhermüller, T.; Hoffmann, R.-D.; Rupp, H.; Müller, P. Angew. Chem. Int. Ed., 2006, 45, 6033-6037] demonstrates a lower driving force for formation, a strongly reduced J(Mn-Cr) exchange, a slightly reduced J(Mn-Mn) exchange, and a significantly longer Mn-N(N[triple bond]C) bond length in [Mn(III)(3)Cr(III)](3+). Taking into account magneto-structural correlations establishes a supramolecular interaction between the two [(talen(t-Bu(2)))Mn(III)(3)](3+) subunits in [Mn(III)(6)Cr(III)](3+) responsible for the structural distortion and the short Mn-N(N[triple bond]C) distance which results in a strong J(Mn-Cr) exchange and thus [Mn(III)(6)Cr(III)](3+) being a single-molecule magnet with a relatively high effective anisotropy barrier of 25.4 K.

Exchange interaction in hexagonal MnRhP from first-principles studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, X. B., E-mail: liuxubo@uta.edu; Zhang, Qiming; Ping Liu, J., E-mail: pliu@uta.edu

2014-05-07

Electronic structure and magnetic properties for MnRhP have been studied from a first-principles density functional calculation. The calculated lattice constants, a = 6.228 Å and c = 3.571 Å, are in good agreement with the experimental values of a = 6.223 Å and c = 3.585 Å. The calculated moment of Mn is 3.1 μ{sub B}/atom, resulting in a total moment of 3.0 μ{sub B}/atom due to small moments induced at Rh and P sites. The magnetic moment of Mn decreases with unit cell size. The exchange interactions are dominated by positive Mn-Mn exchange coupling (J{sub Mn−Mn}), implying a stable ferromagnetic ordering in Mn sublattice. In particular, J{sub Mn−Mn} showsmore » a maximum value (1.5 mRy) at the the optimized unit cell size. The structural distortion or unit cell size change will affect J{sub Mn−Mn}, which is intimately related to the magneto-elastic and magneto-caloric effect.« less

Tuning of Exchange Coupling and Switchable Magnetization Dynamics by Displacing the Bridging Ligands Observed in Two Dimeric Manganese(III) Compounds

NASA Astrophysics Data System (ADS)

Liu, Xiang-Yu; Cen, Pei-Pei; Wu, Li-Zhou; Li, Fei-Fei; Song, Wei-Ming; Xie, Gang; Chen, San-Ping

2017-03-01

Two Mn(III)-based dimers, [Mn2(bpad)2(CH3O)4]n (1) and [Mn2(bpad)2(pa)2]n·2H2O (2) (Hbpad = N3-benzoylpyridine-2-carboxamidrazone, H2pa = phthalic acid), have been assembled from a tridentate Schiff-base chelator and various anionic coligands. Noteworthily, compound 1 could be identified as a reaction precursor to transform to 2 in the presence of phthalic acid, resulting in a rarely structural conversion process in which the bridges between intradimer Mn(III) ions alter from methanol oxygen atom with μ2-O mode in 1 (Mn Mn distance of 3.046 Å) to syn-anti carboxylate in 2 (Mn Mn distance of 4.043 Å), while the Mn(III) centers retain hexa-coordinated geometries with independently distorted octahedrons in two compounds. The dc magnetic determinations reveal that ferromagnetic coupling between two metal centers with J = 1.31 cm-1 exists in 1, whereas 2 displays weak antiferromagnetic interactions with the coupling constant J of -0.56 cm-1. Frequency-dependent ac susceptibilities in the absence of dc field for 1 suggest slow relaxation of the magnetization with an energy barrier of 13.9 K, signifying that 1 features single-molecule magnet (SMM) behavior. This work presents a rational strategy to fine-tune the magnetic interactions and further magnetization dynamics of the Mn(III)-containing dinuclear units through small structural variations driven by the ingenious chemistry.

Manganese-calcium intermixing facilitates heteroepitaxial growth at the (1014) calcite-water interface

DOE PAGES

Xu, Man; Riechers, Shawn L.; Ilton, Eugene S.; ...

2017-09-05

For this research, in situ atomic force microscopy (AFM) measurements were performed to probe surface precipitates that formed on the (10more » $$\\bar{1}$$4) surface of calcite (CaCO 3) single crystals following reaction with Mn2 +-bearing aqueous solutions. Three-dimensional epitaxial islands were observed to precipitate and grow on the surfaces. In situ time-sequenced measurements demonstrated that the growth rates were commensurate with those obtained for epitaxial islands formed on calcite crystals reacted with Cd2 +-bearing aqueous solutions of the same range in supersaturation with respect to the pure metal carbonate phase. This finding was unexpected as rhodochrosite (MnCO 3) and calcite display a 10% lattice mismatch, based on the area of their (10$$\\bar{1}$$4) surface unit cells, whereas the lattice mismatch is only 4% for otavite (CdCO 3) and calcite. Coatings of varying thicknesses were therefore synthesized by reacting calcite single crystals in calcite-equilibrated aqueous solutions with up to 250 μM MnCl 2. Ex situ X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR), and AFM measurements of the reacted crystals demonstrated the formation of an epitaxial (Mn,Ca)CO 3 solid solution. The epitaxial solid solution had a spatially complex composition, whereby the first few nanometers were rich in Ca and the Mn content increased with distance from the original calcite surface, culminating in a topmost region of almost pure MnCO 3 for the thickest coatings. The effective lattice mismatch was therefore much smaller than the nominal mismatch thus explaining the measured growth rates. Lastly, these findings highlight the strong influence played by the substrate on the composition of surface precipitates in aqueous conditions.« less

Large moments in bcc FexCoyMnz ternary alloy thin films

NASA Astrophysics Data System (ADS)

Snow, R. J.; Bhatkar, H.; N'Diaye, A. T.; Arenholz, E.; Idzerda, Y. U.

2018-02-01

The elemental magnetic moments and the average atomic moment of 10-20 nm thick single crystal bcc (bct) FexCoyMnz films deposited on MgO(001) have been determined as a function of a broad range of compositions. Thin film epitaxy stabilized the bcc structure for 80% of the available ternary compositional space compared to only a 23% stability region for the bulk. The films that display ferromagnetism represent 60% of the available compositional possibilities compared to 25% for the bulk. A maximum average atomic moment of 3.25 ± 0.3 μB/atom was observed for a bcc Fe9Co62Mn29 film (well above the limit of the Slater-Pauling binary alloy curve of 2.45 μB/atom). The FexCoyMnz ternary alloys that exhibit high moments can only be synthesized as ultrathin films since the bcc structure is not stable in the bulk for those compositions.

Structural comparative studies on new Mn(II), Cr(III) and Ru(III) complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ).

PubMed

Al-Assy, Waleed H; El-Askalany, Abdel Moneum H; Mostafa, Mohsen M

2013-12-01

The structure of a new Mn(II) complex, [Mn(TPTZ)Cl2(H2O)]⋅H2O, was established by a single crystal X-ray diffraction. Crystal data are as follow: monoclinic, P21/c,a = 8.7202 (3)Å, b = 11.5712 (4)Å, c = 20.8675 (9)Å, β=11 (18) × 1010, V = 2029.27 (13)Å(3), Z = 4. The HOMO, LUMO and other DFT parameters on the atoms have been calculated to confirm the geometry of the ligand and its complexes using material studio program. The complexes were characterized by elemental analyses, spectral, magnetic, thermal and cyclic voltammetry measurements. Electronic spectra and magnetic moments of the complexes suggest distorted-octahedral structures around the metal ions (Mn(II), Cr(III) and Ru(III)). The redox properties were investigated by cyclic voltammetry. Kinetic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. The results of DNA studies of the metal complexes promised to be effective in tumour treatment. Copyright © 2013 Elsevier B.V. All rights reserved.

Structural comparative studies on new MnII, CrIII and RuIII complexes derived from 2,4,6-tri-(2-pyridyl)-1,3,5-triazine (TPTZ)

NASA Astrophysics Data System (ADS)

Al-Assy, Waleed H.; El-Askalany, Abdel Moneum H.; Mostafa, Mohsen M.

2013-12-01

The structure of a new MnII complex, [Mn(TPTZ)Cl2(H2O)]ṡH2O, was established by a single crystal X-ray diffraction. Crystal data are as follow: monoclinic, P21/c, a = 8.7202 (3) Å, b = 11.5712 (4) Å, c = 20.8675 (9) Å, β = 11 (18) × 1010, V = 2029.27 (13) Å3, Z = 4. The HOMO, LUMO and other DFT parameters on the atoms have been calculated to confirm the geometry of the ligand and its complexes using material studio program. The complexes were characterized by elemental analyses, spectral, magnetic, thermal and cyclic voltammetry measurements. Electronic spectra and magnetic moments of the complexes suggest distorted-octahedral structures around the metal ions (MnII, CrIII and RuIII). The redox properties were investigated by cyclic voltammetry. Kinetic parameters were determined using Coats-Redfern and Horowitz-Metzger methods. The results of DNA studies of the metal complexes promised to be effective in tumour treatment.

One pot synthesis of two Mn(II) perchlorate complexes with s-triazine NNN-pincer ligand; molecular structure, Hirshfeld analysis and DFT studies

NASA Astrophysics Data System (ADS)

Soliman, Saied M.; El-Faham, Ayman

2018-07-01

Self assembly of Mn(II) perchlorate and bis(pyrazolo)-s-triazine pincer ligand (L) in methanol-water mixture afforded the homoleptic [MnL2](ClO4)2 complex (1) as plate colorless crystals. Following the crystallization process till the near dryness of the solution, we noted few needle like crystals of the heteroleptic [MnL(H2O)3](ClO4)2·H2O complex (2). Their molecular and supramolecular structures were analyzed using single crystal structure combined with Hirshfeld analysis. The packing of complexes 1 and 2 is dominated by weak Csbnd H⋯O and strong Osbnd H⋯O hydrogen bonds, respectively, as well as anion-π stacking interactions. Using Hirshfeld analysis, the percentages of the O⋯H intermolecular contacts are 32.7% and 36.8% for 1 and 2, respectively. The Mnsbnd N distances correlated well with the atoms in molecules (AIM) topological parameters. The amount of electron density transferred from the ligand units to the manganese centre are nearly the same (0.9 e) in both complexes.

Novel Hybrid Catalyst for the Oxidation of Organic Acids: Pd Nanoparticles Supported on Mn-N-3D-Graphene Nanosheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perry, Albert; Kabir, Sadia; Matanovic, Ivana

This paper reports the fabrication and electrochemical performance of a hybrid catalyst composed of Pd nanoparticles and atomically dispersed Mn active centers integrated into the nitrogen-doped three-dimensional graphene nanosheets (Pd/Mn-N-3D-GNS). Our results show that the synergistic integration of both Pd nanoparticles and atomically dispersed Mn can be used to enhance the activity toward the electrochemical oxidation of organic acids at biologically relevant pH values. The hybrid catalyst (Pd/Mn-N-3D-GNS) showed increased maximum currents toward the oxidation of oxalic acid when compared to its individual catalysts, namely, Pd/3D-GNS and Mn N-3D-GNS catalysts. The hybrid also showed a decreased onset potential for oxidationmore » of mesoxalic acid as compared to Mn-N-3D-GNS and decreased onset potentials for the oxidation of glyoxalic acid when compared to both of its constituent catalysts. Oxidation of formic acid was also tested and the hybrid was shown to catalyze both dehydration and dehydrogenation mechanisms of formic acid electro-oxidation. Using density functional theory calculations, it was elucidated that a two-site catalysis most likely promotes dehydrogenation reaction for formic acid oxidation, which can explain the selectivity of Pd nanoparticles and atomically dispersed Mn towards the dehydrogenation/ dehydration pathway.« less

Novel Hybrid Catalyst for the Oxidation of Organic Acids: Pd Nanoparticles Supported on Mn-N-3D-Graphene Nanosheets

DOE PAGES

Perry, Albert; Kabir, Sadia; Matanovic, Ivana; ...

2017-06-16

This paper reports the fabrication and electrochemical performance of a hybrid catalyst composed of Pd nanoparticles and atomically dispersed Mn active centers integrated into the nitrogen-doped three-dimensional graphene nanosheets (Pd/Mn-N-3D-GNS). Our results show that the synergistic integration of both Pd nanoparticles and atomically dispersed Mn can be used to enhance the activity toward the electrochemical oxidation of organic acids at biologically relevant pH values. The hybrid catalyst (Pd/Mn-N-3D-GNS) showed increased maximum currents toward the oxidation of oxalic acid when compared to its individual catalysts, namely, Pd/3D-GNS and Mn N-3D-GNS catalysts. The hybrid also showed a decreased onset potential for oxidationmore » of mesoxalic acid as compared to Mn-N-3D-GNS and decreased onset potentials for the oxidation of glyoxalic acid when compared to both of its constituent catalysts. Oxidation of formic acid was also tested and the hybrid was shown to catalyze both dehydration and dehydrogenation mechanisms of formic acid electro-oxidation. Using density functional theory calculations, it was elucidated that a two-site catalysis most likely promotes dehydrogenation reaction for formic acid oxidation, which can explain the selectivity of Pd nanoparticles and atomically dispersed Mn towards the dehydrogenation/ dehydration pathway.« less

A X-Ray Absorption Study of Transition Metal Oxides

NASA Astrophysics Data System (ADS)

Bunker, Grant Byrd

This work is an experimental and theoretical study of the x-ray absorption near-edge structure of selected 3d transition metal compounds. The goal is to understand the physical mechanisms of XANES, using the competing multiple scattering (MS) and single scattering formalisms of Durham et al, and of Muller and Schaich, respectively. Careful experimental measurements of the K edge absorption of Mn oxides and KMnO(,4) at 300(DEGREES)K, 140(DEGREES)K and 80(DEGREES)K were made. These materials were chosen because they exhibit a variety of structures and oxidation states. Computer simulations of the XANES using the formalisms above were also performed. The experimental results show that atoms beyond the first coordination shell significantly affect the XANES near and above the edge; in particular the temperature dependent XANES and the "white line" in MnO establish this. We conclude that XANES, like EXAFS, is primarily sensitive to geometrical structure, except within about 1 Rydberg of the Fermi level. Two types of MS are distinguished: type 1 (forward scattering) is important in both XANES and EXAFS regions; type 2 (large angle scattering) is important only at and below the edge. MS of the photoelectron among the first shell Oxygen atoms in KMnO(,4) is observed experimentally, and found to become negligible above (DBLTURN) 1 Rydberg past the edge. The sharp features in XANES are primarily due to scattering from distant atoms, rather than localized states, except below the edge. This is supported by the observation that (alpha)-Mn(,2)O(,3) and Mn(,3)O(,4) spectra are nearly identical; their structures are the same, but the average oxidation states are different. We find the bond length strongly affects the edge position and the intensity of the 3d absorption in tetrahedrally coordinated transition metals. Other new results are the first shell EXAFS amplitude in MnO shows an anomalous energy dependence, which apparently cannot be explained by current theory. A new deconvolution algorithm is proposed to minimize truncation effects in Fourier filtering.

Role of magnetic and atomic ordering in the martensitic transformation of Ni-Mn-In from a first-principles study

NASA Astrophysics Data System (ADS)

Li, Chun-Mei; Luo, Hu-Bin; Hu, Qing-Miao; Yang, Rui; Johansson, Börje; Vitos, Levente

2012-12-01

The composition-dependent lattice parameters, crystal structure, elastic properties, magnetic moment, and electronic structure of Ni2Mn1+xIn1-x (0≤x≤0.6) are studied by using first-principles calculations. It is shown that the martensitic phase transition (MPT) from cubic L21 to tetragonal L10 accompanies the MnMn-MnIn ferromagnetic (FM) to antiferromagnetic (AFM) transition, at around the critical composition x=0.32, in agreement with the experimental measurement. The Mn-In atomic disorder leads to decreasing stability of the martensite relative to the austenite, which depresses the MPT. The shear elastic constant C' of the parent phase first decreases slightly with increasing x and then remains almost unchanged above x=0.32, indicating C' alone cannot account for the increase of the MPT temperature with x. The total magnetic moments for the L21 phase are in good agreement with those determined by experiments, whereas for the L10 phase they are slightly larger than the experimental data due to the possible Mn-In atomic disorder in the sample. The calculated density of states demonstrate that the covalent bonding between the minority spin states of Ni and In plays an important role in both the magnetic and structural stability.

Crystallographic, magnetic, and electronic structures of ferromagnetic shape memory alloys Ni2XGa (X=Mn,Fe,Co) from first-principles calculations

NASA Astrophysics Data System (ADS)

Bai, J.; Raulot, J. M.; Zhang, Y. D.; Esling, C.; Zhao, X.; Zuo, L.

2011-01-01

The crystallographic, magnetic and electronic structures of the ferromagnetic shape memory alloys Ni2XGa (X=Mn, Fe, and Co), are systematically investigated by means of the first-principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The lattice parameters of both austenitic and martensitic phases in Ni2MnGa have been calculated. The formation energies of the cubic phase of Ni2XGa are estimated, and show a destabilization tendency if Mn atom is substituted by Fe or Co. From Ni2MnGa to Ni2CoGa, the down spin total density of states (DOS) at Fermi level is gradually increasing, whereas that of the up spin part remains almost unchanged. This is the main origin of the difference of the magnetic moment in these alloys. The partial DOS is dominated by the Ni and Mn 3d states in the bonding region below EF. There are two bond types existing in Ni2XGa: one is between neighboring Ni atoms in Ni2MnGa; the other is between Ni and X atoms in Ni2FeGa and Ni2CoGa alloys.

Crystal structure of hexagonal MnAl(4).

PubMed

Pauling, L

1987-06-01

A structure is proposed for the hexagonal form of MnAl(4), with a(H) = 28.4 A and c(H) = 12.43 A, on the basis of a high-resolution electron micrograph and comparison with crystals of known structures. The proposed structure involves seven 104-atom complexes of 20 Friauf polyhedra, sharing some atoms with one another. It is closely related to the 23.36-A cubic structure of MnAl(4) and to the 14.19-A cubic structure of Mg(32)(Al,Zn)(49).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aron-Dine, S.; Pomrehn, G. S.; Pribram-Jones, A.

Two quaternary Heusler alloys, equiatomic CuNiMnAl and CuNiMnSn, are studied using density functional theory to understand their tendency for atomic disorder on the lattice and the magnetic effects of disorder. Disordered structures with antisite defects of atoms of the same and different sublattices are considered, with the level of atomic disorder ranging from 3% to 25%. Formation energies and magnetic moments are calculated relative to the ordered ground state and combined with a simple thermodynamical model to estimate temperature effects. We predict the relative levels of disordering in the two equiatomic alloys with good correlation to experimental x-ray diffraction results.more » In conclusion, the effect of swaps involving Mn is also discussed.« less

[μ-10,21-Dimethyl-3,6,14,17-tetra-za-tricyclo-[17.3.1.1]tetra-cosa-1(23),2,6,8,10,12 (24),13,17,19,21-deca-ene-23,24-diolato-κN,N,O,O:κN,N,O,O]bis-(perchlorato-κO)dimanganese(II).

PubMed

Liu, Jing; Pan, Zhi-Quan; Zhou, Hong; Li, Yi-Zhi

2008-11-08

In the centrosymmetric and dinuclear title complex, [Mn(2)(C(22)H(22)N(4)O(2))(ClO(4))(2)], the two Mn atoms are bridged by two phenolate O atoms of the N(4)O(2) macrocycle with an Mn⋯Mn distance of 2.9228 (11) Å. The distorted square-pyramidal N(2)O(3) coordination geometry is completed by an O atom derived from a perchlorate anion.

Structure of the orthorhombic form of Mn(2)Al(7), Fe(2)Al(7), and (Mn(0.7)Fe(0.3))(2)Al(7) that by twinning produces grains with decagonal point-group symmetry.

PubMed

Pauling, L

1988-04-01

Analysis of electron diffraction photographs of grains of Mn(2)Al(7), Fe(2)Al(7), and (Mn(0.7)Fe(0.3))(2)Al(7) leads to the conclusion that they are 5-fold twins of a 1664-atom orthorhombic crystal with a = 32.86 A, b = 31.23 A, and c = 24.80 A and with 16 icosahedral clusters of 104 atoms in positions shifted by small amounts from those of the cubic beta-tungsten structure.

Structure of the orthorhombic form of Mn2Al7, Fe2Al7, and (Mn0.7Fe0.3)2Al7 that by twinning produces grains with decagonal point-group symmetry

PubMed Central

Pauling, Linus

1988-01-01

Analysis of electron diffraction photographs of grains of Mn2Al7, Fe2Al7, and (Mn0.7Fe0.3)2Al7 leads to the conclusion that they are 5-fold twins of a 1664-atom orthorhombic crystal with a = 32.86 Å, b = 31.23 Å, and c = 24.80 Å and with 16 icosahedral clusters of 104 atoms in positions shifted by small amounts from those of the cubic β-tungsten structure. PMID:16593921

Detecting magnetic ordering with atomic size electron probes

DOE PAGES

Idrobo, Juan Carlos; Rusz, Ján; Spiegelberg, Jakob; ...

2016-05-27

While magnetism originates at the atomic scale, the existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that atomic size electron probes with customized phase distributions can detect magnetic circular dichroism. Here, we report a direct experimental real-space detection of magnetic circular dichroism in aberration-corrected scanning transmission electron microscopy (STEM). Using an atomic size-aberrated electron probe with a customized phase distribution, we reveal the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The novel experimental setupmore » presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution.« less

Local atomic and magnetic structure of dilute magnetic semiconductor (Ba ,K ) (Zn,Mn ) 2As2

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; Banerjee, Soham; Chen, Bijuan; Jin, Changqing; Feygenson, Mikhail; Uemura, Yasutomo J.; Billinge, Simon J. L.

2016-09-01

We have studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba ,K )(Zn ,Mn )2As2 through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. We detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of ≲5 Å , resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment of Mn spins along the crystallographic c axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. We discuss these results in the context of other experiments and theoretical studies on this system.

Growth Texture and Mechanism of Zinc Nanowires Produced by Mechanical Elongation of Nanocontacts.

PubMed

Yamabe, Kammu; Kizuka, Tokushi

2018-01-01

Two zinc nanotips were brought into contact and elongated inside a transmission electron microscope, thereby growing single-crystal nanowires. The growth dynamics was observed in situ via a lattice imaging method. The preferential crystal growth directions were identified as [101-0], [112-0], [101-2-], and [0001]. Of these, the nanowires grown along the [101-0] and [112-0] directions accounted for 75% of the total and were surrounded by low-energy side surfaces, i.e., {0001}, {101-1}, and {101-0}. On the basis of these features, models of the nanowire morphology were proposed. In either growth direction, the tensile force aligned parallel to the direction along which slip events corresponding to the predominant slip system were unlikely to occur. This led to a high tensile stress for extracting atoms from the growth region, i.e., the promotion of nanowire growth.

Unique [Mn 6Bi 5] - Nanowires in KMn 6Bi 5: A Quasi-One-Dimensional Antiferromagnetic Metal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bao, Jin-Ke; Tang, Zhang-Tu; Jung, Hee Joon

In this paper, we report a new quasi-one-dimensional compound KMn 6Bi 5 composed of parallel nanowires crystallizing in a monoclinic space group C2/m with a = 22.994(2) Å, b = 4.6128(3) Å, c = 13.3830(13) Å and β = 124.578(6)°. The nanowires are infinite [Mn 6Bi 5] - columns each of which is composed of a nanotube of Bi atoms acting as the cladding with a nanorod of Mn atoms located in the central axis of the nanotubes. The nanorods of Mn atoms inside the Bi cladding are stabilized by Mn–Mn bonding and are defined by distorted Mn-centered cluster icosahedramore » of Mn 13 sharing their vertices along the b axis. The [Mn 6Bi 5] - nanowires are linked with weak internanowire Bi–Bi bonds and charge balanced with K + ions. The [Mn 6Bi 5] - nanowires were directly imaged by high-resolution transmission electron microscopy and scanning transmission electron microscopy. Magnetic susceptibility studies show one-dimensional characteristics with an antiferromagnetic transition at ~75 K and a small average effective magnetic moment (1.56 μ B/Mn for H ∥ b and 1.37 μ B/Mn for H ⊥ b) of Mn from Curie–Weiss fits above 150 K. Specific heat measurements reveal an electronic specific heat coefficient γ of 6.5(2) mJ K –2(mol-Mn) -1 and a small magnetic entropy change ΔS mag ≈ 1.6 J K –1 (mol-Mn) -1 across the antiferromagnetic transition. Finally, in contrast to a metallic resistivity along the column, the resistivity perpendicular to the column shows a change from a semiconducting behavior at high temperatures to a metallic one at low temperatures, indicating an incoherent-to-coherent crossover of the intercolumn tunneling of electrons.« less

Unique [Mn 6Bi 5] - Nanowires in KMn 6Bi 5: A Quasi-One-Dimensional Antiferromagnetic Metal

DOE PAGES

Bao, Jin-Ke; Tang, Zhang-Tu; Jung, Hee Joon; ...

2018-03-01

In this paper, we report a new quasi-one-dimensional compound KMn 6Bi 5 composed of parallel nanowires crystallizing in a monoclinic space group C2/m with a = 22.994(2) Å, b = 4.6128(3) Å, c = 13.3830(13) Å and β = 124.578(6)°. The nanowires are infinite [Mn 6Bi 5] - columns each of which is composed of a nanotube of Bi atoms acting as the cladding with a nanorod of Mn atoms located in the central axis of the nanotubes. The nanorods of Mn atoms inside the Bi cladding are stabilized by Mn–Mn bonding and are defined by distorted Mn-centered cluster icosahedramore » of Mn 13 sharing their vertices along the b axis. The [Mn 6Bi 5] - nanowires are linked with weak internanowire Bi–Bi bonds and charge balanced with K + ions. The [Mn 6Bi 5] - nanowires were directly imaged by high-resolution transmission electron microscopy and scanning transmission electron microscopy. Magnetic susceptibility studies show one-dimensional characteristics with an antiferromagnetic transition at ~75 K and a small average effective magnetic moment (1.56 μ B/Mn for H ∥ b and 1.37 μ B/Mn for H ⊥ b) of Mn from Curie–Weiss fits above 150 K. Specific heat measurements reveal an electronic specific heat coefficient γ of 6.5(2) mJ K –2(mol-Mn) -1 and a small magnetic entropy change ΔS mag ≈ 1.6 J K –1 (mol-Mn) -1 across the antiferromagnetic transition. Finally, in contrast to a metallic resistivity along the column, the resistivity perpendicular to the column shows a change from a semiconducting behavior at high temperatures to a metallic one at low temperatures, indicating an incoherent-to-coherent crossover of the intercolumn tunneling of electrons.« less

Effect of Coulomb Correlation on the Magnetic Properties of Mn Clusters.

PubMed

Huang, Chengxi; Zhou, Jian; Deng, Kaiming; Kan, Erjun; Jena, Puru

2018-05-03

In spite of decades of research, a fundamental understanding of the unusual magnetic behavior of small Mn clusters remains a challenge. Experiments show that Mn 2 is antiferromagnetic while small clusters containing up to five Mn atoms are ferromagnetic with magnetic moments of 5 μ B /atom and become ferrimagnetic as they grow further. Theoretical studies based on density functional theory (DFT), however, find Mn 2 to be ferromagnetic, with ferrimagnetic order setting in at different sizes that depend upon the computational methods used. While quantum chemical techniques correctly account for the antiferromagnetic ground state of Mn 2 , they are computationally too demanding to treat larger clusters, making it difficult to understand the evolution of magnetism. These studies clearly point to the importance of correlation and the need to find ways to treat it effectively for larger clusters and nanostructures. Here, we show that the DFT+ U method can be used to account for strong correlation. We determine the on-site Coulomb correlation, Hubbard U self-consistently by using the linear response theory and study its effect on the magnetic coupling of Mn clusters containing up to five atoms. With a calculated U value of 4.8 eV, we show that the ground state of Mn 2 is antiferromagnetic with a Mn-Mn distance of 3.34 Å, which agrees well with the electron spin resonance experiment. Equally important, we show that on-site Coulomb correlation also plays an important role in the evolution of magnetic coupling in larger clusters, as the results differ significantly from standard DFT calculations. We conclude that for a proper understanding of magnetism of Mn nanostructures (clusters, chains, and layers) one must take into account the effect of strong correlation.

Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects

PubMed Central

Panigrahi, Puspamitra; Araujo, C Moyses; Hussen, Tanveer; Ahuja, Rajeev

2014-01-01

We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn valence state carrying a local moment of 4.3 having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p- and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides. PMID:27877684

Synthesis and characterization of new fluoride-containing manganese vanadates A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.

2016-09-15

Large single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO{sub 4}F{sub 2} building blocks. The A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains ofmore » edge-sharing MnO{sub 4}F{sub 2} units running along the a-axis, and interconnected through V{sub 2}O{sub 7} pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn{sup 2+} indicated that Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} is antiferromagnetic with a Neél temperature, T{sub N}=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}. Mn{sub 2}(VO{sub 4})F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn{sup 2+}. These interpenetrating chains are additionally connected through isolated VO{sub 4} tetrahedra to form the condensed structure. - Graphical abstract: New vanadate fluorides A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}(VO{sub 4})F have been synthesized hydrothermally. Upon cooling, the one-dimensional Mn(II) substructure results in antiferromagnetic ordering. Display Omitted - Highlights: • Single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}, (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown hydrothermally. • The use of fluoride mineralizers in the synthesis led to the formation of new compounds without OH{sup −} groups. • The structure of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} features zigzag chains of MnO{sub 4}F{sub 2} units. • Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} exhibits antiferromagnetic ordering with a Neel temperature of ~3 K. • Mn{sub 2}VO{sub 4}F possesses a condensed framework structure with disordered fluorine atoms.« less

Application of the multireference equation of motion coupled cluster method, including spin-orbit coupling, to the atomic spectra of Cr, Mn, Fe and Co

NASA Astrophysics Data System (ADS)

Liu, Zhebing; Huntington, Lee M. J.; Nooijen, Marcel

2015-10-01

The recently introduced multireference equation of motion (MR-EOM) approach is combined with a simple treatment of spin-orbit coupling, as implemented in the ORCA program. The resulting multireference equation of motion spin-orbit coupling (MR-EOM-SOC) approach is applied to the first-row transition metal atoms Cr, Mn, Fe and Co, for which experimental data are readily available. Using the MR-EOM-SOC approach, the splittings in each L-S multiplet can be accurately assessed (root mean square (RMS) errors of about 70 cm-1). The RMS errors for J-specific excitation energies range from 414 to 783 cm-1 and are comparable to previously reported J-averaged MR-EOM results using the ACESII program. The MR-EOM approach is highly efficient. A typical MR-EOM calculation of a full spin-orbit spectrum takes about 2 CPU hours on a single processor of a 12-core node, consisting of Intel XEON 2.93 GHz CPUs with 12.3 MB of shared cache memory.

Multicomutation flow system for manganese speciation by solid phase extraction and flame atomic absorption spectrometry

NASA Astrophysics Data System (ADS)

Tobiasz, Anna; Sołtys, Monika; Kurys, Ewa; Domagała, Karolina; Dudek-Adamska, Danuta; Walas, Stanisław

2017-08-01

In the paper an application of solid phase extraction technique for speciation analysis of manganese in water samples with the use of flame atomic absorption spectrometry is presented. Two types of sorbents, activated silica gel and Dowex 1 × 4, were used respectively for simultaneously Mn2 + and MnO42 - retention and preconcentration. The whole procedure was realized in multicomutation flow system. Different conditions like: type and concentration of eluent, sample pH and loading time were tested during the study. Under appropriate conditions, it was possible to obtained enrichment factors of 20 and 16 for Mn(II) and Mn(VII), respectively. Precision of the procedure was close to 4% (measured as relative standard deviation), whereas the detection limit (3σ) was 1.4 μg·L- 1 for Mn(II) and 4.8 μg·L- 1 for Mn(VII).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seña, N.; Dussan, A.; Mesa, F.

We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x = 0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the Mn{sub Ga} substitution is the most stable configuration with a formation energy of ∼1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 μ{sub B}/Mn-atom. The results indicate that the magnetic ground statemore » originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors.« less

Atomic-Scale Fingerprint of Mn Dopant at the Surface of Sr3(Ru1−xMnx)2O7

PubMed Central

Li, Guorong; Li, Qing; Pan, Minghu; Hu, Biao; Chen, Chen; Teng, Jing; Diao, Zhenyu; Zhang, Jiandi; Jin, Rongying; Plummer, E. W.

2013-01-01

Chemical doping in materials is known to give rise to emergent phenomena. These phenomena are extremely difficult to predict a priori, because electron-electron interactions are entangled with local environment of assembled atoms. Scanning tunneling microscopy and low energy electron diffraction are combined to investigate how the local electronic structure is correlated with lattice distortion on the surface of Sr3(Ru1−xMnx)2O7, which has double-layer building blocks formed by (Ru/Mn)O6 octahedra with rotational distortion. The presence of doping-dependent tilt distortion of (Ru/Mn)O6 octahedra at the surface results in a C2v broken symmetry in contrast with the bulk C4v counterpart. It also enables us to observe two Mn sites associated with the octahedral rotation in the bulk through the “chirality” of local electronic density of states surrounding Mn, which is randomly distributed. These results serve as fingerprint of chemical doping on the atomic scale. PMID:24108411

NASICON-related Na3.4Mn0.4Fe1.6(PO4)3

PubMed Central

Yatskin, Michael M.; Strutynska, Nataliya Yu.; Baumer, Vyacheslav N.; Ogorodnyk, Ivan V.; Slobodyanik, Nikolay S.

2012-01-01

The solid solution, sodium [iron(III)/manganese(II)] tris­(orthophosphate), Na3.4Mn0.4Fe1.6(PO4)3, was obtained using a flux method. Its crystal structure is related to that of NASICON-type compounds. The [(Mn/Fe)2(PO4)3] framework is built up from an (Mn/Fe)O6 octa­hedron (site symmetry 3.), with a mixed Mn/Fe occupancy, and a PO4 tetra­hedron (site symmetry .2). The Na+ cations are distributed over two partially occupied sites in the cavities of the framework. One Na+ cation (site symmetry -3.) is surrounded by six O atoms, whereas the other Na+ cation (site symmetry .2) is surrounded by eight O atoms. PMID:22807697

Adhesion, friction, and wear of binary alloys in contact with single-crystal silicon carbide

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1980-01-01

Sliding friction experiments, conducted with various iron base alloys (alloying elements are Ti, Cr, Mn, Ni, Rh and W) in contact with a single crystal silicon carbide /0001/ surface in vacuum are discussed. Results indicate atomic size misfit and concentration of alloying elements play a dominant role in controlling adhesion, friction, and wear properties of iron-base binary alloys. The controlling mechanism of the alloy properties is as an intrinsic effect involving the resistance to shear fracture of cohesive bonding in the alloy. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases as the solute-to-iron atomic radius ratio increases or decreases from unity. Alloys having higher solute concentration produce more transfer to silicon carbide than do alloys having low solute concentrations. The chemical activity of the alloying element is also an important parameter in controlling adhesion and friction of alloys.

Cyanide Single-Molecule Magnets Exhibiting Solvent Dependent Reversible "On" and "Off" Exchange Bias Behavior.

PubMed

Pinkowicz, Dawid; Southerland, Heather I; Avendaño, Carolina; Prosvirin, Andrey; Sanders, Codi; Wernsdorfer, Wolfgang; Pedersen, Kasper S; Dreiser, Jan; Clérac, Rodolphe; Nehrkorn, Joscha; Simeoni, Giovanna G; Schnegg, Alexander; Holldack, Karsten; Dunbar, Kim R

2015-11-18

The syntheses, structures, and magnetic properties of four new complex salts, (PPN){[Mn(III)(salphen)(MeOH)]2[M(III)(CN)6]}·7MeOH (Mn2M·7MeOH) (M = Fe, Ru, Os and Co; PPN(+) = bis(triphenylphosphoranylidene)ammonium cation; H2salphen = N,N'-bis(salicylidene)-1,2-diaminobenzene), and a mixed metal Co/Os analogue (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH were undertaken. It was found that all compounds exhibit switchable single-molecule magnet (SMM) and exchange-bias behavior depending on the interstitial methanol content. The pristine (PPN){[Mn(salphen)(MeOH)]2[Os(CN)6]}·7MeOH (Mn2Os·7MeOH) behaves as an SMM with an effective barrier for the magnetization reversal, (Ueff/kB), of 17.1 K. Upon desolvation, Mn2Os exhibits an increase of Ueff/kB to 42.0 K and an opening of the hysteresis loop observable at 1.8 K. Mn2Os·7MeOH shows also exchange-bias behavior with magnetic hysteresis loops exhibiting a shift in the quantum tunneling to 0.25 T from zero-field. The Fe(III) and Ru(III) analogues were prepared as reference compounds for assessing the effect of the 5d versus 4d and 3d metal ions on the SMM properties. These compounds are also SMMs and exhibit similar effects but with lower energy barriers. These findings underscore the importance of introducing heavy transition elements into SMMs to improve their slow relaxation of the magnetization properties. The (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)(CN)6]}·7MeOH (Mn2Co·7MeOH) analogue with a diamagnetic Co(III) central atom and the mixed Co/Os (PPN){[Mn(III)(salphen)(MeOH)]2[Co(III)0.92Os(III)0.08(CN)6]}·7MeOH (Mn2Co/Os·7MeOH) "magnetically diluted" system with a 9:1 Co/Os metal ratio were prepared in order to further probe the nature of the energy barrier increase upon desolvation of Mn2Os. In addition, inelastic neutron scattering and frequency-domain Fourier-transform THz electron paramagnetic resonance spectra obtained on Mn2Os·7MeOH and Mn2Os in combination with the magnetic data revealed the presence of anisotropic exchange interactions between Mn(III) and Os(III) ions.

Solid state synthesis of Mn{sub 5}Ge{sub 3} in Ge/Ag/Mn trilayers: Structural and magnetic studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Myagkov, V.G.; Bykova, L.E.; Matsynin, A.A.

The thin-film solid-state reaction between elemental Ge and Mn across chemically inert Ag layers with thicknesses of (0, 0.3, 1 and 2.2 µm) in Ge/Ag/Mn trilayers was studied for the first time. The initial samples were annealed at temperatures between 50 and 500 °C at 50 °C intervals for 1 h. The initiation temperature of the reaction for Ge/Mn (without a Ag barrier layer) was ~ 120 °C and increased slightly up to ~ 250 °C when the Ag barrier layer thickness increased up to 2.2 µm. In spite of the Ag layer, only the ferromagnetic Mn{sub 5}Ge{sub 3} compoundmore » and the Nowotny phase were observed in the initial stage of the reaction after annealing at 500 °C. The cross-sectional studies show that during Mn{sub 5}Ge{sub 3} formation the Ge is the sole diffusing species. The magnetic and cross-sectional transmission electron microscopy (TEM) studies show an almost complete transfer of Ge atoms from the Ge film, via a 2.2 µm Ag barrier layer, into the Mn layer. We attribute the driving force of the long-range transfer to the long-range chemical interactions between reacting Mn and Ge atoms. - Graphical abstract: The direct visualization of the solid state reaction between Mn and Ge across a Ag buffer layer at 500 °C. - Highlights: • The migration of Ge, via an inert 2.2 µm Ag barrier, into a Mn layer. • The first Mn{sub 5}Ge{sub 3} phase was observed in reactions with different Ag layers. • The Ge is the sole diffusing species during Mn{sub 5}Ge{sub 3} formation • The long-range chemical interactions control the Ge atomic transfer.« less

Anisotropy of magnetic interactions and spin filter behavior in hexagonal (Ga,Mn)As nanoribbons

NASA Astrophysics Data System (ADS)

Nie, Ya; Lan, Mu; Zhang, Xi; Xiang, Gang

2017-09-01

The electronic and magnetic properties of Mn doped hexagonal GaAs nanoribbons ((Ga,Mn)As NRs) have been investigated using spin-polarized density functional theory (DFT), and the spin-resolved transport behaviors of (Ga,Mn)As NRs have also been studied with non-equilibrium Green function theory. The calculations show that every Mn dopant brings 4 Bohr magneton (μB) magnetic moment and the ground states of (Ga,Mn)As NRs are ferromagnetic (FM). The investigation of magnetic anisotropies shows that magnetic interactions are dependent on both the distribution directions of Mn atoms and the edge effect of the NRs. The studies of electronic structures and transport properties show that incorporation of Mn atom turns GaAs NR from semiconducting to half-metallic, which significantly enhances the spin-up conductivity and strongly weakens the spin-down conductivity, resulting in non-monatomic variations of spin-dependent conductivities. The nearly 100% spin polarization shown in (Ga,Mn)As NR may be used for low dimensional spin filters, even with as large a bias as 0.9 V. Also, (Ga,Mn)As NR can be used to generate a relatively stable spin-polarized current in a wide bias interval.

Equatorial Ligand Perturbations Influence the Reactivity of Manganese(IV)-Oxo Complexes.

PubMed

Massie, Allyssa A; Denler, Melissa C; Cardoso, Luísa Thiara; Walker, Ashlie N; Hossain, M Kamal; Day, Victor W; Nordlander, Ebbe; Jackson, Timothy A

2017-04-03

Manganese(IV)-oxo complexes are often invoked as intermediates in Mn-catalyzed C-H bond activation reactions. While many synthetic Mn IV -oxo species are mild oxidants, other members of this class can attack strong C-H bonds. The basis for these reactivity differences is not well understood. Here we describe a series of Mn IV -oxo complexes with N5 pentadentate ligands that modulate the equatorial ligand field of the Mn IV center, as assessed by electronic absorption, electron paramagnetic resonance, and Mn K-edge X-ray absorption methods. Kinetic experiments show dramatic rate variations in hydrogen-atom and oxygen-atom transfer reactions, with faster rates corresponding to weaker equatorial ligand fields. For these Mn IV -oxo complexes, the rate enhancements are correlated with both 1) the energy of a low-lying 4 E excited state, which has been postulated to be involved in a two-state reactivity model, and 2) the Mn III/IV reduction potentials. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

New class of single-source precursors for the synthesis of main group-transition metal oxides: heterobimetallic Pb-Mn beta-diketonates.

PubMed

Zhang, Haitao; Yang, Jen-Hsien; Shpanchenko, Roman V; Abakumov, Artem M; Hadermann, Joke; Clérac, Rodolphe; Dikarev, Evgeny V

2009-09-07

Heterometallic lead-manganese beta-diketonates have been isolated in pure form by several synthetic methods that include solid-state and solution techniques. Two compounds with different Pb/Mn ratios, PbMn(2)(hfac)(6) (1) and PbMn(hfac)(4) (2) (hfac = hexafluoroacetylacetonate), can be obtained in quantitative yield by using different starting materials. Single crystal X-ray investigation revealed that the solid-state structure of 1 contains trinuclear molecules in which lead metal center is sandwiched between two [Mn(hfac)(3)] units, while 2 consists of infinite chains of alternating [Pb(hfac)(2)] and [Mn(hfac)(2)] fragments. The heterometallic structures are held together by strong Lewis acid-base interactions between metal atoms and diketonate ligands acting in chelating-bridging fashion. Spectroscopic investigation confirmed the retention of heterometallic structures in solutions of non-coordinating solvents as well as upon sublimation-deposition procedure. Thermal decomposition of heterometallic diketonates has been systematically investigated in a wide range of temperatures and annealing times. For the first time, it has been shown that thermal decomposition of heterometallic diketonates results in mixed-metal oxides, while both the structure of precursors and the thermolysis conditions have a significant influence on the nature of the resulting oxides. Five different Pb-Mn oxides have been detected by X-ray powder diffraction when studying the decomposition of 1 and 2 in the temperature range 500-800 degrees C. The phase that has been previously reported as "Pb(0.43)MnO(2.18)" was synthesized in the pure form by decomposition of 1, and crystallographically characterized. The orthorhombic unit cell parameters of this oxide, obtained by electron diffraction technique, have been subsequently refined using X-ray powder diffraction data. Besides that, a previously unknown lead-manganese oxide has been obtained at low temperature decomposition and short annealing times. The parameters of its monoclinically distorted unit cell have been determined. The EDX analysis revealed that this compound has a Pb/Mn ratio close to 1:4 and contains no appreciable amount of fluorine.

Crystal structure refinements of tetragonal (OH,F)-rich spessartine and henritermierite garnets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antao, Sytle M.; Cruickshank, Laura A.

Cubic garnet (space group Ia\\overline 3 d) has the general formulaX 3Y 2Z 3O 12, whereX,YandZare cation sites. In the tetragonal garnet (space groupI4 1/acd), the corresponding cation sites areX1 andX2,Y, andZ1 andZ2. In both space groups only theYsite is the same. The crystal chemistry of a tetragonal (OH,F)-rich spessartine sample from Tongbei, near Yunxiao, Fujian Province, China, with composition X(Mn 2.82Fe^{2+}_{0.14}Ca 0.04) Σ3 Y{Al 1.95Fe^{3+}_{0.05}} Σ2 Z[(SiO 4) 2.61(O 4H 4) 0.28(F 4) 0.11] Σ3(Sps 94Alm 5Grs 1) was studied with single-crystal X-ray diffraction and space groupI4 1/acd. The deviation of the unit-cell parameters from cubic symmetry is smallmore » [a= 11.64463(1),c= 11.65481 (2) Å,c/a= 1.0009]. Point analyses and back-scattered electron images, obtained by electron-probe microanalysis, indicate a homogeneous composition. TheZ2 site is fully occupied, but theZ1 site contains vacancies. The occupiedZ1 andZ2 sites with Si atoms are surrounded by four O atoms, as in anhydrous cubic garnets. Pairs of split sites are O1 with F11 and O2 with O22. When theZ1 site is vacant, a larger [(O 2H 2)F 2] tetrahedron is formed by two OH and two F anions in the O22 and F11 sites, respectively. This [(O 2H 2)F 2] tetrahedron is similar to the O 4H 4tetrahedron in hydrogarnets. These results indicate ^{X}{{\\rm Mn}^ {2+}_{3}}\\,^{Y}{\\rm Al}_{2}^{Z}[({\\rm SiO}_{4})_{2}({\\rm O}_{2}{\\rm H}_{2})_{0.5}({\\rm F}_{2})_{0.5}]_{\\Sigma3} as a possible end member, which is yet unknown. The H atom that is bonded to the O22 site is not located because of the small number of OH groups. In contrast, tetragonal henritermierite, ideally ^{X}{\\rm Ca}_{3}\\,^{Y}{\\rm Mn}^{3+}_{2}\\,^{Z}[({\\rm SiO}_{4})_{2}({\\rm O}_{4}{\\rm H}_{4})_1]_{\\Sigma3}, has a vacantZ2 site that contains the O 4H 4tetrahedron. The H atom is bonded to an O3 atom [O3—H3 = 0.73 (2) Å]. Because of O2—Mn 3+—O2 Jahn–Teller elongation of the Mn 3+O 6octahedron, a weak hydrogen bond is formed to the under-bonded O2 atom. This causes a large deviation from cubic symmetry (c/a= 0.9534).« less

Graphene nanoplate-MnO2 composites for supercapacitors: a controllable oxidation approach

NASA Astrophysics Data System (ADS)

Huang, Huajie; Wang, Xin

2011-08-01

Graphene nanoplate-MnO2 composites have been synthesized by oxidising part of the carbon atoms in the framework of graphene nanoplates at ambient temperature. The composites were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). It was found that the oxidation extent of the carbon atoms in the graphene framework in these composites was dependent on the reaction time, which also influenced their microstructure, morphology and electrochemical properties. Compared with MnO2 nanolamellas, the nanocomposite prepared with a reaction time of 3 h reveals better electrochemical properties as a supercapacitor electrode material.Graphene nanoplate-MnO2 composites have been synthesized by oxidising part of the carbon atoms in the framework of graphene nanoplates at ambient temperature. The composites were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). It was found that the oxidation extent of the carbon atoms in the graphene framework in these composites was dependent on the reaction time, which also influenced their microstructure, morphology and electrochemical properties. Compared with MnO2 nanolamellas, the nanocomposite prepared with a reaction time of 3 h reveals better electrochemical properties as a supercapacitor electrode material. Electronic supplementary information (ESI) available: Fig. S1, AFM image (5 μm × 5 μm) of graphene nanoplate-MnO2 composite obtained at 3 h; Fig. S2, nitrogen adsorption/desorption isotherm of graphene nanoplate-MnO2 composite obtained at 3 h. See DOI: 10.1039/c1nr10229j

Magnetic analytic bond-order potential for modeling the different phases of Mn at zero Kelvin

NASA Astrophysics Data System (ADS)

Drain, John F.; Drautz, Ralf; Pettifor, D. G.

2014-04-01

It is known that while group VII 4d Tc and 5d Re have hexagonally close-packed (hcp) ground states, 3d Mn adopts a complex χ-phase ground state, exhibiting complex noncollinear magnetic ordering. Density functional theory (DFT) calculations have shown that without magnetism, the χ phase is still the ground state of Mn implying that magnetism and the resultant atomic-size difference between large- and small-moment atoms are not the critical factors, as is commonly believed, in driving the anomalous stability of the χ phase over hcp. Using a canonical tight-binding (TB) model, it is found that for a more than half-filled d band, while harder potentials stabilize close-packed hcp, a softer potential stabilizes the more open χ phase. By analogy with the structural trend from open to close-packed phases down the group IV elements, the anomalous stability of the χ phase in Mn is shown to be due to 3d valent Mn lacking d states in the core which leads to an effectively softer atomic repulsion between the atoms than in 4d Tc and 5d Re. Subsequently, an analytic bond-order potential (BOP) is developed to investigate the structural and magnetic properties of elemental Mn at 0 K. It is derived within BOP theory directly from a new short-ranged orthogonal d-valent TB model of Mn, the parameters of which are fitted to reproduce the DFT binding energy curves of the four experimentally observed phases of Mn, namely, α, β, γ, δ, and ɛ-Mn. Not only does the BOP reproduce qualitatively the DFT binding energy curves of the five different structure types, it also predicts the complex collinear antiferromagnetic (AFM) ordering in α-Mn, the ferrimagnetic ordering in β-Mn, and the AFM ordering in γ-, δ-, and ɛ-Mn that are found by DFT. A BOP expansion including 14 moments is sufficiently converged to reproduce most of the properties of the TB model with the exception of the elastic shear constants, which require further moments. The current TB model, however, predicts values of the shear moduli and the vacancy formation energies that are approximately a factor of 2 too small, so that a future more realistic model for MD simulations will require these properties to be included from the outset in the fitting database.

Electronic and magnetic properties of Mn-doped WSe2 monolayer under strain

NASA Astrophysics Data System (ADS)

Xin, Qianqian; Zhao, Xu; Wang, Tianxing

2017-04-01

Electronic and magnetic properties of Mn-doped WSe2 monolyer subject to isotropic strain are investigated using the first-principles methods based on the density functional theory. Our results indicate that Mn-doped WSe2 monolayer is a magnetic semiconductor nanomaterial with strong spontaneous magnetism without strain and the total magnetic moment of Mn-doped system is 1.038μB. We applied strain to Mn-doped WSe2 monolayer from -10% to 10%. The doped system transforms from magnetic semiconductor to half-metallic material from -10% to -2% compressive strain and from 2% to 6% tensile strain. The largest half-metallic gap is 0.450 eV at -2% compressive strain. The doped system shows metal property from 7% to 10%. Its maximum magnetic moment comes to 1.181μB at 6% tensile strain. However, the magnetic moment of system decreases to zero sharply when tensile strain arrived at 7%. Strain changes the redistribution of charges and arises to the magnetic effect. The coupling between the 3d orbital of Mn atom, 5d orbital of W atom and 4p orbital of Se atom is analyzed to explain the strong strain effect on the magnetic properties. Our studies predict Mn-doped WSe2 monolayers under strain to be candidates for thin dilute magnetic semiconductors, which is important for application in semiconductor spintronics.

B2+L2{sub 1} ordering in Co{sub 2}MnAl Heusler alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vinesh, A., E-mail: attatappa85@gmail.com; Sudheesh, V. D.; Lakshmi, N.

Magnetic and structural properties of B2 ordered Co{sub 2}MnAl Heusler alloy have been studied by X-ray diffraction and DC magnetization techniques. X-ray diffractogram shows the structure is of B2 type with preferential site disorder between Mn and Al atoms and presence of a small L2{sub 1} phase. DC magnetization studies at low temperature establish that the antiferromagnetic nature arises mainly due to the antiparallel coupling of spin moments of 3d electrons of Co with Mn atoms. Curie temperature (T{sub c}) is 733 K which is close to T{sub c} of the L2{sub 1} phase.

Strain-Engineered Oxygen Vacancies in CaMnO3 Thin Films.

PubMed

Chandrasena, Ravini U; Yang, Weibing; Lei, Qingyu; Delgado-Jaime, Mario U; Wijesekara, Kanishka D; Golalikhani, Maryam; Davidson, Bruce A; Arenholz, Elke; Kobayashi, Keisuke; Kobata, Masaaki; de Groot, Frank M F; Aschauer, Ulrich; Spaldin, Nicola A; Xi, Xiaoxing; Gray, Alexander X

2017-02-08

We demonstrate a novel pathway to control and stabilize oxygen vacancies in complex transition-metal oxide thin films. Using atomic layer-by-layer pulsed laser deposition (PLD) from two separate targets, we synthesize high-quality single-crystalline CaMnO 3 films with systematically varying oxygen vacancy defect formation energies as controlled by coherent tensile strain. The systematic increase of the oxygen vacancy content in CaMnO 3 as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft X-ray absorption spectroscopy (XAS) in conjunction with bulk-sensitive hard X-ray photoemission spectroscopy (HAXPES). The relevant defect states in the densities of states are identified and the vacancy content in the films quantified using the combination of first-principles theory and core-hole multiplet calculations with holistic fitting. Our findings open up a promising avenue for designing and controlling new ionically active properties and functionalities of complex transition-metal oxides via strain-induced oxygen-vacancy formation and ordering.

Crystal structure of hexagonal MnAl4

PubMed Central

Pauling, Linus

1987-01-01

A structure is proposed for the hexagonal form of MnAl4, with aH = 28.4 Å and cH = 12.43 Å, on the basis of a high-resolution electron micrograph and comparison with crystals of known structures. The proposed structure involves seven 104-atom complexes of 20 Friauf polyhedra, sharing some atoms with one another. It is closely related to the 23.36-Å cubic structure of MnAl4 and to the 14.19-Å cubic structure of Mg32(Al,Zn)49. Images PMID:16593837

Ferrimagnetism and disorder of epitaxial Mn2-xCoxVAl Heusler compound thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meinert, Markus; Schmalhorst, Jan-Michael; Reiss, Gunter

The quaternary full Heusler compound Mn{sub 2-x}Co{sub x}VAl with x = 1 is predicted to be a half-metallic antiferromagnet. Thin films of the quaternary compounds with x = 0-2 were prepared by dc and RF magnetron co-sputtering on heated MgO (0 0 1) substrates. The magnetic structure was examined by x-ray magnetic circular dichroism and the chemical disorder was characterized by x-ray diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn{sub 2}VAl (x = 0). For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to Mn. The observed reduced magnetic moments are interpretedmore » with the help of band structure calculations in the coherent potential approximation. Mn{sub 2}VAl is very sensitive to disorder involving Mn, because nearest-neighbour Mn atoms couple antiferromagnetically. Co{sub 2}VAl has B2 order and has reduced magnetization. In the cases with x {ge} 0.9 conventional ferromagnetism was observed, closely related to the atomic disorder in these compounds.« less

Cd{sub 0.9375}Mn{sub 0.0625}S diluted magnetic semiconductor: A DFT study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rani, Anita; Kaur, Kulwinder; Kumar, Ranjan, E-mail: ranianita64@gmail.com

We studied the spin polarized electronic band structures and magnetic properties of the diluted magnetic semiconductor Cd{sub 1-x}Mn{sub x}S in Zinc Blende phase (B3) with 0.0625 Mn by using ab initio method. The calculations were performed by using Density Functional Theory as implemented in the Spanish Initiative for Electronic Simulations with Thousands of Atoms code using local density approximation (LDA). Calculated electronic band structures and magnetic properties of Cd{sub 1-x}Mn{sub x}S are discussed in terms of contribution of Mn 3d{sup 5} 4s{sup 2}, Cd 4d{sup 10} 5s{sup 2}, S 3s{sup 2} 3p{sup 4} orbitals. The total magnetic moment is foundmore » to be 5.00 µb for Cd{sub 1−x}Mn{sub x}S at x=0.0625. This value indicate that Mn atom adds no hole carrier to the perfect CdS crystal. We found that Mn doped systems are ferromagnetic. Calculated results are in good agreement with previous studies.« less

Power generation using spinel manganese-cobalt oxide as a cathode catalyst for microbial fuel cell applications.

PubMed

Mahmoud, Mohamed; Gad-Allah, Tarek A; El-Khatib, K M; El-Gohary, Fatma

2011-11-01

This study focused on the use of spinel manganese-cobalt (Mn-Co) oxide, prepared by a solid state reaction, as a cathode catalyst to replace platinum in microbial fuel cells (MFCs) applications. Spinel Mn-Co oxides, with an Mn/Co atomic ratios of 0.5, 1, and 2, were prepared and examined in an air cathode MFCs which was fed with a molasses-laden synthetic wastewater and operated in batch mode. Among the three Mn-Co oxide cathodes and after 300 h of operation, the Mn-Co oxide catalyst with Mn/Co atomic ratio of 2 (MnCo-2) exhibited the highest power generation 113 mW/m2 at cell potential of 279 mV, which were lower than those for the Pt catalyst (148 mW/m2 and 325 mV, respectively). This study indicated that using spinel Mn-Co oxide to replace platinum as a cathodic catalyst enhances power generation, increases contaminant removal, and substantially reduces the cost of MFCs. Copyright © 2011 Elsevier Ltd. All rights reserved.

Tetragonal-antiprismatic coordination of transition metals in intermetallic compounds: ω1-Mn6Ga29 and its structuralrelationships

NASA Astrophysics Data System (ADS)

Antonyshyn, Iryna; Prots, Yurii; Margiolaki, Irene; Schmidt, Marcus Peter; Zhak, Olga; Oryshchyn, Stepan; Grin, Yuri

2013-03-01

The new phase ω1-Mn6Ga29 was synthesised in single-crystal form from the elements applying the high-temperature centrifugation-aided filtration technique. The crystal structure was determined using diffraction data collected from a twinned specimen: a new prototype, space group P1¯; a=6.3114(2) Å, b=9.9557(3) Å, c=18.920(1) Å, α=90.473(1)°, β=90.847(1)°, γ=90.396(1)°; R1=0.047, wR2=0.117 for 317 variable parameters and 7346 observed reflections; twinning matrix 0 0 -1/3, 0 -1 0, -3 0 0; twin domains ratio 0.830(3):0.170. All manganese atoms in the crystal structure of ω1-Mn6Ga29 are coordinated exclusively by Ga forming distorted tetragonal antiprisms. The monocapped [MnGa8+1] antiprisms condense into pairs by sharing their pseudo-quadratic faces and are interconnected via common apexes and edges to form a 3D framework. The relationship between the crystal structures of ω1-Mn6Ga29 and CuAl2, α-, β-CoSn3, PtSn4, Ti4MnBi2, PdGa5, Rh3Ga16, Rh4Ga21, Al7FeCu2, Co2Al9, and RhBi4 is discussed.

Mechanism of γ-irradiation induced phase transformations in nanocrystalline Mn0.5Zn0.5Fe2O4 ceramics

NASA Astrophysics Data System (ADS)

Jagadeesha Angadi, V.; Anupama, A. V.; Choudhary, Harish K.; Kumar, R.; Somashekarappa, H. M.; Mallappa, M.; Rudraswamy, B.; Sahoo, B.

2017-02-01

The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn0.5Zn0.5Fe2O4 samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-irradiation were investigated in this work and a mechanism of phase transformation/decomposition is provided based on the metastable nature of the Mn-atoms in the spinel lattice. The nano-powder sample was prepared by solution combustion route and the pellets of the sample were exposed to γ-radiation. Up to a dose of 25 kGy of γ-radiation, the sample retained the single phase cubic spinel (Fd-3m) structure, but the disorder in the sample increased. On irradiating the sample with 50 kGy γ-radiation, the spinel phase decomposed into new stable phases such as α-Fe2O3 and ZnFe2O4 phases along with amorphous MnO phase, leading to a change in the surface morphology of the sample. Along with the structural transformations the magnetic properties deteriorated due to breakage of the ferrimagnetic order with higher doses of γ-irradiation. Our results are important for the understanding of the stability, durability and performance of the Mn-Zn ferrite based devices used in space applications.

Utilization of optimized BCR three-step sequential and dilute HCl single extraction procedures for soil-plant metal transfer predictions in contaminated lands.

PubMed

Kubová, Jana; Matús, Peter; Bujdos, Marek; Hagarová, Ingrid; Medved', Ján

2008-05-30

The prediction of soil metal phytoavailability using the chemical extractions is a conventional approach routinely used in soil testing. The adequacy of such soil tests for this purpose is commonly assessed through a comparison of extraction results with metal contents in relevant plants. In this work, the fractions of selected risk metals (Al, As, Cd, Cu, Fe, Mn, Ni, Pb, Zn) that can be taken up by various plants were obtained by optimized BCR (Community Bureau of Reference) three-step sequential extraction procedure (SEP) and by single 0.5 mol L(-1) HCl extraction. These procedures were validated using five soil and sediment reference materials (SRM 2710, SRM 2711, CRM 483, CRM 701, SRM RTH 912) and applied to significantly different acidified soils for the fractionation of studied metals. The new indicative values of Al, Cd, Cu, Fe, Mn, P, Pb and Zn fractional concentrations for these reference materials were obtained by the dilute HCl single extraction. The influence of various soil genesis, content of essential elements (Ca, Mg, K, P) and different anthropogenic sources of acidification on extraction yields of individual risk metal fractions was investigated. The concentrations of studied elements were determined by atomic spectrometry methods (flame, graphite furnace and hydride generation atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry). It can be concluded that the data of extraction yields from first BCR SEP acid extractable step and soil-plant transfer coefficients can be applied to the prediction of qualitative mobility of selected risk metals in different soil systems.

Deformation twinning in Ni-Mn-Ga micropillars with 10M martensite.

PubMed

Reinhold, M; Kiener, D; Knowlton, W B; Dehm, G; Müllner, P

2009-09-01

The maximum actuation frequency of magnetic shape-memory alloys (MSMAs) significantly increases with decreasing size of the transducer making MSMAs interesting candidates for small scale actuator applications. To study the mechanical properties of Ni-Mn-Ga single crystals on small length scales, two single-domain micropillars with dimensions of 10x15x30 mum(3) were fabricated from a Ni-Mn-Ga monocrystal using dual beam focused ion beam machining. The pillars were oriented such that the crystallographic c direction was perpendicular to the loading direction. The pillars were compressed to maximum stresses of 350 and 50 MPa, respectively. Atomic force microscopy and magnetic force microscopy were performed prior to fabrication of the pillars and following the deformation experiments. Both micropillars were deformed by twinning as evidenced by the stress-strain curve. For one pillar, a permanent deformation of 3.6% was observed and ac twins (10M martensite) were identified after unloading. For the other pillar, only 0.7% remained upon unloading. No twins were found in this pillar after unloading. The recovery of deformation is discussed in the light of pseudoelastic twinning and twin-substrate interaction. The twinning stress was higher than in similar macroscopic material. However, further studies are needed to substantiate a size effect.

Local atomic and magnetic structure of dilute magnetic semiconductor ( Ba , K ) ( Zn , Mn ) 2 As 2

DOE PAGES

Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; ...

2016-09-06

We studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba,K)(Zn,Mn) 2As 2 through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. Furthermore, we detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of ≲5Å, resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment ofmore » Mn spins along the crystallographic c axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. Finally, we discuss these results in the context of other experiments and theoretical studies on this system.« less

Neutron diffraction study, magnetic properties and thermal stability of YMn 2D 6 synthesized under high deuterium pressure

NASA Astrophysics Data System (ADS)

Paul-Boncour, V.; Filipek, S. M.; Dorogova, M.; Bourée, F.; André, G.; Marchuk, I.; Percheron-Guégan, A.; Liu, R. S.

2005-01-01

A new phase YMn 2D 6 was synthesized by submitting YMn 2 to 1.7 kbar deuterium pressure at 473 K. According to X-ray and neutron powder diffraction experiments, YMn 2D 6 crystallizes in the Fm3¯m space group with a=6.709(1) Å at 300 K. The Y and half of the Mn atoms occupy statistically the 8 c site whereas the other Mn atoms are located in 4 a site and surrounded by 6 D atoms (24 e). This corresponds to a K 2PtCl 6-type structure with a partially disordered substructure which can be written as [YMn]MnH 6. No ordered magnetic moment is observed in the NPD patterns and the magnetization measurements display a paramagnetic behavior. The study of the thermal stability by Differential Scanning Calorimetry and XRD experiments indicates that this phase decomposes in YD 2 and Mn at 625 K, and is more stable than YMn 2H 4.5.

Ab initio prediction of stable nanotwin double layers and 4O structure in Ni2MnGa

NASA Astrophysics Data System (ADS)

Zelený, Martin; Straka, Ladislav; Sozinov, Alexei; Heczko, Oleg

2016-12-01

The ab initio electronic structure calculations of the Ni2MnGa alloy indicate that the orthorhombic 4O structure exhibits the lowest energy compared to all known martensitic structures. The 4O structure is formed by nanotwin double layers, i.e., oppositely oriented nanotwins consisting of two (101) lattice planes of nonmodulated martensitic structure. It exhibits the lowest occupation of density of states at the Fermi level. The total energy 1.98 meV/atom below the energy of nonmodulated martensite is achieved within structural relaxation by shifting Mn and Ga atoms at the nanotwin boundaries. The same atomic shift can also be found in other martensitic nanotwinned or modulated structures such as 10M and 14M, which indicates the importance of the nanotwin double layer for the stability of these structures. Our discovery shows that the nanotwinning or modulation is a natural property of low-temperature martensitic phases in Ni-Mn-Ga alloys.

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Ruiter, Graham; Carsch, Kurtis M.; Gul, Sheraz

In this paper, we report the synthesis, characterization, and reactivity of [LFe 3(PhPz) 3OMn( sPhIO)][OTf] x (3: x=2; 4: x=3), where 4 is one of very few examples of iodosobenzene–metal adducts characterized by X-ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57Fe Mössbauer and X-ray absorption spectroscopy provided unique insights into how changes in oxidation state (Fe III 2Fe IIMn II vs. Fe III 3Mn II) influence oxygen atom transfer in tetranuclear Fe 3Mn clusters. Finally, in particular, a one-electron redox change atmore » a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude.« less

Coprecipitation of gold(III) complex ions with manganese(II) hydroxide and their stoichiometric reduction to atomic gold (Au(0)): analysis by Mössbauer spectroscopy and XPS.

PubMed

Yamashita, Mamiko; Ohashi, Hironori; Kobayashi, Yasuhiro; Okaue, Yoshihiro; Kurisaki, Tsutomu; Wakita, Hisanobu; Yokoyama, Takushi

2008-03-01

To elucidate the formation process of precursor of gold-supported manganese dioxide (MnO2), the coprecipitation behavior of [AuCl4-n(OH)n](-) (n=0-4) (Au(III)) complex ions with manganese(II) hydroxide (Mn(OH)2 and the change in their chemical state were examined. The Au(III) complex ions were rapidly and effectively coprecipitated with Mn(OH)(2) at pH 9. According to the Mössbauer spectra for gold (Au) coprecipitated with Mn(OH)2, below an Au content of 60 wt% in the coprecipitates, all of the coprecipitated Au existed in the atomic state (Au(0)), while, above an Au content of 65 wt%, part of the gold existed in the Au(III) state, and the proportion increased with increasing coprecipitated Au content. Based on the results of X-ray photoelectron spectroscopy, Mn(II) in Mn(OH)2 converted to Mn(IV) in conjunction with coprecipitation of Au(III) complex ions. These results indicate that the rapid stoichiometric reduction of Au(III) to Au(0) is caused by electron transfer from Mn(II) in Mn(OH)2 to the Au(III) complex ion through an Mn-O-Au bond.

Two halide-containing cesium manganese vanadates: synthesis, characterization, and magnetic properties

DOE PAGES

Smith Pellizzeri, Tiffany M.; McGuire, Michael A.; McMillen, Colin D.; ...

2018-01-24

In this study, two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions. One compound, Cs 3Mn(VO 3) 4Cl, (1) was prepared using a mixed cesium hydroxide/chloride mineralizer, and crystallizes in the polar noncentrosymmetric space group Cmm2, with a = 16.7820(8) Å, b = 8.4765(4) Å, c = 5.7867(3) Å. This structure is built from sinusoidal zig-zag (VO 3) n chains that run along the b-axis and are coordinated to Mn 2+ containing (MnO 4Cl) square-pyramidal units that are linked together to form layers. The cesium cations reside betweenmore » the layers, but also coordinate to the chloride ion, forming a cesium chloride chain that also propagates along the b-axis. The other compound, Cs 2Mn(VO 3) 3F, (2) crystallizes in space group Pbca with a = 7.4286(2) Å, b = 15.0175(5) Å, c = 19.6957(7) Å, and was prepared using a cesium fluoride mineralizer. The structure is comprised of corner sharing octahedral Mn 2+ chains, with trans fluoride ligands acting as bridging units, whose ends are capped by (VO 3) n vanadate chains to form slabs. The cesium atoms reside between the manganese vanadate layers, and also play an integral part in the structure, forming a cesium fluoride chain that runs along the b-axis. Both compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and single-crystal Raman spectroscopy. Additionally, the magnetic properties of 2 were investigated. Lastly, above 50 K, it displays behavior typical of a low dimensional system with antiferromagnetic interactions, as to be expected for linear chains of manganese(II) within the crystal structure.« less

Development of double-pulse lasers ablation system and electron paramagnetic resonance spectroscopy for direct spectral analysis of manganese doped PVA polymer

NASA Astrophysics Data System (ADS)

Khalil, A. A. I.; Morsy, M. A.; El-Deen, H. Z.

2017-11-01

Series of manganese-co-precipitated poly (vinyl alcohol) (PVA) polymer were quantitatively and qualitatively analyzed using laser ablation system (LAS) based on double-pulse laser induced breakdown spectroscopy (DP-LIBS) and electron paramagnetic resonance (EPR) spectroscopy. The collinear nanosecond laser beams of 266 and 1064 nm were optimized to focus on the surface of the PVA polymer target. Both laser beams were employed to estimate the natural properties of the excited Mn-PVA plasma, such as electron number density (Ne), electron temperature (Te), and Mn concentration. Individual transition lines of manganese (Mn), carbon (C), lithium (Li), hydrogen (H) and oxygen (O) atoms are identified based on the NIST spectral database. The results show better responses with DP-LIBS than the single-pulse laser induced breakdown spectroscopy (SP-LIBS). On the other hand, the EPR investigation shows characteristic broad peak of Mn-nano-particles (Mn-NPs) in the range of quantum dots of superparamagnetic materials. The line width (peak-to-peak, ΔHpp) and g-value of the observed Mn-EPR peak are ∼20 mT and 2.0046, respectively. The intensities of Mn-emission line at a wavelength 403.07 nm and the Mn-EPR absorption peak were used to accurate quantify the Mn-content in the polymer matrix. The results produce linear trends within the studied concentration range with regression coefficient (R2) value of ∼0.99, and limit of detection (LOD) of 0.026 mol.% and 0.016 mol.%, respectively. The LOD values are at a fold change of about -0.2 of the studied lowest mol.%. The proposed protocols of trace element detection are of significant advantage and can be applied to the other metal analysis.

Manganese-oxidizing photosynthesis before the rise of cyanobacteria

NASA Astrophysics Data System (ADS)

Johnson, J. E.; Webb, S.; Thomas, K. S.; Ono, S.; Kirschvink, J. L.; Fischer, W. W.

2012-12-01

The evolution of oxygenic photosynthesis was a singularity that fundamentally transformed our planet's core biogeochemical cycles and changed the redox structure of Earth's surface, crust, and mantle. To date, understanding the evolution of this molecular machinery has largely been derived from comparative biology. Several biochemical innovations enabled water-splitting, including a central photosynthetic pigment with a higher redox potential and coupled photosystems. However the critical photochemical invention was the water oxidizing complex (WOC) of photosystem II, a cubane cluster of four redox-active Mn atoms and a Ca atom bound by oxo bridges, that couple the single electron photochemistry of the photosystem to the four-electron oxidation of water to O2. Transitional forms of the WOC have been postulated, including an Mn-containing catalase-like peptide using an H2O2 donor, or uptake and integration of environmental Mn-oxides. One attractive hypothesis from the perspective of modern photo-assembly of the WOC posits an initial Mn(II)-oxidizing photosystem as a precursor to the WOC (Zubay, 1996; Allen and Martin, 2007). To test these hypotheses, we studied the behavior of the ancient Mn cycle captured by 2415 ± 6 Ma scientific drill cores retrieved by the Agouron Drilling Project through the Koegas Subgroup in Griqualand West, South Africa. This succession contains substantial Mn-enrichments (up to 17 wt.% in bulk). To better understand the petrogenesis and textural context of these deposits, we employed a novel X-ray absorption spectroscopy microprobe to make redox maps of ultra-thin sample sections at a 2μm scale. Coupled to light and electron microscopy and C isotopic measurements, we observe that all of the Mn is present as Mn(II), contained within carbonate minerals produced from early diagenetic reduction of Mn-oxide phases with organic matter. To assay the environmental oxidant responsible for the production of the Mn-oxides we examined two independent techniques sensitive to low levels of environmental O2—multiple sulfur isotopes analyzed using whole-rock IRMS and texture-specific SIMS techniques, and the presence of redox-sensitive detrital grains. Despite the conspicuous oxidation of Mn, both proxies reveal a lack of significant molecular oxygen present in the environment at this time (O2 << 1 ppm). These results provide strong geological support for the idea that an early Mn-oxidizing photosystem once existed as a transitional form prior to the evolution of the WOC of photosystem II and oxygenic photosynthesis. [Refs: Zubay J (1996) Origins of Life on the Earth and in the Cosmos, Academic Press: San Diego. Allen JF, Martin W (2007) Evolutionary biology: Out of thin air, Nature, 445, 610-612.

First-principles calculation of the effects of tetragonal distortions on the Gilbert damping parameter of Co2MnSi

NASA Astrophysics Data System (ADS)

Pradines, B.; Arras, R.; Calmels, L.

2017-05-01

We present an ab initio study of the influence of the tetragonal distortion, on the static and dynamic (Gilbert damping parameter) magnetic properties of a Co2MnSi crystal. This tetragonal distortion can for instance be due to strain, when Co2MnSi is grown on a substrate with a small lattice mismatch. Using fully relativistic Korringa-Kohn-Rostoker (KKR) calculations, in conjunction with the coherent potential approximation (CPA) to describe atomic disorder and the linear response formalism to compute the Gilbert damping parameter, we show that a tetragonal distortion can substantially change the properties of Co2MnSi, in a way which depends on the kind of atomic disorder.

The effect of Ga vacancies on the defect and magnetic properties of Mn-doped GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Joongoo; Chang, K. J.; Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea and Korea Institute for Advanced Study, Seoul 130-722

2007-10-15

We perform first-principles theoretical calculations to investigate the effect of the presence of Ga vacancy on the defect and magnetic properties of Mn-doped GaN. When a Ga vacancy (V{sub Ga}) is introduced to the Mn ions occupying the Ga lattice sites, a charge transfer occurs from the Mn d band to the acceptor levels of V{sub Ga}, and strong Mn-N bonds are formed between the Mn ion and the N atoms in the neighborhood of V{sub Ga}. The charge transfer and chemical bonding effects significantly affect the defect and magnetic properties of Mn-doped GaN. In a Mn-V{sub Ga} complex, whichmore » consists of a Ga vacancy and one Mn ion, the dangling bond orbital of the N atom involved in the Mn-N bond is electrically deactivated, and the remaining dangling bond orbitals of V{sub Ga} lead to the shallowness of the defect level. When a Ga vacancy forms a complex with two Mn ions located at a distance of about 6 A, which corresponds to the percolation length in determining the Curie temperature in diluted Mn-doped GaN, the Mn d band is broadened and the density of states at the Fermi level is reduced due to two strong Mn-N bonds. Although the broadening and depopulation of the Mn d band weaken the ferromagnetic stability between the Mn ions, the ferromagnetism is still maintained because of the lack of antiferromagnetic superexchange interactions at the percolation length.« less

Intralayer magnetic ordering in Ge/Mn digital alloys

NASA Astrophysics Data System (ADS)

Otrokov, M. M.; Ernst, A.; Ostanin, S.; Fischer, G.; Buczek, P.; Sandratskii, L. M.; Hergert, W.; Mertig, I.; Kuznetsov, V. M.; Chulkov, E. V.

2011-04-01

We present a first-principles investigation of the electronic properties of Ge/Mn digital alloys obtained by the insertion of Mn monolayers in the Ge host. The main attention is devoted to the study of the magnetic properties of the Mn layers for various types of ordering of the Mn atoms. Depending on the type of Mn position three different structures are considered: substitutional, interstitial, and combined substitutional-interstitial. In all three cases numerical structural relaxation of the atomic positions has been performed. We find that the intralayer exchange parameters depend strongly on the crystal structure. For the substitutional and interstitial types of structure the stable magnetic order was found to be ferromagnetic. For the mixed substitutional-interstitial structure the ferromagnetic configuration appears unstable and a complex ferrimagnetic structure forms. The spin-wave excitations are calculated within the Heisenberg model. The critical temperatures of the magnetic phase transitions are determined using Monte Carlo simulations with interatomic exchange parameters obtained for two different magnetic reference states: a ferromagnetic and a disordered local moment state.

Mutual neutralization of He{sup +} with the anions Cl{sup −}, Br{sup −}, I{sup −}, and SF{sub 6}{sup −}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiens, Justin P.; Shuman, Nicholas S.; Miller, Thomas M.

2016-05-28

Mutual neutralization (MN) rate coefficients k{sub MN} for He{sup +} with the anions Cl{sup −}, Br{sup −}, I{sup −}, and SF{sub 6}{sup −} are reported from 300 to 500 K. The measured rate coefficients may contain a contribution from transfer ionization, i.e., double ionization of the anion. The large rate coefficient for He{sup +} + SF{sub 6}{sup −} (2.4 × 10{sup −7} cm{sup 3} s{sup −1} at 300 K) is consistent with earlier polyatomic MN results found to have a reduced mass dependence of μ{sup −1/2}. Neutralization of He{sup +} by the atomic halides follows the trend observed earlier for Ne{sup +},more » Ar{sup +}, Kr{sup +}, and Xe{sup +} neutralized by atomic halides, k{sub MN} (Cl{sup −}) < k{sub MN} (Br{sup −}) < k{sub MN} (I{sup −}). Only an upper limit could be measured for the neutralization of He{sup +} by Cl{sup −}. Predictions of the rate coefficients from a previously proposed simple model of atomic–atomic MN results are consistent with the present He{sup +}–halide rate coefficients. The temperature dependences are modestly negative for Br{sup −} and I{sup −}, while that for SF{sub 6}{sup −} is small or negligible.« less

Electronic structure and magnetism of epitaxial Ni-Mn-Ga(-Co) thin films with partial disorder: a view across the phase transition

NASA Astrophysics Data System (ADS)

Schleicher, B.; Klar, D.; Ollefs, K.; Diestel, A.; Walecki, D.; Weschke, E.; Schultz, L.; Nielsch, K.; Fähler, S.; Wende, H.; Gruner, M. E.

2017-11-01

The influence of Co-doping in off-stoichiometric Ni-Mn-Ga and Ni-Mn-Ga-Co thin films on the magnetic coupling of the atoms is investigated with x-ray magnetic circular dichroism in both the martensitic as well as austenitic phase, respectively. Additionally, first principles calculations were performed to compare the experimentally obtained absorption spectra with theoretical predictions. Calculated exchange constants and density of states for the different atomic sites underline the large influence of chemical and magnetic order on the magnetocaloric properties of the material.

Effects of axial coordination on immobilized Mn(salen) catalysts.

PubMed

Teixeira, Filipe; Mosquera, Ricardo A; Melo, André; Freire, Cristina; Cordeiro, M Natália D S

2014-11-13

The consequences of anchoring Mn(salen) catalysts onto a supporting material using one of the vacant positions of the metal center are tackled by studying several Mn(salen) complexes with different axial ligands attached. This is accomplished using Density Functional Theory at the X3LYP/Triple-ζ level of theory and the Atom In Molecules formalism. The results suggest that both Mn(salen) complexes and their oxo derivatives should lie in a triplet ground state. Also, the choice of the axial ligand bears a moderate effect on the energy involved in the oxidation of the former to oxo-Mn(salen) complexes, as well as in the stability of such complexes toward ligand removal by HCl. AIM analysis further suggests that the salen ligand acts as a "charge reservoir" for the metal center, with strong correlations being obtained between the charge of salen and the electron population donated by the axial ligand to the metal center. Moreover, the results suggest that the Mn atom in Mn(salen) complexes holds different hybridization of its valence orbitals depending on the type of axial ligand present in the system.

(Pt1-xCux)3Cu2B and Pt9Cu3B5, the first examples of copper platinum borides. Observation of superconductivity in a novel boron filled β-Mn-type compound

NASA Astrophysics Data System (ADS)

Salamakha, Leonid P.; Sologub, Oksana; Stöger, Berthold; Michor, Herwig; Bauer, Ernst; Rogl, Peter F.

2015-09-01

New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt1-xCux)3Cu2B (x=0.33) forms a B-filled β-Mn-type structure (space group P4132; a=0.6671(1) nm). Cu atoms are distributed preferentially on the 8c atom sites, whereas the 12d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β-Mn-type structure. Pt9Cu3B5 (space group P-62m; a=0.9048(3) nm, c=0.2908(1) nm) adopts the Pt9Zn3B5-δ-type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt6] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt6] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt6] and [Pt6] trigonal prisms, rotated perpendicularly to the central one. There is no B-B contact as well as Cu-B contact in the structure. The relationships of Pt9Cu3B5 structure with the structure of Ti1+xOs2-xRuB2 as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt1-xCux)3Cu2B (x=0.3) (B-filled β-Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ0HC2(0)WHH of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt9Cu3B5 (Pt9Zn3B5-δ-type structure) from electrical resistivity measurements.

Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

NASA Astrophysics Data System (ADS)

Letellier, F.; Lechevallier, L.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

2014-11-01

Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

Occupational exposure to manganese-containing welding fumes and pulmonary function indices among natural gas transmission pipeline welders.

PubMed

Hassani, Hamid; Golbabaei, Farideh; Ghahri, Asghar; Hosseini, Mostafa; Shirkhanloo, Hamid; Dinari, Behnam; Eskandari, Davood; Fallahi, Majid

2012-01-01

The objectives of this study were to evaluate manganese (Mn)-containing welding fumes' exposure, assess urinary Mn as a biomarker for Mn exposure and investigate the correlation of Mn in air, total fumes and urinary Mn with pulmonary function indices in 118 welders and 37 unexposed controls from two regions in Iran, Assaluyeh and Borujen. Air samples were collected on mixed cellulose ester membrane filters in personal air samplers and then analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) (NIOSH Method 7300). For all participants, urine samples were collected during the entire work shift, and Mn in urine was determined by graphite furnace atomic absorption spectroscopy according to NIOSH Method 8310. Spirometric measurements were also done for participants. The maximum exposures to airborne Mn and total fumes were 0.304 ± 0.256 mg/m(3) and 21.52 ± 9.40 mg/m(3), respectively. The urine Mn levels in the various groups ranged between 0.77 to 7.58 μg/l. The correlation between airborne Mn and urinary Mn was significant for total whole participants. Some values of spirometric indices were statistically lower in welders rather than controls. Our results indicate that many welders have been exposed to higher concentrations of Mn-containing welding fumes. Urinary Mn can be used as a biomarker for Mn exposure. There were weak inverse correlations between Mn-containing welding fumes and pulmonary function indices, and the inverse correlation between urinary Mn with forced vital capacities (FVC) and forced expiratory volume in 1 s (FEV1) was significant.

Magnetic properties of the CrMnFeCoNi high-entropy alloy

DOE PAGES

Schneeweiss, Oldřich; Friák, Martin; Dudová, Marie; ...

2017-07-28

In this paper, we present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of 0.006more » ± 0.001 emu T. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and 2 μ B), while the local moments of Ni atoms effectively vanish. Finally, these results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.« less

The estimation of H-bond and metal ion-ligand interaction energies in the G-Quadruplex ⋯ Mn+ complexes

NASA Astrophysics Data System (ADS)

Mostafavi, Najmeh; Ebrahimi, Ali

2018-06-01

In order to characterize various interactions in the G-quadruplex ⋯ Mn+ (G-Q ⋯ Mn+) complexes, the individual H-bond (EHB) and metal ion-ligand interaction (EMO) energies have been estimated using the electron charge densities (ρs) calculated at the X ⋯ H (X = N and O) and Mn+ ⋯ O (Mn+ is an alkaline, alkaline earth and transition metal ion) bond critical points (BCPs) obtained from the atoms in molecules (AIM) analysis. The estimated values of EMO and EHB were evaluated using the structural parameters, results of natural bond orbital analysis (NBO), aromaticity indexes and atomic charges. The EMO value increase with the ratio of ionic charge to radius, e/r, where a linear correlation is observed between EMO and e/r (R = 0.97). Meaningful relationships are also observed between EMO and indexes used for aromaticity estimation. The ENH value is higher than EOH in the complexes; this is in complete agreement with the trend of N⋯Hsbnd N and O⋯Hsbnd N angles, the E (2) value of nN → σ*NH and nO → σ*NH interactions and the difference between the natural charges on the H-bonded atom and the hydrogen atom of guanine (Δq). In general, the O1MO2 angle becomes closer to 109.5° with the increase in EMO and decrease in EHB in the presence of metal ion.

Manganese-calcium intermixing facilitates heteroepitaxial growth at the 10 1 ¯ 4 calcite-water interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Man; Riechers, Shawn L.; Ilton, Eugene S.

2017-10-01

In situ atomic force microscopy (AFM) measurements were performed to probe surface precipitates that formed on the (10-14) surface of calcite (CaCO3) single crystals following reaction with Mn2+-bearing aqueous solutions with a range of initial concentrations. Three-dimensional epitaxial islands were observed to precipitate and grow on the surfaces and in situ time-sequenced measurements demonstrated that their growth rates were commensurate with those obtained for epitaxial islands formed on calcite crystals reacted with Cd2+-bearing aqueous solutions of the same range in supersaturation with respect to the pure metal carbonate phase. This finding was unexpected as rhodochrosite (MnCO3) and calcite display amore » 10% lattice mismatch, based on the area of their (10-14) surface unit cells, whereas the lattice mismatch is only 4% for otavite (CdCO3) and calcite. Coatings of varying thicknesses were therefore synthesized by reacting calcite single crystals with calcite-equilibrated aqueous solutions with concentrations of up to 250 µM MnCl2 and analyzed to determine the composition of the surface precipitates. Ex situ X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray reflectivity (XRR), and AFM measurements of the reacted crystals demonstrated the formation of an epitaxial (Mn,Ca)CO3 solid solution with a spatially complex composition atop the calcite surface, whereby the first few nanometers were rich in Ca and the Mn content increased with distance from the original calcite surface, culminating in a topmost region of almost pure MnCO3 for the thickest coatings. These findings explain the measured growth rates (the effective lattice mismatch was much smaller than nominal mismatch) and highlight the strong influence played by the substrate on the composition of surface precipitates in aqueous conditions.« less

Atomic-scale electrochemistry on the surface of a manganite

DOE PAGES

Vasudevan, Rama K.; Tselev, Alexander; Baddorf, Arthur P.; ...

2015-04-09

The doped manganese oxides (manganites) have been widely studied for their colossal magnetoresistive effects, for potential applications in oxide spintronics, electroforming in resistive switching devices, and are materials of choice as cathodes in modern solid oxide fuel cells. However, little experimental knowledge of the dynamics of the surfaces of perovskite manganites at the atomic scale exists. Here, through in-situ scanning tunnelling microscopy (STM), we demonstrate atomic resolution on samples of La 0.625Ca 0.375MnO 3 grown on (001) SrTiO 3 by pulsed laser deposition (PLD). Furthermore, by applying triangular DC waveforms of increasing amplitude to the STM tip, and measuring themore » tunnelling current, we demonstrate the ability to both perform and monitor surface electrochemical processes at the atomic level, including, for the first time in a manganite, formation of single and multiple oxygen vacancies, disruption of the overlying manganite layers, and removal and deposition of individual atomic units or clusters. Our work paves the way for better understanding of surface oxygen reactions in these systems.« less

Thin film Heusler compounds manganese nickel gallium

NASA Astrophysics Data System (ADS)

Jenkins, Catherine Ann

Multiferroic Heusler compounds Mn3--xNi xGa (x=0,1,2) have a tetragonal unit cell that can variously be used for magneto-mechanically coupled shape memory ( x=1,2) and spin-mechanical applications (x=0). The first fabrication of fully epitaxial thin films of these and electronically related compounds by sputtering is discussed. Traditional and custom lab characterization of the magnetic and temperature driven multiferroic behavior is augmented by more detailed synchrotron-based high energy photoemission spectroscopic techniques to describe the atomic and electronic structure. Integration of the MnNi2Ga magnetic shape memory compound in microwave patch antennas and active free-standing structures represents a fraction of the available and promising applications for these compounds. Prototype magnetic tunnel junctions are demonstrated by Mn3Ga electrodes with perpendicular anisotropy for spin torque transfer memory structures. The main body of the work concentrates on the definition and exploration of the material series Mn3--xNi xGa (x=0,1,2) and the relevant multiferroic phenomena exhibited as a function of preparation and external stimuli. Engineering results on each x=0,1,2 are presented with device prototypes where relevant. In the appendices the process of the materials design undertaken with the goal of developing new ternary intermetallics with enhanced properties is presented with a full exploration of the road from band structure calculations to device implementation. Cobalt based compounds in single crystal and nanoparticle form are fabricated with an eye to developing the production methods for new cobalt- and iron-based magnetic shape memory compounds for device applications in different forms. Mn2CoSn, a compound isolectronic and with similar atomic ordering to Mn2NiGa is experimentally determined to be a nearly half-metallic ferromagnet in contrast to the metallic ferrimagnetism in the parent compound. High energy photoemission spectroscopy is shown to be applicable to the analysis and observation of deeply buried metallic and semiconducting interface in an analysis of chalcopyrite solar cell heterolayers and model magnetic tunnel junctions with half-metalic Heusler electrodes.

Magnetic moment enhancement and spin polarization switch of the manganese phthalocyanine molecule on an IrMn(100) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, X.; National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047; Wang, B.

2014-07-21

The geometric, electronic, and magnetic structures of a manganese phthalocyanine (MnPc) molecule on an antiferromagnetic IrMn(100) surface are studied by density functional theory calculations. Two kinds of orientation of the adsorbed MnPc molecule are predicted to coexist due to molecular self-assembly on the surface—a top-site geometry with the Mn–N bonds aligned along the 〈100〉 direction, and a hollow-site orientation in which the Mn–N bonds are parallel to the 〈110〉 direction. The MnPc molecule is antiferromagnetically coupled to the substrate at the top site with a slight reduction in the magnetic moment of the Mn atom of the MnPc molecule (Mn{submore » mol}). In contrast, the magnetic moment of the Mn{sub mol} is enhanced to 4.28 μB at the hollow site, a value larger than that in the free MnPc molecule (3.51 μB). Molecular distortion induced by adsorption is revealed to be responsible for the enhancement of the magnetic moment. Furthermore, the spin polarization of the Mn{sub mol} atom at around the Fermi level is found to change from negative to positive through an elongation of the Mn–N bonds of the MnPc. We propose that a reversible switch of the low/high magnetic moment and negative/positive spin polarization might be realized through some mechanical engineering methods.« less

Preparation of Mo-Re-C samples containing Mo{sub 7}Re{sub 13}C with the β-Mn-type structure by solid state reaction of planetary-ball-milled powder mixtures of Mo, Re and C, and their crystal structures and superconductivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oh-ishi, Katsuyoshi, E-mail: oh-ishi@kc.chuo-u.ac.jp; Nagumo, Kenta; Tateishi, Kazuya

Mo-Re-C compounds containing Mo{sub 7}Re{sub 13}C with the β-Mn structure were synthesized with high-melting-temperature metals Mo, Re, and C powders using a conventional solid state method with a planetary ball milling machine instead of the arc melting method. Use of the ball milling machine was necessary to obtain Mo{sub 7}Re{sub 13}C with the β-Mn structure using the solid state method. Almost single-phase Mo{sub 7}Re{sub 13}C with a trace of impurity were obtained using the synthesis method. By XRF and lattice parameter measurements on the samples, Fe element existed in the compound synthesized using the planetary ball milling machine with amore » pot and balls made of steel, though Fe element was not detected in the compound synthesized using a pot and balls made of tungsten carbide. The former compound containg the Fe atom did not show superconductivity but the latter compound without the Fe atom showed superconductivity at 6.1 K. - Graphical abstract: Temperature dependence of the magnetic susceptibility measured under 10 Oe for the superconducting PBM-T samples without Fe element and non-superconducting PBM-S with Fe element. The inset is the enlarged view of the data for the PBM-S sample.« less

What Controls the Magnetic Exchange and Anisotropy in a Family of Tetranuclear {Mn2IIMn2III} Single-Molecule Magnets?

PubMed

Vignesh, Kuduva R; Langley, Stuart K; Gartshore, Christopher J; Moubaraki, Boujemaa; Murray, Keith S; Rajaraman, Gopalan

2017-02-20

Twelve heterovalent, tetranuclear manganese(II/III) planar diamond or "butterfly" complexes, 1-12, have been synthesized and structurally characterized, and their magnetic properties have been probed using experimental and theoretical techniques. The 12 structures are divided into two distinct "classes". Compounds 1-8 place the Mn(III), S = 2, ions in the body positions of the butterfly metallic core, while the Mn(II), S = 5/2, ions occupy the outer wing sites and are described as "Class 1". Compounds 9-12 display the reverse arrangement of ions and are described as "Class 2". Direct current susceptibility measurements for 1-12 reveal ground spin states ranging from S = 1 to S = 9, with each complex displaying unique magnetic exchange parameters (J). Alternating current susceptibility measurements found that that slow magnetic relaxation is observed for all complexes, except for 10 and 12, and display differing anisotropy barriers to magnetization reversal. First, we determined the magnitude of the magnetic exchange parameters for all complexes. Three exchange coupling constants (J bb , J wb , and J ww ) were determined by DFT methods which are found to be in good agreement with the experimental fits. It was found that the orientation of the Jahn-Teller axes and the Mn-Mn distances play a pivotal role in determining the sign and strength of the J bb parameter. Extensive magneto-structural correlations have been developed for the two classes of {Mn II 2 Mn III 2 } butterfly complexes by varying the Mn b -O distance, Mn w -O distance, Mn b -O-Mn b angle (α), Mn b -O-Mn b -O dihedral angle (γ), and out-of-plane shift of the Mn w atoms (β). For the magnetic anisotropy the DFT calculations yielded larger negative D value for complexes 2, 3, 4, and 6 compared to the other complexes. This is found to be correlated to the electron-donating/withdrawing substituents attached to the ligand moiety and suggests a possible way to fine tune the magnetic anisotropy in polynuclear Mn ion complexes.

An Investigation into the Effects of Mn Promotion on the Activity and Selectivity of Co/SiO 2 for Fischer–Tropsch Synthesis: Evidence for Enhanced CO Adsorption and Dissociation

DOE PAGES

Johnson, Gregory R.; Werner, Sebastian; Bell, Alexis T.

2015-08-27

Mn is an effective promoter for improving the activity and selectivity of Co-based Fischer-Tropsch synthesis (FTS) catalysts, but the mechanism by which this promoter functions is poorly understood. The work reported here was aimed at defining the manner in which Mn interacts with Co and determining how these interactions affect the activity and selectivity of Co. Detailed measurements are reported for the kinetics of FTS as a function of Mn/Co ratio, temperature, and reactant partial pressure. These data are described by a single, two-parameter rate expression. Mn promotion was found to increase both the apparent rate constant for CO consumptionmore » and the CO adsorption constant. Further evidence for enhanced CO adsorption and dissociation was obtained from measurements of temperature-programmed desorption of CO and CO disproportionation rates, respectively. Quantitative analysis of elemental maps obtained by STEM-EDS revealed that the promoter accumulates preferentially on the surface of Co nanoparticles at low Mn loadings, resulting in a rapid onset of improvements in the product selectivity as the Mn loading increases. Furthermore, for catalysts prepared with loadings higher than Mn/Co = 0.1, the additional Mn accumulates in the form of nanometer-scale particles of MnO on the support. In situ IR spectra of adsorbed CO show that Mn promotion increases the abundance of adsorbed CO with weakened C-O bonds. It is proposed that the cleavage of the C-O bond is promoted through Lewis acid-base interactions between the Mn 2+ cations located at the edges of MnO islands covering the Co nanoparticles and the O atom of CO adsorbates adjacent to the MnO islands. Finally, the observed decrease in selectivity to CH 4 and the increased selectivity to C 5+ products with increasing Mn/Co ratio are attributed to a decrease in the ratio of adsorbed H to CO on the surface of the supported Co nanoparticles.« less

An Investigation into the Effects of Mn Promotion on the Activity and Selectivity of Co/SiO 2 for Fischer - Tropsch Synthesis: Evidence for Enhanced CO Adsorption and Dissociation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Gregory R.; Werner, Sebastian; Bell, Alexis T.

2016-03-04

Mn is an effective promoter for improving the activity and selectivity of Co-based Fischer-Tropsch synthesis (FTS) catalysts, but the mechanism by which this promoter functions is poorly understood. The work reported here was aimed at defining the manner in which Mn interacts with Co and determining how these interactions affect the activity and selectivity of Co. Detailed measurements are reported for the kinetics of FTS as a function of Mn/Co ratio, temperature, and reactant partial pressure. These data are described by a single, two-parameter rate expression. Mn promotion was found to increase both the apparent rate constant for CO consumptionmore » and the CO adsorption constant. Further evidence for enhanced CO adsorption and dissociation was obtained from measurements of temperature-programmed desorption of CO and CO disproportionation rates, respectively. Our quantitative analysis of elemental maps obtained by STEM-EDS revealed that the promoter accumulates preferentially on the surface of Co nanoparticles at low Mn loadings, resulting in a rapid onset of improvements in the product selectivity as the Mn loading increases. For catalysts prepared with loadings higher than Mn/Co = 0.1, the additional Mn accumulates in the form of nanometer-scale particles of MnO on the support. In situ IR spectra of adsorbed CO show that Mn promotion increases the abundance of adsorbed CO with weakened C-O bonds. Furthermore, it is proposed that the cleavage of the C-O bond is promoted through Lewis acid-base interactions between the Mn 2+ cations located at the edges of MnO islands covering the Co nanoparticles and the O atom of CO adsorbates adjacent to the MnO islands. The observed decrease in selectivity to CH 4 and the increased selectivity to C 5+ products with increasing Mn/Co ratio are attributed to a decrease in the ratio of adsorbed H to CO on the surface of the supported Co nanoparticles.« less

Magnetic and electrical properties of several Mn-based amorphous alloys

NASA Astrophysics Data System (ADS)

Obi, Y.; Morita, H.; Fujimori, H.

1987-03-01

Magnetic and electrical properties of amorphous Mn-Y, Mn-Zr, and Mn-Nb alloys have been investigated. All these alloys have a temperature-dependent susceptibility which is well fitted by a Curie-Weiss law. This implies the existence of localized magnetic moments associated with the Mn atoms. In addition, amorphous Mn-Y alloys exhibit spin-glass characteristics at low temperature. The experimental results of the electrical resistivity show that the temperature coefficient of resistivity (TCR) of both Mn-Y and Mn-Zr are negative, while Mn-Nb has a positive TCR. On the other hand, the resistivity-temperature curves of Mn-Zr and Mn-Nb have nearly the same tendency but are different from that of Mn-Y.

EMR studies of the internal motion of Mn4+ ions in the Sr overdoped (La1-xSrx)(Ga1-yMny)O3 (x/y up to 8) supplemented by magnetic and optical spectroscopy measurements

NASA Astrophysics Data System (ADS)

Aleshkevych, Pavlo; Fink-Finowicki, Jan; Zayarnyuk, Tatiana; Radelytskyi, Igor; Berkowski, Marek; Rudowicz, Czeslaw; Gnutek, Pawel

2015-06-01

The effect of the Sr doping on electronic structure in single crystals of (La1-xSrx)(Ga1-yMny)O3 solid solutions (LSGM) is investigated by means of electron magnetic resonance (EMR). The EMR results are supplemented by magnetic susceptibility and optical spectroscopy measurements. The compositions with small concentration of Mn doping (y < 1%) and overdoped content of Sr (the ratio x(Sr)/y(Mn) up to 8) are used to maximally enhance the role of divalent doping. The experimental results provide evidence of the holes delocalization in the overdoped compound (x(Sr)/y(Mn) > 1). This delocalization is accompanied by appearance of the new charge transfer transitions in the optical spectrum and dynamical valence change of manganese atoms. Additionally we observe the thermally activated narrowing of resonance EMR lines due to the internal motion, which is characterized by the energy barrier depending strongly on the ratio x(Sr)/y(Mn). The energy barrier is found to be associated with the charge carrier (hole) self-trapped energy. Fitting the EMR spectra in three orthogonal planes to an orthorhombic spin Hamiltonian enables extracting the zero-field splitting (ZFS) parameters and the Zeeman g-factors for Mn4+ (S = 3/2) ions in LSGM. The experimental ZFS parameters are modeled using superposition model analysis based on an orthorhombic symmetry approximation.

Common Polymorphisms in the Solute Carrier SLC30A10 are Associated With Blood Manganese and Neurological Function

PubMed Central

Kippler, Maria; Alhamdow, Ayman; Rahman, Syed Moshfiqur; Smith, Donald R.; Vahter, Marie; Lucchini, Roberto G.; Broberg, Karin

2016-01-01

Manganese (Mn) is an essential nutrient in humans, but excessive exposure to Mn may cause neurotoxicity. Despite homeostatic regulation, Mn concentrations in blood vary considerably among individuals. We evaluated if common single-nucleotide polymorphisms (SNPs) in SLC30A10, which likely encodes an Mn transporter, influence blood Mn concentrations and neurological function. We measured blood Mn concentrations by ICP-MS or atomic absorption spectroscopy and genotyped 2 SLC30A10 non-coding SNPs (rs2275707 and rs12064812) by TaqMan PCR in cohorts from Bangladesh (N = 406), the Argentinean Andes (N = 198), and Italy (N = 238). We also measured SLC30A10 expression in whole blood by TaqMan PCR in a sub-group (N = 101) from the Andean cohort, and neurological parameters (sway velocity and finger-tapping speed) in the Italian cohort. The rs2275707 variant allele was associated with increased Mn concentrations in the Andes (8%, P = .027) and Italy (10.6%, P = .012), but not as clear in Bangladesh (3.4%, P = .21; linear regression analysis adjusted for age, gender, and plasma ferritin). This allele was also associated with increased sway velocity (15%, P = .033; adjusted for age and sex) and reduced SLC30A10 expression (−24.6%, P = .029). In contrast, the rs12064812 variant homozygous genotype was associated with reduced Mn concentrations, particularly in the Italian cohort (−18.4%, P = .04), and increased finger-tapping speed (8.7%, P = .025). We show that common SNPs in SLC30A10 are associated with blood Mn concentrations in 3 unrelated cohorts and that their influence may be mediated by altered SLC30A10 expression. Moreover, the SNPs appeared to influence neurological functions independent of blood Mn concentrations, suggesting that SLC30A10 could regulate brain Mn levels. PMID:26628504

Mechanical properties, microstructure and thermal stability of a nanocrystalline CoCrFeMnNi high-entropy alloy after severe plastic deformation

DOE PAGES

Schuh, B.; Mendez-Martin, F.; Völker, B.; ...

2015-06-24

An equiatomic CoCrFeMnNi high-entropy alloy (HEA), produced by arc melting and drop casting, was subjected to severe plastic deformation (SPD) using high-pressure torsion. This process induced substantial grain refinement in the coarse-grained casting leading to a grain size of approximately 50 nm. As a result, strength increased significantly to 1950 MPa, and hardness to similar to 520 MV. Analyses using transmission electron microscopy (TEM) and 3-dimensional atom probe tomography (3D-APT) showed that, after SPD, the alloy remained a true single-phase solid solution down to the atomic scale. Subsequent investigations characterized the evolution of mechanical properties and microstructure of this nanocrystallinemore » HEA upon annealing. Isochronal (for 1 h) and isothermal heat treatments were performed followed by microhardness and tensile tests. The isochronal anneals led to a marked hardness increase with a maximum hardness of similar to 630 HV at about 450 degrees C before softening set in at higher temperatures. The isothermal anneals, performed at this peak hardness temperature, revealed an additional hardness rise to a maximum of about 910 MV after 100 h. To clarify this unexpected annealing response, comprehensive microstructural analyses were performed using TEM and 3D-APT. New nano-scale phases were observed to form in the originally single-phase HEA. After times as short as 5 min at 450 degrees C, a NiMn phase and Cr-rich phase formed. With increasing annealing time, their volume fractions increased and a third phase, FeCo, also formed. It appears that the surfeit of grain boundaries in the nanocrystalline HEA offer many fast diffusion pathways and nucleation sites to facilitate this phase decomposition. The hardness increase, especially for the longer annealing times, can be attributed to these nano-scaled phases embedded in the HEA matrix. The present results give new valuable insights into the phase stability of single-phase high-entropy alloys as well as the mechanisms controlling the mechanical properties of nanostructured multiphase composites. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd.« less

Native structure of photosystem II at 1.95 Å resolution viewed by femtosecond X-ray pulses.

PubMed

Suga, Michihiro; Akita, Fusamichi; Hirata, Kunio; Ueno, Go; Murakami, Hironori; Nakajima, Yoshiki; Shimizu, Tetsuya; Yamashita, Keitaro; Yamamoto, Masaki; Ago, Hideo; Shen, Jian-Ren

2015-01-01

Photosynthesis converts light energy into biologically useful chemical energy vital to life on Earth. The initial reaction of photosynthesis takes place in photosystem II (PSII), a 700-kilodalton homodimeric membrane protein complex that catalyses photo-oxidation of water into dioxygen through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been solved by X-ray diffraction (XRD) at 1.9 ångström resolution, which revealed that the OEC is a Mn4CaO5-cluster coordinated by a well defined protein environment. However, extended X-ray absorption fine structure (EXAFS) studies showed that the manganese cations in the OEC are easily reduced by X-ray irradiation, and slight differences were found in the Mn-Mn distances determined by XRD, EXAFS and theoretical studies. Here we report a 'radiation-damage-free' structure of PSII from Thermosynechococcus vulcanus in the S1 state at a resolution of 1.95 ångströms using femtosecond X-ray pulses of the SPring-8 ångström compact free-electron laser (SACLA) and hundreds of large, highly isomorphous PSII crystals. Compared with the structure from XRD, the OEC in the X-ray free electron laser structure has Mn-Mn distances that are shorter by 0.1-0.2 ångströms. The valences of each manganese atom were tentatively assigned as Mn1D(III), Mn2C(IV), Mn3B(IV) and Mn4A(III), based on the average Mn-ligand distances and analysis of the Jahn-Teller axis on Mn(III). One of the oxo-bridged oxygens, O5, has significantly longer distances to Mn than do the other oxo-oxygen atoms, suggesting that O5 is a hydroxide ion instead of a normal oxygen dianion and therefore may serve as one of the substrate oxygen atoms. These findings provide a structural basis for the mechanism of oxygen evolution, and we expect that this structure will provide a blueprint for the design of artificial catalysts for water oxidation.

Direct Measurements of Magnetic Polarons in Cd 1–xMn x Se Nanocrystals from Resonant Photoluminescence

DOE PAGES

Rice, W. D.; Liu, W.; Pinchetti, V.; ...

2017-04-07

In semiconductors, quantum confinement can greatly enhance the interaction between band carriers (electrons and holes) and dopant atoms. One manifestation of this enhancement is the increased stability of exciton magnetic polarons in magnetically doped nanostructures. In the limit of very strong 0D confinement that is realized in colloidal semiconductor nanocrystals, a single exciton can exert an effective exchange field B ex on the embedded magnetic dopants that exceeds several tesla. Here we use the very sensitive method of resonant photoluminescence (PL) to directly measure the presence and properties of exciton magnetic polarons in colloidal Cd 1–xMn xSe nanocrystals. Despite smallmore » Mn 2+ concentrations (x = 0.4–1.6%), large polaron binding energies up to ~26 meV are observed at low temperatures via the substantial Stokes shift between the pump laser and the resonant PL maximum, indicating nearly complete alignment of all Mn 2+ spins by B exex ≈ 10 T in these nanocrystals, in good agreement with theoretical estimates. Further, the emission line widths provide direct insight into the statistical fluctuations of the Mn 2+ spins. In conclusion, these resonant PL studies provide detailed insight into collective magnetic phenomena, especially in lightly doped nanocrystals where conventional techniques such as nonresonant PL or time-resolved PL provide ambiguous results.« less

Surface chemistry, friction, and wear of Ni-Zn and Mn-Zn ferrites in contact with metals

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1983-01-01

X-ray photoelectron and Auger electron spectroscopy analysis were used in sliding friction experiments. These experiments were conducted with hot-pressed polycrystalline Ni-Zn and Mn-Zn ferrites, and single-crystal Mn-Zn ferrite in contact with various transition metals at room temperature in both vacuum and argon. The results indicate that Ni2O3 and Fe3O4 were present on the Ni-Zn ferrite surface in addition to the nominal bulk constituents, while MnO2 and Fe3O4 were present on the Mn-Zn ferrite surface in addition to the nominal bulk constituents. The coefficients of friction for the ferrites in contact with metals were related to the relative chemical activity of these metals. The more active the metal, the higher is the coefficient of friction. The coefficients of friction for the ferrites were correlated with the free energy of formation of the lowest metal oxide. The interfacial bond can be regarded as a chemical bond between the metal atoms and the oxygen anions in the ferrite surfaces. The adsorption of oxygen on clean metal and ferrite does strengthen the metal-ferrite contact and increase the friction. The ferrites exhibit local cracking and fracture with sliding under adhesive conditions. All the metals transferred to the surfaces of the ferrites in sliding. Previously announced in STAR as N83-19901

Surface chemistry, friction and wear of Ni-Zn and Mn-Zn ferrites in contact with metals

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron and Auger electron spectroscopy analysis were used in sliding friction experiments. These experiments were conducted with hot-pressed polycrystalline Ni-Zn and Mn-Zn ferrites, and single-crystal Mn-Zn ferrite in contact with various transition metals at room temperature in both vacuum and argon. The results indicate that Ni2O3 and Fe3O4 were present on the Ni-Zn ferrite surface in addition to the nominal bulk constituents, while MnO2 and Fe3O4 were present on the Mn-Zn ferrite surface in addition to the nominal bulk constituents. The coefficients of friction for the ferrites in contact with metals were related to the relative chemical activity of these metals. The more active the metal, the higher is the coefficient of friction. The coefficients of friction for the ferrites were correlated with the free energy of formation of the lowest metal oxide. The interfacial bond can be regarded as a chemical bond between the metal atoms and the oxygen anions in the ferrite surfaces. The adsorption of oxygen on clean metal and ferrite does strengthen the metal-ferrite contact and increase the friction. The ferrites exhibit local cracking and fracture with sliding under adhesive conditions. All the metals transferred to he surfaces of the ferrites in sliding.

Direct Measurements of Magnetic Polarons in Cd 1–xMn x Se Nanocrystals from Resonant Photoluminescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rice, W. D.; Liu, W.; Pinchetti, V.

In semiconductors, quantum confinement can greatly enhance the interaction between band carriers (electrons and holes) and dopant atoms. One manifestation of this enhancement is the increased stability of exciton magnetic polarons in magnetically doped nanostructures. In the limit of very strong 0D confinement that is realized in colloidal semiconductor nanocrystals, a single exciton can exert an effective exchange field B ex on the embedded magnetic dopants that exceeds several tesla. Here we use the very sensitive method of resonant photoluminescence (PL) to directly measure the presence and properties of exciton magnetic polarons in colloidal Cd 1–xMn xSe nanocrystals. Despite smallmore » Mn 2+ concentrations (x = 0.4–1.6%), large polaron binding energies up to ~26 meV are observed at low temperatures via the substantial Stokes shift between the pump laser and the resonant PL maximum, indicating nearly complete alignment of all Mn 2+ spins by B exex ≈ 10 T in these nanocrystals, in good agreement with theoretical estimates. Further, the emission line widths provide direct insight into the statistical fluctuations of the Mn 2+ spins. In conclusion, these resonant PL studies provide detailed insight into collective magnetic phenomena, especially in lightly doped nanocrystals where conventional techniques such as nonresonant PL or time-resolved PL provide ambiguous results.« less

Oxygen trapped by rare earth tetrahedral clusters in Nd4FeOS6: Crystal structure, electronic structure, and magnetic properties

NASA Astrophysics Data System (ADS)

Lin, Qisheng; Taufour, Valentin; Zhang, Yuemei; Wood, Max; Drtina, Thomas; Bud'ko, Sergey L.; Canfield, Paul C.; Miller, Gordon J.

2015-09-01

Single crystals of Nd4FeOS6 were grown from an Fe-S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd4MnOSe6-type structure (P63mc, a=9.2693(1) Å, c=6.6650(1)Å, V=495.94(1) Å3, Z=2), featuring parallel chains of face-sharing [FeS6×1/2]4- trigonal antiprisms and interlinked [Nd4OS3]4+ cubane-like clusters. Oxygen atoms were found to be trapped by Nd4 clusters in the [Nd4OS3]4+ chains. Structural differences among Nd4MnOSe6-type Nd4FeOS6 and the related La3CuSiS7- and Pr8CoGa3-type structures have been described. Magnetic susceptibility measurements on Nd4FeOS6 suggested the dominance of antiferromagnetic interactions at low temperature, but no magnetic ordering down to 2 K was observed. Spin-polarized electronic structure calculations revealed magnetic frustration with dominant antiferromagnetic interactions.

Photoemission and x-ray absorption studies of the isostructural to Fe-based superconductors diluted magnetic semiconductor Ba1 -xKx(Zn1 -yMny)2As2

NASA Astrophysics Data System (ADS)

Suzuki, H.; Zhao, K.; Shibata, G.; Takahashi, Y.; Sakamoto, S.; Yoshimatsu, K.; Chen, B. J.; Kumigashira, H.; Chang, F.-H.; Lin, H.-J.; Huang, D. J.; Chen, C. T.; Gu, Bo; Maekawa, S.; Uemura, Y. J.; Jin, C. Q.; Fujimori, A.

2015-04-01

The electronic and magnetic properties of a new diluted magnetic semiconductor (DMS) Ba1 -xKx (Zn1 -yMny )2As2 , which is isostructural to so-called 122-type Fe-based superconductors, are investigated by x-ray absorption spectroscopy (XAS) and resonance photoemission spectroscopy (RPES). Mn L2 ,3-edge XAS indicates that the doped Mn atoms have a valence 2+ and strongly hybridize with the 4 p orbitals of the tetrahedrally coordinating As ligands. The Mn 3 d partial density of states obtained by RPES shows a peak around 4 eV and is relatively high between 0 and 2 eV below the Fermi level (EF) with little contribution at EF, similar to that of the archetypal DMS Ga1 -xMnxAs . This energy level creates a d5 electron configuration with S =5 /2 local magnetic moments at the Mn atoms. Hole carriers induced by K substitution for Ba atoms go into the top of the As 4 p valence band and are weakly bound to the Mn local spins. The ferromagnetic correlation between the local spins mediated by the hole carriers induces ferromagnetism in Ba1 -xKx (Zn1 -yMny )2As2 .

The friction and wear of metals and binary alloys in contact with an abrasive grit of single-crystal silicon carbide

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1979-01-01

Sliding friction experiments were conducted with various metals and iron-base binary alloys (alloying elements Ti, Cr, Mn, Ni, Rh and W) in contact with single crystal silicon carbide riders. Results indicate that the friction force in the plowing of metal and the groove height (corresponding to the wear volume of the groove) decrease linearly as the shear strength of the bulk metal increases. The coefficient of friction and groove height generally decrease, and the contact pressure increases with an increase in solute content of binary alloys. There appears to be very good correlation of the solute to iron atomic ratio with the decreasing rate of change of coefficient of friction, the decreasing rate of change of groove height and the increasing rate of change of contact pressure with increasing solute content. These rates of change increase as the solute to iron atomic radius ratio increases or decreases from unity.

Syntheses and characterizations of transition-metal-substituted aluminophosphate molecular sieves |(C3N2H5) 8|[M8Al16P24O96] (M = Co, Mn, Zn) with zeotype LAU topology.

PubMed

Song, Xiaowei; Li, Jiyang; Guo, Yanan; Pan, Qinhe; Gan, Lin; Yu, Jihong; Xu, Ruren

2009-01-05

Three transitional-metal-substituted aluminophosphate molecular sieves, |(C3N2H5)8|[M8Al16P24O96] (denoted MAPO-LAU, M = Co, Mn, Zn), have been synthesized under solvothermal conditions in the presence of imidazole as the structure-directing agent. Their structures are determined by single-crystal X-ray diffraction and further characterized by powder X-ray diffraction, inductively coupled plasma, thermogravimetric, and diffuse reflectance spectroscopy (UV-vis) analyses. The structure of MAPO-LAU is based on the strict alternation of MO4/AlO4 tetrahedra and PO4 tetrahedra through vertex oxygen atoms. Their frameworks are analogous to the zeotype LAU structure in which 33% of the aluminum sites are replaced by transitional-metal ions. The protonated imidazole cations resided in the 10-ring channels. These compounds show photoluminescent properties due to the existence of imidazole molecules in the structures. Magnetic measurements reveal that there is very weak antiferromagnetic interaction among the metal centers of MnAPO-LAU.

Lattice sites of ion-implanted Mn, Fe and Ni in 6H-SiC

NASA Astrophysics Data System (ADS)

Costa, A. R. G.; Wahl, U.; Correia, J. G.; David-Bosne, E.; Amorim, L. M.; Augustyns, V.; Silva, D. J.; da Silva, M. R.; Pereira, L. M. C.

2018-01-01

Using radioactive isotopes produced at the CERN-ISOLDE facility, the lattice location of the implanted transition metal (TM) ions 56Mn, 59Fe and 65Ni in n-type single-crystalline hexagonal 6H-SiC was studied by means of the emission channeling technique. TM probes on carbon coordinated tetrahedral interstitial sites (T C) and on substitutional silicon sites (S Si,h+k ) were identified. We tested for but found no indication that the TM distribution on S Si sites deviates from the statistical mixture of 1/3 hexagonal and 2/3 cubic sites present in the 6H crystal. The TM atoms partially disappear from T C positions during annealing at temperatures between 500 °C and 700 °C which is accompanied by an increase on S Si and random sites. From the temperature associated with these site changes, interstitial migration energies of 1.7-2.7 eV for Mn and Ni, and 2.3-3.2 eV for Fe were estimated. TM lattice locations are compared to previous results obtained in 3C-SiC using the same technique.

Dramatic Influence of an Anionic Donor on the Oxygen-Atom Transfer Reactivity of a MnV–Oxo Complex

PubMed Central

Neu, Heather M; Quesne, Matthew G; Yang, Tzuhsiung; Prokop-Prigge, Katharine A; Lancaster, Kyle M; Donohoe, James; DeBeer, Serena; de Visser, Sam P; Goldberg, David P

2014-01-01

Addition of an anionic donor to an MnV(O) porphyrinoid complex causes a dramatic increase in 2-electron oxygen-atom-transfer (OAT) chemistry. The 6-coordinate [MnV(O)(TBP8Cz)(CN)]− was generated from addition of Bu4N+CN− to the 5-coordinate MnV(O) precursor. The cyanide-ligated complex was characterized for the first time by Mn K-edge X-ray absorption spectroscopy (XAS) and gives Mn–O=1.53 Å, Mn–CN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN− complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e−-reduced MnIII(CN)− complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000-fold versus the same reaction for the parent 5-coordinate complex. An Eyring analysis gives ΔH≠=14 kcal mol−1, ΔS≠=−10 cal mol−1 K−1. Computational studies fully support the structures, spin states, and relative reactivity of the 5- and 6-coordinate MnV(O) complexes. PMID:25256417

Studies on Electronic Structure and Magnetic Properties of an Organic Magnet with Metallic Mn2+ and Cu2+ Ions

NASA Astrophysics Data System (ADS)

Yao, Jian-Guo; Peng, Guang-Xiong

2004-11-01

The electronic structure and the magnetic properties of the non-pure organic ferromagnetic compound MnCu(pbaOH)(H2O)3 with pbaOH = 2-hydroxy-1, 3-propylenebis (oxamato) are studied by using the density-functional theory with local-spin-density approximation. The density of states, total energy, and the spin magnetic moment are calculated. The calculations reveal that the compound MnCu(pbaOH)(H20)3 has a stable metal-ferromagnetic ground state, and the spin magnetic moment per molecule is 2.208 μB, and the spin magnetic moment is mainly from Mn ion and Cu ion. An antiferromagnetic order is expected and the antiferromagnetic exchange interaction of d-electrons of Cu and Mn passes through the antiferromagnetic interaction between the adjacent C, O, and N atoms along the path linking the atoms Cu and Mn. The project supported by National Natural Science Foundation of China under Grant No. 10375074 and Hubei Automotive Industries Institute Foundation under Grant No. QY2002-16

Orientation of Calcium in the Mn4Ca Cluster of the Oxygen-Evolving Complex Determined Using Polarized Strontium EXAFS of Photosystem II Membranes†

PubMed Central

Cinco, Roehl M.; Robblee, John H.; Messinger, Johannes; Fernandez, Carmen; Holman, Karen L. McFarlane; Sauer, Kenneth; Yachandra, Vittal K.

2014-01-01

The oxygen-evolving complex of photosystem II (PS II) in green plants and algae contains a cluster of four Mn atoms in the active site, which catalyzes the photoinduced oxidation of water to dioxygen. Along with Mn, calcium and chloride ions are necessary cofactors for proper functioning of the complex. The current study using polarized Sr EXAFS on oriented Sr-reactivated samples shows that Fourier peak II, which fits best to Mn at 3.5 Å rather than lighter atoms (C, N, O, or Cl), is dichroic, with a larger magnitude at 10° (angle between the PS II membrane normal and the X-ray electric field vector) and a smaller magnitude at 80°. Analysis of the dichroism of the Sr EXAFS yields a lower and upper limit of 0° and 23° for the average angle between the Sr–Mn vectors and the membrane normal and an isotropic coordination number (number of Mn neighbors to Sr) of 1 or 2 for these layered PS II samples. The results confirm the contention that Ca (Sr) is proximal to the Mn cluster and lead to refined working models of the heteronuclear Mn4Ca cluster of the oxygen-evolving complex in PS II. PMID:15491134

A comparitive investigation of electrochemical charge storage properties on β, γ, δ and λ-MnO2 nanoparticles

NASA Astrophysics Data System (ADS)

Shafi, P. Muhammed; Johnson, Chelsea; Bose, A. Chandra

2018-04-01

Manganese dioxide and Manganese dioxide based materials have long been used in various energy storage systems because of their outstanding electrochemical behavior, low cost, and environmental compatibility. In recent years, many studies had focused on its nano scale applications due to the structural flexibility and the unique physicochemical properties. The basic crystal structure of manganese dioxide configures of one manganese atom surrounded by six oxygen atoms to form an octahedron. Here β-MnO2, γ-MnO2, λ-MnO2 and δ-MnO2 nanoparticles have been successfully synthesized by simple precipitation methods. Powder X-Ray Diffraction (XRD) analyses were performed for the identification and examination of the crystalline phase structures. Presence of functional groups and purity of the sample were evaluated by Fourier Transform Infrared Spectroscopy (FTIR). Morphology studies were carried out via Scanning Electron Microscopy (SEM). Electrochemical performances of the β, γ and δ phases were characterized by cyclic voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). Among the four electrodes, δ-MnO2 exhibited the highest value for specific capacitance. These results show that the prepared MnO2 electrodes are good materials for supercapacitor application, especially δ-MnO2.

catena-Poly[[[aqua­(2,2′-bipyridine)manganese(II)]-μ-5-methoxy­iso­phthalato-κ3 O,O′:O′′] monohydrate

PubMed Central

Shen, Su-Mei

2009-01-01

In the title compound, {[Mn(C8H4O4)(C10H8N2)(H2O)]·H2O}n, the MnII centre is octa­hedrally coordinated by three O atoms from two 5-methoxy­isophthalate (CH3O-ip) ligands, a fourth from a coordinated water mol­ecule and two N atoms from one chelating 2,2′-bipyridine (2,2-bipy) ligand. Each pair of adjacent MnII atoms is bridged by a CH3O-ip ligand, forming a helical chain running along a crystallographic 21 axis in the c-axis direction. These chains are decorated with 2,2′-bipy ligands on alternating sides. O—H⋯O hydrogen bonding involving the water molecules stabilizes the crystal structure. PMID:21577709

Structural control of polyhedral compression in synthetic braunite, Mn2+Mn3+6O8SiO4

NASA Astrophysics Data System (ADS)

Miletich, R.; Allan, D. R.; Angel, R. J.

The compression of synthetic braunite, Mn2+Mn3+6O8SiO4, was studied by high-pressure single-crystal X-ray diffraction carried out in a diamond-anvil cell. The equation of state at room temperature (third-order Birch-Murnaghan equation of state: V0=1661.15(8) Å3, K0,298=180.7+/-0.9 GPa, K'=6.5+/-0.3) was determined from unit-cell volume data to 9.18 GPa. Crystal structures were determined at 6 different pressures to 7.69 GPa. Compression of the structure (space group I41/acd) was found to be slightly anisotropic (a0=9.4262(4) Å, Ka=499+/-4 GPa, Ka'=19.7+/-0.9 c0=18.6964(6) Å, Kc=657+/-6 GPa, Kc'=15.7+/-1.4) which can be attributed to the fact that the Mn3+-O bonds, which are the most compressible bonds, are aligned closer to the (001) plane than to the c axis. The large bulk modulus is the result of the structural topology in which 2/3 and 1/2 of the edges of the Mn2+O8 and Mn3+O6 polyhedra share edges with other polyhedra. The Mn2+O8 polyhedra were found to compress isotropically, whereas anisotropic compressional behaviour was observed for all three Mn3+O6 octahedra. Although the polyhedral geometry of all three crystallographically independent Mn3+ sites shows the same type of uniaxially elongated distortion, the compression of the individual octahedral configurations was found to be strongly dependent upon both the geometry of the polyhedron itself and the types of, and the connectivity to, the neighbouring polyhedra. The differences in the configuration of the different oxygen atoms, and therefore the structural topology, is one of the major factors determining the type and degree of the pressure-induced distortion, while the Jahn-Teller effect plays a subordinate role.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Meng; Wang, Yachun; Yao, Jinlei

MnB{sub 4} was newly synthesized to crystallize in a monoclinic P2{sub 1}/c structure, different from previous experimental and theoretical reports. Here, based on first-principles calculations, we perform a comparative study of geometric and energetic features, mechanical behaviors, electronic property and chemical bonding of the experimentally identified monoclinic MnB{sub 4}, as well as orthorhombic CrB{sub 4} and FeB{sub 4}. The results demonstrate that the presence of distorted rhomboidal-B{sub 4} units and one-dimensional Mn chains in the monoclinic MnB{sub 4} breaks the structural symmetry and lowers the total energy in comparison to the orthorhombic phase. The opening of band gap in MnB{submore » 4} is induced by Peierls-paired Mn atoms, differing from the metallic behaviors of recently studied tetraborides. Specifically, the preservations of covalent bonding in distorted boron-rhomboids in MnB{sub 4} explain the relatively higher incompressibility and hardness. - Graphical abstract: P2{sub 1}/c-type structure for MnB{sub 4} characterizes rhomboid-B{sub 4} units and alternately short and long Mn–Mn chains. - Highlights: • The novel P2{sub 1}/c-type MnB{sub 4} compound is studied by first-principles calculations. • P2{sub 1}/c-type MnB{sub 4} has lower total energy and relatively higher stability. • An energy gap opening is found for P2{sub 1}/c-type MnB{sub 4} induced by Mn atom pairs. • P2{sub 1}/c-type MnB{sub 4} exhibits excellent mechanical properties. • The mechanical properties of TcB{sub 4} and ReB{sub 4} in P2{sub 1}/c structure are also studied.« less

Ultra-precise single-ion atomic mass measurements on deuterium and helium-3

NASA Astrophysics Data System (ADS)

Zafonte, S. L.; Van Dyck, R. S., Jr.

2015-04-01

The former University of Washington Penning Trap Mass Spectrometer (UW-PTMS), now located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, was used in the decade before the move to determine new values for the deuteron atomic mass, M (2H+) = 2.013 553 212 745(40) u, and the deuterium atomic mass, M (2H) = 2.014 101 778 052(40) u, both of which are now more than an order-of-magnitude more accurate than the previous best 1994-MIT measurements of these quantities. The new value for the deuteron’s mass can then be used with the accepted 2010-CODATA proton mass and the most recent 1999-measurement of the 2.2 MeV gamma-ray binding energy of the deuteron to refine the neutron’s mass to mn = 1.008 664 916 018(435) u which has about half the uncertainty relative to the value computed using that previous 1994-MIT deuterium measurement. As a result, further improvements of mn must now come from a more accurate determination of the wavelength of this gamma ray. In this same period of time, this spectrometer has also been used to determine new values for the helion atomic mass, M (3He2+) = 3.014 932 246 668(43) u, and the neutral helium-3 atomic mass, M (3He) = 3.016 029 321 675(43) u, which are both about 60 times more accurate than the 2006-SMILETRAP measurements, but disagree with the 4.4-times less-accurate 2015-Florida-State measurements by 0.76 nu. It is expected that these helium-3 results will be used in the future 3H/3He mass ratio (to be determined by the Heidelberg, Germany version of the old UW-PTMS) in order to generate a more accurate value for the tritium atomic mass.

Insight into the Atomic Structure of High-Voltage Spinel LiNi 0.5Mn 1.5O4 Cathode Material in the First Cycle

DOE PAGES

Huang, Xuejie; Yu, Xiqian; Lin, Mingxiang; ...

2014-12-22

Application of high-voltage spinel LiNi 0.5Mn 1.5O4 cathode material is the closest and the most realistic approach to meeting the midterm goal of lithium-ion batteries for electric vehicles (EVs) and plug-in hybrid electric vehicles (HEVs). However, this application has been hampered by long-standing issues, such as capacity degradation and poor first-cycle Coulombic efficiency of LiNi 0.5Mn 1.5O4 cathode material. Although it is well-known that the structure of LiNi 0.5Mn 1.5O4 into which Li ions are reversibly intercalated plays a critical role in the above issues, performance degradation related to structural changes, particularly in the first cycle, are not fully understood.more » Here, we report detailed investigations of local atomic-level and average structure of LiNi 0.5Mn 1.5O4 during first cycle (3.5–4.9 V) at room temperature. We observed two types of local atomic-level migration of transition metals (TM) ions in the cathode of a well-prepared LiNi 0.5Mn 1.5O4//Li half-cell during first charge via an aberration-corrected scanning transmission electron microscopy (STEM). Surface regions (~2 nm) of the cycled LiNi 0.5Mn 1.5O4 particles show migration of TM ions into tetrahedral Li sites to form a Mn 3O 4-like structure. However, subsurface regions of the cycled particles exhibit migration of TM ions into empty octahedral sites to form a rocksalt-like structure. The migration of these TM ions are closely related to dissolution of Ni/Mn ions and building-up of charge transfer impedance, which contribute significantly to the capacity degradation and the poor first-cycle Coulombic efficiency of spinel LiNi 0.5Mn 1.5O4 cathode material. Accordingly, we provide suggestions of effective stabilization of LiNi 0.5Mn 1.5O4 structure to obtain better electrochemical performance.« less

First-principles study on the ferrimagnetic half-metallic Mn{sub 2}FeAs alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Santao; Zhang, Chuan-Hui, E-mail: zhangch@ustb.edu.cn; Chen, Bao

2015-05-15

Mn-based full-Heusler alloys are kinds of promising candidates for new half-metallic materials. Basing on first principles, the electronic structures and magnetic properties of the Mn{sub 2}FeAs full-Heusler alloy have been investigated in detail. The Hg{sub 2}CuTi-type Mn{sub 2}FeAs compound obeys the Slater-Pauling rule, while the anti-parallel alignment atomic magnetic moments of Mn locating at different sites indicate it a ferrimagnetic alloy. The calculated spin-down bands behave half-metallic character, exhibiting a direct gap of 0.46 eV with a 100% spin polarization at the Fermi level. More studies show the compound would maintain half-metallic nature in a large range of variational latticemore » constants. We expect that our calculated results may trigger Mn{sub 2}FeAs applying in the future spintronics field. - Graphical abstract: The d orbitals of Mn and Fe atoms split into multi-degenerated levels which create new bonding and nonbonding states. These exchange splitting shift the Fermi level to origin band gap.▪ - Highlights: • The electronic structure and magnetic properties of Mn{sub 2}FeAs full-Heusler alloy were studied. • A total magnetic moment of 3μ{sub B} was obtained for Mn{sub 2}FeAs alloy, following the SP rule M{sub t}=Z{sub t}−24. • The origin of ferrimagnetism and half-metallic character in Mn{sub 2}FeAs were discussed.« less

Pentacoordinate and Hexacoordinate Mn(III) Complexes of Tetradentate Schiff-Base Ligands Containing Tetracyanidoplatinate(II) Bridges and Revealing Uniaxial Magnetic Anisotropy.

PubMed

Nemec, Ivan; Herchel, Radovan; Trávníček, Zdeněk

2016-12-08

Crystal structures and magnetic properties of polymeric and trinuclear heterobimetallic Mn III ···Pt II ···Mn III coordination compounds, prepared from the Ba[Pt(CN)₄] and [Mn(L4A/B)(Cl)] ( 1a / b ) precursor complexes, are reported. The polymeric complex [{Mn(L4A)}₂{μ⁴-Pt(CN)₄}] n ( 2a ), where H₂L4A = N , N '-ethylene-bis(salicylideneiminate), comprises the {Mn(L4A)} moieties covalently connected through the [Pt(CN)₄] 2- bridges, thus forming a square-grid polymeric structure with the hexacoordinate Mn III atoms. The trinuclear complex [{Mn(L4B)}₂{μ-Pt(CN)₄}] ( 2b ), where H₂L4B = N , N '-benzene-bis(4-aminodiethylene-salicylideneiminate), consists of two [{Mn(L4B)} moieties, involving pentacoordinate Mn III atoms, bridged through the tetracyanidoplatinate (II) bridges to which they are coordinated in a trans fashion. Both complexes possess uniaxial type of magnetic anisotropy, with D (the axial parameter of zero-field splitting) = -3.7(1) in 2a and -2.2(1) cm -1 in 2b . Furthermore, the parameters of magnetic anisotropy 2a and 2b were also thoroughly studied by theoretical complete active space self-consistent field (CASSCF) methods, which revealed that the former is much more sensitive to the ligand field strength of the axial ligands.

Antiferromagnetic MnN layer on the MnGa(001) surface

NASA Astrophysics Data System (ADS)

Guerrero-Sánchez, J.; Takeuchi, Noboru

2016-12-01

Spin polarized first principles total energy calculations have been applied to study the stability and magnetic properties of the MnGa(001) surface and the formation of a topmost MnN layer with the deposit of nitrogen. Before nitrogen adsorption, surface formation energies show a stable gallium terminated ferromagnetic surface. After incorporation of nitrogen atoms, the antiferromagnetic manganese terminated surface becomes stable due to the formation of a MnN layer (Mn-N bonding at the surface). Spin density distribution shows a ferromagnetic/antiferromagnetic arrangement in the first surface layers. This thermodynamically stable structure may be exploited to growth MnGa/MnN magnetic heterostructures as well as to look for exchange biased systems.

Local and electronic structure around manganese in Cd0.98Mn0.02Te0.97Se0.03 studied by XAFS

NASA Astrophysics Data System (ADS)

Radisavljević, I.; Novaković, N.; Romčević, N.; Ivanović, N.

2013-04-01

X-ray Absorption Fine Structure (XAFS) technique was employed to study local electronic and structural features of Mn ions incorporated in Cd0.98Mn0.02Te0.97Se0.03. XAFS measurements performed at Mn K edge revealed that manganese Mn(II) ions are well incorporated into the host CdTe lattice (cubic zinc-blende structure type) and their immediate surrounding is found to be composed exclusively of Te atoms. The observed preference of Mn ions distribution around Te opposes earlier observations on the similar systems, where preferential Mn-Se over Mn-Te paring was found.

Magnetism in La₂O₃(Fe₁₋ xMn x)₂Se₂ tuned by Fe/Mn ratio

DOE PAGES

Lei, Hechang; Bozin, Emil S.; Llobet, A.; ...

2012-09-17

We report the evolution of structural and magnetic properties in La₂O₃(Fe₁₋ xMn x)₂Se₂. Heat capacity and bulk magnetization indicate an increased ferromagnetic component of the long-range magnetic order and possible increased degree of frustration. Atomic disorder on Fe(Mn) sites suppresses the temperature of the long-range order whereas intermediate alloys show a rich magnetic phase diagram.

Photochemical water oxidation by crystalline polymorphs of manganese oxides: structural requirements for catalysis.

PubMed

Robinson, David M; Go, Yong Bok; Mui, Michelle; Gardner, Graeme; Zhang, Zhijuan; Mastrogiovanni, Daniel; Garfunkel, Eric; Li, Jing; Greenblatt, Martha; Dismukes, G Charles

2013-03-06

Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ≫ λ-MnO2, where the latter is derived from spinel LiMn2O4 following partial Li(+) removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and λ-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration e(g)(1) which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface.

Structural and electronic properties of M-MOF-74 (M = Mg, Co or Mn)

NASA Astrophysics Data System (ADS)

de Oliveira, Aline; de Lima, Guilherme Ferreira; De Abreu, Heitor Avelino

2018-01-01

The Metal-Organic Frameworks M-MOF-74 (M = Mg, Co or Mn) were investigated through Density Functional Theory calculations. Structural parameters and band gap energies were determined in agreement with experimental data, with errors under 2%. The methods Electron Localization Function and Quantum Theory of Atoms in Molecules were applied to the analyses of the electronic density topology of the three solids. These methodologies indicated that the bonds between the metallic cations and the oxygen atoms are predominantly ionic while the other ones are predominantly covalent. Furthermore, non-conventional hydrogen bonds were identified to Mg-MOF-74 and Co-MOF-74, which were not observed to Mn-MOF-74.

Site occupancy trend of Co in Ni{sub 2}MnIn: Ab initio approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pal, Soumyadipta, E-mail: soumyadipta.pal@gmail.com; Mahadevan, Priya; Biswas, C.

2015-06-24

The trend of site occupation of Co at Ni sites of Ni{sub 2}MnIn system is studied in austenitic phase having L2{sub 1} structure by ab initio density functional theory (DFT) calculation. The Co atoms prefer to be at Ni sites rather than Mn site and are ferromagetically coupled with Ni and Mn. The ground state has tetragonal structure for Ni{sub 1.5}Co{sub 0.5}MnIn and Ni{sub 1.25}Co{sub 0.75}MnIn. The Co tends to form cluster.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneeweiss, Oldřich; Friák, Martin; Dudová, Marie

In this paper, we present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of 0.006more » ± 0.001 emu T. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and 2 μ B), while the local moments of Ni atoms effectively vanish. Finally, these results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.« less

Comparison of digestion methods for total elemental analysis of peat and separation of its organic and inorganic components

USGS Publications Warehouse

Papp, C.S.E.; Harms, T.F.

1985-01-01

In order to find the most efficient digestion method for the total elemental recovery in peat, ten samples were subjected to different techniques and analysed for Ca, Mg, Fe, AI, Na, K, Mn, P, Zn, Cu, Li, Cd, Co, Ni, Pb and Si using atomic-absorption spectrophotometry. The most satisfactory procedures were dry ashing followed by hydrofluoric acid treatment and wet digestion using a mixture of hot nitric, perchloric and hydrofluoric acids. The wet digestion offers the advantage of a single decomposition method for the determination of Ca, Mg, Fe, AI, K, Na, Mn, Cu, Li, Zn and P. An alkaline fusion technique was required for the determination of Si. Hydrogen peroxide was used to separate the peat into its organic and inorganic components, leading to the total recovery of the elements for both fractions.

Strain-induced oxygen vacancies in ultrathin epitaxial CaMnO3 films

NASA Astrophysics Data System (ADS)

Chandrasena, Ravini; Yang, Weibing; Lei, Qingyu; Delgado-Jaime, Mario; de Groot, Frank; Arenholz, Elke; Kobayashi, Keisuke; Aschauer, Ulrich; Spaldin, Nicola; Xi, Xiaoxing; Gray, Alexander

Dynamic control of strain-induced ionic defects in transition-metal oxides is considered to be an exciting new avenue towards creating materials with novel electronic, magnetic and structural properties. Here we use atomic layer-by-layer laser molecular beam epitaxy to synthesize high-quality ultrathin single-crystalline CaMnO3 films with systematically varying coherent tensile strain. We then utilize a combination of high-resolution soft x-ray absorption spectroscopy and bulk-sensitive hard x-ray photoemission spectroscopy in conjunction with first-principles theory and core-hole multiplet calculations to establish a direct link between the coherent in-plane strain and the oxygen-vacancy content. We show that the oxygen vacancies are highly mobile, which necessitates an in-situ-grown capping layer in order to preserve the original strain-induced oxygen-vacancy content. Our findings open the door for designing and controlling new ionically active properties in strongly-correlated transition-metal oxides.

Ansa-Complexes of [Mn(η(5) -C5 H5 )(η(6) -C6 H6 )]: Preparation, Characterization, and Reactivity of [n]Manganoarenophanes (n=1, 2, 3).

PubMed

Braunschweig, Holger; Damme, Alexander; Dück, Klaus; Fuß, Marco; Hörl, Christian; Kramer, Thomas; Krummenacher, Ivo; Kupfer, Thomas; Paprocki, Valerie; Schneider, Christoph

2015-10-12

We report the synthesis of [n]manganoarenophanes (n=1, 2) featuring boron, silicon, germanium, and tin as ansa-bridging elements. Their preparation was achieved by salt-elimination reactions of the dilithiated precursor [Mn(η(5) -C5 H4 Li)(η(6) -C6 H5 Li)]⋅pmdta (pmdta=N,N,N',N',N''-pentamethyldiethylenetriamine) with corresponding element dichlorides. Besides characterization by multinuclear NMR spectroscopy and elemental analysis, the identity of two single-atom-bridged derivatives, [Mn(η(5) -C5 H4 )(η(6) -C6 H5 )SntBu2 ] and [Mn(η(5) -C5 H4 )(η(6) -C6 H5 )SiPh2 ], could also be determined by X-ray structural analysis. We investigated for the first time the reactivity of these ansa-cyclopentadienyl-benzene manganese compounds. The reaction of the distannyl-bridged complex [Mn(η(5) -C5 H4 )(η(6) -C6 H5 )Sn2 tBu4 ] with elemental sulfur was shown to proceed through the expected oxidative addition of the Sn-Sn bond to give a triatomic ansa-bridge. The investigation of the ring-opening polymerization (ROP) capability of [Mn(η(5) -C5 H4 )(η(6) -C6 H5 )SntBu2 ] with [Pt(PEt3 )3 ] showed that an unexpected, unselective insertion into the Cipso -Sn bonds of [Mn(η(5) -C5 H4 )(η(6) -C6 H5 )SntBu2 ] had occurred. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Three NiAs-Ni 2In Type Structures in the Mn-Sn System

NASA Astrophysics Data System (ADS)

Elding-Pontén, Margareta; Stenberg, Lars; Larsson, Ann-Kristin; Lidin, Sven; Ståhl, Kenny

1997-03-01

TheB8-type structure field of the Mn-Sn system has been investigated. Two high temperature phases (HTP1 and HTP2) and one low temperature phase (Mn3Sn2) were found. They all crystallize with the NiAs structure type with part of the trigonal bipyramidal interstices filled by manganese atoms in an ordered manner. The ordering as well as the manganese content is different for the three phases, giving rise to three different orthorhombic superstructures. Mn3Sn2seems to have the lowest manganese content, since the corresponding basal unit cell is smaller than for HTP1-2. Structural models of the phases are based on selected area electron diffraction, X-ray powder diffraction, and preliminary single crystal X-ray measurements. The ideal cell parameters found are (a=7ahex,b=3ahex,c=chex), (a=5ahex,b=3ahex,c=chex), and (a=2ahex,b=3ahex,c=chex) for HTP1, HTP2, and Mn3Sn2, respectively. The crystal structure of Mn3Sn2has been refined by means of the Rietveld method from X-ray powder diffraction data. Mn3Sn2is orthorhombic,Pnma,a=7.5547(2),b=5.4994(2),c=8.5842(2) Å,Z=4. (Pbnmin the setting above.) The compound is isostructural with Ni3Sn2andγ‧-Co3Sn2(H. Fjellvåg and A. Kjekshus,Acta Chem. Scand.A40, 23-30 (1986)). FinalRp=8.97%,Rwp=11.44%, GOF=2.86, andRBragg=4.11% using 43 parameters and 5701 observations and 330 Bragg reflections.

Elucidation of electronic structure by the analysis of hyperfine interactions: The MnH A 7Π-X 7Sigma + (0,0) band

NASA Astrophysics Data System (ADS)

Varberg, Thomas D.; Field, Robert W.; Merer, Anthony J.

1991-08-01

We present a complete analysis of the hyperfine structure of the MnH A 7Π-X 7Σ+ (0,0) band near 5680 Å, studied with sub-Doppler resolution by intermodulated fluorescence spectroscopy. Magnetic hyperfine interactions involving both the 55Mn (I=5/2) and 1H (I=1/2) nuclear spins are observed as well as 55Mn electric quadrupole effects. The manganese Fermi contact interaction in the X 7Σ+ state is the dominant contributor to the observed hyperfine splittings; the ΔF=0, ΔN=0, ΔJ=±1 matrix elements of this interaction mix the electron spin components of the ground state quite strongly at low N, destroying the ``goodness'' of J as a quantum number and inducing rotationally forbidden, ΔJ=±2 and ±3 transitions. The hyperfine splittings of over 50 rotational transitions covering all 7 spin components of both states were analyzed and fitted by least squares, allowing the accurate determination of 14 different hyperfine parameters. Using single electronic configurations to describe the A 7Π and X 7Σ+ states and Herman-Skillman atomic radial wave functions to represent the molecular orbitals, we calculated a priori values for the 55Mn and 1H hyperfine parameters which agree closely with experiment. We show that the five high-spin coupled Mn 3d electrons do not contribute to the manganese hyperfine structure but are responsible for the observed proton magnetic dipolar couplings. Furthermore, the results suggest that the Mn 3d electrons are not significantly involved in bonding and demonstrate that the molecular hyperfine interactions may be quantitatively understood using simple physical interpretations.

Oxygen Isotope Signatures of Biogenic Manganese(III/IV) Oxides

NASA Astrophysics Data System (ADS)

Sutherland, K. M.; Hansel, C. M.; Wankel, S. D.

2015-12-01

Manganese (Mn) oxide minerals are pervasive throughout a number of surface earth environments as rock varnishes, ferromanganese nodules, crusts around deep-sea vents, and cave deposits among many other marine, freshwater, and terrestrial deposits. Mn(III,IV) oxides are also among the strongest sorbents and oxidants in surface earth environments and are crucial to understanding the fate of organic matter in sedimentary environments. The precipitation of Mn oxide minerals proceeds via both abiotic and biotic oxidation pathways, the latter due to the indirect or direct activity of Mn(II)- oxidizing microorganisms, including bacteria and fungi. Although the precipitation of Mn oxides is believed to be primarily controlled by Mn(II)-oxidizing organisms in most surface earth environments, confirmation of this generally held notion has remained illusive and limits our understanding of their formation on Earth and beyond (e.g., Mars). Previous work provided evidence that O atom incorporation by specific Mn oxidation pathways may exhibit unique and predictable isotopic fractionation. In this study, we expand upon this evidence by measuring the oxygen isotope signature of several biogenic and abiogenic Mn oxide minerals synthesized under a range of oxygen-18 labeled water. These results allow us to determine the relative amount oxygen atoms derived from water and molecular oxygen that are incorporated in the oxide and shed light on corresponding isotope fractionation factors. Additionally, we show that, once precipitated, Mn oxide isotope signatures are robust with respect to aqueous oxygen isotope exchange. The study provides a foundation on which to study and interpret Mn oxides in natural environments and determine which environmental controls may govern Mn(II) oxidation.

3D Polymer Hydrogel for High-Performance Atomic Fe and Mn Catalysts for Oxygen Reduction in Challenging Acids

NASA Astrophysics Data System (ADS)

Qiao, Zhi

Current platinum group metal (PGM)-free carbon nanocomposite catalysts for the oxygen reduction reaction (ORR) in acidic electrolyte often suffer from rapid degradation associated with carbon corrosion due to the use of large amount of the amorphoous carbon black supports. Here, we developed a new concept of using freestanding 3D hydrogel to design support-free Fe-N-C catalysts. A 3D polyaniline (PANI)-based hydrogel approach was used for preparing a new type of single atomic iron site-rich catalyst, which has exhibited exceptionally enhanced activity and stability compared to conventional Fe-N-C catalysts supported on amorphous carbon blacks. The achieved performance metric on the hydrogel PANI-Fe catalysts is one of the best ever reported PGM-free catalysts, reaching a half-wave potential up to 0.83 V vs. RHE and only leaving 30 mV gap with Pt/C catalysts (60mugPt/cm 2) in challenging acidic media. Remarkable ORR stability was accomplished as well on the same catalyst evidenced by using harsh potential cycling tests. The well dispersion of atomic iron into partially graphitized carbon, featured with dominance of micropores and porous network structures, is capable of accommodating increased number of active sites, strengthening local bonding among iron, nitrogen and carbon, and facilitating mass transfer. On the other hand, in order to decrease the produced Fenton reagent, which will oxidize the proton exchange membrane and ionomer in membrane electrode assembly (MEA), we produce Mn-based catalysts by this novel hydrogel method. This is the first time that Mn-based catalysts can show such outstanding performance in acid media, whose half-wave potential is up to 0.80 V vs. RHE. The work related to the performance improvement is still in processing. We believe the 3D polymer hydrogel approach would be a new pathway to advance PGM-free catalysts.

Spin coherence in a Mn3 single-molecule magnet

NASA Astrophysics Data System (ADS)

Abeywardana, Chathuranga; Mowson, Andrew M.; Christou, George; Takahashi, Susumu

2016-01-01

Spin coherence in single crystals of the spin S = 6 single-molecule magnet (SMM) [Mn3O(O2CEt)3(mpko)3]+ (abbreviated Mn3) has been investigated using 230 GHz electron paramagnetic resonance spectroscopy. Coherence in Mn3 was uncovered by significantly suppressing dipolar contribution to the decoherence with complete spin polarization of Mn3 SMMs. The temperature dependence of spin decoherence time (T2) revealed that the dipolar decoherence is the dominant source of decoherence in Mn3 and T2 can be extended up to 267 ns by quenching the dipolar decoherence.

Thermally activated decomposition of (Ga,Mn)As thin layer at medium temperature post growth annealing

NASA Astrophysics Data System (ADS)

Melikhov, Y.; Konstantynov, P.; Domagala, J.; Sadowski, J.; Chernyshova, M.; Wojciechowski, T.; Syryanyy, Y.; Demchenko, I. N.

2016-05-01

The redistribution of Mn atoms in Ga1-xMnxAs layer during medium-temperature annealing, 250-450 oC, by Mn K-edge X-ray absorption fine structure (XAFS) recorded at ALBA facility, was studied. For this purpose Ga1-xMnxAs thin layer with x=0.01 was grown on AlAs buffer layer deposited on GaAs(100) substrate by molecular beam epitaxy (MBE) followed by annealing. The examined layer was detached from the substrate using a “lift-off” procedure in order to eliminate elastic scattering in XAFS spectra. Fourier transform analysis of experimentally obtained EXAFS spectra allowed to propose a model which describes a redistribution/diffusion of Mn atoms in the host matrix. Theoretical XANES spectra, simulated using multiple scattering formalism (FEFF code) with the support of density functional theory (WIEN2k code), qualitatively describe the features observed in the experimental fine structure.

Chemical composition of individual aerosol particles in workplace air during production of manganese alloys.

PubMed

Gunst, S; Weinbruch, S; Wentzel, M; Ortner, H M; Skogstad, A; Hetland, S; Thomassen, Y

2000-02-01

Aerosol particle samples were collected at ELKEM ASA ferromanganese (FeMn) and silicomanganese (SiMn) smelters at Porsgrunn, Norway, during different production steps: raw material mixing, welding of protective steel casings, tapping of FeMn and slag, crane operation moving the ladles with molten metal, operation of the Metal Oxygen Refinement (MOR) reactor and casting of SiMn. Aerosol fractions were assessed for the analysis of the bulk elemental composition as well as for individual particle analysis. The bulk elemental composition was determined by inductively coupled plasma atomic emission spectrometry. For individual particle analysis, an electron microprobe was used in combination with wavelength-dispersive techniques. Most particles show a complex composition and cannot be attributed to a single phase. Therefore, the particles were divided into six groups according to their chemical composition: Group I, particles containing mainly metallic Fe and/or Mn; Group II, slag particles containing mainly Fe and/or Mn oxides; Group III, slag particles consisting predominantly of oxidized flux components such as Si, Al, Mg, Ca, Na and K; Group IV, particles consisting mainly of carbon; Group V, mixtures of particles from Groups II, III and IV; Group VI, mixtures of particles from Groups II and III. In raw material mixing, particles originating from the Mn ores were mostly found. In the welding of steel casings, most particles were assigned to Group II, Mn and Fe oxides. During the tapping of slag and metal, mostly slag particles from Group III were found (oxides of the flux components). During movement of the ladles, most particles came from Group II. At the MOR reactor, most of the particles belonged to the slag phase consisting of the flux components (Group III). The particles collected during the casting of SiMn were mainly attributed to the slag phase (Groups III and V). Due to the compositional complexity of the particles, toxicological investigations on the kinetics of pure compounds may not be easily associated with the results of this study.

A DFT study of the stability of SIAs and small SIA clusters in the vicinity of solute atoms in Fe

NASA Astrophysics Data System (ADS)

Becquart, C. S.; Ngayam Happy, R.; Olsson, P.; Domain, C.

2018-03-01

The energetics, defect volume and magnetic properties of single SIAs and small SIA clusters up to size 6 have been calculated by DFT for different configurations like the parallel 〈110〉 dumbbell, the non parallel 〈110〉 dumbbell and the C15 structure. The most stable configurations of each type have been further analyzed to determine the influence on their stability of various solute atoms (Ti, V, Cr, Mn, Co, Ni, Cu, Mo, W, Pd, Al, Si, P), relevant for steels used under irradiation. The results show that the presence of solute atoms does not change the relative stability order among SIA clusters. The small SIA clusters investigated can bind to both undersized and oversized solutes. Several descriptors have been considered to derive interesting trends from results. It appears that the local atomic volume available for the solute is the main physical quantity governing the binding energy evolution, whatever the solute type (undersized or oversized) and the cluster configuration (size and type).

First Principles Study on the CO Oxidation on Mn-Embedded Divacancy Graphene

PubMed Central

Jiang, Quanguo; Zhang, Jianfeng; Ao, Zhimin; Huang, Huajie; He, Haiyan; Wu, Yuping

2018-01-01

The CO oxidation mechanism on graphene with divacancy (DG) embedded with transition metal from Sc to Zn has been studied by using first principles calculations. The results indicate that O2 molecule is preferentially adsorbed on Sc, Ti, V, Cr, Mn, and Fe-DG, which can avoid the CO poisoning problem that many catalysts facing and is beneficial to the CO oxidation progress. Further study indicates that Mn-DG shows the best catalytic properties for CO oxidation with consideration of both Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) oxidation mechanisms. Along the ER mechanism, the reaction energy barrier for the first step (CO free + O2 pre-adsorbed → OOCO) is 0.96 eV. Along the LH mechanism, the energy barrier for the rate limiting step (CO adsorbed + O2 adsorbed → OOCO) is only 0.41 eV, indicating that the CO oxidation on Mn-DG will occur along LH mechanism. The Hirshfeld charge distributions of O2 and CO molecules is tuned by the embedded Mn atom, and the charge transfer from the embedded Mn atom to the adsorbed molecules plays an important role for the CO oxidation. The result shows that the Mn-embedded divacancy graphene is a noble-metal free and efficient catalyst for CO oxidation at low temperature.

Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity

DOE PAGES

Leto, Domenick F.; Massie, Allyssa A.; Rice, Derek B.; ...

2016-11-01

The mononuclear Mn(IV)-oxo complex [Mn IV(O)(N4py)] 2+, where N4py is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine, we propose to attack C–H bonds by an excited-state reactivity pattern [Cho, K.-B.; Shaik, S.; Nam, W. J. Phys. Chem. Lett. 2012, 3, 2851-2856 (DOI: 10.1021/jz301241z)]. In this model, a 4E excited state is utilized to provide a lower-energy barrier for hydrogen-atom transfer. This proposal is intriguing, as it offers both a rationale for the relatively high hydrogen-atom-transfer reactivity of [Mn IV(O)(N4py)] 2+ and a guideline for creating more reactive complexes through ligand modification. Here we employ a combination of electronic absorption and variable-temperature magnetic circularmore » dichroism (MCD) spectroscopy to experimentally evaluate this excited-state reactivity model. Using these spectroscopic methods, in conjunction with time-dependent density functional theory (TD-DFT) and complete-active space self-consistent-field calculations (CASSCF), we define the ligand-field and charge-transfer excited states of [MnIV(O)(N4py)]2+. Through a graphical analysis of the signs of the experimental C-term MCD signals, we unambiguously assign a low-energy MCD feature of [Mn IV(O)(N4py)] 2+ as the 4E excited state predicted to be involved in hydrogen-atom-transfer reactivity. The CASSCF calculations predict enhanced Mn III-oxyl character on the excited-state 4E surface, consistent with previous DFT calculations. Potential-energy surfaces, developed using the CASSCF methods, are used to determine how the energies and wave functions of the ground and excited states evolved as a function of Mn=O distance. Furthermore, the unique insights into ground- and excited-state electronic structure offered by these spectroscopic and computational studies are harmonized with a thermodynamic model of hydrogen-atom-transfer reactivity, which predicts a correlation between transition-state barriers and driving force« less

Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leto, Domenick F.; Massie, Allyssa A.; Rice, Derek B.

The mononuclear Mn(IV)-oxo complex [Mn IV(O)(N4py)] 2+, where N4py is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine, we propose to attack C–H bonds by an excited-state reactivity pattern [Cho, K.-B.; Shaik, S.; Nam, W. J. Phys. Chem. Lett. 2012, 3, 2851-2856 (DOI: 10.1021/jz301241z)]. In this model, a 4E excited state is utilized to provide a lower-energy barrier for hydrogen-atom transfer. This proposal is intriguing, as it offers both a rationale for the relatively high hydrogen-atom-transfer reactivity of [Mn IV(O)(N4py)] 2+ and a guideline for creating more reactive complexes through ligand modification. Here we employ a combination of electronic absorption and variable-temperature magnetic circularmore » dichroism (MCD) spectroscopy to experimentally evaluate this excited-state reactivity model. Using these spectroscopic methods, in conjunction with time-dependent density functional theory (TD-DFT) and complete-active space self-consistent-field calculations (CASSCF), we define the ligand-field and charge-transfer excited states of [MnIV(O)(N4py)]2+. Through a graphical analysis of the signs of the experimental C-term MCD signals, we unambiguously assign a low-energy MCD feature of [Mn IV(O)(N4py)] 2+ as the 4E excited state predicted to be involved in hydrogen-atom-transfer reactivity. The CASSCF calculations predict enhanced Mn III-oxyl character on the excited-state 4E surface, consistent with previous DFT calculations. Potential-energy surfaces, developed using the CASSCF methods, are used to determine how the energies and wave functions of the ground and excited states evolved as a function of Mn=O distance. Furthermore, the unique insights into ground- and excited-state electronic structure offered by these spectroscopic and computational studies are harmonized with a thermodynamic model of hydrogen-atom-transfer reactivity, which predicts a correlation between transition-state barriers and driving force« less

Major and trace element concentrations in samples from 72275 and 72255. [chemical composition of lunar rocks

NASA Technical Reports Server (NTRS)

Haskin, L. A.; Blanchard, D. P.; Korotev, R.; Jacobs, J. W.; Brannon, J. A.; Herrmann, A. G.

1974-01-01

Analytical data have been obtained for Co, Sc, Hf, Zn, Cr, Ga, Rb, Cs, Ni, major elements, and rare earth elements in eight samples from boulder 1. The data for trace elements were obtained by radiochemical neutron activation analysis. Major elements, except Na and Mn, were obtained by atomic absorption spectral photometry. Values for Na and Mn were obtained by neutron activation analysis of the same powder that was later dissolved to provide the atomic absorption analyses.

[Determination of metal elements in Achyranthis bidentatae radix from various habitats].

PubMed

Tu, Wan-Qian; Zhang, Liu-Ji

2011-12-01

To establish an atomic absorption spectrometry method for determination of the contents of metal elements in Achyranthis Bidentatae Radix and analyze 21 batches of samples from different areas. Fe, Mn, Ca, Mg, K, Zn and Cu were detected by atomic absorption spectrometry with hydrogen flame detector, Pb, As and Cd were detected by graphite furnace atomic absorption, Hg was detected by cold atomic absorption. The heavy metal contents met the requirement of Chinese Pharmacopoeia. The contents of K, Mg, Cu and Mn in the samples of geo-authentic areas were higher,while the contents of Fe, Zn, Hg and Pb in the samples of non-authentic areas were higher. This method is sample, accurate, repeatable and could be used to evaluate the quality of Achyranthis Bidentatae Radix.

Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Y.; Gottwald, T.; Mattolat, C.

We have demonstrated three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d 54s5s f 6S 5/2 level at 49 415.35 cm -1, while Rydberg transitions were reached from the 3d 54s4d e 6D 9/2,7/2,5/2) levels at around 47 210 cm -1. Analyses of the strong Rydberg transitions associated with the 3d 54s4d e 6D 7/2 lower level indicate that they belong to the dipole-allowed 4dmore » → nf 6F° 9/2,7/2,5/2 series converging to the 3d 54s 7S 3 ground state of Mn II. From this series, an ionization potential of 59 959.56 ± 0.01 cm -1 is obtained for Mn. At high ion source temperatures the semi-forbidden 4d → nf 8 F°9/2,7/2,5/2 series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.« less

Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers

DOE PAGES

Liu, Y.; Gottwald, T.; Mattolat, C.; ...

2015-05-08

We have demonstrated three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti: sapphire lasers. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d 54s5s f 6S 5/2 level at 49 415.35 cm -1, while Rydberg transitions were reached from the 3d 54s4d e 6D 9/2,7/2,5/2) levels at around 47 210 cm -1. Analyses of the strong Rydberg transitions associated with the 3d 54s4d e 6D 7/2 lower level indicate that they belong to the dipole-allowed 4dmore » → nf 6F° 9/2,7/2,5/2 series converging to the 3d 54s 7S 3 ground state of Mn II. From this series, an ionization potential of 59 959.56 ± 0.01 cm -1 is obtained for Mn. At high ion source temperatures the semi-forbidden 4d → nf 8 F°9/2,7/2,5/2 series was also observed. The overall ionization efficiency for Mn has been measured to be about 0.9% when using the strong AI transition in the third excitation step and 0.3% when employing an intense Rydberg transition. Experimental data indicate that the ionization efficiency was limited by the interaction of Mn atoms with ion source materials at high temperatures.« less

Crystal structure of tetra­aqua­bis­(pyrimidin-1-ium-4,6-diolato-κO 4)manganese(II)

PubMed Central

Shennara, Khaled A.

2017-01-01

The MnII ion in the structure of the mononuclear title compound, [Mn(C4H3N2O2)2(H2O)4], is situated on an inversion center and is coordinated by two O atoms from two deprotonated 4,6-di­hydroxy­pyrimidine ligands and by four O atoms from water mol­ecules giving rise to a slightly distorted octa­hedral coordination sphere. The complex includes an intra­molecular hydrogen bond between an aqua ligand and the non-protonated N ring atom. The extended structure is stabilized by inter­molecular hydrogen bonds between aqua ligands, by hydrogen bonds between N and O atoms of the ligands of adjacent mol­ecules, and by hydrogen bonds between aqua ligands and the non-coordinating O atom of an adjacent mol­ecule. PMID:28435734

High-energy X-ray powder diffraction and atomic-pair distribution-function studies of charged/discharged structures in carbon-hybridized Li2MnSiO4 nanoparticles as a cathode material for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Moriya, Maki; Miyahara, Masahiko; Hokazono, Mana; Sasaki, Hirokazu; Nemoto, Atsushi; Katayama, Shingo; Akimoto, Yuji; Hirano, Shin-ichi; Ren, Yang

2014-10-01

The stable cycling performance with a high discharge capacity of ∼190 mAh g-1 in a carbon-hybridized Li2MnSiO4 nanostructured powder has prompted an experimental investigation of the charged/discharged structures using synchrotron-based and laboratory-based X-rays and atomic-pair distribution-function (PDF) analyses. A novel method of in-situ spray pyrolysis of a precursor solution with glucose as a carbon source enabled the successful synthesis of the carbon-hybridized Li2MnSiO4 nanoparticles. The XRD patters of the discharged (lithiated) samples exhibit a long-range ordered structure characteristic of the (β) Li2MnSiO4 crystalline phase (space group Pmn21) which dissipates in the charged (delithiated) samples. However, upon discharging the long-range ordered structure recovers in each cycle. The disordered structure, according to the PDF analysis, is mainly due to local distortions of the MnO4 tetrahedra which show a mean Mn-O nearest neighbor distance shorter than that of the long-range ordered phase. These results corroborate the notion of the smaller Mn3+/Mn4+ ionic radii in the Li extracted phase versus the larger Mn2+ ionic radius in Li inserted phase. Thus Li extraction/insertion drives the fluctuation between the disordered and the long-range ordered structures.

Hierarchically porous MnO2 microspheres doped with homogeneously distributed Fe3O4 nanoparticles for supercapacitors.

PubMed

Zhu, Jian; Tang, Shaochun; Xie, Hao; Dai, Yuming; Meng, Xiangkang

2014-10-22

Hierarchically porous yet densely packed MnO2 microspheres doped with Fe3O4 nanoparticles are synthesized via a one-step and low-cost ultrasound assisted method. The scalable synthesis is based on Fe(2+) and ultrasound assisted nucleation and growth at a constant temperature in a range of 25-70 °C. Single-crystalline Fe3O4 particles of 3-5 nm in diameter are homogeneously distributed throughout the spheres and none are on the surface. A systematic optimization of reaction parameters results in isolated, porous, and uniform Fe3O4-MnO2 composite spheres. The spheres' average diameter is dependent on the temperature, and thus is controllable in a range of 0.7-1.28 μm. The involved growth mechanism is discussed. The specific capacitance is optimized at an Fe/Mn atomic ratio of r = 0.075 to be 448 F/g at a scan rate of 5 mV/s, which is nearly 1.5 times that of the extremely high reported value for MnO2 nanostructures (309 F/g). Especially, such a structure allows significantly improved stability at high charging rates. The composite has a capacitance of 367.4 F/g at a high scan rate of 100 mV/s, which is 82% of that at 5 mV/s. Also, it has an excellent cycling performance with a capacitance retention of 76% after 5000 charge/discharge cycles at 5 A/g.

X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi{sub 2}Se{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins-McIntyre, L. J.; Watson, M. D.; Zhang, S. L.

2014-12-15

We report the growth of Mn-doped Bi{sub 2}Se{sub 3} thin films by molecular beam epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ∼7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mnmore » is observed with increasing doping concentration. A magnetic moment of 5.1 μ{sub B}/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 μ{sub B}/Mn from surface-sensitive XMCD. At ∼2.5 K, XMCD at the Mn L{sub 2,3} edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.« less

In-plane/out-of-plane disorder influence on the magnetic anisotropy of Fe{sub 1−y}Mn{sub y}Pt-L1{sub 0} bulk alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuadrado, R.; Catalan Institute of Nanoscience and Nanotechnology; Liu, Kai

2016-03-21

The random substitution of a non-magnetic species instead of Fe atoms in FePt-L1{sub 0} bulk alloy will permit to tune the magnetic anisotropy energy of this material. We have performed by means of first principles calculations a study of Fe{sub 1−y}Mn{sub y}Pt-L1{sub 0} (y = 0.0, 0.08, 0.12, 0.17, 0.22, and 0.25) bulk alloy for a fixed Pt concentration when the Mn species have ferro-/antiferromagnetic (FM,AFM) alignment at the same(different) atomic plane(s). This substitution will promote several in-plane lattice values for a fixed amount of Mn. Charge hybridization will change compared to the FePt-L1{sub 0} bulk due to this lattice variation leadingmore » to a site resolved magnetic moment modification. We demonstrate that this translates into a total magnetic anisotropy reduction for the AFM phase and an enhancement for the FM alignment. Several geometric configurations were taken into account for a fixed Mn concentration because of different possible Mn positions in the simulation cell.« less

Heteroepitaxial Growth of Ferromagnetic MnSb(0001) Films on Ge/Si(111) Virtual Substrates.

PubMed

Burrows, Christopher W; Dobbie, Andrew; Myronov, Maksym; Hase, Thomas P A; Wilkins, Stuart B; Walker, Marc; Mudd, James J; Maskery, Ian; Lees, Martin R; McConville, Christopher F; Leadley, David R; Bell, Gavin R

2013-11-06

Molecular beam epitaxial growth of ferromagnetic MnSb(0001) has been achieved on high quality, fully relaxed Ge(111)/Si(111) virtual substrates grown by reduced pressure chemical vapor deposition. The epilayers were characterized using reflection high energy electron diffraction, synchrotron hard X-ray diffraction, X-ray photoemission spectroscopy, and magnetometry. The surface reconstructions, magnetic properties, crystalline quality, and strain relaxation behavior of the MnSb films are similar to those of MnSb grown on GaAs(111). In contrast to GaAs substrates, segregation of substrate atoms through the MnSb film does not occur, and alternative polymorphs of MnSb are absent.

Graphene nanoplate-MnO2 composites for supercapacitors: a controllable oxidation approach.

PubMed

Huang, Huajie; Wang, Xin

2011-08-01

Graphene nanoplate-MnO(2) composites have been synthesized by oxidising part of the carbon atoms in the framework of graphene nanoplates at ambient temperature. The composites were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). It was found that the oxidation extent of the carbon atoms in the graphene framework in these composites was dependent on the reaction time, which also influenced their microstructure, morphology and electrochemical properties. Compared with MnO(2) nanolamellas, the nanocomposite prepared with a reaction time of 3 h reveals better electrochemical properties as a supercapacitor electrode material. This journal is © The Royal Society of Chemistry 2011

Atomic data on inelastic processes in low-energy manganese-hydrogen collisions

NASA Astrophysics Data System (ADS)

Belyaev, Andrey K.; Voronov, Yaroslav V.

2017-10-01

Aims: The aim of this paper is to calculate cross sections and rate coefficients for inelastic processes in low-energy Mn + H and Mn+ + H- collisions, especially, for processes with high and moderate rate coefficients. These processes are required for non-local thermodynamic equilibrium (non-LTE) modeling of manganese spectra in cool stellar atmospheres, and in particular, for metal-poor stars. Methods: The calculations of the cross sections and the rate coefficients were performed by means of the quantum model approach within the framework of the Born-Oppenheimer formalism, that is, the asymptotic semi-empirical method for the electronic MnH molecular structure calculation followed by the nonadiabatic nuclear dynamical calculation by means of the multichannel analytic formulas. Results: The cross sections and the rate coefficients for low-energy inelastic processes in manganese-hydrogen collisions are calculated for all transitions between 21 low-lying covalent states and one ionic state. We show that the highest values of the cross sections and the rate coefficients correspond to the mutual neutralization processes into the final atomic states Mn(3d54s(7S)5s e 6S), Mn(3d54s(7S)5p y 8P°), Mn(3d54s(7S)5s e 8S), Mn(3d54s(7S)4d e 8D) [the first group], the processes with the rate coefficients (at temperature T = 6000 K) of the values 4.38 × 10-8, 2.72 × 10-8, 1.98 × 10-8, and 1.59 × 10-8 cm3/ s, respectively, that is, with the rate coefficients exceeding 10-8 cm3/ s. The processes with moderate rate coefficients, that is, with values between 10-10 and 10-8 cm3/ s include many excitation, de-excitation, mutual neutralization and ion-pair formation processes. In addition to other processes involving the atomic states from the first group, the processes from the second group include those involving the following atomic states: Mn(3d5(6S)4s4p (1P°) y 6P°), Mn(3d54s(7S)4d e 6D), Mn(3d54s(7S)5p w 6P°), Mn(3d5(4P)4s4p (3P°) y 6D°), Mn(3d5(4G)4s4p (3P°) y 6F°). The processes with the highest and moderate rate coefficients are expected to be important for non-LTE modeling of manganese spectra in stellar atmospheres. Rate coefficients Kif(T) for the excitation, de-excitation, mutual neutralization, and ion-pair formation processes in manganese-hydrogen collisions are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A106

Speciation of Mn(II), Mn(VII) and total manganese in water and food samples by coprecipitation-atomic absorption spectrometry combination.

PubMed

Citak, Demirhan; Tuzen, Mustafa; Soylak, Mustafa

2010-01-15

A speciation procedure based on the coprecipitation of manganese(II) with zirconium(IV) hydroxide has been developed for the investigation of levels of manganese species. The determination of manganese levels was performed by flame atomic absorption spectrometry (FAAS). Total manganese was determined after the reduction of Mn(VII) to Mn(II) by ascorbic acid. The analytical parameters including pH, amount of zirconium(IV), sample volume, etc., were investigated for the quantitative recoveries of manganese(II). The effects of matrix ions were also examined. The recoveries for manganese(II) were in the range of 95-98%. Preconcentration factor was calculated as 50. The detection limit for the analyte ions based on 3 sigma (n=21) was 0.75 microg L(-1) for Mn(II). The relative standard deviation was found to be lower than 7%. The validation of the presented procedure was performed by analysis of certified reference material having different matrices, NIST SRM 1515 (Apple Leaves) and NIST SRM 1568a (Rice Flour). The procedure was successfully applied to natural waters and food samples.

[Variation in soil Mn fractions as affected by long-term manure amendment using atomic absorption spectrophotometer in a typical grassland of inner Mongolia].

PubMed

Fu, Ming-ming; Jiang, Yong; Bai, Yong-fei; Zhang, Yu-ge; Xu, Zhu-wen; Li, Bo

2012-08-01

The effect of sheep manure amendment on soil manganese fractions was conducted in a 11 year experiment at inner Mongolia grassland, using sequential extraction procedure in modified Community Bureau of Reference, and determined by atomic absorption spectrophotometer. Five treatments with dry sheep manure addition rate 0, 50, 250, 750, and 1500 g x m(-2) x yr(-1), respectively, were carried out in this experiment. Results showed that the recovery rate for total Mn was 91.4%-105.9%, as the percentage recovered from the summation of the improved BCR results with aqua regia extractable contents, and it was 97.2%-102.9% from certified soil reference materials. Plant available exchangeable Mn could be enhanced by 47.89%, but reducible and total Mn contents decreased significantly under heavy application of manure at depth of 0-5 cm. The effect of manure amendment on Mn fractions was greater in 0-5 cm than in 5-10 cm soil layer. The results are benefit to micronutrient fractions determination and nutrient management in grassland soils.

Fast Atomic-Scale Chemical Imaging of Crystalline Materials and Dynamic Phase Transformations.

PubMed

Lu, Ping; Yuan, Ren Liang; Ihlefeld, Jon F; Spoerke, Erik David; Pan, Wei; Zuo, Jian Min

2016-04-13

Atomic-scale phenomena fundamentally influence materials form and function that makes the ability to locally probe and study these processes critical to advancing our understanding and development of materials. Atomic-scale chemical imaging by scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) is a powerful approach to investigate solid crystal structures. Inefficient X-ray emission and collection, however, require long acquisition times (typically hundreds of seconds), making the technique incompatible with electron-beam sensitive materials and study of dynamic material phenomena. Here we describe an atomic-scale STEM-EDS chemical imaging technique that decreases the acquisition time to as little as one second, a reduction of more than 100 times. We demonstrate this new approach using LaAlO3 single crystal and study dynamic phase transformation in beam-sensitive Li[Li0.2Ni0.2Mn0.6]O2 (LNMO) lithium ion battery cathode material. By capturing a series of time-lapsed chemical maps, we show for the first time clear atomic-scale evidence of preferred Ni-mobility in LNMO transformation, revealing new kinetic mechanisms. These examples highlight the potential of this approach toward temporal, atomic-scale mapping of crystal structure and chemistry for investigating dynamic material phenomena.

Measurement of atomic Stark parameters of many Mn I and Fe I spectral lines using GMAW process

NASA Astrophysics Data System (ADS)

Zielinska, S.; Pellerin, S.; Dzierzega, K.; Valensi, F.; Musiol, K.; Briand, F.

2010-11-01

The particular character of the welding arc working in pure argon, whose emission spectrum consists of many spectral lines strongly broadened by the Stark effect, has allowed measurement, sometimes for the first time, of the Stark parameters of 15 Mn I and 10 Fe I atomic spectral lines, and determination of the dependence on temperature of normalized Stark broadening in Ne = 1023 m-3 of the 542.4 nm atomic iron line. These results show that special properties of the MIG plasma may be useful in this domain because composition of the wire-electrode may be easily adapted to the needs of an experiment.

Conciliatory Inductive Model Explaining the Origin of Changes in the η(2)-SiH Bond Length Caused by Presence of Strongly Electronegative Atoms X (X = F, Cl) in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] (n = 0-3) Complexes.

PubMed

Jabłoński, Mirosław

2016-06-23

Using three theoretical methods, QTAIM, IQA, and NCI, we analyze an influence of halogen atoms X (X = F, Cl) substituted at various positions in the -SiH3-nXn group on the charge density distribution within the η(2)-SiH bond and on the SiH bond energies in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes and isolated HSiH3-nXn molecules. It is shown that shortening of the η(2)-SiH bond in Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes should be considered as a normal inductive result of halogenation. This η(2)-SiH bond's compression may, however, be overcome by a predominant elongation resulting from a contingent presence of a halogen atom at position trans to the η(2)-SiH bond. This trans effect is particularly large for bulky and highly polarizable chlorine. Moreover, peculiar properties of the trans chlorine atom are manifested in several ways. To explain the origin of all the observed changes in both the length and the electron charge distribution of the η(2)-SiH bond in investigated Cp(OC)2Mn[η(2)-H(SiH3-nXn)] complexes a new model, called the Conciliatory Inductive Model, is being proposed.

Atomic Resolution Structural and Chemical Imaging Revealing the Sequential Migration of Ni, Co, and Mn upon the Battery Cycling of Layered Cathode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Pengfei; Zheng, Jianming; Zhang, Ji-Guang

Layered lithium transition metal oxides (LTMO) are promising candidate cathode materials for next generation high energy density lithium ion battery. The challenge for using this category of cathode is the capacity and voltage fading, which is believed to be associated with the layered structure disordering, a process that is initiated from the surface or solid-electrolyte interface and facilitated by transition metal (TM) reduction and oxygen vacancy formation. However, the atomic level dynamic mechanism of such a layered structure disordering is still not fully clear. In this work, utilizing atomic resolution electron energy loss spectroscopy (EELS), we map, for the firstmore » time at atomic scale, the spatial evolution of Ni, Co and Mn in a cycled LiNi1/3M1/3Co1/3O2 layered cathode. In combination with atomic level structural imaging, we discovered the direct correlation of TM ions migration behavior with lattice disordering, featuring the residing of TM ions in the tetrahedral site and a sequential migration of Ni, Co, and Mn upon the increased lattice disordering of the layered structure. This work highlights that Ni ions, though acting as the dominant redox species in many LTMO, are labile to migrate to cause lattice disordering upon battery cycling; while the Mn ions are more stable as compared with Ni and Co and can act as pillar to stabilize layered structure. Direct visualization of the behavior of TM ions during the battery cycling provides insight for designing of cathode with structural stability and correspondingly a superior performance.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Mukhtiyar; Saini, Hardev S.; Thakur, Jyoti

Heusler alloys based thin-films often exhibit a degree of atomic disorder which leads to the lowering of spin polarization in spintronic devices. We present ab-initio calculations of atomic disorder effects on spin polarization and half-metallicity of Mn{sub 2}CoSi inverse Heusler alloy. The five types of disorder in Mn{sub 2}CoSi have been proposed and investigated in detail. The A2{sub a}-type and B2-type disorders destroy the half-metallicity whereas it sustains for all disorders concentrations in DO{sub 3a}- and A2{sub b}-type disorder and for smallest disorder concentration studied in DO{sub 3b}-type disorder. Lower formation energy/atom for A2{sub b}-type disorder than other four disordersmore » in Mn{sub 2}CoSi advocates the stability of this disorder. The total magnetic moment shows a strong dependence on the disorder and the change in chemical environment. The 100% spin polarization even in the presence of disorders explicitly supports that these disorders shall not hinder the use of Mn{sub 2}CoSi inverse Heusler alloy in device applications. - Graphical abstract: Minority-spin gap (E{sub g↓}) and HM gap (E{sub sf}) as a function of concentrations of various possible disorder in Mn{sub 2}CoSi inverse Heusler alloy. The squares with solid line (black color)/dotted line (blue color)/dashed line (red color) reperesents E{sub g↓} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi and the spheres with solid line (black color)/dottedline (blue color)/dashed line (red color) represents E{sub sf} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi. - Highlights: • The DO{sub 3}- and A2-type disorders do not affect the half-metallicity in Mn{sub 2}CoSi. • The B2-type disorder solely destroys half-metallicity in Mn{sub 2}CoSi. • The A2-type disorder most probable to occur out of all three types. • The total spin magnetic moment strongly depends on the disorder concentrations.« less

Photodiodes based in La0.7Sr0.3MnO3/single layer MoS2 hybrid vertical heterostructures

NASA Astrophysics Data System (ADS)

Niu, Yue; Frisenda, Riccardo; Svatek, Simon A.; Orfila, Gloria; Gallego, Fernando; Gant, Patricia; Agraït, Nicolás; Leon, Carlos; Rivera-Calzada, Alberto; Pérez De Lara, David; Santamaria, Jacobo; Castellanos-Gomez, Andres

2017-09-01

The fabrication of artificial materials by stacking of individual two-dimensional (2D) materials is amongst one of the most promising research avenues in the field of 2D materials. Moreover, this strategy to fabricate new man-made materials can be further extended by fabricating hybrid stacks between 2D materials and other functional materials with different dimensionality making the potential number of combinations almost infinite. Among all these possible combinations, mixing 2D materials with transition metal oxides can result especially useful because of the large amount of interesting physical phenomena displayed separately by these two material families. We present a hybrid device based on the stacking of a single layer MoS2 onto a lanthanum strontium manganite (La0.7Sr0.3MnO3) thin film, creating an atomically thin device. It shows a rectifying electrical transport with a ratio of 103, and a photovoltaic effect with V oc up to 0.4 V. The photodiode behaviour arises as a consequence of the different doping character of these two materials. This result paves the way towards combining the efforts of these two large materials science communities.

Modeling of LMM-MVV Auger-Auger Coincidence Spectra From Solids

NASA Astrophysics Data System (ADS)

Sundaramoorthy, R.; Weiss, A. H.; Hulbert, S. L.; Bartynski, R. A.

2006-03-01

Atoms that are highly excited due to the presence of a hole in an inner shell often relax via an Auger transition. This auto-ionizing process results in a final state with two or more holes from an Auger cascade. We present results of the direct measurements of the second and third Auger decays in this sequence. We have measured the Mn MVV Auger spectra from a single-crystal sample of MnO in time coincidence with Auger electrons emitted from prior Mn LMM Auger decays and find these to be much wider than the MVV spectrum measured in time coincidence with M core photoelectron emission. We present a model which attributes the increased energy width of the MVV transitions that follow LMM decays to the rearrangement of ``not so innocent'' bystander hole(s) in the valence band. The energetics of the Auger cascade process are modeled mathematically in terms of correlation integral(s) and convolution integral(s) over the valence band density of states. Comparisons with recent Auger-Auger coincidence studies of Ag and Pd will be made. Acknowledgements: Welch Foundation, NSF DMR98-12628, NSF DMR98-01681, and DOE DE-AC02-98CH10886.

Quantum Dots

NASA Astrophysics Data System (ADS)

Tartakovskii, Alexander

2012-07-01

Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by Lithographic Techniques: III-V Semiconductors and Carbon: 15. Electrically controlling single spin coherence in semiconductor nanostructures Y. Dovzhenko, K. Wang, M. D. Schroer and J. R. Petta; 16. Theory of electron and nuclear spins in III-V semiconductor and carbon-based dots H. Ribeiro and G. Burkard; 17. Graphene quantum dots: transport experiments and local imaging S. Schnez, J. Guettinger, F. Molitor, C. Stampfer, M. Huefner, T. Ihn and K. Ensslin; Part VI. Single Dots for Future Telecommunications Applications: 18. Electrically operated entangled light sources based on quantum dots R. M. Stevenson, A. J. Bennett and A. J. Shields; 19. Deterministic single quantum dot cavities at telecommunication wavelengths D. Dalacu, K. Mnaymneh, J. Lapointe, G. C. Aers, P. J. Poole, R. L. Williams and S. Hughes; Index.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Y. B.; Liu, S. Q.; Zhao, H.

Here, a comprehensive study of the structural and magnetic properties of the Ni 2Mn 1.48Sb 0.52 compound is presente using neutron diffraction and magnetic measurements. It is found that Mn atoms on 4a and 4 sites are ferrimagnetic coupled in the austenitic phase. At 300 K, the magnetic moments of Mn (4a) an Mn (4b) are determined to be 2.72(3) μ B and -2.67(5) μ B, respectively. From 260 K to 4 K, the compound is in martensite phase and the magnetic moments of Mn (2a), Mn (2f), Mn (2b), Mn (2e) at 4 K ar 2.2(5) μ B, 2.3(5)more » μ B, -2.1(5) μ B, and -2.6(5) μ B, respectively.« less

Fourier transform imaging of impurities in the unit cells of crystals: Mn in GaAs

NASA Astrophysics Data System (ADS)

Lee, T.-L.; Bihler, C.; Schoch, W.; Limmer, W.; Daeubler, J.; Thieß, S.; Brandt, M. S.; Zegenhagen, J.

2010-06-01

The lattice sites of Mn in ferromagnetic (Ga,Mn)As thin films were imaged using the x-ray standing wave technique. The model-free images, obtained straightforwardly by Fourier inversion, disclose immediately that the Mn mostly substitutes the Ga with a small fraction residing on minority sites. The images further reveal variations in the Mn concentrations of the different sites upon post-growth treatments. Subsequent model refinement based on the directly reconstructed images resolves with high precision the complete Mn site distributions. It is found that post-growth annealing increases the fraction of substitutional Mn at the expense of interstitial Mn whereas hydrogenation has little influence on the Mn site distribution. Our study offers an element-specific high-resolution imaging approach for accurately determining the detailed site distributions of dilute concentrations of atoms in crystals.

Mild hydrothermal crystal growth of new uranium(IV) fluorides, Na3.13Mg1.43U6F30 and Na2.50Mn1.75U6F30: Structures, optical and magnetic properties

NASA Astrophysics Data System (ADS)

Yeon, Jeongho; Smith, Mark D.; Tapp, Joshua; Möller, Angela; zur Loye, Hans-Conrad

2016-04-01

Two new uranium(IV) fluorides, Na3.13Mg1.43U6F30 (1) and Na2.50Mn1.75U6F30 (2), were synthesized through an in situ mild hydrothermal route, and were structurally characterized by single crystal X-ray diffraction. The compounds exhibit complex crystal structures composed of corner- or edge-shared UF9 and MF6 (M=Mg, Mn) polyhedra, forming hexagonal channels in the three-dimensional framework, in which ordered or disordered divalent metal and sodium atoms reside. The large hexagonal voids contain the nearly regular M(II)F6 octahedra and sodium ions, whereas the small hexagonal cavities include M(II) and sodium ions on a mixed-occupied site. Magnetic susceptibility measurements yielded effective magnetic moments of 8.36 and 11.6 μB for 1 and 2, respectively, confirming the presence and oxidation states of U(IV) and Mn(II). The large negative Weiss constants indicate the spin gap between a triplet and a singlet state in the U(IV). Magnetization data as a function of applied fields revealed that 2 exhibits paramagnetic behavior due to the nonmagnetic singlet ground state of U(IV) at low temperature. UV-vis diffuse reflectance and X-ray photoelectron spectroscopy data were also analyzed.

The A{sup 2+}Mn{sub 5}(SO{sub 4}){sub 6} family of triangular lattice, ferrimagnetic sulfates

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, D.V., E-mail: barelytone@gmail.co; McQueen, T.M.; Posen, I.D.

2009-06-15

A new family of anhydrous sulfates, A{sup 2+}Mn{sub 5}(SO{sub 4}){sub 6} (A=Pb, Ba, Sr) is reported. The crystal structures of PbMn{sub 5}(SO{sub 4}){sub 6} and SrMn{sub 5}(SO{sub 4}){sub 6} are solved by powder X-ray and neutron diffraction. BaMn{sub 5}(SO{sub 4}){sub 6} is isostructural. PbMn{sub 5}(SO{sub 4}){sub 6} crystallizes with P3-bar symmetry and unit cell parameters of a=14.551(1) A and c=7.535(1) A. The structure has rich features, including dimers of face-sharing MnO{sub 6} octahedra, and two complementary triangular layers of Mn atoms. All compounds undergo a magnetic ordering transition at 10 K, below which, the magnetic susceptibility of the compounds variesmore » systematically with the radius of the non-magnetic cation. Low temperature neutron diffraction shows that the complementary triangular layers result in a ferrimagnet with a net moment corresponding to one high spin Mn{sup 2+} per unit cell, correlating well with the magnetization data. The non-magnetic variant PbMg{sub 5}(SO{sub 4}){sub 6} is also reported. - Graphical abstract: A new family sulfates, A{sup 2+}Mn{sub 5}(SO{sub 4}){sub 6} (A=Pb, Ba, Sr) is reported. Structures are solved by powder neutron diffraction. PbMn{sub 5}(SO{sub 4}){sub 6} is trigonal with lattice parameters of a=14.551(1) A and c=7.535(1) A. The structure has dimers of face-sharing MnO{sub 6} octahedra, and two complementary triangular layers of Mn atoms that result in a ferrimagnet. All compounds magnetically order at 10 K. Low field susceptibility varies systematically with non-magnetic cation radius.« less

Spectral Interferences Manganese (Mn) - Europium (Eu) Lines in X-Ray Fluorescence Spectrometry Spectrum

NASA Astrophysics Data System (ADS)

Tanc, Beril; Kaya, Mustafa; Gumus, Lokman; Kumral, Mustafa

2016-04-01

X-ray fluorescence (XRF) spectrometry is widely used for quantitative and semi quantitative analysis of many major, minor and trace elements in geological samples. Some advantages of the XRF method are; non-destructive sample preparation, applicability for powder, solid, paste and liquid samples and simple spectrum that are independent from chemical state. On the other hand, there are some disadvantages of the XRF methods such as poor sensitivity for low atomic number elements, matrix effect (physical matrix effects, such as fine versus course grain materials, may impact XRF performance) and interference effect (the spectral lines of elements may overlap distorting results for one or more elements). Especially, spectral interferences are very significant factors for accurate results. In this study, semi-quantitative analyzed manganese (II) oxide (MnO, 99.99%) was examined. Samples were pelleted and analyzed with XRF spectrometry (Bruker S8 Tiger). Unexpected peaks were obtained at the side of the major Mn peaks. Although sample does not contain Eu element, in results 0,3% Eu2O3 was observed. These result can occur high concentration of MnO and proximity of Mn and Eu lines. It can be eliminated by using correction equation or Mn concentration can confirm with other methods (such as Atomic absorption spectroscopy). Keywords: Spectral Interferences; Manganese (Mn); Europium (Eu); X-Ray Fluorescence Spectrometry Spectrum.

Electron induced surface reactions of (η5-C5H5)Fe(CO)2Mn(CO)5, a potential heterobimetallic precursor for focused electron beam induced deposition (FEBID).

PubMed

Unlu, Ilyas; Spencer, Julie A; Johnson, Kelsea R; Thorman, Rachel M; Ingólfsson, Oddur; McElwee-White, Lisa; Fairbrother, D Howard

2018-03-14

Electron-induced surface reactions of (η 5 -C 5 H 5 )Fe(CO) 2 Mn(CO) 5 were explored in situ under ultra-high vacuum conditions using X-ray photoelectron spectroscopy and mass spectrometry. The initial step involves electron-stimulated decomposition of adsorbed (η 5 -C 5 H 5 )Fe(CO) 2 Mn(CO) 5 molecules, accompanied by the desorption of an average of five CO ligands. A comparison with recent gas phase studies suggests that this precursor decomposition step occurs by a dissociative ionization (DI) process. Further electron irradiation decomposes the residual CO groups and (η 5 -C 5 H 5 , Cp) ligand, in the absence of any ligand desorption. The decomposition of CO ligands leads to Mn oxidation, while electron stimulated Cp decomposition causes all of the associated carbon atoms to be retained in the deposit. The lack of any Fe oxidation is ascribed to either the presence of a protective carbonaceous matrix around the Fe atoms created by the decomposition of the Cp ligand, or to desorption of both CO ligands bound to Fe in the initial decomposition step. The selective oxidation of Mn in the absence of any Fe oxidation suggests that the fate of metal atoms in mixed-metal precursors for focused electron beam induced deposition (FEBID) will be sensitive to the nature and number of ligands in the immediate coordination sphere. In related studies, the composition of deposits created from (η 5 -C 5 H 5 )Fe(CO) 2 Mn(CO) 5 under steady state deposition conditions, representative of those used to create nanostructures in electron microscopes, were measured and found to be qualitatively consistent with predictions from the UHV surface science studies.

MN15-L: A New Local Exchange-Correlation Functional for Kohn-Sham Density Functional Theory with Broad Accuracy for Atoms, Molecules, and Solids.

PubMed

Yu, Haoyu S; He, Xiao; Truhlar, Donald G

2016-03-08

Kohn-Sham density functional theory is widely used for applications of electronic structure theory in chemistry, materials science, and condensed-matter physics, but the accuracy depends on the quality of the exchange-correlation functional. Here, we present a new local exchange-correlation functional called MN15-L that predicts accurate results for a broad range of molecular and solid-state properties including main-group bond energies, transition metal bond energies, reaction barrier heights, noncovalent interactions, atomic excitation energies, ionization potentials, electron affinities, total atomic energies, hydrocarbon thermochemistry, and lattice constants of solids. The MN15-L functional has the same mathematical form as a previous meta-nonseparable gradient approximation exchange-correlation functional, MN12-L, but it is improved because we optimized it against a larger database, designated 2015A, and included smoothness restraints; the optimization has a much better representation of transition metals. The mean unsigned error on 422 chemical energies is 2.32 kcal/mol, which is the best among all tested functionals, with or without nonlocal exchange. The MN15-L functional also provides good results for test sets that are outside the training set. A key issue is that the functional is local (no nonlocal exchange or nonlocal correlation), which makes it relatively economical for treating large and complex systems and solids. Another key advantage is that medium-range correlation energy is built in so that one does not need to add damped dispersion by molecular mechanics in order to predict accurate noncovalent binding energies. We believe that the MN15-L functional should be useful for a wide variety of applications in chemistry, physics, materials science, and molecular biology.

Unusual stoichiometry control in the atomic layer deposition of manganese borate films from manganese bis(tris(pyrazolyl)borate) and ozone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klesko, Joseph P.; Bellow, James A.; Saly, Mark J.

The atomic layer deposition (ALD) of films with the approximate compositions Mn{sub 3}(BO{sub 3}){sub 2} and CoB{sub 2}O{sub 4} is described using MnTp{sub 2} or CoTp{sub 2} [Tp = tris(pyrazolyl)borate] with ozone. The solid state decomposition temperatures of MnTp{sub 2} and CoTp{sub 2} are ∼370 and ∼340 °C, respectively. Preparative-scale sublimations of MnTp{sub 2} and CoTp{sub 2} at 210 °C/0.05 Torr afforded >99% recoveries with <0.1% nonvolatile residues. Self-limited ALD growth was demonstrated at 325 °C for MnTp{sub 2} or CoTp{sub 2} with ozone as the coreactant. The growth rate for the manganese borate process was 0.19 Å/cycle within the ALD window of 300–350 °C. The growth ratemore » for the cobalt borate process was 0.39–0.42 Å/cycle at 325 °C. X-ray diffraction of the as-deposited films indicated that they were amorphous. Atomic force microscopy of 35–36 nm thick manganese borate films grown within the 300–350 °C ALD window showed root mean square surface roughnesses of 0.4–0.6 nm. Film stoichiometries were assessed by x-ray photoelectron spectroscopy and time of flight-elastic recoil detection analysis. The differing film stoichiometries obtained from the very similar precursors MnTp{sub 2} and CoTp{sub 2} are proposed to arise from the oxidizing ability of the intermediate high valent manganese oxide layers and lack thereof for cobalt.« less

The development of a wide field UV imager for planetary space missions

NASA Astrophysics Data System (ADS)

Molyneux, Philippa Mary

2012-03-01

This thesis describes experimental work carried out on bilayer manganites with the general composition R{2-2x}A{1+2x}Mn2O7, where R is a trivalent rare earth cation and A is a divalent alkaline-earth cation. Experiments have been carried out primarily using Scanning Tunnelling Microscopy (STM) and Spectroscopy (STS); bulk electrical transport, MPMS and LEED measurements have also been made. The primary results are obtained from single crystal samples of PrSr2Mn2O7. This compound provides a surface suitable for STM study when cleaved at low temperature in ultra-high vacuum: atomic resolution can be readily achieved. The expected square lattice is observed, together with a larger scale surface modulation which is not presently explained. In some areas of the PrSr2Mn2O7 surface a population of adatoms and surface vacancies is observed. STS data indicate that adatoms carry a negative charge compared to the rest of the surface, and vacancies a positive charge: the adatoms and vacancies are interpreted as oxygen adatoms and oxygen vacancies. A detailed study is made of the oxygen adatoms and vacancies: this is believed to be the firrst such study made on a manganite surface. Oxygen adatoms on the PrSr2Mn2O7 surface are found to be mobile: hopping and adatom-vacancy recombination are observed. Additional results are reported on the layered manganite compound La{2-2x}Sr{1+2x}Mn2O7 at a range of cation doping x. For the LaSr2Mn2O7 compound (x = 0.5) spectroscopic variation has been identified in a variable-temperature STS survey. This indicates the coexistence of two surface electronic phases, possibly the charge ordered and antiferromagnetic phases.

Anomalous behavior of the magnetic hyperfine field at 140Ce impurities at La sites in LaMnSi2

NASA Astrophysics Data System (ADS)

Domienikan, C.; Bosch-Santos, B.; Cabrera-Pasca, G. A.; Saxena, R. N.; Carbonari, A. W.

2018-05-01

Magnetic hyperfine field has been measured in the orthorhombic intermetallic compound LaMnSi2 with perturbed angular correlation (PAC) spectroscopy using radioactive 140La(140Ce) nuclear probes. Magnetization measurements were also carried out in this compound with MPSM-SQUID magnetometer. Samples of LaMnSi2 compound were prepared by arc melting the component metals with high purity under argon atmosphere followed by annealing at 1000°C for 60 h under helium atmosphere and quenching in water. X-ray analysis confirmed the samples to be in a single phase with correct crystal structure expected for LaMnSi2 compound. The radioactive 140La (T1/2 = 40 h) nuclei were produced by direct irradiation of the sample with neutrons in the IEA-R1 nuclear research reactor at IPEN with a flux of ˜ 1013 n cm-2s-1 for about 3 - 4 min. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. Temperature dependence of the hyperfine field, Bhf was found to be anomalous. A modified two-state model explained this anomalous behavior where the effective magnetic hyperfine field at 140Ce is believed to have two contributions, one from the unstable localized spins at Ce impurities and another from the magnetic Mn atoms of the host. The competition of these two contributions explains the anomalous behavior observed for the temperature dependence of the magnetic hyperfine field at 140Ce. The ferromagnetic transition temperature (TC) of LaMnSi2 was determined to be 400(1) K confirming the magnetic measurements.

Bio-inspired Design of Electrocatalysts for Oxalate Oxidation: a Combined Experimental and Computational Study of Mn–N–C Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matanovic, Ivana; Babanova, Sofia; Perry, Albert

2015-05-28

We report a novel non-platinum group metal (non-PGM) catalyst derived from Mn and amino- antipyrine (MnAAPyr) that shows electrochemical activity towards the oxidation of oxalic acid comparable to Pt with an onset potential for oxalate oxidation measured to be 0.714 * 0.002 V vs. SHE at pH = 4. The material has been synthesized using a templating Sacrificial Support Method with manganese nitrate and 4-aminoantipyrine as precursors. This catalyst is a nano-structured material in which Mn is atomically dispersed on a nitrogendoped graphene matrix. XPS studies reveal high abundance of pyridinic, Mn–Nx, and pyrrolic nitrogen pointing towards the conclusion thatmore » pyridinic nitrogen atoms coordinated to manganese constitute the active centers. Thus, the main features of the MnAAPyr catalyst are it exhibits similarity to the active sites of naturally occurring enzymes that are capable of efficient and selective oxidation of oxalic acid. Density functional theory in plane wave formalism with Perdew, Burke and Ernzerhof functional was further used to study the stability and activity of different one-metal active centers that could exist in the catalyst. The results show that the stability of the Mn–Nx sites changes in the following order: MnN4 4 MnN3C 4 MnN2C2 4 MnN3. Based on the overpotentials of 0.64 V and 0.71 V vs. SHE, calculated using the free energy diagrams for the oxalate oxidation mechanism, we could conclude that the MnN3C and MnN2C2 sites are most probable Mn–Nx sites responsible for the reported catalytic activity of the new catalyst.« less

An ab initio study of the effects of vacancies on the static and dynamic magnetic properties of Co2MnSi

NASA Astrophysics Data System (ADS)

Pradines, B.; Arras, R.; Calmels, L.

2017-10-01

The full-Heusler alloy Co2MnSi is a promising highly spin-polarized magnetic metal for spintronic applications. However, significant differences have been reported between the computed properties of the ideal material and the properties of real samples measured in experiments. In this paper, we study the influence of atom vacancies on the electronic structure and on the magnetic properties of Co2MnSi, as these defects could explain the disagreement between the expected and measured behavior of this alloy. The effects of atom vacancies have been calculated from first principles, using the fully relativistic Korringa-Kohn-Rostoker (KKR) method in conjunction with the coherent potential approximation (CPA) and the linear response formalism.

Optimal doping control of magnetic semiconductors via subsurfactant epitaxy.

PubMed

Zeng, Changgan; Zhang, Zhenyu; van Benthem, Klaus; Chisholm, Matthew F; Weitering, Hanno H

2008-02-15

"Subsurfactant epitaxy" is established as a conceptually new approach for introducing manganese as a magnetic dopant into germanium. A kinetic pathway is devised in which the subsurface interstitial sites on Ge(100) are first selectively populated with Mn, while lateral diffusion and clustering on or underneath the surface are effectively suppressed. Subsequent Ge deposition as a capping layer produces a novel surfactantlike phenomenon as the interstitial Mn atoms float towards newly defined subsurface sites at the growth front. Furthermore, the Mn atoms that failed to float upwards are uniformly distributed within the Ge capping layer. The resulting doping levels of order 0.25 at. % would normally be considered too low for ferromagnetic ordering, but the Curie temperature exceeds room temperature by a comfortable margin. Subsurfactant epitaxy thus enables superior dopant control in magnetic semiconductors.

Chemistry of impact events on Mercury

NASA Astrophysics Data System (ADS)

Berezhnoy, Alexey A.

2018-01-01

Based on the equilibrium thermochemical approach and quenching theory, formation of molecules and dust grains in impact-produced clouds formed after collisions between meteoroids and Mercury is considered. Based on observations of Al, Fe, and Mn atoms in the exosphere of Mercury and new results of studies of the elemental composition of the surface of Mercury, quenching temperatures and pressures of main chemical reactions and condensation of dust particles were estimated. The behavior of the main Na-, K-, Ca-, Fe-, Al-, Mn-, Mg-, Si-, Ti, Ni-, Cr-, Co, Zn-, O-, H-, S-, C-, Cl-, N-, and P-containing species delivered to the Hermean exosphere during meteoroid impacts was studied. The importance of meteoroid bombardment as a source of Na, K, Ca, Fe, Al, Mn, Mg, and O atoms in the exosphere of Mercury is discussed.

Neutron diffraction investigation of γ manganese hydride

NASA Astrophysics Data System (ADS)

Fedotov, V. K.; Antonov, V. E.; Kolesnikov, A. I.; Beskrovnyi, A. I.; Grosse, G.; Wagner, F. E.

1998-08-01

A profile analysis of the neutron diffraction spectrum of the fcc high pressure hydride λ-MnH 0.41 measured under ambient conditions showed that hydrogen is randomly distributed over the octahedral interstices of the fcc metal lattice and that the hydride is an antiferromagnet with the same collinear spin structure as pure λ-Mn, but with a smaller magnetic moment of about 1.9 Bohr magnetons per Mn atom.

Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy.

PubMed

Pennycook, Timothy J; Jones, Lewys; Pettersson, Henrik; Coelho, João; Canavan, Megan; Mendoza-Sanchez, Beatriz; Nicolosi, Valeria; Nellist, Peter D

2014-12-22

Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

Growth mode and structures of magnetic Mn clusters on graphene

DOE PAGES

Liu, Xiaojie; Wang, Cai-Zhuang

2016-06-22

We present a systematic study of Mn clusters on graphene by first-principles calculations. We show that the growth of Mn on graphene follows a three-dimensional (3D) mode. Both adsorption and attachment energies show that (Mn) 3 and (Mn) 6 on graphene are energetically favorable in the size range (Mn) 1-7. Moreover, larger formation energy for Mn cluster on graphene implies the incoming Mn atoms are likely to nucleate and grow into bigger and bigger Mn clusters on graphene. The magnetic moments of (Mn) 1,5,7 on graphene are enhanced by 11%, 186%, and 26% from their values at free-standing clusters, respectively.more » By contrast, the net magnetic moment of (Mn) 2,3,4,6 on graphene is reduced from that of the corresponding free-standing clusters. The origin of the magnetic moment changes can be attributed to the charge transfer within the Mn clusters and between the clusters and graphene upon adsorption.« less

First-principles study of Mn-S codoped anatase TiO2

NASA Astrophysics Data System (ADS)

Li, Senlin; Huang, Jinliang; Ning, Xiangmei; Chen, Yongcha; Shi, Qingkui

2018-04-01

In this work, the CASTEP program in Materials Studio 2017 software package was applied to calculate the electronic structures and optical properties of pure anatase TiO2, S-doped, Mn-doped and Mn-S co-doped anatase TiO2 by GGA + U methods based on the density function theory (DFT). The results indicate that the lattice is distorted and the lattice constant is reduce due to doping. The doping also introduces impurity energy levels into the forbidden band. After substitution of Mn for Ti atom, band gap narrowing of anatase TiO2 is caused by the impurity energy levels appearance in the near Fermi surface, which are contributed by Mn-3d orbital, Ti-3d orbital and O-2p orbital hybridization. After substitution of S for O atom, band gap narrowing is creited with the shallow accepter level under the conduction hand of S-3p orbital. The Mn-S co-doped anatase TiO2 could be a potential candidate for a photocatalyst because of tis enhanced absorption ability of visible light. The results can well explain the immanent cause of a band gap narrowing as well as a red shift in the spectrum for doped anatase TiO2.

Determination of Fe, Hg, Mn, and Pb in three-rings of poplar (Populus alba L.) by U-shaped DC arc

NASA Astrophysics Data System (ADS)

Marković, D. M.; Novović, I.; Vilotić, D.; Ignjatović, Lj.

2007-09-01

The U-shaped DC arc with aerosol supply was applied for the determination of Fe, Hg, Mn, and Pb in poplar (Populus alba L.) tree-rings. By optimization of the operating parameters and by selection of the most appropriate signal integration time (20 s for Fe, Mn, and Pb and 30 s for Hg), the obtained limits of detection for Fe, Hg, Mn, and Pb are 5.8, 2.6, 1.6, and 2.0 ng/ml, respectively. The detection limits achieved by this method for Fe, Hg, Mn, and Pb are comparable with the detection limits obtained for these elements by such methods as inductively coupled plasma-atomic emission spectrometry (ICP-AES), direct coupled plasmatomic emission spectrometry (DCP-AES), and microwave-induced plasma-atomic emission spectrometry (MIP-AES). We used the tree-rings of poplar from two different locations. The first one is in the area close to the power plant “Nikola Tesla” TENT A, Obrenovac, while the other one is in the urban area of Novi Sad. In almost all cases, samples from the location at Obrenovac registered elevated average concentrations of Fe, Hg, Mn, and Pb in the tree-rings of poplar.

Molecular structure, natural bond analysis, vibrational and electronic spectra, surface enhanced Raman scattering and Mulliken atomic charges of the normal modes of [Mn(DDTC)2] complex.

PubMed

Téllez S, Claudio A; Costa, Anilton C; Mondragón, M A; Ferreira, Glaucio B; Versiane, O; Rangel, J L; Lima, G Müller; Martin, A A

2016-12-05

Theoretical and experimental bands have been assigned for the Fourier Transform Infrared and Raman spectra of the bis(diethyldithiocarbamate)Mn(II) complex, [Mn(DDTC)2]. The calculations have been based on the DFT/B3LYP method, second derivative spectra and band deconvolution analysis. The UV-vis experimental spectra were measured in acetonitrile solution, and the calculated electronic spectrum was obtained using the TD/B3LYP method with 6-311G(d, p) basis set for all atoms. Charge transfer bands and those d-d spin forbidden were assigned in the UV-vis spectrum. The natural bond orbital analysis was carried out using the DFT/B3LYP method and the Mn(II) hybridization leading to the planar geometry of the framework was discussed. Surface enhanced Raman scattering (SERS) was also performed. Mulliken charges of the normal modes were obtained and related to the SERS enhanced bands. Copyright © 2016 Elsevier B.V. All rights reserved.

Microstructure and Phase Analysis in Mn-Al and Zr-Co Permanent Magnets

NASA Astrophysics Data System (ADS)

Lucis, Michael J.

In America's search for energy independence, the development of rare-earth free permanent magnets is one hurdle that still stands in the way. Permanent magnet motors provide a higher efficiency than induction motors in applications such as hybrid vehicles and wind turbines. This thesis investigates the ability of two materials, Mn-Al and Zr-Co, to fill this need for a permanent magnet material whose components are readily available within the U.S. and whose supply chain is more stable than that of the rare-earth materials. This thesis focuses on the creation and optimization of these two materials to later be used as the hard phase in nanocomposites with high energy products (greater than 10 MGOe). Mn-Al is capable of forming the pure L10 structure at a composition of Mn54Al43C3. When Mn is replaced by Fe or Cu using the formula Mn48Al43C3T6 the anisotropy constant is lowered from 1.3·107 ergs/cm3 to 1.0·107 ergs/cm3 and 0.8·10 7 ergs/cm3 respectively. Previous studies have reported a loss in magnetization in Mn-Al alloys during mechanical milling. The reason for this loss in magnetization was investigated and found to be due to the formation of the equilibrium beta-Mn phase of the composition Mn3Al2 and not due to oxidation or site disorder. It was also shown that fully dense Mn-Al permanent magnets can be created at hot pressing temperatures at or above 700°C and that the epsilon-phase to tau-phase transition and consolidation can be combined into a single processing step. The addition of small amounts of Cu to the alloy, 3% atomic, can increase the compaction density allowing high densities to be achieved at lower pressing temperatures. While the structure is still under debate, alloys at the composition Zr2Co11 in the Zr-Co system have been shown to have hard magnetic properties. This thesis shows that multiple structures exist at this Zr2Co11 composition and that altering the cooling rate during solidification of the alloy affects the ratio of the phase composition and therefore affects the magnetic properties. Phase diagrams for the Zr-Co system show that the Zr2Co11 phase is stable to a temperature of 1272°C, at which point the Zr6Co23 phase is the most favorable. However, this thesis shows that the Zr6Co23 phase forms at room temperature during high energy mechanical milling and at annealing temperatures as low as 600°C. Since high energy mechanical milling was not a potential method to creating single crystalline particles, hydrogen embrittlement was investigated. Hydrochloric acid was used to induce hydrogen embrittlement in the Zr2Co11 alloy, modifying the fracture characteristics of the alloy causing it to occur primarily along grain boundaries resulting in single crystalline particles with remanent magnetization enhancement.

Magnetic structure and phase transition of Ni 2Mn 1.48Sb 0.52 magnetic shape memory compound

DOE PAGES

Yang, Y. B.; Liu, S. Q.; Zhao, H.; ...

2016-02-06

Here, a comprehensive study of the structural and magnetic properties of the Ni 2Mn 1.48Sb 0.52 compound is presente using neutron diffraction and magnetic measurements. It is found that Mn atoms on 4a and 4 sites are ferrimagnetic coupled in the austenitic phase. At 300 K, the magnetic moments of Mn (4a) an Mn (4b) are determined to be 2.72(3) μ B and -2.67(5) μ B, respectively. From 260 K to 4 K, the compound is in martensite phase and the magnetic moments of Mn (2a), Mn (2f), Mn (2b), Mn (2e) at 4 K ar 2.2(5) μ B, 2.3(5)more » μ B, -2.1(5) μ B, and -2.6(5) μ B, respectively.« less

Electrochemical hydrogen storage alloys and batteries fabricated from Mg containing base alloys

DOEpatents

Ovshinsky, Stanford R.; Fetcenko, Michael A.

1996-01-01

An electrochemical hydrogen storage material comprising: (Base Alloy).sub.a M.sub.b where, Base Alloy is an alloy of Mg and Ni in a ratio of from about 1:2 to about 2:1, preferably 1:1; M represents at least one modifier element chosen from the group consisting of Co, Mn, Al, Fe, Cu, Mo, W, Cr, V, Ti, Zr, Sn, Th, Si, Zn, Li, Cd, Na, Pb, La, Mm, and Ca; b is greater than 0.5, preferably 2.5, atomic percent and less than 30 atomic percent; and a+b=100 atomic percent. Preferably, the at least one modifier is chosen from the group consisting of Co, Mn, Al, Fe, and Cu and the total mass of the at least one modifier element is less than 25 atomic percent of the final composition. Most preferably, the total mass of said at least one modifier element is less than 20 atomic percent of the final composition.

Effect of Fe and Co substitution on the martensitic stability and the elastic, electronic, and magnetic properties of Mn2NiGa : Insights from ab initio calculations

NASA Astrophysics Data System (ADS)

Kundu, Ashis; Ghosh, Sheuly; Ghosh, Subhradip

2017-11-01

We investigate the effects of Fe and Co substitutions on the phase stability of the martensitic phase and mechanical, electronic, and magnetic properties of the magnetic shape memory system Mn2NiGa by first-principles density functional theory calculations. The evolution of these aspects upon substitution of Fe and Co at different crystallographic sites is investigated by computing the electronic structure, mechanical properties (tetragonal shear constant, Pugh ratio, and Cauchy pressure), and magnetic exchange parameters. We find that the austenite phase of Mn2NiGa gradually stabilizes with increase in concentration of Fe/Co due to the weakening of the minority spin hybridization of Ni and Mn atoms occupying crystallographically equivalent sites. The interplay between relative structural stability and the compositional changes is understood from the variations in the elastic moduli and electronic structures. We find that like in the Ni2MnGa -based systems, the elastic shear modulus C' can be considered as a predictor of composition dependence of martensitic transformation temperature Tm in substituted Mn2NiGa , thus singling it out as the universally acceptable predictor for martensitic transformation in Ni-Mn-Ga compounds over a wide composition range. The magnetic properties of Mn2NiGa are found to be greatly improved by the substitutions due to stronger ferromagnetic interactions in the compounds. The gradually weaker (stronger) Jahn-Teller distortion (covalent bonding) in the minority spin densities of states due to substitutions leads to a half-metallic-like gap in these compounds resulting in materials with high spin polarization when the substitutions are complete. The substitutions at the Ga site result in the two compounds Mn2NiFe and Mn2NiCo with very high magnetic moments and Curie temperatures. Thus, our work indicates that although the substitutions destroy the martensitic transformation and thus the possibility of realization of shape memory properties in Mn2NiGa , magnetic materials with very good magnetic parameters that are potentially useful for novel magnetic applications can be obtained. This can trigger interest in the experimental community in further research on substituted Mn2NiGa .

Characterization and dioxygen reactivity of a new series of coordinatively unsaturated thiolate-ligated manganese(II) complexes.

PubMed

Coggins, Michael K; Toledo, Santiago; Shaffer, Erika; Kaminsky, Werner; Shearer, Jason; Kovacs, Julie A

2012-06-18

The synthesis, structural, and spectroscopic characterization of four new coordinatively unsaturated mononuclear thiolate-ligated manganese(II) complexes ([Mn(II)(S(Me2)N(4)(6-Me-DPEN))](BF(4)) (1), [Mn(II)(S(Me2)N(4)(6-Me-DPPN))](BPh(4))·MeCN (3), [Mn(II)(S(Me2)N(4)(2-QuinoPN))](PF(6))·MeCN·Et(2)O (4), and [Mn(II)(S(Me2)N(4)(6-H-DPEN)(MeOH)](BPh(4)) (5)) is described, along with their magnetic, redox, and reactivity properties. These complexes are structurally related to recently reported [Mn(II)(S(Me2)N(4)(2-QuinoEN))](PF(6)) (2) (Coggins, M. K.; Kovacs, J. A. J. Am. Chem. Soc.2011, 133, 12470). Dioxygen addition to complexes 1-5 is shown to result in the formation of five new rare examples of Mn(III) dimers containing a single, unsupported oxo bridge: [Mn(III)(S(Me2)N(4)(6-Me-DPEN)](2)-(μ-O)(BF(4))(2)·2MeOH (6), [Mn(III)(S(Me2)N(4)(QuinoEN)](2)-(μ-O)(PF(6))(2)·Et(2)O (7), [Mn(III)(S(Me2)N(4)(6-Me-DPPN)](2)-(μ-O)(BPh(4))(2) (8), [Mn(III)(S(Me2)N(4)(QuinoPN)](2)-(μ-O)(BPh(4))(2) (9), and [Mn(III)(S(Me2)N(4)(6-H-DPEN)](2)-(μ-O)(PF(6))(2)·2MeCN (10). Labeling studies show that the oxo atom is derived from (18)O(2). Ligand modifications, involving either the insertion of a methylene into the backbone or the placement of an ortho substituent on the N-heterocyclic amine, are shown to noticeably modulate the magnetic and reactivity properties. Fits to solid-state magnetic susceptibility data show that the Mn(III) ions of μ-oxo dimers 6-10 are moderately antiferromagnetically coupled, with coupling constants (2J) that fall within the expected range. Metastable intermediates, which ultimately convert to μ-oxo bridged 6 and 7, are observed in low-temperature reactions between 1 and 2 and dioxygen. Complexes 3-5, on the other hand, do not form observable intermediates, thus illustrating the effect that relatively minor ligand modifications have upon the stability of metastable dioxygen-derived species.

Polarity dependence of Mn incorporation in (Ga,Mn)N superlattices

NASA Astrophysics Data System (ADS)

Tropf, L.; Kunert, G.; Jakieła, R.; Wilhelm, R. A.; Figge, S.; Grenzer, J.; Hommel, D.

2016-03-01

In the context of recent efforts to combine high Mn concentrations in (Ga,Mn)N with a pronounced p-type carrier density, (Ga,Mn)N/GaN:Mg-superlattices have been fabricated using plasma-assisted molecular beam epitaxy. Profiles of the dopant atomic densities in the heterostructures are obtained by secondary ion mass spectroscopy. They show an abrupt drop of two to three orders of magnitude in both Mn and Mg concentrations after the first GaN:Mg layer above a critical Mg-flux. Scanning electron microscopy before and after selective etching reveals a polarity inversion from originally Ga-face to N-face GaN in samples in which high Mg fluxes were applied. From our observations, we are able to draw an analogy between the impurity incorporation laws of Mg and Mn.

Poly[[tetra-μ-cyanido-κ8 C:N-dodeca-cyanido-κ12 C-tris­(N,N-di­methyl­formamide-κO)tris­(methanol-κO)tris­(3,4,7,8-tetra­methyl-1,10-phenanthroline-κ2 N,N′)trimanganese(II)ditungstate(V)] dihydrate

PubMed Central

Yang, Fei-Lin; Yang, Dan

2014-01-01

The asymmetric unit of the title compound, {[Mn3{W(CN)8}2(C16H16N2)3(C3H7NO)3(CH3OH)3]·2H2O}n, consists of three [Mn(N,N-di­methyl­formamide)(methanol)(3,4,7,8-tetra­methyl-1,10-phenanthroline)]2+ cations, two [W(CN)8]3− anions and two water mol­ecules. Each water mol­ecule is disordered over three sets of sites, with a refined occupancy ratio of 0.310 (9):0.275 (9):0.415 (9) for one mol­ecule and 0.335 (9):0.288 (9):0.377 (9) for the other mol­ecule. The MnII atoms exhibit a distorted octa­hedral geometry, while the WV atoms adopt a distorted square-anti­prismatic geometry. The MnII and WV atoms are linked alternatively through cyanide groups, forming a tetra­nuclear 12-atom rhombic metallacycle. Adjacent metallacycles are further connected by μ2-bridging cyanide anions, generating a 3,2-chain structure running parallel to [101]. Inter­chain π–π inter­actions are observed [centroid–centroid distances = 3.763 (3) and 3.620 (2) Å]. PMID:24860305

Competition of the self-activated and Mn-related luminescence in ZnS single crystals

NASA Astrophysics Data System (ADS)

Bacherikov, Yu. Yu.; Vorona, I. P.; Markevich, I. V.; Korsunska, N. O.; Kurichka, R. V.

2018-06-01

The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of ZnS single crystals thermally doped from ZnS/MnS mixture were studied at 300 and 77 K. PL spectra exhibit bands caused by Mn-related centers and centers of self-activated (SA) emission. Besides intrinsic maximum, a number of narrow peaks corresponded to Mn-related absorption are found in the PLE spectra of both SA and Mn-related emission. A redistribution of SA and Mn-related emission intensities is observed with temperature change. The mechanism of this phenomenon involving free hole trapping by MnZn and the possible position of a ground energy level of substitutional Mn are discussed.

Interstitial Fe in MgO

NASA Astrophysics Data System (ADS)

Mølholt, T. E.; Mantovan, R.; Gunnlaugsson, H. P.; Svane, A.; Masenda, H.; Naidoo, D.; Bharuth-Ram, K.; Fanciulli, M.; Gislason, H. P.; Johnston, K.; Langouche, G.; Ólafsson, S.; Sielemann, R.; Weyer, G.

2014-01-01

Isolated 57Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of 57Mn decaying to 57Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe2+ and Fe3+, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

Magnetic properties of mechanically alloyed Mn-Al-C powders

NASA Astrophysics Data System (ADS)

Kohmoto, O.; Kageyama, N.; Kageyama, Y.; Haji, H.; Uchida, M.; Matsushima, Y.

2011-01-01

We have prepared supersaturated-solution Mn-Al-C alloy powders by mechanical alloying using a planetary high-energy mill. The starting materials were pure Mn, Al and C powers. The mechanically-alloyed powders were subjected to a two-step heating. Although starting particles are Al and Mn with additive C, the Al peak disappears with MA time. With increasing MA time, transition from α-Mn to β-Mn does not occur; the α-Mn structure maintains. At 100 h, a single phase of supersaturated-solution α-Mn is obtained. The lattice constant of α-Mn decreases with increasing MA time. From the Scherrer formula, the crystallite size at 500 h is obtained as 200Å, which does not mean amorphous state. By two-step heating, high magnetization (66 emu/g) was obtained from short-time-milled powders (t=10 h). The precursor of the as-milled powder is not a single phase α-Mn but contains small amount of fcc Al. After two-step heating, the powder changes to τ-phase. Although the saturation magnetization increases, the value is less than that by conventional bulk MnAl (88 emu/g). Meanwhile, long-time-milled powder of single α-Mn phase results in low magnetization (5.2 emu/g) after two-step heating.

Investigations on rectifying behavior of Y{sub 0.95}Ca{sub 0.05}MnO{sub 3}/Si junction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhruv, Davit; V.V.P. Engineering College, Gujarat Technological University, Rajkot – 360 005; Joshi, Zalak

2016-05-06

In this communication, we report the rectifying properties observed across the junction, consists of Ca{sup +2} doped hexagonal YMnO{sub 3} manganite film, grown on n-type (100) Si single crystalline substrate. The junction was grown using cost effective chemical solution deposition (CSD) technique by employing spin coating method. Surface morphology of Y{sub 0.9}5Ca{sub 0.05}MnO{sub 3}/Si (YCMO/Si) film was carried out by atomic force microscopy and magnetic response of film was studied by magnetic force microscopy. Current – voltage characteristics of the junction was carried out by using Keithley source meter in current perpendicular to plane (CPP) mode at different temperatures. Rectificationmore » in I – V behavior has been observed for the junction at all the temperatures studied. With increase in temperature, rectification ratio, in the range of 10{sup 4}, increases across the junction. Results have been discussed in the context of thermal effects.« less

Curie temperatures of cubic (Ga, Mn)N diluted magnetic semiconductors from the RKKY spin model.

PubMed

Zhu, Li-Fang; Liu, Bang-Gui

2009-11-04

We explore how much the RKKY spin interaction can contribute to the high-temperature ferromagnetism in cubic (Ga, Mn)N diluted magnetic semiconductors. The usual coupling constant is used and effective carriers are considered independent of doped magnetic atoms, as is shown experimentally. Our Monte Carlo simulated results show that maximal Curie temperature is reached at the optimal carrier concentration for a given Mn concentration, equaling 373 K for 5% Mn and 703 K for 8% Mn. Because such a Monte Carlo method does not overestimate transition temperatures, these calculations indicate that the RKKY spin interaction alone can yield high-enough Curie temperatures in cubic (Ga, Mn)N under optimized conditions.

Constructing MnO{sub 2}/single crystalline ZnO nanorod hybrids with enhanced photocatalytic and antibacterial activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Weiwei; Liu, Tiangui, E-mail: tianguiliu@gmail.com; Cao, Shiyi

In order to improve the photocatalytic and antibacterial activity of ZnO nanorods, ZnO nanorods decorated with MnO{sub 2} nanoparticles (MnO{sub 2}/ZnO nanorod hybrids) were prepared by using microwave assisted coprecipitation method under the influence of hydrogen peroxide, and the structure, photocatalytic activity and antibacterial property of the products were studied. Experimental results indicated that MnO{sub 2} nanoparticles are decorated on the surface of single crystalline ZnO nanorods. Moreover, the resultant MnO{sub 2}/ZnO nanorod hybrids have been proven to possess good photocatalytic and antibacterial activity, which their degradated efficiency for Rhodamin B (RhB) is twice as the pure ZnO nanorods. Enhancementmore » for photocatalytic and antibacterial activity is mainly attributed to the low band gap energy and excellent electrochemical properties of MnO{sub 2} nanoparticles. - Graphical abstract: The MnO{sub 2}/single crystalline ZnO nanorods hybrids, which MnO{sub 2} nanoparticles are loaded on the surface of ZnO nanorods, were prepared by the step-by-step precipitation method under the assistance of ammonia and hydrogen peroxide. Display Omitted - Highlights: • MnO{sub 2}/ZnO nanorod hybrids were prepared by the step-by-step assembly method. • Single crystalline ZnO nanorods can be decorated by MnO{sub 2} nanoparticles. • MnO{sub 2}/ZnO nanorod hybrids possess good photocatalytic and antibacterial activity. • MnO{sub 2} can improve the photocatalytic activity of ZnO nanorods under visible light.« less

(Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B{sub 5}, the first examples of copper platinum borides. Observation of superconductivity in a novel boron filled β-Mn-type compound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salamakha, Leonid P.; Sologub, Oksana, E-mail: oksana.sologub@univie.ac.at; Stöger, Berthold

New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt{sub 1−x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.33) forms a B-filled β-Mn-type structure (space group P4{sub 1}32; a=0.6671(1) nm). Cu atoms are distributed preferentially on the 8c atom sites, whereas the 12d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β-Mn-type structure. Pt{sub 9}Cu{sub 3}B{sub 5} (space group P-62m; a=0.9048(3) nm, c=0.2908(1) nm) adopts the Pt{sub 9}Zn{submore » 3}B{sub 5–δ}-type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt{sub 6}] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt{sub 6}] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt{sub 6}] and [Pt{sub 6}] trigonal prisms, rotated perpendicularly to the central one. There is no B–B contact as well as Cu–B contact in the structure. The relationships of Pt{sub 9}Cu{sub 3}B{sub 5} structure with the structure of Ti{sub 1+x}Os{sub 2−x}RuB{sub 2} as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt{sub 1–x}Cu{sub x}){sub 3}Cu{sub 2}B (x=0.3) (B-filled β-Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ{sub 0}H{sub C2}(0){sup WHH} of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt{sub 9}Cu{sub 3}B{sub 5} (Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure) from electrical resistivity measurements. - Highlights: • First two copper platinum borides, (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B and Pt{sub 9}Cu{sub 3}B{sub 5} were obtained. • (Pt{sub 0.67}Cu{sub 0.33}){sub 3}Cu{sub 2}B forms a B-filled β-Mn-type structure. • Pt{sub 9}Cu{sub 3}B{sub 5} adopts a Pt{sub 9}Zn{sub 3}B{sub 5–δ}-type structure. • Boron atoms exhibit octahedral and trigonal prismatic coordination. • (Pt{sub 1–x}Cu{sub x})3Cu{sub 2}B (x=0.3) is a bulk superconductor with T{sub c} 2.06 K.« less

Single component Mn-doped perovskite-related CsPb2ClxBr5-x nanoplatelets with a record white light quantum yield of 49%: a new single layer color conversion material for light-emitting diodes.

PubMed

Wu, Hao; Xu, Shuhong; Shao, Haibao; Li, Lang; Cui, Yiping; Wang, Chunlei

2017-11-09

Single component nanocrystals (NCs) with white fluorescence are promising single layer color conversion media for white light-emitting diodes (LED) because the undesirable changes of chromaticity coordinates for the mixture of blue, green and red emitting NCs can be avoided. However, their practical applications have been hindered by the relative low photoluminescence (PL) quantum yield (QY) for traditional semiconductor NCs. Though Mn-doped perovskite nanocube is a potential candidate, it has been unable to realize a white-light emission to date. In this work, the synthesis of Mn-doped 2D perovskite-related CsPb 2 Cl x Br 5-x nanoplatelets with a pure white emission from a single component is reported. Unlike Mn-doped perovskite nanocubes with insufficient energy transfer efficiency, the current reported Mn-doped 2D perovskite-related CsPb 2 Cl x Br 5-x nanoplatelets show a 10 times higher energy transfer efficiency from perovskite to Mn impurities at the required emission wavelengths (about 450 nm for perovskite emission and 580 nm for Mn emission). As a result, the Mn/perovskite dual emission intensity ratio surprisingly elevates from less than 0.25 in case of Mn-doped nanocubes to 0.99 in the current Mn-doped CsPb 2 Cl x Br 5-x nanoplatelets, giving rise to a pure white light emission with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.35, 0.32). More importantly, the highest PL QY for Mn-doped perovskite-related CsPb 2 Cl x Br 5-x nanoplatelets is up to 49%, which is a new record for white-emitting nanocrystals with single component. These highly luminescent nanoplatelets can be blended with polystyrene (PS) without changing the white light emission but dramatically improving perovskite stability. The perovskite-PS composites are available not only as a good solution processable coating material for assembling LED, but also as a superior conversion material for achieving white light LED with a single conversion layer.

Theory and Application of Photoelectron Diffraction for Complex Oxide Systems

NASA Astrophysics Data System (ADS)

Chassé, Angelika; Chassé, Thomas

2018-06-01

X-ray photoelectron diffraction (XPD) has been used to investigate film structures and local sites of surface and dopant atoms in complex oxide materials. We have performed angular-resolved measurements of intensity distribution curves (ADCs) and patterns (ADPs) of elemental core level intensities from binary to quaternary mixed oxide samples and compared them to multiple-scattering cluster (MSC) calculations in order to derive information on structural models and related parameters. MSC calculations permitted to describe both bulk diffraction features of binary oxide MnO(001) and the thickness-dependence of the tetragonal distortion of epitaxial MnO films on Ag(001). XPD was further used to investigate the surface termination of perovskite SrTiO3 and BaTiO3 substrates in order to evaluate influence of different ex situ and in situ preparation procedures on the surface layers, which are crucial for quality of following film growth. Despite the similarity of local environments of Sr (Ba) and Ti atoms in the perovskite film structure an angular region in the ADCs was identified as a fingerprint with the help of MSC simulations which provided clear conclusions on the perovskite oxide surfaces. Dopant sites in quaternary perovskite manganites La1-xCaxMnO3, La1-xSrxMnO3, and La1-xCexMnO3 were studied with polar angle scans of the photoemission intensities of host and dopant atoms. Both direct comparison of experimental ADCs and to the simulations within MSC models confirm the occupation of A sites by the dopants and the structural quality of the complex oxide films.

Biocompatible and high-performance amino acids-capped MnWO4 nanocasting as a novel non-lanthanide contrast agent for X-ray computed tomography and T1-weighted magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Dong, Kai; Liu, Zhen; Liu, Jianhua; Huang, Sa; Li, Zhenhua; Yuan, Qinghai; Ren, Jinsong; Qu, Xiaogang

2014-01-01

In the present work, a novel non-lanthanide dual-modality contrast agent, manganese tungstate (MnWO4), has been successfully constructed by a facile and versatile hydrothermal route. With the merits of a high atomic number and a well-positioned K-edge energy of tungsten, our well-prepared non-lanthanide nanoprobes provide a higher contrast efficacy than routine iodine-based agents in clinics. Additionally, the presence of Mn in these nanoparticles endow them with excellent T1-weighted MR imaging capabilities. As an alternative to T2-weighted MRI and CT dual-modality contrast agents, the nanoprobes can provide a positive contrast signal, which prevents confusion with the dark signals from hemorrhage and blood clots. To the best of our knowledge, this is the first report that a non-lanthanide imaging nanoprobe is applied for CT and T1-weighted MRI simultaneously. Moreover, comparing with gadolinium-based T1-weighted MRI and CT dual-modality contrast agents that were associated with nephrogenic systemic fibrosis (NSF), our contrast agents have superior biocompatibility, which is proved by a detailed study of the pharmacokinetics, biodistribution, and in vivo toxicology. Together with excellent dispersibility, high biocompatibility and superior contrast efficacy, these nanoprobes provide detailed and complementary information from dual-modality imaging over traditional single-mode imaging and bring more opportunities to the new generation of non-lanthanide nanoparticulate-based contrast agents.In the present work, a novel non-lanthanide dual-modality contrast agent, manganese tungstate (MnWO4), has been successfully constructed by a facile and versatile hydrothermal route. With the merits of a high atomic number and a well-positioned K-edge energy of tungsten, our well-prepared non-lanthanide nanoprobes provide a higher contrast efficacy than routine iodine-based agents in clinics. Additionally, the presence of Mn in these nanoparticles endow them with excellent T1-weighted MR imaging capabilities. As an alternative to T2-weighted MRI and CT dual-modality contrast agents, the nanoprobes can provide a positive contrast signal, which prevents confusion with the dark signals from hemorrhage and blood clots. To the best of our knowledge, this is the first report that a non-lanthanide imaging nanoprobe is applied for CT and T1-weighted MRI simultaneously. Moreover, comparing with gadolinium-based T1-weighted MRI and CT dual-modality contrast agents that were associated with nephrogenic systemic fibrosis (NSF), our contrast agents have superior biocompatibility, which is proved by a detailed study of the pharmacokinetics, biodistribution, and in vivo toxicology. Together with excellent dispersibility, high biocompatibility and superior contrast efficacy, these nanoprobes provide detailed and complementary information from dual-modality imaging over traditional single-mode imaging and bring more opportunities to the new generation of non-lanthanide nanoparticulate-based contrast agents. Electronic supplementary information (ESI) available: TEM images of MnWO4 nanoparticles synthesized at pH = 7, 180 °C pH = 9, 180 °C pH = 6, 200 °C with various amino acid molecules as capped agents, survey XPS spectra, FTIR spectrum of glycine capped MnWO4 nanorods, photos of glycine capped MnWO4 nanorods in various solutions including PBS, DMEM cell medium, and FBS, in vivo coronal view CT images of a rat before and after intravenous injection of iobitridol at different timed intervals, in vivo CT imaging of the rat one month after intravenous injection of MnWO4 nanorods, CT values of the heart, liver, spleen and kidney of a rat before and after intravenous administration of MnWO4 nanorods and iobitridol at different time intervals, hematology analysis and blood biochemical assay. See DOI: 10.1039/c3nr05455a

A single-phase Ba{sub 9}Lu{sub 2}Si{sub 6}O{sub 24}:Eu{sup 2+}, Ce{sup 3+}, Mn{sup 2+} phosphor with tunable full-color emission for NUV-based white LED applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Changhua; Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201; Liu, Yongfu, E-mail: liuyongfu@nimte.ac.cn

Highlights: • A single phase Ba{sub 9}Lu{sub 2}Si{sub 6}O{sub 24}:Eu{sup 2+}, Ce{sup 3+}, Mn{sup 2+} phosphor with full-color emission was obtained by solid-state reactions. • Eu{sup 2+}, Ce{sup 3+}, and Mn{sup 2+} acts as blue, green, and red luminescence centers, respectively. • The BLS:Eu{sup 2+}, Ce{sup 3+}, Mn{sup 2+} phosphor shows a high quantum efficient of ∼62% and a good color stability. • Combining this single phosphor with a 395 nm NUV-chip, an ideal white LED with a high CRI of 85 and a CCT of 6300 K was obtained. - Abstract: We obtained a single phase BLS:Eu{sup 2+}, Ce{supmore » 3+}, Mn{sup 2+} phosphor by solid-state reactions. Eu{sup 2+}, Ce{sup 3+}, and Mn{sup 2+} gives rise to the blue, green, and red emission, respectively. The Mn{sup 2+} red emission can be effectively enhanced via energy transfers from both Eu{sup 2+} and Ce{sup 3+}. Thus a tunable full color emission from 410 to 750 nm was realized in this single phosphor. The Eu{sup 2+} → Mn{sup 2+} energy transfer mechanism was investigated by the fluorescence decay curves. This single phosphor exhibits an efficient excitation band covering from 390 to 410 nm, which matches well with the emission light of the efficient NUV chips. The optimized BLS:Eu{sup 2+}, Ce{sup 3+}, Mn{sup 2+} phosphor shows a high quantum efficient of ∼62% and a good color stability. When this single phosphor was combined with a 395 nm NUV-chip, an ideal white LED with a high color render index (CRI) of 85 and a correlated color temperature (CCT) of 6300 K was obtained. This demonstrates the promising application of the BLS:Eu{sup 2+}, Ce{sup 3+}, Mn{sup 2+} single phosphor for the NUV-based white LEDs.« less

Single-layer ZnMN2 (M = Si, Ge, Sn) zinc nitrides as promising photocatalysts.

PubMed

Bai, Yujie; Luo, Gaixia; Meng, Lijuan; Zhang, Qinfang; Xu, Ning; Zhang, Haiyang; Wu, Xiuqiang; Kong, Fanjie; Wang, Baolin

2018-05-30

Searching for two-dimensional semiconductor materials that are suitable for visible-light photocatalytic water splitting provides a sustainable solution to deal with the future energy crisis and environmental problems. Herein, based on first-principles calculations, single-layer ZnMN2 (M = Si, Ge, Sn) zinc nitrides are proposed as efficient photocatalysts for water splitting. Stability analyses show that the single-layer ZnMN2 zinc nitrides exhibit energetic and dynamical stability. The electronic properties reveal that all of the single-layer ZnMN2 zinc nitrides are semiconductors. Interestingly, single-layer ZnSnN2 is a direct band gap semiconductor with a desirable band gap (1.74 eV), and the optical adsorption spectrum confirms its optical absorption in the visible light region. The hydrogen evolution reaction (HER) calculations show that the catalytic activity for single-layer ZnMN2 (M = Ge, Sn) is better than that of single-layer ZnSiN2. Furthermore, the band gaps and band edge positions for the single-layer ZnMN2 zinc nitrides can be effectively tuned by biaxial strain. Especially, single-layer ZnGeN2 can be effectively tuned to match better with the redox potentials of water and enhance the light absorption in the visible light region at a tensile strain of 5%, which is confirmed by the corresponding optical absorption spectrum. Our results provide guidance for experimental synthesis efforts and future searches for single-layer materials suitable for photocatalytic water splitting.

Simultaneous multielement atomic absorption spectrometry with graphite furnace atomization

NASA Astrophysics Data System (ADS)

Harnly, James M.; Miller-Ihli, Nancy J.; O'Haver, Thomas C.

The extended analytical range capability of a simultaneous multielement atomic absorption continuum source spectrometer (SIMAAC) was tested for furnace atomization with respect to the signal measurement mode (peak height and area), the atomization mode (from the wall or from a platform), and the temperature program mode (stepped or ramped atomization). These parameters were evaluated with respect to the shapes of the analytical curves, the detection limits, carry-over contamination and accuracy. Peak area measurements gave more linear calibration curves. Methods for slowing the atomization step heating rate, the use of a ramped temperature program or a platform, produced similar calibration curves and longer linear ranges than atomization with a stepped temperature program. Peak height detection limits were best using stepped atomization from the wall. Peak area detection limits for all atomization modes were similar. Carry-over contamination was worse for peak area than peak height, worse for ramped atomization than stepped atomization, and worse for atomization from a platform than from the wall. Accurate determinations (100 ± 12% for Ca, Cu, Fe, Mn, and Zn in National Bureau of Standards' Standard Reference Materials Bovine Liver 1577 and Rice Flour 1568 were obtained using peak area measurements with ramped atomization from the wall and stepped atomization from a platform. Only stepped atomization from a platform gave accurate recoveries for K. Accurate recoveries, 100 ± 10%, with precisions ranging from 1 to 36 % (standard deviation), were obtained for the determination of Al, Co, Cr, Fe, Mn, Mo, Ni. Pb, V and Zn in Acidified Waters (NBS SRM 1643 and 1643a) using stepped atomization from a platform.

Optoelectronic and magnetic properties of Mn-doped indium tin oxide: A first-principles study

NASA Astrophysics Data System (ADS)

Nath Tripathi, Madhvendra; Saeed Bahramy, Mohammad; Shida, Kazuhito; Sahara, Ryoji; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

2012-10-01

The manganese doped indium tin oxide (ITO) has integrated magnetics, electronics, and optical properties for next generation multifunctional devices. Our first-principles density functional theory (DFT) calculations show that the manganese atom replaces b-site indium atom, located at the second coordination shell of the interstitial oxygen in ITO. It is also found that both anti-ferromagnetic and ferromagnetic behaviors are realizable. The calculated magnetic moment of 3.95μB/Mn as well as the high transmittance of ˜80% for a 150 nm thin film of Mn doped ITO is in good agreement with the experimental data. The inclusion of on-site Coulomb repulsion corrections via DFT + U methods turns out to improve the optical behavior of the system. The optical behaviors of this system reveal its suitability for the magneto-opto-electronic applications.

Dramatic influence of an anionic donor on the oxygen-atom transfer reactivity of a Mn(V) -oxo complex.

PubMed

Neu, Heather M; Quesne, Matthew G; Yang, Tzuhsiung; Prokop-Prigge, Katharine A; Lancaster, Kyle M; Donohoe, James; DeBeer, Serena; de Visser, Sam P; Goldberg, David P

2014-11-03

Addition of an anionic donor to an Mn(V) (O) porphyrinoid complex causes a dramatic increase in 2-electron oxygen-atom-transfer (OAT) chemistry. The 6-coordinate [Mn(V) (O)(TBP8 Cz)(CN)](-) was generated from addition of Bu4 N(+) CN(-) to the 5-coordinate Mn(V) (O) precursor. The cyanide-ligated complex was characterized for the first time by Mn K-edge X-ray absorption spectroscopy (XAS) and gives MnO=1.53 Å, MnCN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN(-) complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e(-) -reduced Mn(III) (CN)(-) complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000-fold versus the same reaction for the parent 5-coordinate complex. An Eyring analysis gives ΔH(≠) =14 kcal mol(-1) , ΔS(≠) =-10 cal mol(-1)  K(-1) . Computational studies fully support the structures, spin states, and relative reactivity of the 5- and 6-coordinate Mn(V) (O) complexes. © 2014 The Authors. Published by Wiley-VCHVerlag GmbH & Co. KGaA. This is an open access article under the terms ofthe Creative Commons Attribution License, which permits use, distribution andreproduction in any medium, provided the original work is properly cited.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antropov, Vladimir P; Antonov, Victor N

We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li 2(Li 1-xM x)N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magnetic anisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropymore » of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magnetic anisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L 2,3 spectra in LiFeN are also predicted.« less

Doping effects on the relaxation of frustration and magnetic properties of YMn0.9Cu0.1O3

NASA Astrophysics Data System (ADS)

Xiao, L. X.; Xia, Z. C.; Wang, X.; Ni, Y.; Yu, W.; Shi, L. R.; Jin, Z.; Xiao, G. L.

2017-12-01

The crystal structure and magnetic properties of hexagonal YMn0.9Cu0.1O3 single crystal are systematically investigated. The refinement results of XRD show the lattice constant decreases, which is unusually due to the doped Cu2+ ion has a larger ionic radius than the Mn3+ ions. The XPS results show that the coexistence of Mn2+, Mn3+ and Mn4+ ions in YMn0.9Cu0.1O3 single crystal. Magnetization measurements show that Cu doped YMn0.9Cu0.1O3 and parent YMnO3 have almost the same antiferromagnetic transition temperature TN, which indicates the AFM interaction is robust in the geometry frustrated system. Because doping directly destroy some of the Mn3+ ions nets, the relaxation of frustration of Mn in-plane 2D triangular geometry network leads to the significantly decrease of Mn3+ ions AFM interaction. In addition, the coexistence and competition between the ferromagnetic and antiferromagnetic interactions among the Mn2+, Mn3+ and Mn4+ ions lead to a complicated and irreversible magnetization behavior in YMn0.9Cu0.1O3 single crystal.

A binuclear Mn(III) complex of a scorpiand-like ligand displaying a single unsupported Mn(III)-O-Mn(III) bridge.

PubMed

Blasco, Salvador; Cano, Joan; Clares, M Paz; García-Granda, Santiago; Doménech, Antonio; Jiménez, Hermas R; Verdejo, Begoña; Lloret, Francesc; García-España, Enrique

2012-11-05

The crystal structure of a binuclear Mn(III) complex of a scorpiand-like ligand (L) displays an unsupported single oxo bridging ligand with a Mn(III)-O-Mn(III) angle of 174.7°. Magnetic susceptibility measurements indicate strong antiferromagnetic coupling between the two metal centers. DFT calculations have been carried out to understand the magnetic behavior and to analyze the nature of the observed Jahn-Teller distortion. Paramagnetic (1)H NMR has been applied to rationalize the formation and magnetic features of the complexes formed in solution.

High-quality single crystal growth and magnetic property of Mn4Ta2O9

NASA Astrophysics Data System (ADS)

Cao, Yiming; Xu, Kun; Yang, Ya; Yang, Wangfan; Zhang, Yuanlei; Kang, Yanru; He, Xijia; Zheng, Anmin; Liu, Mian; Wei, Shengxian; Li, Zhe; Cao, Shixun

2018-06-01

A large-size single crystal of Mn4Ta2O9 with ∼3.5 mm in diameter and ∼65 mm in length was successfully grown for the first time by a newly designed one-step method based on the optical floating zone technique. Both the clear Laue spots and sharp XRD Bragg reflections suggest the high quality of the single crystal. In Mn4Ta2O9 single crystal, an antiferromagnetic phase transition was observed below Néel temperature 102 K along c axis, which is similar to the isostructural compound Mn4Nb2O9, but differs from the isostructural Co4Nb2O9. Relative dielectric constant at 30 kOe suggests that no magnetoelectric coupling exists in Mn4Ta2O9.

Magnetic phase change in Mn-doped ZnSnAs2 thin films depending on Mn concentration

NASA Astrophysics Data System (ADS)

Uchitomi, Naotaka; Hidaka, Shiro; Saito, Shin; Asubar, Joel T.; Toyota, Hideyuki

2018-04-01

The relationship between Mn concentration and Curie temperature (TC) is studied for Mn-doped ZnSnAs2 ferromagnetic semiconductors, epitaxially grown on InP substrates by molecular beam epitaxy. In the ferromagnetic phase, Mn distributions in a (Zn,Mn,Sn)As2 thin film with 7.2 cation percent (cat. %) Mn are investigated using three-dimensional atom probe tomography. The results indicate an inhomogeneous distribution which spreads to a relatively high Mn concentration of 9.0 at. % (at. %). In the paramagnetic phase, it is found that the paramagnetic to ferromagnetic transition takes place sharply with a TC of 334 K when the Mn doping concentration increases to about 4 cat. % Mn, which corresponds to a magnetic percolation threshold for ferromagnetism in (Zn,Mn,Sn)As2. An effective Curie temperature ⟨TC⟩ is considered to bridge the Curie temperatures obtained experimentally to those calculated theoretically in inhomogeneous magnetic semiconductors. The behavior of magnetism in Mn-doped ZnSnAs2 can be explained by three different phases within the present framework.

Changes in Brain Metallome/Metabolome Pattern due to a Single i.v. Injection of Manganese in Rats

PubMed Central

Neth, Katharina; Lucio, Marianna; Walker, Alesia; Zorn, Julia; Schmitt-Kopplin, Philippe; Michalke, Bernhard

2015-01-01

Exposure to high concentrations of Manganese (Mn) is known to potentially induce an accumulation in the brain, leading to a Parkinson related disease, called manganism. Versatile mechanisms of Mn-induced brain injury are discussed, with inactivation of mitochondrial defense against oxidative stress being a major one. So far, studies indicate that the main Mn-species entering the brain are low molecular mass (LMM) compounds such as Mn-citrate. Applying a single low dose MnCl2 injection in rats, we observed alterations in Mn-species pattern within the brain by analysis of aqueous brain extracts by size-exclusion chromatography—inductively coupled plasma mass spectrometry (SEC-ICP-MS). Additionally, electrospray ionization—ion cyclotron resonance-Fourier transform-mass spectrometry (ESI-ICR/FT-MS) measurement of methanolic brain extracts revealed a comprehensive analysis of changes in brain metabolisms after the single MnCl2 injection. Major alterations were observed for amino acid, fatty acid, glutathione, glucose and purine/pyrimidine metabolism. The power of this metabolomic approach is the broad and detailed overview of affected brain metabolisms. We also correlated results from the metallomic investigations (Mn concentrations and Mn-species in brain) with the findings from metabolomics. This strategy might help to unravel the role of different Mn-species during Mn-induced alterations in brain metabolism. PMID:26383269

The role of C and Mn at the austenite/pearlite reaction front during non-steady-state pearlite growth in a Fe-C-Mn steel

DOE PAGES

Aranda, M. M.; Rementeria, R.; Poplawsky, Jonathan D.; ...

2015-04-18

The role of C and Mn during the growth of pearlite under non-steady state conditions is analyzed by comparing the phase compositions of austenite, ferrite and cementite (γ+α+θ) through the use of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and atom probe tomography (APT) measurements across the austenite/pearlite interface. Furthermore, a local Mn enrichment and C depletion at the austenite/pearlite interface has been measured, which causes a change in the driving force with time during divergent pearlite growth.

Modulating the electronic and magnetic properties of bilayer borophene via transition metal atoms intercalation: from metal to half metal and semiconductor

NASA Astrophysics Data System (ADS)

Zhang, Xiuyun; Sun, Yi; Ma, Liang; Zhao, Xinli; Yao, Xiaojing

2018-07-01

Borophene, a two-dimensional monolayer made of boron atoms, has attracted wide attention due to its appealing properties. Great efforts have been devoted to fine tuning its electronic and magnetic properties for desired applications. Herein, we theoretically investigate the versatile electronic and magnetic properties of bilayer borophene (BLB) intercalated by 3d transition metal (TM) atoms, TM@BLBs (TM = Ti-Fe), using ab initio calculations. Four allotropes of AA-stacking (α 1-, β-, β 12- and χ 3-) BLBs with different intercalation concentrations of TM atoms are considered. Our results show that the TM atoms are strongly bonded to the borophene layers with fairly large binding energies, around 6.31 ∼ 15.44 eV per TM atom. The BLBs with Cr and Mn intercalation have robust ferromagnetism, while for the systems decorated with Fe atoms, fruitful magnetic properties, such as nonmagnetic, ferromagnetic or antiferromagnetic, are identified. In particular, the α 1- and β-BLBs intercalated by Mn or Fe atom can be transformed into a semiconductor, half metal or graphene-like semimetal. Moreover, some heavily doped TM@BLBs expose high Curie temperatures above room temperature. The attractive properties of TM@BLBs entail an efficient way to modulate the electronic and magnetic properties of borophene sheets for advanced applications.

Effect of the nano-oxide layer as a Mn diffusion barrier in specular spin valves

NASA Astrophysics Data System (ADS)

Jang, S. H.; Kang, T.; Kim, H. J.; Kim, K. Y.

2002-07-01

In previous work an enhanced giant magnetoresistance (GMR) effect in spin valves (SVs) with a nano-oxide layer (NOL) after annealing at about 250-300 degC has been reported. We have shown that SVs with a NOL also have higher thermal stability of the MR ratio at 300 degC. From secondary-ion-mass spectroscopy and x-ray photoelectron spectroscopy depth profile analysis, the mechanism of the improved thermal stability of the SVs with a NOL is shown to be related to MnO formation within the NOL. Thus, Mn atoms from the FeMn layer are trapped, and Mn diffusion is inhibited by the NOL during annealing.

Electronic band structure study of colossal magnetoresistance in Tl 2Mn 2O 7

NASA Astrophysics Data System (ADS)

Seo, D.-K.; Whangbo, M.-H.; Subramanian, M. A.

1997-02-01

The electronic structure of Tl 2Mn 2O 7 was examined by performing tight binding band calculations. The overlap between the Mn t 2g- and Tl 6 s-block bands results in a partial filling of the Tl 6 s-block bands. The associated Fermi surface consists of 12 cigar-shape electron pockets with each electron pocket about {1}/{1000} of the first Brillouin zone in size. The Tl 6 s-block bands have orbital contributions from the Mn atoms, and the carrier density is very low. These are important for the occurrence of a colossal magnetoresistance in Tl 2Mn 2O 7.

Spectroscopic characterization and reactivity studies of a mononuclear nonheme Mn(III)-hydroperoxo complex.

PubMed

So, Hee; Park, Young Jun; Cho, Kyung-Bin; Lee, Yong-Min; Seo, Mi Sook; Cho, Jaeheung; Sarangi, Ritimukta; Nam, Wonwoo

2014-09-03

We report the first example of a mononuclear nonheme manganese(III)-hydroperoxo complex derived from protonation of an isolated manganese(III)-peroxo complex bearing an N-tetramethylated cyclam (TMC) ligand, [Mn(III)(TMC)(OOH)](2+). The Mn(III)-hydroperoxo intermediate is characterized with various spectroscopic methods as well as with density functional theory (DFT) calculations, showing the binding of a hydroperoxide ligand in an end-on fashion. The Mn(III)-hydroperoxo species is a competent oxidant in oxygen atom transfer (OAT) reactions, such as the oxidation of sulfides. The electrophilic character of the Mn(III)-hydroperoxo complex is demonstrated unambiguously in the sulfoxidation of para-substituted thioanisoles.

Biosorption of copper, nickel and manganese using non-living biomass of marine alga, Ulva lactuca.

PubMed

Omar, Hanan Hafez

2008-04-01

The adsorption of Cu2+, Ni2+ and Mn2+ onto the marine algal biomass of Ulva lactuca was investigated in single and multimetal solutions. This study was intended to determine the role of different pH values (2-8) on the biosorption of metals at different concentrations (10, 20 and 30 mg L(-1)). The biosorption capacity of Cu2+, Ni2+ and Mn2+ for 10 mg L(-1) was the same as 20 and 30 mg L(-1), increase with increasing pH up to pH 5.0 and then decreased, in single and multimetal solutions. The optimum pH value was observed in the pH range 4-5 for Cu2+ and pH 5-6 for Ni2+ and Mn2+. The maximum biosorption capacities of tested alga for Cu2+, Ni2+ and Mn2+ were 92, 80 and 75%, respectively in single metal solution at 10 mg L(-1) and pH 5.0. At a further increase of pH (8.0) the biosorption process for Cu2+, Ni2+ and Mn2+ (75, 69 and 63%, respectively at 10 mg L(-1)) was decreased. The minimum biosorptions were 60, 49 and 44% for Cu2+, Ni2+ and Mn2+, respectively in single metal solution at 10 mg L(-1) and pH 2.0. In the multimetal solution, algal biomass exhibited the maximum and the minimum biosorption capacity at different pH values the same as in single metal solution. The inhibitory role of other ions on sorption process can be well observed in multimetal mixture, where biosorption capacity of Cu2+, Ni2+ and Mn2+ were significantly decreased in the multimetal solutions. The maximum biosorption was recorded for Cu2+ (83%) in solution of Cu2+ + Mn2+, Mn2+ (67%) in solution of Ni2 + Mn2+ and for Ni2+ (74%) in solution of Ni2+ + Mn2+ at the concentration 10 mg L(-1) and pH 5.0. The observed reduction in the biosorption of Cu2+, Ni2+ and Mn2+ (65, 57 and 52%, respectively at 10 mg L(-1) and pH 5.0) was more pronounced in the multimetal solution of Cu2 + Ni2+ + Mn2+ as compared with single metal solution. The results demonstrated that the affinity of the tested alga for sorption of the investigated metal ions in single and multimetal solutions runs in the order Cu2+ > Ni2+ > Mn2+. Biosorption equilibrium was established by the Langmuir and Freundlich isotherm models. According to the analyses conducted, the biosorption of Cu2+, Ni2+ and Mn2+ to Ulva lactuca was more consistent with Freundlich isotherm.

Bond angles in transition metal tetracarbonyl compounds: A further test of the theory of hybrid bond orbitals*

PubMed Central

Pauling, Linus

1978-01-01

An equation for the bond angles OC—M—CO for tetracarbonyl groups in which the transition metal atom M is enneacovalent, derived from the simple theory of hybrid sp3d5 bond orbitals, is tested by comparison of the calculated values of the angles with the experimental values reported for many compounds containing M(CO)4 groups, especially those with M = Fe, Mn, Re, Cr, or Mo. The importance of the energy of resonance of single bonds and double bonds in stabilizing octahedral complexes of chromium and manganese with carbonyl, phosphine, arsine, and thio groups is also discussed. PMID:16592490

Tuning the reactivity of mononuclear nonheme manganese(iv)-oxo complexes by triflic acid

DOE PAGES

Chen, Junying; Yoon, Heejung; Lee, Yong -Min; ...

2015-04-14

Triflic acid (HOTf)-bound nonheme Mn( IV)-oxo complexes, [(L)Mn IV(O)] 2+–(HOTf) 2 (L = N4Py and Bn-TPEN; N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine and Bn-TPEN = N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine), were synthesized by adding HOTf to the solutions of the [(L)Mn IV(O)] 2+ complexes and were characterized by various spectroscopies. The one-electron reduction potentials of the Mn IV(O) complexes exhibited a significant positive shift upon binding of HOTf. The driving force dependences of electron transfer (ET) from electron donors to the Mn IV(O) and Mn IV(O)–(HOTf) 2 complexes were examined and evaluated in light of the Marcus theory of ET to determine the reorganization energies of ET.more » The smaller reorganization energies and much more positive reduction potentials of the [(L)Mn IV(O)] 2+–(HOTf) 2 complexes resulted in greatly enhanced oxidation capacity towards one-electron reductants and para-X-substituted-thioanisoles. The reactivities of the Mn(IV)-oxo complexes were markedly enhanced by binding of HOTf, such as a 6.4 × 10 5-fold increase in the oxygen atom transfer (OAT) reaction (i.e., sulfoxidation). Such a remarkable acceleration in the OAT reaction results from the enhancement of ET from para-X-substituted-thioanisoles to the MnIV(O) complexes as revealed by the unified ET driving force dependence of the rate constants of OAT and ET reactions of [(L)Mn IV(O)] 2+–(HOTf) 2. In contrast, deceleration was observed in the rate of H-atom transfer (HAT) reaction of [(L)Mn IV(O)] 2+–(HOTf) 2 complexes with 1,4-cyclohexadiene as compared with those of the [(L)Mn IV(O)] 2+ complexes. Thus, the binding of two HOTf molecules to the Mn IV(O) moiety resulted in remarkable acceleration of the ET rate when the ET is thermodynamically feasible. When the ET reaction is highly endergonic, the rate of the HAT reaction is decelerated due to the steric effect of the counter anion of HOTf.« less

L'etude de l'InP et du GaP suite a l'implantation ionique de Mn et a un recuit thermique

NASA Astrophysics Data System (ADS)

Bucsa, Ioan Gigel

Cette these est dediee a l'etude des materiaux InMnP et GaMnP fabriques par implantation ionique et recuit thermique. Plus precisement nous avons investigue la possibilite de former par implantation ionique des materiaux homogenes (alliages) de InMnP et GaMnP contenant de 1 a 5 % atomiques de Mn qui seraient en etat ferromagnetique, pour des possibles applications dans la spintronique. Dans un premier chapitre introductif nous donnons les motivations de cette recherche et faisons une revue de la litterature sur ce sujet. Le deuxieme chapitre decrit les principes de l'implantation ionique, qui est la technique utilisee pour la fabrication des echantillons. Les effets de l'energie, fluence et direction du faisceau ionique sur le profil d'implantation et la formation des dommages seront mis en evidence. Aussi dans ce chapitre nous allons trouver des informations sur les substrats utilises pour l'implantation. Les techniques experimentales utilisees pour la caracterisation structurale, chimique et magnetique des echantillons, ainsi que leurs limitations sont presentees dans le troisieme chapitre. Quelques principes theoriques du magnetisme necessaires pour la comprehension des mesures magnetiques se retrouvent dans le chapitre 4. Le cinquieme chapitre est dedie a l'etude de la morphologie et des proprietes magnetiques des substrats utilises pour implantation et le sixieme chapitre, a l'etude des echantillons implantes au Mn sans avoir subi un recuit thermique. Notamment nous allons voir dans ce chapitre que l'implantation de Mn a plus que 1016 ions/cm 2 amorphise la partie implantee du materiau et le Mn implante se dispose en profondeur sur un profil gaussien. De point de vue magnetique les atomes implantes se trouvent dans un etat paramagnetique entre 5 et 300 K ayant le spin 5/2. Dans le chapitre 7 nous presentons les proprietes des echantillons recuits a basses temperatures. Nous allons voir que dans ces echantillons la couche implantee est polycristalline et les atomes de Mn sont toujours dans un etat paramagnetique. Dans les chapitres 8 et 9, qui sont les plus volumineux, nous presentons les resultats des mesures sur les echantillons recuits a hautes temperatures: il s'agit d'InP et du GaP implantes au Mn, dans le chapitre 8 et d'InP co-implante au Mn et au P, dans le chapitre 9. D'abord, dans le chapitre 8 nous allons voir que le recuit a hautes temperatures mene a une recristallisation epitaxiale du InMnP et du GaMnP; aussi la majorite des atomes de Mn se deplacent vers la surface a cause d'un effet de segregation. Dans les regions de la surface, concentres en Mn, les mesures XRD et TEM identifient la formation de MnP et d'In cristallin. Les mesures magnetiques identifient aussi la presence de MnP ferromagnetique. De plus dans ces mesures on trouve qu'environ 60 % du Mn implante est en etat paramagnetique avec la valeur du spin reduite par rapport a celle trouvee dans les echantillons non-recuits. Dans les echantillons InP co-implantes au Mn et au P la recristallisation est seulement partielle mais l'effet de segregation du Mn a la surface est beaucoup reduit. Dans ce cas plus que 50 % du Mn forme des particules MnP et le restant est en etat paramagnetique au spin 5/2, dilue dans la matrice de l'InP. Finalement dans le dernier chapitre, 10, nous presentons les conclusions principales auxquels nous sommes arrives et discutons les resultats et leurs implications. Mots cles: implantation ionique, InP, GaP, amorphisation, MnP, segregation, co-implantation, couche polycristalline, paramagnetisme, ferromagnetisme.

Some connectivity indices and zagreb index of polyhex nanotubes.

PubMed

Farahani, Mohammad Reza

2012-12-01

Several topological indices are investigated in polyhex nanotubes: Randić connectivity index, sum-connectivity index, atom-bond connectivity index, geometric-arithmetic index, First and Second Zagreb indices and Zagreb polynomials. Formulas for calculating the above topological descriptors in polyhex zigzag TUZC6[m,n] and armchair TUAC6[m,n] nanotube families are given.

119Sn Mössbauer spectroscopy for assessing the local stress and defect state towards the tuning of Ni-Mn-Sn alloys

NASA Astrophysics Data System (ADS)

Unzueta, I.; López-García, J.; Sánchez-Alarcos, V.; Recarte, V.; Pérez-Landazábal, J. I.; Rodríguez-Velamazán, J. A.; Garitaonandia, J. S.; García, J. A.; Plazaola, F.

2017-05-01

The influence of defects and local stresses on the magnetic properties and martensitic transformation in Ni50Mn35Sn15 is studied at macroscopic and atomic scale levels. We show that both the structural and magnetic properties of the alloy are very sensitive to slight microstructural distortions. Even though no atomic disorder is induced by milling, the antiphase boundaries linked to dislocations promote the antiferromagnetic coupling of Mn, resulting in a significant decrease in the saturation magnetization. On the other hand, the temperature range of the transformation is considerably affected by the mechanically induced local stresses, which in turn does not affect the equilibrium temperature between the austenitic and martensitic phases. Finally, we demonstrate that the recovery of the martensitic transformation is directly related to the intensity of the non-magnetic component revealed by 119Sn Mössbauer spectroscopy. This result opens the possibility of quantifying the whole contribution of defects and the local stresses on the martensitic transformation in Ni-Mn-Sn alloys.

Polycrystalline La1-xSrxMnO3 films on silicon: Influence of post-Deposition annealing on structural, (Magneto-)Optical, and (Magneto-)Electrical properties

NASA Astrophysics Data System (ADS)

Thoma, Patrick; Monecke, Manuel; Buja, Oana-Maria; Solonenko, Dmytro; Dudric, Roxana; Ciubotariu, Oana-Tereza; Albrecht, Manfred; Deac, Iosif G.; Tetean, Romulus; Zahn, Dietrich R. T.; Salvan, Georgeta

2018-01-01

The integration of La1-xSrxMnO3 (LSMO) thin film technology into established industrial silicon processes is regarded as challenging due to lattice mismatch, thermal expansion, and chemical reactions at the interface of LSMO and silicon. In this work, we investigated the physical properties of thin La0.73Sr0.27MnO3 films deposited by magnetron sputtering on silicon without a lattice matching buffer layer. The influence of a post-deposition annealing treatment on the structural, (magneto-)optical, and (magneto-)electrical properties was investigated by a variety of techniques. Using Rutherford backscattering spectroscopy, atomic force microscopy, Raman spectroscopy, and X-ray diffraction we could show that the thin films exhibit a polycrystalline, rhombohedral structure after a post-deposition annealing of at least 700 °C. The dielectric tensor in the spectral range from 1.7 eV to 5 eV determined from spectroscopic ellipsometry in combination with magneto-optical Kerr effect spectroscopy was found to be comparable to that of lattice matched films on single crystal substrates reported in literature [1]. The values of the metal-isolator transition temperature and temperature-dependent resistivities also reflect a high degree of crystalline quality of the thermally treated films.

Magnetic and electronic properties of SrMnO3 thin films

NASA Astrophysics Data System (ADS)

Mandal, Arup Kumar; Panchal, Gyanendra; Choudhary, R. J.; Phase, D. M.

2018-05-01

Single phase hexagonal bulk SrMnO3 (SMO) was prepared by solid state route and it was used for depositing thin films by pulsed laser deposition (PLD) technique on single crystalline (100) oriented SrTiO3 (STO) substrate. X-ray diffraction shows that the thin film is deposited in cubic SrMnO3 phase. From X-ray absorption at the Mn L edge we observed the mixed valency of Mn (Mn3+& Mn4+) due to strain induced by the lattice mismatching between SMO and STO. Due to this mixed valency of Mn ion in SMO film, the ferromagnetic nature is observed at lower temperature because of double exchange. After post annealing with very low oxygen partial pressure, magnetic and electronic property of SMO films are effectively modified.

Magnetic properties of doped Mn-Ga alloys made by mechanical milling and heat treatment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Daniel R.; National High Magnetic Field Laboratory, Tallahassee, FL 32310; Han, Ke

2016-05-15

Mn-Ga alloys have shown hard magnetic properties, even though these alloys contain no rare-earth metals. However, much work is needed before rare-earth magnets can be replaced. We have examined the magnetic properties of bulk alloys made with partial replacement of both the Mn and Ga elements in the Mn{sub 0.8}Ga{sub 0.2} system. Bulk samples of Mn-Ga-Bi, Mn-Ga-Al, Mn-Fe-Ga and Mn-(FeB)-Ga alloys were fabricated and studied using mechanically milling and heat treatments while altering the atomic percentage of the third element between 2.5 and 20 at%. The ternary alloy exhibits all hard magnetic properties at room temperature with large coercivity. Annealedmore » Mn-Ga-X bulk composites exhibit high coercivities up to 16.6 kOe and remanence up to 9.8 emu/g, that is increased by 115% over the binary system.« less

Investigation the electroplating behavior of self formed CuMn barrier.

PubMed

Wu, Chia-Yang; Lee, Wen-Hsi; Chang, Shih-Chieh; Wang, Ying-Lang

2013-08-01

The electrical and material properties of Copper (Cu) mixed with [0-10 atomic% manganese (Mn)] and pure Cu films deposited on silicon oxide (SiO2)/silicon (Si) are explored. Cu electroplating on self formed CuMn barrier was investigated with different Mn content. The electrochemical deposition of the Cu thin film onto the electrode using CuMn barrier was investigated. Scanning electron microscopic (SEM) micrographs of copper electroplating on CuMn films were examined, and the copper nucleation behaviors changed with the Mn content. Since the electrochemical impedance spectroscopy (EIS) is widely recognized as a powerful tool for the investigation of electrochemical behaviors, the tool was also used to verify the phenomena during plating. It was found that the charge-trasfer impedance decrease with the rise in the Mn content below 5%, but increase with the rise in the Mn content higher than 5%. The result was corresponded to the surface energy, the surface morphology, the corrosion and the oxidation of the substrate.

Influence of the local environment on Mn acceptors in GaAs

NASA Astrophysics Data System (ADS)

Lee, Donghun; Gohlke, David; Benjamin, Anne; Gupta, Jay A.

2015-04-01

As transistors continue to shrink toward nanoscale dimensions, their characteristics are increasingly dependent on the statistical variations of impurities in the semiconductor material. The scanning tunneling microscope (STM) can be used to not only study prototype devices with atomically precise placement of impurity atoms, but can also probe how the properties of these impurities depend on the local environment. Tunneling spectroscopy of Mn acceptors in GaAs indicates that surface-layer Mn act as a deep acceptor, with a hole binding energy that can be tuned by positioning charged defects nearby. Band bending induced by the tip or by these defects can also tune the ionization state of the acceptor complex, evident as a ring-like contrast in STM images. The interplay of these effects is explored over a wide range of defect distances, and understood using iterative simulations of tip-induced band bending.

Bis(O-n-butyl dithio­carbonato-κ2 S,S′)bis­(pyridine-κN)manganese(II)

PubMed Central

Alam, Naveed; Ehsan, Muhammad Ali; Zeller, Matthias; Mazhar, Muhammad; Arifin, Zainudin

2011-01-01

The structure of the title manganese complex, [Mn(C5H9OS2)2(C5H5N)2] or [Mn(S2CO-n-Bu)2(C5H5N)2], consists of discrete monomeric entities with Mn2+ ions located on centres of inversion. The metal atom is coordinated by a six-coordinate trans-N2S4 donor set with the pyridyl N atoms located in the apical positions. The observed slight deviations from octa­hedral geometry are caused by the bite angle of the bidentate κ2-S2CO-n-Bu ligands [69.48 (1)°]. The O(CH2)3(CH3) chains of the O-n-butyl dithio­carbonate units are disordered over two sets of sites with an occupancy ratio of 0.589 (2):0.411 (2). PMID:22090847

Bis(O-n-butyl dithio-carbonato-κS,S')bis-(pyridine-κN)manganese(II).

PubMed

Alam, Naveed; Ehsan, Muhammad Ali; Zeller, Matthias; Mazhar, Muhammad; Arifin, Zainudin

2011-08-01

The structure of the title manganese complex, [Mn(C(5)H(9)OS(2))(2)(C(5)H(5)N)(2)] or [Mn(S(2)CO-n-Bu)(2)(C(5)H(5)N)(2)], consists of discrete monomeric entities with Mn(2+) ions located on centres of inversion. The metal atom is coordinated by a six-coordinate trans-N(2)S(4) donor set with the pyridyl N atoms located in the apical positions. The observed slight deviations from octa-hedral geometry are caused by the bite angle of the bidentate κ(2)-S(2)CO-n-Bu ligands [69.48 (1)°]. The O(CH(2))(3)(CH(3)) chains of the O-n-butyl dithio-carbonate units are disordered over two sets of sites with an occupancy ratio of 0.589 (2):0.411 (2).

Dependence of magnetic field and electronic transport of Mn4 Single-molecule magnet in a Single-Electron Transistor

NASA Astrophysics Data System (ADS)

Rodriguez, Alvar; Singh, Simranjeet; Haque, Firoze; Del Barco, Enrique; Nguyen, Tu; Christou, George

2012-02-01

Dependence of magnetic field and electronic transport of Mn4 Single-molecule magnet in a Single-Electron Transistor A. Rodriguez, S. Singh, F. Haque and E. del Barco Department of Physics, University of Central Florida, 4000 Central Florida Blvd., Orlando, Florida 32816 USA T. Nguyen and G. Christou Department of Chemistry, University of Florida, Gainesville, Florida 32611 USA Abstract We have performed single-electron transport measurements on a series of Mn-based low-nuclearity single-molecule magnets (SMM) observing Coulomb blockade. SMMs with well isolated and low ground spin states, i.e. S = 9/2 (Mn4) and S = 6 (Mn3) were chosen for these studies, such that the ground spin multiplet does not mix with levels of other excited spin states for the magnetic fields (H = 0-8 T) employed in the experiments. Different functionalization groups were employed to change the mechanical, geometrical and transport characteristics of the molecules when deposited from liquid solution on the transistors. Electromigration-broken three-terminal single-electron transistors were used. Results obtained at temperatures down to 240 mK and in the presence of high magnetic fields will be shown.

A hierarchical nanostructure consisting of amorphous MnO 2, Mn 3O 4 nanocrystallites, and single-crystalline MnOOH nanowires for supercapacitors

NASA Astrophysics Data System (ADS)

Hu, Chi-Chang; Hung, Ching-Yun; Chang, Kuo-Hsin; Yang, Yi-Lin

In this communication, a porous hierarchical nanostructure consisting of amorphous MnO 2 (a-MnO 2), Mn 3O 4 nanocrystals, and single-crystalline MnOOH nanowires is designed for the supercapacitor application, which is prepared by a simple two-step electrochemical deposition process. Because of the gradual co-transformation of Mn 3O 4 nanocrystals and a-MnO 2 nanorods into an amorphous manganese oxide, the cycle stability of a-MnO 2 is obviously enhanced by adding Mn 3O 4. This unique ternary oxide nanocomposite with 100-cycle CV activation exhibits excellent capacitive performances, i.e., excellent reversibility, high specific capacitances (470 F g -1 in CaCl 2), high power property, and outstanding cycle stability. The highly porous microstructures of this composite before and after the 10,000-cycle CV test are examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Transition metal atoms absorbed on MoS2/h-BN heterostructure: stable geometries, band structures and magnetic properties.

PubMed

Wu, Yanbing; Huang, Zongyu; Liu, Huating; He, Chaoyu; Xue, Lin; Qi, Xiang; Zhong, Jianxin

2018-06-15

We have studied the stable geometries, band structures and magnetic properties of transition-metal (V, Cr, Mn, Fe, Co and Ni) atoms absorbed on MoS2/h-BN heterostructure systems by first-principles calculations. By comparing the adsorption energies, we find that the adsorbed transition metal (TM) atoms prefer to stay on the top of Mo atoms. The results of the band structure without spin-orbit coupling (SOC) interaction indicate that the Cr-absorbed systems behave in a similar manner to metals, and the Co-absorbed system exhibits a half-metallic state. We also deduce that the V-, Mn-, Fe-absorbed systems are semiconductors with 100% spin polarization at the HOMO level. The Ni-absorbed system is a nonmagnetic semiconductor. In contrast, the Co-absorbed system exhibits metallic state, and the bandgap of V-absorbed system decreases slightly according to the SOC calculations. In addition, the magnetic moments of all the six TM atoms absorbed on the MoS2/h-BN heterostructure systems decrease when compared with those of their free-standing states.

High-resolution structural studies of ultra-thin magnetic, transition metal overlayers and two-dimensional transition metal oxides using synchrotron radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kellar, S.A.

This thesis report the surface-structure determination of three, ultra-thin magnetic transition-metal films, Fe/Au(100), Mn/Ni(100), and Mn/Cu(100) using Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) and photoelectron holography. These structural studies are the first to use non-s initial states in the ARPEFS procedure. This thesis also reports an ARPEFS surface-structure determination of a two-dimensional transition-metal oxide, [(1 x 1)O/W(110)] x 12. The authors have analyzed the ARPFES signal from the Au 4f{sub 7/5} core level of the Au(1 ML)/Fe(15 ML)/Au(100) system. The analysis shows that the Fe grows layer by layer with one monolayer of gold, acting as a surfactant, remaining onmore » top of the growing Fe layers. These surface gold atoms sit in the four-fold hollow site, 1.67 {+-} 0.02 A above the iron surface. The grown Fe layer is very much like the bulk, bcc iron, with an interlayer spacing of 1.43 {+-} 0.03 A. Analysis of the Mn 3p ARPEFS signals from c(2 x 2)Mn/Ni(100) and c(2 x 2)Mn/Cu(100) shows that the Mn forms highly corrugated surface alloys. The corrugation of the Mn/Ni(100) and Mn/Cu(100) systems are 0.24 {+-} 0.02 A and 0.30 {+-} 0.04 A respectively. In both cases the Mn is sticking above the plane of the surface substrate atoms. For the Mn/Ni(100) system the first layer Ni is contracted 4% from the bulk value. The Mn/Cu(100) system shows bulk spacing for the substrate Cu. Photoelectron holography shows that the Mn/Ni interface is very abrupt with very little Mn leaking into the second layer, while the Mn/Cu(100) case has a significant amount of Mn leaking into the second layer. A new, five-element electrostatic electron lens was developed for hemispherical electron-energy analyzers. This lens system can be operated at constant transverse or constants angular magnification, and has been optimized for use with the very small photon-spot sizes. Improvements to the hemispherical electron-energy analyzer are also discussed.« less

Phosphate forms an unusual tripodal complex with the Fe–Mn center of sweet potato purple acid phosphatase

PubMed Central

Schenk, Gerhard; Gahan, Lawrence R.; Carrington, Lyle E.; Mitić, Nataša; Valizadeh, Mohsen; Hamilton, Susan E.; de Jersey, John; Guddat, Luke W.

2005-01-01

Purple acid phosphatases (PAPs) are a family of binuclear metalloenzymes that catalyze the hydrolysis of phosphoric acid esters and anhydrides. A PAP in sweet potato has a unique, strongly antiferromagnetically coupled Fe(III)–Mn(II) center and is distinguished from other PAPs by its increased catalytic efficiency for a range of activated and unactivated phosphate esters, its strict requirement for Mn(II), and the presence of a μ-oxo bridge at pH 4.90. This enzyme displays maximum catalytic efficiency (kcat/Km) at pH 4.5, whereas its catalytic rate constant (kcat) is maximal at near-neutral pH, and, in contrast to other PAPs, its catalytic parameters are not dependent on the pKa of the leaving group. The crystal structure of the phosphate-bound Fe(III)–Mn(II) PAP has been determined to 2.5-Å resolution (final Rfree value of 0.256). Structural comparisons of the active site of sweet potato, red kidney bean, and mammalian PAPs show several amino acid substitutions in the sweet potato enzyme that can account for its increased catalytic efficiency. The phosphate molecule binds in an unusual tripodal mode to the two metal ions, with two of the phosphate oxygen atoms binding to Fe(III) and Mn(II), a third oxygen atom bridging the two metal ions, and the fourth oxygen pointing toward the substrate binding pocket. This binding mode is unique among the known structures in this family but is reminiscent of phosphate binding to urease and of sulfate binding to λ protein phosphatase. The structure and kinetics support the hypothesis that the bridging oxygen atom initiates hydrolysis. PMID:15625111

Atomistic Insights Into the Oriented Attachment of Tunnel-Based Oxide Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Yifei; Wood, Stephen M; He, Kun

Controlled synthesis of nanomaterials is one of the grand challenges facing materials scientists. In particular, how tunnel-based nanomaterials aggregate during synthesis while maintaining their well-aligned tunneled structure is not fully understood. Here, we describe the atomistic mechanism of oriented attachment (OA) during solution synthesis of tunneled α-MnO2 nanowires based on a combination of in situ liquid cell transmission electron microscopy (TEM), aberration-corrected scanning TEM with subangstrom spatial resolution, and first-principles calculations. It is found that primary tunnels (1 × 1 and 2 × 2) attach along their common {110} lateral surfaces to form interfaces corresponding to 2 × 3 tunnelsmore » that facilitate their short-range ordering. The OA growth of α-MnO2 nanowires is driven by the stability gained from elimination of {110} surfaces and saturation of Mn atoms at {110}-edges. During this process, extra [MnOx] radicals in solution link the two adjacent {110} surfaces and bond with the unsaturated Mn atoms from both surface edges to produce stable nanowire interfaces. Our results provide insights into the controlled synthesis and design of nanomaterials in which tunneled structures can be tailored for use in catalysis, ion exchange, and energy storage applications.« less

Crystallographic features of the approximant H (Mn7Si2V) phase in the Mn-Si-V alloy system

NASA Astrophysics Data System (ADS)

Nakayama, Kei; Komatsuzaki, Takumi; Koyama, Yasumasa

2018-07-01

The intermetallic compound H (Mn7Si2V) phase in the Mn-Si-V alloy system can be regarded as an approximant phase of the dodecagonal quasicrystal as one of the two-dimensional quasicrystals. To understand the features of the approximant H phase, in this study, the crystallographic features of both the H phase and the (σ → H) reaction in Mn-Si-V alloy samples were investigated, mainly by transmission electron microscopy. It was found that, in the H phase, there were characteristic structural disorders with respect to an array of a dodecagonal structural unit consisting of 19 dodecagonal atomic columns. Concretely, penetrated structural units consisting of two dodecagonal structural units were presumed to be typical of such disorders. An interesting feature of the (σ → H) reaction was that regions with a rectangular arrangement of penetrated structural units (RAPU) first appeared in the σ matrix as the initial state, and H regions were then nucleated in contact with RAPU regions. The subsequent conversion of RAPU regions into H regions eventually resulted in the formation of the approximant H state as the final state. Furthermore, atomic positions in both the H structure and the dodecagonal quasicrystal were examined using a simple plane-wave model with 12 plane waves.

Crystal structure of dimanganese(II) zinc bis­[ortho­phosphate(V)] monohydrate

PubMed Central

Alhakmi, Ghaleb; Assani, Abderrazzak; Saadi, Mohamed; El Ammari, Lahcen

2015-01-01

The title compound, Mn2Zn(PO4)2·H2O, was obtained under hydro­thermal conditions. The structure is isotypic with other transition metal phosphates of the type M 3− xM′x(PO4)2·H2O, but shows no statistical disorder of the three metallic sites. The principal building units are distorted [MnO6] and [MnO5(H2O)] octa­hedra, a distorted [ZnO5] square pyramid and two regular PO4 tetra­hedra. The connection of the polyhedra leads to a framework structure. Two types of layers parallel to (-101) can be distinguished in this framework. One layer contains [Zn2O8] dimers linked to PO4 tetra­hedra via common edges. The other layer is more corrugated and contains [Mn2O8(H2O)2] dimers and [MnO6] octa­hedra linked together by common edges. The PO4 tetra­hedra link the two types of layers into a framework structure with channels parallel to [101]. The H atoms of the water mol­ecules point into the channels and form O—H⋯O hydrogen bonds (one of which is bifurcated) with framework O atoms across the channels. PMID:25878806

Reduction of thermal conductivity in MnSi{sub 1.7} multi-layered thin films with artificially inserted Si interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurosaki, Y., E-mail: yosuke.kurosaki.uy@hitachi.com; Yabuuchi, S.; Nishide, A.

We report a lowered lattice thermal conductivity in nm-scale MnSi{sub 1.7}/Si multilayers which were fabricated by controlling thermal diffusions of Mn and Si atoms. The thickness of the constituent layers is 1.5–5.0 nm, which is comparable to the phonon mean free path of both MnSi{sub 1.7} and Si. By applying the above nanostructures, we reduced the lattice thermal conductivity down to half that of bulk MnSi{sub 1.7}/Si composite materials. The obtained value of 1.0 W/K m is the experimentally observed minimum in MnSi{sub 1.7}-based materials without any heavy element doping and close to the minimum thermal conductivity. We attribute the reduced latticemore » thermal conductivity to phonon scattering at the MnSi{sub 1.7}/Si interfaces in the multilayers.« less

Near-edge X-ray absorption spectra for metallic Cu and Mn

NASA Astrophysics Data System (ADS)

Greaves, G. N.; Durham, P. J.; Diakun, G.; Quinn, P.

1981-11-01

The measurement of X-ray absorption fine structure of metals- both in the extended region (EXAFS) as well as in the near edge region (XANES)-has been widely discussed (see refs 1-6 for Cu and refs 7-9 for Mn). The recent availability of intense X-ray fluxes from storage rings has usually been exploited for EXAFS leaving the XANES often with poorer resolution than earlier work performed on conventional sources (for example, compare the near edge structure for copper in ref. 1 with refs 3 or 6). In addition, whilst the theory and analysis of EXAFS is relatively well-established2,10, a theory for the strong scattering regime near to the absorption edge has only recently been developed11. We report here the first high resolution XANES spectra for Cu and Mn which were performed at the SRS storage ring at Daresbury. Although both metals have close-packed structures consisting of atoms of similar size their local atomic structure is different in detail. Significant differences are found in their respective XANES reflecting the senstivity of this region of the X-ray absorption fine structure to the local atomic structure. Spectra for the two metals have been analysed using the new multiple scattering formalism. This is a real space calculation and unlike a conventional band structure approach it does not require structural periodicity but works from the local arrangement of atoms.

Malonate-containing manganese(III) complexes: synthesis, crystal structure, and magnetic properties of AsPh4[Mn(mal)2(H2O)2].

PubMed

Delgado, Fernando S; Kerbellec, Nicolas; Ruiz-Pérez, Catalina; Cano, Joan; Lloret, Francesc; Julve, Miguel

2006-02-06

The novel manganese(III) complexes PPh4[Mn(mal)2(H2O)2] (1) and AsPh4[Mn(mal)2(H2O)2] (2) (PPh4+ = tetraphenylphosphonium cation, AsPh4+ = tetraphenylarsonium cation, and H2mal = malonic acid) have been prepared, and the structure of 2 was determined by X-ray diffraction analysis. 2 is a mononuclear complex whose structure is made up of trans-diaquabis(malonato)manganate(III) units and tetraphenylarsonium cations. Two crystallographically independent manganese(III) ions (Mn(1) and Mn(2)) occur in 2 that exhibit elongated octahedral surroundings with four oxygen atoms from two bidentate malonate groups in equatorial positions (Mn(1)-O = 1.923(6) and 1.9328(6) A and Mn(2)-O = 1.894(6) and 1.925(6) A) and two trans-coordinated water molecules in the axial sites (Mn(1)-Ow = 2.245(6) A and Mn(2)-Ow = 2.268(6) A). The [Mn(mal)2(H2O)2]- units are linked through hydrogen bonds involving the free malonate-oxygen atoms and the coordinated water molecules to yield a quasi-square-type anionic layer growing in the ab plane. The shortest intralayer metal-metal separations are 7.1557(7) and 7.1526(7) A (through the edges of the square). The anionic sheets are separated from each other by layers of AsPh4+ where sextuple- and double-phenyl embraces occur. The magnetic behavior of 1 and 2 in the temperature range 1.9-290 K reveals the occurrence of weak intralayer ferromagnetic interactions (J = +0.081(1) (1) and +0.072(2) cm(-1) (2)). These values are compared to those of the weak antiferromagnetic coupling [J = -0.19(1) cm(-1)], which is observed in the chain compound K2[Mn(mal)2(MeOH)2][Mn(mal)2] (3), where the exchange pathway involves the carboxyate-malonate bridge in the anti-syn conformation. The structure of 3 was reported elsewhere. Theoretical calculations on fragment models of 2 and 3 were performed to analyze and substantiate both the nature and magnitude of the magnetic couplings observed.

Lipophilicity of potent porphyrin-based antioxidants. Comparison of ortho and meta isomers of Mn(III) N-alkylpyridylporphyrins

PubMed Central

Kos, Ivan; Rebouças, Júlio S.; DeFreitas-Silva, Gilson; Salvemini, Daniela; Vujaskovic, Zeljko; Dewhirst, Mark W.; Spasojevic, Ivan; Batinic-Haberle, Ines

2009-01-01

Mn(III) N-alkylpyridylporphyrins are among the most potent known SOD mimics and catalytic peroxynitrite scavengers, and modulators of redox-based cellular transcriptional activity. In addition to their intrinsic antioxidant capacity, bioavailability plays major role in their in vivo efficacy. While of identical antioxidant capacity, lipophilic MnTnHex-2-PyP is up to 120-fold more efficient in reducing oxidative stress injuries than hydrophilic MnTE-2-PyP. Due to limitations of analytical nature, porphyrin lipophilicity has been often estimated by thin-layer chromatographic Rf parameter, instead of the standard n-octanol/water partition coefficient, POW. Herein we used a new methodological approach to finally describe the MnP lipophilicity, by the conventional log POW means, for a series of biologically active ortho and meta isomers of Mn(III) N-alkylpyridylporphyrins. Three new porphyrins (MnTnBu-3-PyP, MnTnHex-3-PyP and MnTnHep-2-PyP) were synthesized to strengthen the conclusions. The log POW was linearly related to Rf and to the number of carbons in the alkyl chain (nC) for both isomer series; the meta isomers being 10-fold more lipophilic than the analogous ortho porphyrins. Increasing the length of the alkyl chain for 1 carbon atom increases the log POW value ~ 1 log unit with both isomers. Dramatic ~4 and ~5 orders of magnitude increase in lipophilicity of ortho isomers by extending pyridyl alkyl chains from 2 (MnTE-2-PyP, log POW = −6.25) to 6 (MnTnHex-2-PyP, log POW = −2.29) and 8 carbon atoms (MnTnOct-2-PyP, log POW = −0.77) parallels the increased efficacy in several oxidative-stress injury models, particularly those of the central nervous system where transport across the blood-brain barrier is critical. Although meta isomers are only slightly less potent SOD mimics and antioxidants than their ortho analogues, their higher lipophilicity and smaller bulkiness may lead to a higher cellular uptake and overall similar effectiveness in vivo. PMID:19361553

(3+1)D superspace structural determination of two new modulated composite phases: Sr 1+ x(Cu xMn 1- x)O 3; x=3/11 and x=0.3244

NASA Astrophysics Data System (ADS)

El Abed, Ahmed; Gaudin, Etienne; zur Loye, Hans-Conrad; Darriet, Jacques

2003-01-01

We report the structure determination of two new phases belonging to the A 1+ x(A' xB 1- x)O 3 family of oxides with A=Sr, A'=Cu, and B=Mn, where x=3/11 and x=0.3244, corresponding to a commensurate and incommensurate composite structure, respectively. These two compounds are the first examples of oxides belonging to the Sr 1+ x(Cu xMn 1- x)O 3 family. Their structures were solved in the (3+1) dimensional superspace formalism as modulated composite structures with two subsystems [(Cu,Mn)O 3] and [Sr]. The superspace group used to solve the structures is R 3¯m(00γ)0s . The first phase ( x=3/11), corresponding to the chemical formula Sr 14Cu 3Mn 8O 33, was obtained as a single crystal with unit cell parameters of a=9.6025(3) Å and c1=2.5660(8) Å ( q=7/11 c1∗, Z=3), where c1 is the lattice parameter corresponding to the c-axis of the trigonal subsystem [(Cu,Mn)O 3]. The second phase ( x=0.3244(1)), is a polycrystalline sample with unit cell parameters of a=9.5933(7) and c1=2.5933(3) ( q=0.6622 c1∗, Z=3). In both structures, one dimensional chains run along the c-axis which contain octahedra and trigonal prisms occupied by manganese and copper atoms, respectively. The refinement results show that in both cases copper occupies the rectangular faces of the trigonal prism while manganese occupies the octahedral sites. The magnetic measurements of the polycrystalline phase (Sr 1+ x(Cu xMn 1- x)O 3, x=0.3244(2)) and the Curie constant obtained from the high temperature susceptibility are in agreement with a spin state configuration of S=3/2 for Mn 4+ and S=1/2 for Cu 2+.

Ab initio investigation of the thermodynamics of cation distribution and of the electronic and magnetic structures in the LiMn2O4 spinel

NASA Astrophysics Data System (ADS)

Santos-Carballal, David; Ngoepe, Phuti E.; de Leeuw, Nora H.

2018-02-01

The spinel-structured lithium manganese oxide (LiMn2O4 ) is a material currently used as cathode for secondary lithium-ion batteries, but whose properties are not yet fully understood. Here, we report a computational investigation of the inversion thermodynamics and electronic behavior of LiMn2O4 derived from spin-polarized density functional theory calculations with a Hubbard Hamiltonian and long-range dispersion corrections (DFT+U-D3). Based on the analysis of the configurational free energy, we have elucidated a partially inverse equilibrium cation distribution for the LiMn2O4 spinel. This equilibrium degree of inversion is rationalized in terms of the crystal field stabilization effects and the difference between the size of the cations. We compare the atomic charges with the oxidation numbers for each degree of inversion. We found segregation of the Mn charge once these ions occupy the tetrahedral and octahedral sites of the spinel. We have obtained the atomic projections of the electronic band structure and density of states, showing that the normal LiMn2O4 has half-metallic properties, while the fully inverse spinel is an insulator. This material is in the ferrimagnetic state for the inverse and partially inverse cation arrangement. The optimized lattice and oxygen parameters, as well as the equilibrium degree of inversion, are in agreement with the available experimental data. The partial equilibrium degree of inversion is important in the interpretation of the lithium ion migration and surface properties of the LiMn2O4 spinel.

Raman study of transition-metal oxides with perovskite-like structure

NASA Astrophysics Data System (ADS)

Kolev, Nikolay Iliev

Perovskite-like oxides exhibit a rich variety of properties of fundamental scientific interest and potential application value. The motivation for this work is to contribute to our knowledge of perovskite-like systems and strongly correlated systems in general. The polarized Raman spectra of single crystal and thin film CaCu3Ti4O12, single crystal and thin film CaRuO3, microcrystals of La0.5Ca 0.5MnO3, and ceramic and thin film CaMnO3 have been investigated. In close comparison to results from lattice dynamics calculations most of the Raman lines in the CaCu3Ti4O12, CaRuO3, La0.5Ca0.5MnO3 and CaMnO 3 spectra, have been assigned to definite phonon modes. The validity of the model for twin orientation in the Pnma structure for CaRuO3 and La0.5Ca0.5MnO3 is confirmed. The analysis of the CaMnO3 spectra contributed to the development of a model, based on four basic distortions of the (distorted) perovskite structure. The temperature behavior of the CaCu3Ti4O 12 spectra shows that there is no evidence for structural phase transition in the temperature range 20--600 K, so such a transition cannot be responsible for the sharp drop in the dielectric constant below 100 K. The Raman spectra indirectly support the mechanism of formation of barrier layer capacitances in CaCu3Ti4O12.The observation of additional Raman mode of nominal Ag symmetry is discussed in terms of coexistence of domains of different atomic arrangement, or alternatively of non-stoichiometry (Cu deficiency). In the case of the thin film, the tetragonal distortions could be responsible for the greater separation of the additional Ag line. No anomalies in the temperature behavior of the Raman lines of CaRuO3 is observed, which is an indirect evidence for its lack of long-range magnetic ordering at low temperatures (depending on whether this ordering would be observable by Raman spectroscopy through spin-phonon coupling). In La0.5Ca0.5MnO 3 the appearance of several Raman lines below TN is analyzed in terms of ordering and freezing of the Jahn-Teller distortions in a superstructure. Polarized Raman spectra confirmed their usefulness in studying thin films and their properties.

cis-Dichloridobis-(5,5'-dimethyl-2,2'-bipyridine)-manganese(II) 2.5-hydrate.

PubMed

Lopes, Lívia Batista; Corrêa, Charlane Cimini; Diniz, Renata

2011-07-01

The metal site in the title compound [MnCl(2)(C(12)H(12)N(2))(2)]·2.5H(2)O has a distorted octa-hedral geometry, coordinated by four N atoms of two 5,5'-dimethyl-2,2'-dipyridine ligands and two Cl atoms. Two and a half water molecules of hydration per complex unit are observed in the crystal structure. The compounds extend along the c axis with O-H⋯Cl, O-H⋯O, C-H⋯Cl and C-H⋯O hydrogen bonds and π-π inter-actions [centroid-centroid distance = 3.70 (2) Å] contributing substanti-ally to the crystal packing. The Mn and one of the water O atoms, the latter being half-occupied, are located on special positions, in this case a rotation axis of order 2.

Theoretical investigation of the reaction of Mn+ with ethylene oxide.

PubMed

Li, Yuanyuan; Guo, Wenyue; Zhao, Lianming; Liu, Zhaochun; Lu, Xiaoqing; Shan, Honghong

2012-01-12

The potential energy surfaces of Mn(+) reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO(+), MnO, MnCH(2)(+), MnCH(3), and MnH(+) are described in detail. Two types of encounter complexes of Mn(+) with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn(+) would insert into a C-O bond or the C-C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO(+)/MnO and MnH(+) are formed in the C-O activation mechanism, while both C-O and C-C activations account for the MnCH(2)(+)/MnCH(3) formation. Products MnO(+), MnCH(2)(+), and MnH(+) could be formed adiabatically on the quintet surface, while formation of MnO and MnCH(3) is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a(5)D is calculated to be more reactive than the ground state a(7)S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.

Transition-metal dispersion on carbon-doped boron nitride nanostructures: Applications for high-capacity hydrogen storage

NASA Astrophysics Data System (ADS)

Chen, Ming; Zhao, Yu-Jun; Liao, Ji-Hai; Yang, Xiao-Bao

2012-07-01

Using density-functional theory calculations, we investigated the adsorption of transition-metal (TM) atoms (TM = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) on carbon doped hexagonal boron nitride (BN) sheet and the corresponding cage (B12N12). With carbon substitution of nitrogen, Sc, V, Cr, and Mn atoms were energetically favorable to be dispersed on the BN nanostructures without clustering or the formation of TM dimers, due to the strong binding between TM atoms and substrate, which contains the half-filled levels above the valence bands maximum. The carbon doped BN nanostructures with dispersed Sc could store up to five and six H2, respectively, with the average binding energy of 0.3 ˜ 0.4 eV, indicating the possibility of fabricating hydrogen storage media with high capacity. We also demonstrated that the geometrical effect is important for the hydrogen storage, leading to a modulation of the charge distributions of d levels, which dominates the binding between H2 and TM atoms.

Flow injection analysis-flame atomic absorption spectrometry system for indirect determination of sulfite after on-line reduction of solid-phase manganese (IV) dioxide reactor.

PubMed

Zare-Dorabei, Rouholah; Boroun, Shokoufeh; Noroozifar, Meissam

2018-02-01

A new and simple flow injection method followed by atomic absorption spectrometry was developed for indirect determination of sulfite. The proposed method is based on the oxidation of sulfite to sulphate ion using solid-phase manganese dioxide (30% W/W suspended on silica gel beads) reactor. MnO 2 will be reduced to Mn(II) by sample injection in to the column under acidic carrier stream of HNO 3 (pH 2) with flow rate of 3.5mLmin -1 at room temperature. Absorption measurement of Mn(II) which is proportional to the concentration of sulfite in the sample was carried out by atomic absorption spectrometry. The calibration curve was linear up to 25mgL -1 with a detection limit (DL) of 0.08mgL -1 for 400µL injection sample volume. The presented method is efficient toward sulfite determination in sugar and water samples with a relative standard deviation (RSD) less than 1.2% and a sampling rate of about 60h -1 . Copyright © 2017 Elsevier B.V. All rights reserved.

Mn valence, magnetic, and electrical properties of LaMnO3+δ nanofibers by electrospinning.

PubMed

Zhou, Xianfeng; Xue, Jiang; Zhou, Defeng; Wang, Zhongli; Bai, Yijia; Wu, Xiaojie; Liu, Xiaojuan; Meng, Jian

2010-10-01

LaMnO3+δ nanofibers have been prepared by electrospinning. The nearly 70% of Mn atoms is Mn4+, which is much higher than that in the nanoparticles. The average grain size of our fibers is approximately 20 nm, which is the critical size producing the nanoscale effect. The nanofibers exhibit a very broad magnetic transition with Tc≈255 K, and the Tc onset is around 310 K. The blocking temperature TB is 180 K. The sample shows weak ferromagnetic property above the TB and below Tc and superparamagnetic property near the Tc onset. The resistivity measurements show a metal-insulator transition near 210 K and an upturn at about 45 K.

Semiconductor-metal nanostructures: Scanning tunneling microscopy investigation of the fullerene-gold and manganese-germanium-silicon system

NASA Astrophysics Data System (ADS)

Liu, Hui

Nanostructures, assembled from a layer or cluster of atoms with size of the order of nanometers, have attracted much attention for decades, because it has been widely recognized that the properties of nanoscale materials are remarkably different from those of materials of large scale. As one of the most powerful techniques, Scanning Tunneling Microscopy (STM) has become an indispensable technique for studies in nanotechnology. This dissertation is focused on the investigation of the C60-Au system, which is relevant in photovoltaic applications and organic electronic devices, and the Mn-Ge-Si system which is central to the development of advanced spintronics system. The first part of the dissertation focuses on the C60-Au system. Exploring how fullerene molecules interact physically and electronically with each other and with other elements is highly relevant to the advancement of fullerene-based nanotechnology applications. The initial growth stage of C 60 thin film on graphite substrate has been investigated by STM at room temperature. It is observed that the C60 layer grows in a quasi-layer-by-layer mode and forms round 1st layer islands on the graphite surface. The fractal-dendritic growth of the 2nd layer islands has been successfully described by a combination of Monte Carlo simulation and molecular dynamics simulations. As a next step towards the application of fullerenes in device structures, the growth mechanisms of Au clusters on fullerene layers and co-deposition of Au and C60 were explored. The most prominent features of the growth of Au on C60 are the preferential nucleation of Au clusters at the graphite-first fullerene layer islands edge and the co-deposition of C60 and Au on graphite leading to the formation of highly organized structures, in which Au clusters are embedded in a ring of fullerene molecules with a constant width of about 4 nm. The second part of this dissertation concentrates on the Mn-Ge-Si system, a semiconductor/metal system, which is a potential building-block structure for the development of complex spin-electronic devices. In recent years the study of thin film magnetic materials and the doping of semiconductors with magnetically active dopant atoms has received increased attention due their potential applications in magnetic memory devices and spintronics. In particular, the importance of Mn-Ge-Si system emerges since it combines a technically relevant semiconductor surface with a metallic element with a large magnetic moment. The goal in this part is the early growth stage of Mn on a Si (100) 2x1surface, the formation of Mn-nanostructure and the interaction between Mn and Ge on the Si surface. The position of Mn atoms with respect to Si surface has been determined by high resolution STM images. It is found that Mn adatoms form relatively short monoatomic wires, with a typical length of 5 to about 20 atoms, which are oriented perpendicular to the Si-dimer rows. And at the same time, the modification of Si surface around Mn wires was observed. The formation of Mn silicide after annealing the sample was also studied. The stability of Mn wires during the growth of a Ge overlayer was investigated by comparing several STM images, which were taken at different bias voltages. Because of the different local density of states, Mn and Ge may be partially distinguished in STM images. It is turned out that Mn wires preserve their structures after the deposition of a small amount of Ge on the sample. And the growth of Ge at the early stage on Si surface has not been significantly influenced by the presence of Mn adatoms. In summary, an investigation of two semiconductor-metal nanostructures by STM has been reported in this dissertation.

Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl(6) and other alloys are twinned cubic crystals.

PubMed

Pauling, L

1987-06-01

It is shown that the x-ray powder diffraction patterns of rapidly quenched MnAl(6) and Mg(32)(Al,Zn)(49) and the neutron powder diffraction pattern of MnAl(6) are compatible with the proposed 820-atom primitive cubic structure [Pauling, L. (1987) Phys. Rev. Lett. 58, 365-368]. The values found for the edge of the unit cube are 23.365 A (x-ray) and 23.416 A (neutron) for MnAl(6) and 24.313 A (x-ray) for Mg(32)(Al,Zn)(49).

Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl6 and other alloys are twinned cubic crystals

PubMed Central

Pauling, Linus

1987-01-01

It is shown that the x-ray powder diffraction patterns of rapidly quenched MnAl6 and Mg32(Al,Zn)49 and the neutron powder diffraction pattern of MnAl6 are compatible with the proposed 820-atom primitive cubic structure [Pauling, L. (1987) Phys. Rev. Lett. 58, 365-368]. The values found for the edge of the unit cube are 23.365 Å (x-ray) and 23.416 Å (neutron) for MnAl6 and 24.313 Å (x-ray) for Mg32(Al,Zn)49. PMID:16593841

The beta(+) decay and cosmic-ray half-life of Mn-54

NASA Astrophysics Data System (ADS)

Dacruz, M. T. F.; Norman, E. B.; Chan, Y. D.; Garcia, A.; Larimer, R. M.; Lesko, K. T.; Stokstad, R. G.; Wietfeldt, F. E.

1993-03-01

We performed a search for the beta(+) branch of Mn-54 decay. As a cosmic ray, Mn-54, deprived of its atomic electrons, can decay only via beta(+) and beta(-) decay, with a half-life of the order of 106 yr. This turns Mn-54 into a suitable cosmic chronometer for the study of cosmic-ray confinement times. We searched for coincident back-to-back 511-keV gamma-rays using two germanium detectors inside a Nal(Tl) annulus. An upper limit of 2 x 10-8 was found for the beta(+) decay branch, corresponding to a lower limit of 13.7 for the log ft value.

Electrodeposited nanostructured MnO{sub 2} for non-enzymatic hydrogen peroxide sensing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saha, B., E-mail: barnamala.saha@gmail.com; Jana, S. K.; Banerjee, S.

2015-06-24

Electrodeposited MnO{sub 2} nanostructure was synthesized on indium tin oxide coated glass electrode by cyclic voltammetry. The as obtained samples were subsequently characterized by atomic force microscopy and their electro-catalytic response towards hydrogen peroxide in alkaline medium of 0.1M NaOH was studied using cyclic voltammetry and amperometry.

Site preference, magnetism and lattice vibrations of intermetallics Lu₂Fe 17–xT x (T=Cr, Mn, Ru)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jin-Chun; Qian, Ping, E-mail: qianpinghu@sohu.com; Zhang, Zhen-Feng

We present an atomistic study on the phase stability, site preference and lattice constants of the rare earth intermetallics Lu₂Fe 17–xT x (T=Cr, Mn, Ru). The calculated preferential occupation site of ternary element T is found to be the 4f site. The order of site preference is given as 4f, 12k, 12j and 6g for Lu₂Fe 17–xT x. The calculated lattice parameters are corresponding to the experimental results. We have calculated the magnetic moments of Lu₂Fe 17–xT x compounds. Results show that the calculated total magnetic moment of Lu₂Fe₁₇ compound is M=37.34 μ B/f.u. In addition, the total and partialmore » phonon densities of states are evaluated first for these complicated structures. - Graphical abstract: The vibrational modes are mostly excited by Fe atoms, Lu contributes to the lower frequencies modes, and the contribution of Ru atoms is the same as Fe atoms. Highlights: • There are no reports on lattice vibrations of Lu₂(Fe, T) 17–x (T=Cr, Mn, Ru) compounds. • The phase stability and site preference are evaluated first for the complex structures of Lu₂(Fe, T) 17–x (T=Cr, Mn, Ru) compounds. • The lattice inversion method to obtain the interatomic pair potential is the unique one.« less

Multivalent Mn-doped TiO2 thin films

NASA Astrophysics Data System (ADS)

Lin, C. Y. W.; Channei, D.; Koshy, P.; Nakaruk, A.; Sorrell, C. C.

2012-07-01

Thin films of TiO2 doped with Mn were deposited on F-doped SnO2-coated glass using spin coating. The concentration of the dopant was in the range 0-7 wt% Mn (metal basis). The films were examined in terms of the structural, chemical, and optical properties. Glancing angle X-ray diffraction data show that the films consisted of the anatase polymorph of TiO2, without any contaminant phases. The X-ray photoelectron spectroscopy data indicate the presence of Mn3+ and Mn4+ in the doped films as well as atomic disorder and associated structural distortion. Ultraviolet-visible spectrophotometry data show that the optical indirect band gap of the films decreased significantly with increasing manganese doping, from 3.32 eV for the undoped composition to 2.90 eV for that doped with 7 wt% Mn.

Prediction of the electronic structures, thermodynamic and mechanical properties in manganese doped magnesium-based alloys and their saturated hydrides based on density functional theory

NASA Astrophysics Data System (ADS)

Zhang, Ziying; Zhang, Huizhen; Zhao, Hui; Yu, Zhishui; He, Liang; Li, Jin

2015-04-01

The crystal structures, electronic structures, thermodynamic and mechanical properties of Mg2Ni alloy and its saturated hydride with different Mn-doping contents are investigated using first-principles density functional theory. The lattice parameters for the Mn-doped Mg2Ni alloys and their saturated hydrides decreased with an increasing Mn-doping content because of the smaller atomic size of Mn compared with that of Mg. Analysis of the formation enthalpies and electronic structures reveal that the partial substitution of Mg with Mn reduces the stability of Mg2Ni alloy and its saturated hydride. The calculated elastic constants indicate that, although the partial substitution of Mg with Mn lowers the toughness of the hexagonal Mg2Ni alloy, the charge/discharge cycles are elevated when the Mn-doping content is high enough to form the predicted intermetallic compound Mg3MnNi2.

Two spin-canting textures in the antiferromagnetic phase AF1 of MnWO4 based on the new polar atomistic model in P2

NASA Astrophysics Data System (ADS)

Park, S.-H.; Liu, B.-Q.; Behal, D.; Pedersen, B.; Schneidewind, A.

2018-04-01

The low temperature antiferromagnetic (AF) phase of MnWO4 (the so-called AF1 phase) exhibits different spin-canting configurations at two Mn2+ sublattices of the (3  +  1)-dimensional magnetic structure. The suggested superspace group {{\\boldsymbol P}}2.1^\\prime(α, 1/2, γ)0s is a significant consequence of the polar space group {{\\boldsymbol P}} 2 true for the nuclear structure of MnWO4. Density functional theory calculations showed that its ground state prefers this two spin-canting system. The structural difference between two independent atomic sites for Mn (Mn a , Mn b ) is too small to allow microscopically detectable electric polarisation. However, this hidden intrinsic polar character allows AF1 two commensurately modulated spin-canting textures. This is considered as the prerequisite onset of the improper ferroelectricity enhanced by the helical spin order in the multiferroic phase AF2 of MnWO4.

Structure and properties of CdO-B2O3 and CdO-MnO-B2O3 glasses; Criteria of getting the fraction of four coordinated boron atoms from infrared spectra

NASA Astrophysics Data System (ADS)

Doweidar, H.; El-Damrawi, G.; El-Stohy, Sh.

2017-11-01

IR spectra of CdO-B2O3 and xCdO·(50 - x)MnO·50B2O3 glasses (0 ≤ x ≤ 50 mol%) have been analyzed. The fraction N4 of four coordinated boron atoms obtained from the integrated area under the IR spectra of CdO-B2O3 glasses is markedly higher than the reported NMR values. In both cases, N4 does not change with CdO content. The difference between N4 values of both techniques has been correlated with the relative absorption coefficient of BO4 unit with respect to BO3 unit, as suggested by Chryssikos et al. N4 data of xCdO·(50 - x)MnO·50B2O3 glasses could be used to calculate the fraction of modifier and former CdO and MnO in the borate matrix, as a function of composition. There is a linear increase in both the density and molar volume with increasing CdO content. The change has been correlated with the contribution of CdO and MnO. Electric conduction is assumed to take place via hopping of small polarons. There is a decrease in conductivity with increasing CdO concentration, which suggests that the electrons related to Cd sites are more localized than those at Mn sites.

Tunable multiple emissions in manganese-concentrated sulfide through simultaneous tailoring of Mn-site coordination and Mn-Mn pair geometry

NASA Astrophysics Data System (ADS)

Chen, Zitao; Song, Enhai; Ye, Shi; Zhang, Qinyuan

2017-12-01

In contrast to generally single-band visible emission feature from Mn2+, simultaneous visible (VIS) and near-infrared (NIR) multiple emissions are demonstrated in Mn2+ concentrated sulfide (MnS) by only involving a single crystallographic site. Upon varying the Mn2+-site coordination and/or Mn-Mn pairs geometry in different structural MnS, the multiple emissions from divalent manganese can be easily tuned from 575 to 720 nm (VIS) or from 880 to 900 or 1380 nm (NIR), respectively. The excitation spectroscopy and the luminescent decay, together with crystal structural analyses, are employed to investigate the electronic transition and the excited state dynamics of these Mn2+ concentrated systems. It is found that the VIS and NIR emissions can be ascribed to the isolated Mn2+ ion and exchange coupled Mn-Mn pair center, respectively. The effect of crystal field and bridging geometry, as well as temperature on the exchange coupled Mn2+ pairs NIR emissive center, is also investigated in detail. This work not only provides keen insights into the de-excitation pathway of Mn2+-concentrated material, but also offers the possibilities of designing a novel NIR emitting source for various photonic applications.

Modulating the electronic and magnetic properties of bilayer borophene via transition metal atoms intercalation: from metal to half metal and semiconductor.

PubMed

Zhang, Xiuyun; Sun, Yi; Ma, Liang; Zhao, Xinli; Yao, Xiaojing

2018-07-27

Borophene, a two-dimensional monolayer made of boron atoms, has attracted wide attention due to its appealing properties. Great efforts have been devoted to fine tuning its electronic and magnetic properties for desired applications. Herein, we theoretically investigate the versatile electronic and magnetic properties of bilayer borophene (BLB) intercalated by 3d transition metal (TM) atoms, TM@BLBs (TM = Ti-Fe), using ab initio calculations. Four allotropes of AA-stacking (α 1 -, β-, β 12 - and χ 3 -) BLBs with different intercalation concentrations of TM atoms are considered. Our results show that the TM atoms are strongly bonded to the borophene layers with fairly large binding energies, around 6.31 ∼ 15.44 eV per TM atom. The BLBs with Cr and Mn intercalation have robust ferromagnetism, while for the systems decorated with Fe atoms, fruitful magnetic properties, such as nonmagnetic, ferromagnetic or antiferromagnetic, are identified. In particular, the α 1 - and β-BLBs intercalated by Mn or Fe atom can be transformed into a semiconductor, half metal or graphene-like semimetal. Moreover, some heavily doped TM@BLBs expose high Curie temperatures above room temperature. The attractive properties of TM@BLBs entail an efficient way to modulate the electronic and magnetic properties of borophene sheets for advanced applications.

Does an infrasonic acoustic shock wave resonance of the manganese 3+ loaded/copper depleted prion protein initiate the pathogenesis of TSE?

PubMed

Purdey, Mark

2003-06-01

Intensive exposures to natural and artificial sources of infrasonic acoustic shock (tectonic disturbances, supersonic aeroplanes, etc.) have been observed in ecosystems supporting mammalian populations that are blighted by clusters of traditional and new variant strains of transmissible spongiform encephalopathy (TSE). But TSEs will only emerge in those 'infrasound-rich' environments which are simultaneously influenced by eco-factors that induce a high manganese (Mn)/low copper (Cu)-zinc (Zn) ratio in brains of local mammalian populations. Since cellular prion protein (PrPc) is a cupro-protein expressed throughout the circadian mediated pathways of the body, it is proposed that PrP's Cu component performs a role in the conduction and distribution of endogenous electromagnetic energy; energy that has been transduced from incoming ultraviolet, acoustic, geomagnetic radiations. TSE pathogenesis is initiated once Mn substitutes at the vacant Cu domain on PrPc and forms a nonpathogenic, protease resistant, 'sleeping' prion. A second stage of pathogenesis comes into play once a low frequency wave of infrasonic shock metamorphoses the piezoelectric atomic structure of the Mn 3+ component of the prion, thereby 'priming' the sleeping prion into its fully fledged, pathogenic TSE isoform - where the paramagnetic status of the Mn 3+ atom is transformed into a stable ferrimagnetic lattice work, due to the strong electron-phonon coupling resulting from the dynamic 'Jahn-Teller' type distortions of the oxygen octahedra specific to the trivalent Mn species. The so called 'infectivity' of the prion is a misnomer and should be correctly defined as the contagious field inducing capacity of the ferrimagnetic Mn 3+ component of the prion; which remains pathogenic at all temperatures below the 'curie point'. A progressive domino-like 'metal to ligand to metal' ferrimagnetic corruption of the conduits of electromagnetic superexchange is initiated. The TSE diseased brain can be likened to a solar charged battery on continuous charge; where the Mn contaminated/Cu depleted circadian-auditory pathways absorb and pile up, rather than conduct the vital life force energies of incoming ultra violet, acoustic and geomagnetic radiation. Instead of harnessing these energies for the body's own bio-rhythmic requirements, an infrasonic shock induced metamorphosis of the Mn atom intervenes; initiating an explosive pathogenesis that perverts the healthy pathways of darkness and light; Cu prions are replaced by hyperpolarized Mn 3+ prions that seed self perpetuating 'cluster bombs' of free radical mediated neurodegeneration. TSE ensues.

Mn-oxidizing Bacteria in Oak Ridge, TN and the Potential for Mercury Remediation

NASA Astrophysics Data System (ADS)

Wright, K. L.; McNeal, K. S.; Han, F. X.

2012-12-01

East Fork Poplar Creek (EFPC) in Oak Ridge, TN was highly contaminated with elemental mercury in the 1950 and 1960. The area is still experiencing the effects of mercury contamination, and researchers are searching for ways to remediate the EFPC. One possible mechanism for bioremediation is the use of biogenic Mn oxides to remove heavy metals from water systems. Six native Pseudomonas bacteria species were isolated from the EFPC in order to examine biogenic Mn oxides production and bioremediation of Oak Ridge slurries. To investigate the biochemical interactions of Pseudomonas and the native microbial communities with Hg, Mn, Fe, S, six different slurry treatment groups were compared using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and cold vapor atomic absorption spectrometry (CVAAS). Oak Ridge slurries were autoclaved to inhibit microbial growth (group 1), autoclaved and amended with HgS (group 2), autoclaved and amended with Pseudomonas isolates and additional HgS (group 3), untreated slurry (group 4), normal slurry amended with HgS (group 5), and normal slurry amended with Pseudomonas isolates and additional HgS (group 6). The comparison of the autoclaved groups with the counterpart untreated and normal Oak Ridge slurries highlighted important microbial interactions. Also, the Pseudomonas isolates were grown separately in a MnSO4 media, and the individual bacteria were monitored for Mn-oxidization using ICP-AES and transmission electron microscopy (TEM). In the slurry sediments, the Pseudomonas isolates did produce Mn oxides which bound to mercury, and mercury bound to organic matter significantly decreased. However, after a significant decrease of dissolved mercury in the water, dissolved mercury was cycled back into the water system on day 10 of the study. Additionally, two individual native Oak Ridge Pseudomonas isolates demonstrated Mn-oxidization. Biogenic Mn oxides have the potential to decrease mercury cycling, however there is need for more in depth and long-term studies to confirm their sustained use as Hg bioremediators.

Structural and Electronic Properties of Transition-Metal Oxides Attached to a Single-Walled CNT as a Lithium-Ion Battery Electrode: A First-Principles Study.

PubMed

Tack, Liew Weng; Azam, Mohd Asyadi; Seman, Raja Noor Amalina Raja

2017-04-06

Single-walled carbon nanotubes (SWCNTs) and metal oxides (MOs), such as manganese(IV) oxide (MnO 2 ), cobalt(II, III) oxide (Co 3 O 4 ), and nickel(II) oxide (NiO) hybrid structures, have received great attention because of their promising application in lithium-ion batteries (LIBs). As electrode materials for LIBs, the structure of SWCNT/MOs provides high power density, good electrical conductivity, and excellent cyclic stability. In this work, first-principles calculations were used to investigate the structural and electronic properties of MOs attached to (5, 5) SWCNT and Li-ion adsorption to SWCNT/metal oxide composites as electrode materials in LIBs. Emphasis was placed on the synergistic effects of the composite on the electrochemical performance of LIBs in terms of adsorption capabilities and charge transfer of Li-ions attached to (5, 5) SWCNT and metal oxides. Also, Li adsorption energy on SWCNTs and three different metal oxides (NiO, MnO 2 , and Co 3 O 4 ) and the accompanying changes in the electronic properties, such as band structure, density of states and charge distribution as a function of Li adsorption were calculated. On the basis of the calculation results, the top C atom was found to be the most stable position for the NiO and MnO 2 attachment to SWCNT, while the Co 3 O 4 molecule, the Co 2+ , was found to be the most stable attachment on SWCNT. The obtained results show that the addition of MOs to the SWCNT electrode enables an increase in specific surface area and improves the electronic conductivity and charge transfer of an LIB.

The Dynamical Mean Field Study of Competition between Ferromagnetism and Disorder in Ferromagnetic Semiconductors

NASA Astrophysics Data System (ADS)

Aryanpour, Karan

2003-03-01

We employ the Dynamical Mean Field Approximation (DMFA) to study the Janko-Zarand model [1] for the combination of large spin-orbit coupling and spatial disorder effects in GaAs doped with Mn. In this model the electronic dispersion and the spin-orbit coupling are simultaneously diagonalized and therefore, the Hamiltonian for the pure system takes a surprisingly simple form. The price for this simplicity is that the quantization axis for the spin must be rotated along the direction of momentum. This chiral basis greatly complicates the form of the hole-impurity interaction at a single site i. In the DMFA, since all the crossing Feynman diagrams for the hole-impurity interaction vanish, the problem simplifies to the local diagrams for the holes scattering off of a single Mn impurity site only. The diagrammatics for the self-energy reduces to the local Green functions and potentials in the non-chiral basis in which they have very simple forms. We first calculate the initial green function G(k) in the chiral basis and then rotate G(k) back into the non chiral basis and coarse grain it over all the k momenta. The hole-impurity interaction is greatly simplified in the non-chiral basis and can be averaged over all the spin configurations and orientations of the Mn atoms on the lattice.The self energy may be extracted from the averaged Green function, and used to recalculate the initial cluster Green function, etc. completing the DMFA self-consistent loop. We intend to calculate the spin and charge transport coefficients, and spectra such as the AC susceptibility and the ARPES which may be directly compared with experiment. [1] Phys. Rev. Lett.89,047201/1-4 (2002)

Ferromagnetic GaAs structures with single Mn delta-layer fabricated using laser deposition.

PubMed

Danilov, Yuri A; Vikhrova, Olga V; Kudrin, Alexey V; Zvonkov, Boris N

2012-06-01

The new technique combining metal-organic chemical vapor epitaxy with laser ablation of solid targets was used for fabrication of ferromagnetic GaAs structures with single Mn delta-doped layer. The structures demonstrated anomalous Hall effect, planar Hall effect, negative and anisotropic magnetoresistance in temperature range of 10-35 K. In GaAs structures with only single Mn delta-layer (without additional 2D hole gas channel or quantum well) ferromagnetism was observed for the first time.

Manganese L-edge X-ray absorption spectroscopy of manganese catalase from Lactobacillus plantarum and mixed valence manganese complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grush, M.M.; Chen, J.; George, S.J.

1996-01-10

The first Mn L-edge absorption spectra of a Mn metalloprotein are presented in this paper. Both reduced and superoxidized Mn catalase have been examined by fluorescence-detected soft X-ray absorption spectroscopy, and their Mn L-edge spectra are dramatically different. The spectrum of reduced Mn(II)Mn(II) catalase has been interpreted by ligand field atomic multiplet calculations and by comparison to model compound spectra. The analysis finds a 10 Dq value of nearly 1.1 eV, consistent with coordination by predominately nitrogen and oxygen donor ligands. For interpretation of mixed valence Mn spectra, an empirical simulation procedure based on the addition of homovalent model compoundmore » spectra has been developed and was tested on a variety of Mn complexes and superoxidized Mn catalase. This routine was also used to determine the oxidation state composition of the Mn in [Ba{sub 8}Na{sub 2}ClMn{sub 16}(OH){sub 8}(CO{sub 3}){sub 4}L{sub 8}] .53 H{sub 2}O (L=1,3-diamino-2-hydroxypropane-N,N,N`N`-tetraacetic acid). 27 refs., 6 figs.« less

Single molecule magnet behavior of a pentanuclear Mn-based metallacrown complex: solid state and solution magnetic studies.

PubMed

Zaleski, Curtis M; Tricard, Simon; Depperman, Ezra C; Wernsdorfer, Wolfgang; Mallah, Talal; Kirk, Martin L; Pecoraro, Vincent L

2011-11-21

The magnetic behavior of the pentanuclear complex of formula Mn(II)(O(2)CCH(3))(2)[12-MC(Mn(III)(N)shi)-4](DMF)(6), 1, was investigated using magnetization and magnetic susceptibility measurements both in the solid state and in solution. Complex 1 has a nearly planar structure, made of a central Mn(II) ion surrounded by four peripheral Mn(III) ions. Solid state variable-field dc magnetic susceptibility experiments demonstrate that 1 possesses a low value for the total spin in the ground state; fitting appropriate expressions to the data results in antiferromangetic coupling both between the peripheral Mn(III) ions (J = -6.3 cm(-1)) and between the central Mn(II) ion and the Mn(III) ones (J' = -4.2 cm(-1)). In order to obtain a reasonable fit, a relatively large single ion magnetic anisotropy (D) value of 1 cm(-1) was necessary for the central Mn(II) ion. The single crystal magnetization measurements using a microsquid array display a very slight opening of the hysteresis loop but only at a very low temperature (0.04 K), which is in line with the ac susceptibility data where a slow relaxation of the magnetization occurs just around 2 K. In frozen solution, complex 1 displays a frequency dependent ac magnetic susceptibility signal with an energy barrier to magnetization reorientation (E) and relaxation time at an infinite temperature (τ(o)) of 14.7 cm(-1) and 1.4 × 10(-7) s, respectively, demonstrating the single molecule magnetic behavior in solution.

Dependence of the magnetic properties of the dilute magnetic semiconductor Zn1-xMnxO nanorods on their Mn doping levels

NASA Astrophysics Data System (ADS)

Thongjamroon, S.; Ding, J.; Herng, T. S.; Tang, I. M.; Thongmee, S.

2017-10-01

The effects of Mn doping on the ferromagnetic properties of the dilute magnetic semiconductor Zn1-xMnxO nanorods (NR's) having the nominal composit-ions x = 0, 0.01, 0.03, 0.04 and 0.05 grown by a low temperature hydrothermal method are studied. Energy dispersive X-ray (EDX) is used to determine the actual amounts of the elements in each NR's. X-ray diffraction, scanning electron microscopy, photoluminescence and vibrating sample magnetometer measurements are used to observe the effects of the Mn substitution on the properties of the doped ZnO and to relate the changes in the properties to changes in the defect content. It is observed that the saturation magnetization of the Mn ions in the wurtzite structure varies from 0.0210 μB/Mn2+ to 0.0234 μB/Mn2+ reaching a high of 0.0251 μB/Mn2+ as the Mn concentrations is varied from 0.9 to 7.36 atomic%. It is argued that the changes in the saturation magnetization are due to the competition between the direct Mn-Mn exchange interaction and the indirect Mn-O-Mn exchange interaction in the doped Mn ZnO NP's.

Ionic Strength-Controlled Mn (Hydr)oxide Nanoparticle Nucleation on Quartz: Effect of Aqueous Mn(OH)2.

PubMed

Jung, Haesung; Jun, Young-Shin

2016-01-05

The early formation of manganese (hydr)oxide nanoparticles at mineral-water interfaces is crucial in understanding how Mn oxides control the fate and transport of heavy metals and the cycling of nutrients. Using atomic force microscopy, we investigated the heterogeneous nucleation and growth of Mn (hydr)oxide under varied ionic strengths (IS; 1-100 mM NaNO3). Experimental conditions (i.e., 0.1 mM Mn(2+) (aq) concentration and pH 10.1) were chosen to be relevant to Mn remediation sites. We found that IS controls Mn(OH)2 (aq) formation, and that the controlled Mn(OH)2 (aq) formation can affect the system's saturation and subsequent Mn(OH)2 (s) and further Mn3O4 (s) nanoparticle formation. In 100 mM IS system, nucleated Mn (hydr)oxide particles had more coverage on the quartz substrate than those in 1 mM and 10 mM IS systems. This high IS also resulted in low supersaturation ratio and thus favor heterogeneous nucleation, having better structural matching between nucleating Mn (hydr)oxides and quartz. The unique information obtained in this work improves our understanding of Mn (hydr)oxide formation in natural as well as engineered aqueous environments, such as groundwater contaminated by natural leachate and acid mine drainage remediation.

Floating zone growth of α-Na 0.90MnO 2 single crystals

DOE PAGES

Dally, Rebecca; Clement, Raphaele J.; Chisnell, Robin; ...

2016-12-03

Here, single crystal growth of α-Na xMnO 2 (x=0.90) is reported via the floating zone technique. The conditions required for stable growth and intergrowth-free crystals are described along with the results of trials under alternate growth atmospheres. Chemical and structural characterizations of the resulting α-Na 0.90MnO 2 crystals are performed using ICP-AES NMR, XANES, XPS, and neutron diffraction measurements. As a layered transition metal oxide with large ionic mobility and strong correlation effects, α-Na xMnO 2 is of interest to many communities, and the implications of large volume, high purity, single crystal growth are discussed.

A DFT investigation on geometry and chemical bonding of isoelectronic Si8N6V-, Si8N6Cr, and Si8N6Mn+ clusters

NASA Astrophysics Data System (ADS)

Tam, Nguyen Minh; Pham, Hung Tan; Cuong, Ngo Tuan; Tung, Nguyen Thanh

2017-10-01

The geometric feature and chemical bonding of isoelectronic systems Si8N6Mq (M = V, Cr, Mn and q = -1, 0, 1, respectively) are investigated by means of density-functional-theory calculations. The encapsulated form is found for all ground-state structures, where the metal atom locates at the central site of the hollow Si8N6 cage. The Si8N6 cage is established by adding two Si atoms to a distorted Si6N6 prism, which is a combination of Si4N2 and Si2N4 strings. Chemical bonding of Si8N6Mq systems is explored by using the electron localization indicator and theory of atom in molecule, revealing the vital role of metal center in stabilizing the clusters.

cis-Dichloridobis­(5,5′-dimethyl-2,2′-bipyridine)­manganese(II) 2.5-hydrate

PubMed Central

Lopes, Lívia Batista; Corrêa, Charlane Cimini; Diniz, Renata

2011-01-01

The metal site in the title compound [MnCl2(C12H12N2)2]·2.5H2O has a distorted octa­hedral geometry, coordinated by four N atoms of two 5,5′-dimethyl-2,2′-dipyridine ligands and two Cl atoms. Two and a half water molecules of hydration per complex unit are observed in the crystal structure. The compounds extend along the c axis with O—H⋯Cl, O—H⋯O, C—H⋯Cl and C—H⋯O hydrogen bonds and π–π inter­actions [centroid-centroid distance = 3.70 (2) Å] contributing substanti­ally to the crystal packing. The Mn and one of the water O atoms, the latter being half-occupied, are located on special positions, in this case a rotation axis of order 2. PMID:21836893

Atomic structure of a decagonal Al-Pd-Mn phase

NASA Astrophysics Data System (ADS)

Mihalkovič, Marek; Roth, Johannes; Trebin, Hans-Rainer

2017-12-01

We present a detailed structure solution for the 16 -Å decagonal quasicrystal in the Al-Pd-Mn system by means of cluster decoration and ab initio energy minimization. It is based on structure models of the ɛ and other approximant phases. The ɛ phases can be represented as subsets of a hexagon-boat-star (HBS) tiling. The decagonal phase comprises further HBS tiles. We have constructed several fictitious HBS approximants and optimized their structures individually. All tiles are decorated by two types of atomic clusters: the pseudo-Mackay icosahedron (PMI) and the large bicapped pentagonal prism (LBPP). It turns out that, whereas the PMI clusters can be kept essentially unchanged, the LBPP clusters must be adjusted in occupancy with Al atoms depending on their positions in the various tiles. In this way we obtain cluster decorations for all tiles of the decagonal quasicrystal. The calculations were confirmed by evaluation of an effective tile Hamiltonian.

Magnetostriction of Hexagonal HoMnO3 and YMnO3 Single Crystals

NASA Astrophysics Data System (ADS)

Pavlovskii, N. S.; Dubrovskii, A. A.; Nikitin, S. E.; Semenov, S. V.; Terent'ev, K. Yu.; Shaikhutdinov, K. A.

2018-03-01

We report on the magnetostriction of hexagonal HoMnO3 and YMnO3 single crystals in a wide range of applied magnetic fields (up to H = 14 T) at all possible combinations of the mutual orientations of magnetic field H and magnetostriction Δ L/L. The measured Δ L/L( H, T) data agree well with the magnetic phase diagram of the HoMnO3 single crystal reported previously by other authors. It is shown that the nonmonotonic behavior of magnetostriction of the HoMnO3 crystal is caused by the Ho3+ ion; the magnetic moment of the Mn3+ ion parallel to the hexagonal crystal axis. The anomalies established from the magnetostriction measurements of HoMnO3 are consistent with the phase diagram of these compounds. For the isostructural YMnO3 single crystal with a nonmagnetic rare-earth ion, the Δ L/L( H, T) dependences are described well by a conventional quadratic law in a wide temperature range (4-100 K). In addition, the magnetostriction effect is qualitatively estimated with regard to the effect of the crystal electric field on the holmium ion.

The growth rates of KDP crystals in solutions with potassium permanganate additives

NASA Astrophysics Data System (ADS)

Egorova, A. E.; Vorontsov, D. A.; Nezhdanov, A. V.; Noskova, A. N.; Portnov, V. N.

2017-01-01

We have found that growth of the {101} faces of a KDP (KH2PO4) crystal is suppressed, and the growth rate of the {100} faces passes through the maximum with increasing addition of KMnO4 to a solution with pH=4.7. We have concluded that the [MnH2PO4]2+ complex and MnO2 particles affect the growth kinetics. The X-ray and electronic paramagnetic resonance data show that manganese is incorporated into the crystal in the form of Mn3+ and Mn4+. The local excess of a positive charge in the area with incorporated [MnH2PO4]2+ complex can be compensated by the shift of the hydrogen atoms in the KDP structure.

Structural Changes Correlated with Magnetic Spin State Isomorphism in the S2 State of the Mn4CaO5 Cluster in the Oxygen-Evolving Complex of Photosystem II

PubMed Central

Chatterjee, Ruchira; Han, Guangye; Kern, Jan; Gul, Sheraz; Fuller, Franklin D.; Garachtchenko, Anna; Young, Iris; Weng, Tsu-Chien; Nordlund, Dennis; Alonso-Mori, Roberto; Bergmann, Uwe; Sokaras, Dimosthenis; Hatakeyama, Makoto; Yachandra, Vittal K.; Yano, Junko

2016-01-01

The Mn4CaO5 cluster in Photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (Si, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in the S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. Such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis. PMID:28044099

Synthesis and first use of pyridine-2,6-diylbis(pyrazine-2-ylmethanone) in metal cluster chemistry: a {Mn(III)3Na2} complex with an ideal trigonal bipyramidal geometry.

PubMed

Giannopoulos, Dimosthenis P; Wilson-Konderka, Cody; Gagnon, Kevin J; Teat, Simon J; Escuer, Albert; Metallinos, Costa; Stamatatos, Theocharis C

2015-03-07

The successful organic synthesis of a new dipyrazole/pyridine-dicarbonyl organic molecule, namely pyridine-2,6-diylbis(pyrazine-2-ylmethanone) [(pz)CO(py)CO(pz)], followed by its employment in Mn coordination chemistry has yielded the neutral cluster compound [Mn3Na2O(N3)3(L)3] (1), where L(2-) is the (pz)C(CH2COCH3)(O(-))(py)C(CH2COCH3)(O(-))(pz) dianion. The latter group was formed in situ, presumably by the nucleophilic attack of the carbanion (-)CH2COCH3 to the carbonyl carbon atoms of (pz)CO(py)CO(pz), in the presence of Mn(n+) ions under basic conditions and in solvent Me2CO. Complex 1 possesses an almost ideal trigonal bipyramidal topology, with the two Na(I) ions occupying the apical positions and the three Mn(III) ions residing in the equatorial trigonal plane. The bridging ligation about the metal ions is provided by a μ3-O(2-) ion and six μ-OR(-) groups from the L(2-) ligand, while peripheral ligation is completed by three terminal azido groups and the pyridine N and carbonyl O atoms of L(2-). Magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the paramagnetic Mn(III) centres; the use of an anisotropic, equilateral Mn(III)3 triangle model allowed us to fit the magnetic data and obtain the best-fit parameters: J = -10.8 cm(-1), D = -5.3 cm(-1), and g = 1.99. The combined results demonstrate the rich chemical reactivity of carbonyl groups and the ability of poly-ketone ligands to stabilize cluster compounds with unprecedented structural motifs and interesting architectures.

Structural changes correlated with magnetic spin state isomorphism in the S 2 state of the Mn 4CaO 5 cluster in the oxygen-evolving complex of photosystem II

DOE PAGES

Chatterjee, Ruchira; Han, Guangye; Kern, Jan; ...

2016-05-09

The Mn 4CaO 5 cluster in photosystem II catalyzes the four-electron redox reaction of water oxidation in natural photosynthesis. This catalytic reaction cycles through four intermediate states (S i, i = 0 to 4), involving changes in the redox state of the four Mn atoms in the cluster. Recent studies suggest the presence and importance of isomorphous structures within the same redox/intermediate S-state. It is highly likely that geometric and electronic structural flexibility play a role in the catalytic mechanism. Among the catalytic intermediates that have been identified experimentally thus far, there is clear evidence of such isomorphism in themore » S2 state, with a high-spin (5/2) (HS) and a low spin (1/2) (LS) form, identified and characterized by their distinct electron paramagnetic resonance (EPR spectroscopy) signals. We studied these two S2 isomers with Mn extended X-ray absorption fine structure (EXAFS) and absorption and emission spectroscopy (XANES/XES) to characterize the structural and electronic structural properties. The geometric and electronic structure of the HS and LS S2 states are different as determined using Mn EXAFS and XANES/XES, respectively. The Mn K-edge XANES and XES for the HS form are different from the LS and indicate a slightly lower positive charge on the Mn atoms compared to the LS form. Based on the EXAFS results which are clearly different, we propose possible structural differences between the two spin states. As a result, such structural and magnetic redox-isomers if present at room temperature, will likely play a role in the mechanism for water-exchange/oxidation in photosynthesis.« less

Thermodynamic and kinetic modeling of Mn-Ni-Si precipitates in low-Cu reactor pressure vessel steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ke, Huibin; Wells, Peter; Edmondson, Philip D.

Formation of large volume fractions of Mn-Ni-Si precipitates (MNSPs) causes excess irradiation embrittlement of reactor pressure vessel (RPV) steels at high, extended-life fluences. Thus, a new and unique, semi-empirical cluster dynamics model was developed to study the evolution of MNSPs in low-Cu RPV steels. The model is based on CALPHAD thermodynamics and radiation enhanced diffusion kinetics. The thermodynamics dictates the compositional and temperature dependence of the free energy reductions that drive precipitation. The model treats both homogeneous and heterogeneous nucleation, where the latter occurs on cascade damage, like dislocation loops. The model has only four adjustable parameters that were fitmore » to an atom probe tomography (APT) database. The model predictions are in semi-quantitative agreement with systematic Mn, Ni and Si composition variations in alloys characterized by APT, including a sensitivity to local tip-to-tip variations even in the same steel. The model predicts that heterogeneous nucleation plays a critical role in MNSP formation in lower alloy Ni contents. Single variable assessments of compositional effects show that Ni plays a dominant role, while even small variations in irradiation temperature can have a large effect on the MNSP evolution. Within typical RPV steel ranges, Mn and Si have smaller effects. Furthermore, the delayed but then rapid growth of MNSPs to large volume fractions at high fluence is well predicted by the model. For purposes of illustration, the effect of MNSPs on transition temperature shifts are presented based on well-established microstructure-property and property-property models.« less

Thermodynamic and kinetic modeling of Mn-Ni-Si precipitates in low-Cu reactor pressure vessel steels

DOE PAGES

Ke, Huibin; Wells, Peter; Edmondson, Philip D.; ...

2017-07-12

Formation of large volume fractions of Mn-Ni-Si precipitates (MNSPs) causes excess irradiation embrittlement of reactor pressure vessel (RPV) steels at high, extended-life fluences. Thus, a new and unique, semi-empirical cluster dynamics model was developed to study the evolution of MNSPs in low-Cu RPV steels. The model is based on CALPHAD thermodynamics and radiation enhanced diffusion kinetics. The thermodynamics dictates the compositional and temperature dependence of the free energy reductions that drive precipitation. The model treats both homogeneous and heterogeneous nucleation, where the latter occurs on cascade damage, like dislocation loops. The model has only four adjustable parameters that were fitmore » to an atom probe tomography (APT) database. The model predictions are in semi-quantitative agreement with systematic Mn, Ni and Si composition variations in alloys characterized by APT, including a sensitivity to local tip-to-tip variations even in the same steel. The model predicts that heterogeneous nucleation plays a critical role in MNSP formation in lower alloy Ni contents. Single variable assessments of compositional effects show that Ni plays a dominant role, while even small variations in irradiation temperature can have a large effect on the MNSP evolution. Within typical RPV steel ranges, Mn and Si have smaller effects. Furthermore, the delayed but then rapid growth of MNSPs to large volume fractions at high fluence is well predicted by the model. For purposes of illustration, the effect of MNSPs on transition temperature shifts are presented based on well-established microstructure-property and property-property models.« less

General molecular mechanics method for transition metal carboxylates and its application to the multiple coordination modes in mono- and dinuclear Mn(II) complexes.

PubMed

Deeth, Robert J

2008-08-04

A general molecular mechanics method is presented for modeling the symmetric bidentate, asymmetric bidentate, and bridging modes of metal-carboxylates with a single parameter set by using a double-minimum M-O-C angle-bending potential. The method is implemented within the Molecular Operating Environment (MOE) with parameters based on the Merck molecular force field although, with suitable modifications, other MM packages and force fields could easily be used. Parameters for high-spin d (5) manganese(II) bound to carboxylate and water plus amine, pyridyl, imidazolyl, and pyrazolyl donors are developed based on 26 mononuclear and 29 dinuclear crystallographically characterized complexes. The average rmsd for Mn-L distances is 0.08 A, which is comparable to the experimental uncertainty required to cover multiple binding modes, and the average rmsd in heavy atom positions is around 0.5 A. In all cases, whatever binding mode is reported is also computed to be a stable local minimum. In addition, the structure-based parametrization implicitly captures the energetics and gives the same relative energies of symmetric and asymmetric coordination modes as density functional theory calculations in model and "real" complexes. Molecular dynamics simulations show that carboxylate rotation is favored over "flipping" while a stochastic search algorithm is described for randomly searching conformational space. The model reproduces Mn-Mn distances in dinuclear systems especially accurately, and this feature is employed to illustrate how MM calculations on models for the dimanganese active site of methionine aminopeptidase can help determine some of the details which may be missing from the experimental structure.

Synthesis, characterization, X-ray crystal structure and conductometry studying of a number of new Schiff base complexes; a new example of binuclear square pyramidal geometry of Cu(II) complex bridged with an oxo group

NASA Astrophysics Data System (ADS)

Golbedaghi, Reza; Alavipour, Ehsan

2015-11-01

Three new binuclear Cu(II), Mn(II), Co(II) complexes [Cu2(L) (ClO4)](ClO4)2 (1), [Mn2(L) (ClO4)](ClO4)2 (2), and [Co2(L) (ClO4)](ClO4)2 (3), {L = 1,3-bis(2-((Z)-(2-aminopropylimino)methyl)phenoxy)propan-2-ol} have been synthesized. Single crystal X-ray structure analysis of complex 1 showed that the complex is binuclear and all nitrogen and oxygen atoms of ligand (N4O3) are coordinated to two Cu(II) center ions. In addition, the crystal structure studying shows, a perchlorate ion has been bridged to the Cu(II) metal centers. However, two distorted square pyramidal Cu(II) ions are bridged asymmetrically by a perchlorate ion and oxygen of hydroxyl group of Schiff base ligand. In addition, the conductometry behaviors of all complexes were studied in acetonitrile solution.

Atom Probe Tomographic Characterization of Nanoscale Cu-Rich Precipitates in 17-4 Precipitate Hardened Stainless Steel Tempered at Different Temperatures.

PubMed

Wang, Zemin; Fang, Xulei; Li, Hui; Liu, Wenqing

2017-04-01

The formation of copper-rich precipitates of 17-4 precipitate hardened stainless steel has been investigated, after tempering at 350-570°C for 4 h, by atom probe tomography (APT). The results reveal that the clusters, enriched only with Cu, were observed after tempering at 420°C. Segregation of Ni, Mn to the Cu-rich clusters took place at 450°C, contributing to the increased hardening. After tempering at 510°C, Ni and Mn were rejected from Cu-rich precipitates and accumulated at the precipitate/matrix interfaces. Al and Si were present and uniformly distributed in the precipitates that were <1.5 nm in radius, but Ni, Mn, Al, and Si were enriched at the interfaces of larger precipitates/matrix. The proxigram profiles of the Cu-rich precipitates formed at 570°C indicated that Ni, Mn, Al, and Si segregated to the precipitate/matrix interfaces to form a Ni(Fe, Mn, Si, Al) shell, which significantly reduced the interfacial energy as the precipitates grew into an elongated shape. In addition, the number density of Cu-rich precipitates was increased with the temperature elevated from 350 up to 450°C and subsequently decreased at higher temperatures. Also, the composition of the matrix and the precipitates were measured and found to vary with temperature.

Electronic and magnetic behaviors of B, N, and 3d transition metal substitutions in germanium carbide monolayer

NASA Astrophysics Data System (ADS)

Xu, Zhuo; Li, Yangping; Liu, Zhengtang; Liu, Shengzhong (Frank)

2018-04-01

The structural, electronic, and magnetic behaviors of two-dimensional GeC (2D-GeC) with single vacancy, substitutional B, N, and 3d transition metal atoms (Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) are investigated based on the density functional theory. These impurities are tightly bonded to the surrounding atoms and found energetically more favorable at Ge sub-lattice site. In addition, the electronic band structures and magnetic properties of the doped systems indicate that (i) tunable electronic structures and magnetic moments of 2D-GeC can be obtained depending on different dopant species and sub-lattice sites, (ii) systems such as VC@Sc, VC@Fe, VC@Co, VGe@Fe, and VGe@Co are found to be half-metals, while the other systems all show semiconductor behavior. Simple models of the impurity-vacancy interaction is put forwards to illustrate the origin of the electronic structures and magnetic moments.

First Principle and Experimental Study for Site Preferences of Formability Improved Alloying Elements in Mg Crystal

NASA Astrophysics Data System (ADS)

Zeng, Ying; Jiang, Bin; Shi, Ouling; Quan, Gaofen; Al-Ezzi, Salih; Pan, FuSheng

2018-07-01

Some alloying elements (Al, Er, Gd, Li, Mn, Sn, Y, Zn) were proved recently by calculations or experiments to improve the formability of Mg alloys, but ignoring their site preference in Mg crystals during the calculated process. A crystallographic model was built via first principle calculations to predict the site preferences of these elements. Regularities between doping elements and site preferences were summarized. Meanwhile, in the basis of the crystallographic model, a series of formulas were deduced combining the diffraction law. It predicted that a crystal plane with abnormal XRD peak intensity of the Mg-based solid solutions, compared to that of the pure Mg, prefers to possess solute atoms. Thus, three single-phase solid solution alloys were then prepared through an original In-situ Solution Treatment, and their XRD patterns were compared. Finally, the experiment further described the site preferences of these solute atoms in Mg crystal, verifying the calculation results.

First Principle and Experimental Study for Site Preferences of Formability Improved Alloying Elements in Mg Crystal

NASA Astrophysics Data System (ADS)

Zeng, Ying; Jiang, Bin; Shi, Ouling; Quan, Gaofen; Al-Ezzi, Salih; Pan, FuSheng

2018-03-01

Some alloying elements (Al, Er, Gd, Li, Mn, Sn, Y, Zn) were proved recently by calculations or experiments to improve the formability of Mg alloys, but ignoring their site preference in Mg crystals during the calculated process. A crystallographic model was built via first principle calculations to predict the site preferences of these elements. Regularities between doping elements and site preferences were summarized. Meanwhile, in the basis of the crystallographic model, a series of formulas were deduced combining the diffraction law. It predicted that a crystal plane with abnormal XRD peak intensity of the Mg-based solid solutions, compared to that of the pure Mg, prefers to possess solute atoms. Thus, three single-phase solid solution alloys were then prepared through an original In-situ Solution Treatment, and their XRD patterns were compared. Finally, the experiment further described the site preferences of these solute atoms in Mg crystal, verifying the calculation results.

Structure, reactivity and electronic properties of Mn doped Ni13 clusters

NASA Astrophysics Data System (ADS)

Banerjee, Radhashyam; Datta, Soumendu; Mookerjee, Abhijit

2013-06-01

In this work we have studied the structural and magnetic properties of Ni13 cluster mono- and bi-doped with Mn atoms. We have noted their tendency of being reactive toward the H2 molecule. We have found unusually enhanced stability in the mono-doped cluster (i.e. of the Ni12Mn) and the diminished stability of the corresponding chemisorbed cluster, Ni12MnH2. Our analysis of the stability and HOMO-LUMO gap explains this unusual behavior. Interestingly, we have also seen the quenching in the net magnetic moment upon H2 absorption in the doped NiMnm alloy clusters. This has been reported earlier for smaller Nin clusters [1].

Tunable magnetism of 3d transition metal doped BiFeO3

NASA Astrophysics Data System (ADS)

Lu, S.; Li, C.; Zhao, Y. F.; Gong, Y. Y.; Niu, L. Y.; Liu, X. J.; Wang, T.

2017-10-01

Electronic polarization or bond relaxation can effectively alter the electronic and magnetic behavior of materials by doping impurity atom. For this aim, the thermodynamic, electronic and magnetic performances of cubic BiFeO3 have been modulated by the 3d transition metal (TM) dopants (Sc, Ti, V, Cr, Mn, Co, Ni, Cu and Zn) based on the density functional theory. Results show that the doped specimen with low impurity concentration is more stable than that with high impurity concentration. The Mulliken charge values and spin magnetic moments of TM element are making major changes, while those of all host atoms are making any major changes. Especially, it is the linear relation between the spin magnetic moments of TM dopants and the total magnetic moment of doped specimens; thus, the variations of total magnetic moment of doped specimens are decided by the spin magnetic moments of TM dopants, thought the total magnetic moments of doped specimens mainly come from Fe atom and TM dopants. Besides, as double TM atoms substitution the Fe atoms, the Sc-, Ti-, Mn-, Co- and Zn-doped specimens show AFM state, while the V-, Cr-, Ni- and Cu-doped specimens show FM state.

Study of temperature-dependent Raman spectroscopy and electrical properties in [001]-oriented 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3-Mn single crystals

NASA Astrophysics Data System (ADS)

Liu, Xing; Fang, Bijun; Deng, Ji; Yan, Hong; Deng, Hao; Yue, Qingwen; Ding, Jianning; Zhao, Xiangyong; Luo, Haosu

2016-01-01

In this work, the temperature-dependent Raman spectra and electrical properties of the [001]-oriented 0.5 mol. % Mn-doped 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3-Mn (PIMNT-Mn) single crystals were investigated. All the unpoled and poled PIMNT-Mn single crystals experience a ferroelectric tetragonal phase to paraelectric cubic phase transition (FET-PC) around 183 °C (TC), which exhibits a second-order transition behavior. Whereas, the poled PIMNT-Mn single crystals exhibit another two dielectric anomalies around 130 °C (TRM) and 148 °C (TMT), in which the ferroelectric rhombohedral phase to ferroelectric monoclinic phase (FER-FEM) and the ferroelectric monoclinic phase to ferroelectric tetragonal phase (FEM-FET) transitions take place, respectively. Both the two ferroelectric phase transitions exhibit a first-order transition behavior. The discontinuous change of the phase degree (θ) and frequencies (fr and fa) around TRM suggest the occurrence of the FER-FEM phase transition in the poled PIMNT-Mn single crystals. The narrowing of the 510 cm-1 and 582 cm-1 Raman modes around the TRM, TMT, and TC temperatures shown in the temperature-dependent Raman spectra suggests their increased ordering of the local structure. The intensity ratio of I272 cm-1/I801 cm-1 increases obviously around the phase transition temperatures (TRM, TMT, and TC), indicating the reduction of the long-range order. The anomalous broadening of the 272 cm-1 Raman mode around the TRM, TMT, and TC temperatures indicates the occurrence of the successive ferroelectric phase transitions (FER-FEM, FEM-FET, and FET-PC) with increasing temperature in the poled PIMNT-Mn single crystals.

Nano-sized layered Mn oxides as promising and biomimetic water oxidizing catalysts for water splitting in artificial photosynthetic systems.

PubMed

Najafpour, Mohammad Mahdi; Heidari, Sima; Amini, Emad; Khatamian, Masoumeh; Carpentier, Robert; Allakhverdiev, Suleyman I

2014-04-05

One challenge in artificial photosynthetic systems is the development of artificial model compounds to oxidize water. The water-oxidizing complex of Photosystem II which is responsible for biological water oxidation contains a cluster of four Mn ions bridged by five oxygen atoms. Layered Mn oxides as efficient, stable, low cost, environmentally friendly and easy to use, synthesize, and manufacture compounds could be considered as functional and structural models for the site. Because of the related structure of these Mn oxides and the catalytic centre of the active site of the water oxidizing complex of Photosystem II, the study of layered Mn oxides may also help to understand more about the mechanism of water oxidation by the natural site. This review provides an overview of the current status of layered Mn oxides in artificial photosynthesis and discuss the sophisticated design strategies for Mn oxides as water oxidizing catalysts. Copyright © 2014 Elsevier B.V. All rights reserved.

Mechanism of MnS Precipitation on Al2O3-SiO2 Inclusions in Non-oriented Silicon Steel

NASA Astrophysics Data System (ADS)

Li, Fangjie; Li, Huigai; Huang, Di; Zheng, Shaobo; You, Jinglin

2018-05-01

This study investigates the mechanism of MnS precipitation on Al2O3-SiO2 inclusions during the solidification of non-oriented silicon steel, especially the influence of the phase structures and sizes of the oxides on the MnS precipitation, by scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectrometry. The investigation results show that MnS tends to nucleate on submicron-sized Al2O3-SiO2 inclusions formed by interdendritic segregation and that it covers the oxides completely. In addition, MnS can precipitate on micron-sized oxides and its precipitation behavior is governed by the phase structure of the oxides. The MnS embryo formed in a MnO-containing oxide can act as a substrate for MnS precipitation, thus permitting further growth via diffusion of solute atoms from the matrix. MnS also precipitates in a MnO-free oxide by the heterogeneous nucleation mechanism. Furthermore, MnS is less prone to precipitation in the Al2O3-rich regions of the Al2O3-SiO2 inclusions; this can be explained by the high lattice disregistry between MnS and Al2O3.

Comparison of data transformation procedures to enhance topographical accuracy in time-series analysis of the human EEG.

PubMed

Hauk, O; Keil, A; Elbert, T; Müller, M M

2002-01-30

We describe a methodology to apply current source density (CSD) and minimum norm (MN) estimation as pre-processing tools for time-series analysis of single trial EEG data. The performance of these methods is compared for the case of wavelet time-frequency analysis of simulated gamma-band activity. A reasonable comparison of CSD and MN on the single trial level requires regularization such that the corresponding transformed data sets have similar signal-to-noise ratios (SNRs). For region-of-interest approaches, it should be possible to optimize the SNR for single estimates rather than for the whole distributed solution. An effective implementation of the MN method is described. Simulated data sets were created by modulating the strengths of a radial and a tangential test dipole with wavelets in the frequency range of the gamma band, superimposed with simulated spatially uncorrelated noise. The MN and CSD transformed data sets as well as the average reference (AR) representation were subjected to wavelet frequency-domain analysis, and power spectra were mapped for relevant frequency bands. For both CSD and MN, the influence of noise can be sufficiently suppressed by regularization to yield meaningful information, but only MN represents both radial and tangential dipole sources appropriately as single peaks. Therefore, when relating wavelet power spectrum topographies to their neuronal generators, MN should be preferred.

Precipitation Behaviors of TiN Inclusion in GCr15 Bearing Steel Billet

NASA Astrophysics Data System (ADS)

Tian, Qianren; Wang, Guocheng; Zhao, Yang; Li, Jing; Wang, Qi

2018-06-01

There are many types of non-metallic TiN-based inclusions observed in GCr15 bearing steel, including single-particle TiN, multi-particle polymerized TiN, and complex inclusions like TiN-MnS, TiN-MgO-MgAl2O4 (TiN-MgO-MA), and TiN-MgAl2O4-MnS (TiN-MA-MnS). Thermodynamic calculations suggest that single-particle TiN precipitates dominate the mushy zone of GCr15 bearing steel. Kinetic calculations regarding TiN growth suggest that the final size of the single-particle TiN ranges between 1 and 6 μm in the initial concentration range of [pct Ti] = 0.0060 to 0.0079 and [pct N] = 0.0049 to 0.0070, at 1620 to 1640 K and a local cooling rate of 0.5 to 10 K/s. The multi-particle polymerized TiN are formed by single TiN particles in three stages: single-particle TiN inclusions approach each other drawn by the cavity bridge force (CBF), local active angles consolidate, and neck region sintering occurs. Based on the thermodynamic calculations of TiN, MnS, and MgO precipitation, the formation behaviors of complex inclusions of TiN-MnS, TiN-MgO-MA, and TiN-MA-MnS were investigated.

Long range ferromagnetism in (Zn, Mn, Li)Se with competition between double exchange and p-d exchange

NASA Astrophysics Data System (ADS)

Zhu, Y.; Liu, T.; Zhang, X. Y.; Pan, Y. F.; Wei, X. Y.; Ma, C. L.; Shi, D. N.; Fan, J. Y.

2017-04-01

In this paper, we elucidate the mechanism for Li co-dopant induced enhancement of the ferromagnetism in 2 × 2 × 2 and 3 × 3 × 3 cubic (Zn, Mn)Se using density functional calculations. The doping atoms tend to congregate together according to the ferromagnetic (FM) energy. All configurations are strongly FM ones due to double exchange (DE) and p-d exchange (PE). DE and PE are shown in the partial density of states. The hole is uniformly distributed in the cubic (Zn, Mn, Li)Se, and it is the one and only parameter to decide the exchange energy, when impurity atoms stay further away from each other. The average exchange energy of these configurations is considered to be a function of the square root of the hole concentration. The fitting data to a polynomial function shows that DE and PE have roles of similar importance in the exchange energy.

[Determination of Al, Be, Cd, Co, Cr, Mn, Ni, Pb, Se and Tl in whole blood by atomic absorption spectrometry without preliminary sample digestion].

PubMed

Ivanenko, N B; Ivanenko, A A; Solov'ev, N D; Navolotskiĭ, D V; Pavlova, O V; Ganeev, A A

2014-01-01

Methods of whole blood trace element determination by Graphite furnace atomic absorption spectrometry (in the variant of Zeeman's modulation polarization spectrometry) have been proposed. They do not require preliminary sample digestion. Furnace programs, modifiers and blood dilution factors were optimized. Seronorm™ human whole blood reference materials were used for validation. Dynamic ranges (for undiluted blood samples) were: Al 8 ¸ 210 мg/L; Be 0.3 ¸ 50 мg/L; Cd 0.2 ¸ 75 мg/L; Сo 5 ¸ 350 мg/L; Cr 10 ¸ 100 мg/L; Mn 6 ¸ 250 мg/L; Ni 10 ¸ 350 мg/L; Pb 3 ¸ 240 мg/L; Se 10 ¸ 500 мg/L; Tl 2 ¸ 600 мg/L. Precision (RSD) for the middle of dynamic range ranged from 5% for Mn to 11 for Se.

Magnetic interactions at Ce impurities in REMn2Ge2 (RE = La, Ce, Pr, Nd) compounds

NASA Astrophysics Data System (ADS)

Bosch-Santos, B.; Cabrera-Pasca, G. A.; Saxena, R. N.; Burimova, A. N.; Carbonari, A. W.

2018-05-01

In the work reported in this paper, the temperature dependence of the magnetic hyperfine field (Bh f) at 140Ce nuclei replacing Pr atoms in PrMn2Ge2 compound was measured by the perturbed angular correlation technique to complete the sequence of measurements in REMn2Ge2 (RE = La, Ce, Pr, Nd). Results show an anomalous behavior different from the expected Brillouin curve. A model was used to fit the data showing that the Ce impurity contribution (Bhfimp) to Bhf is negative for NdMn2Ge2 below 210 K. The impurity contribution (Bhfimp) at 0 K for all compounds is much smaller than that for the free Ce3+, showing that the 4f band of Ce is more likely highly hybridized with 5d band of the host. Results show that direction of the localized magnetic moment at Mn atoms strongly affects the exchange interaction at Ce impurities.

The effect of Mn and B on the magnetic and structural properties of nanostructured Fe60Al40 alloys produced by mechanical alloying.

PubMed

Rico, M M; Alcázar, G A Pérez; Zamora, L E; González, C; Greneche, J M

2008-06-01

The effect of Mn and B on the magnetic and structural properties of nanostructured samples of the Fe60Al40 system, prepared by mechanical alloying, was studied by 57Fe Mössbauer spectrometry, X-ray diffraction and magnetic measurements. In the case of the Fe(60-x)Mn(x)Al40 system, 24 h milling time is required to achieve the BCC ternary phase. Different magnetic structures are observed according to the temperature and the Mn content for alloys milled during 48 h: ferromagnetic, antiferromagnetic, spin-glass, reentrant spin-glass and superparamagnetic behavior. They result from the bond randomness behaviour induced by the atomic disorder introduced by the MA process and from the competitive interactions of the Fe-Fe ferromagnetic interactions and the Mn-Mn and Fe-Mn antiferromagnetic interactions and finally the presence of Al atoms acting as dilutors. When B is added in the Fe60Al40 alloy and milled for 12 and 24 hours, two crystalline phases were found: a prevailing FeAl BCC phase and a Fe2B phase type. In addition, one observes an additional contribution attributed to grain boundaries which increases when both milling time and boron composition increase. Finally Mn and B were added to samples of the Fe60Al40 system prepared by mechanical alloying during 12 and 24 hours. Mn content was fixed to 10 at.% and B content varied between 0 and 20 at.%, substituting Al. X-ray patterns show two crystalline phases, the ternary FeMnAl BCC phase, and a (Fe,Mn)2B phase type. The relative proportion of the last phase increases when the B content increases, in addition to changes of the grain size and the lattice parameter. Such behavior was observed for both milling periods. On the other hand, the magnetic hyperfine field distributions show that both phases exhibit chemical disorder, and that the contribution attributed to the grain boundaries is less important when the B content increases. Coercive field values of about 10(2) Oe slightly increase with boron content. Comparison with previous results on FeAIB alloys shows that Mn promotes the structural stability of the nanostructured powders.

Surface sealing using self-assembled monolayers and its effect on metal diffusion in porous low-k dielectrics studied using monoenergetic positron beams

NASA Astrophysics Data System (ADS)

Uedono, Akira; Armini, Silvia; Zhang, Yu; Kakizaki, Takeaki; Krause-Rehberg, Reinhard; Anwand, Wolfgang; Wagner, Andreas

2016-04-01

Surface sealing effects on the diffusion of metal atoms in porous organosilicate glass (OSG) films were studied by monoenergetic positron beams. For a Cu(5 nm)/MnN(3 nm)/OSG(130 nm) sample fabricated with pore stuffing, C4F8 plasma etch, unstuffing, and a self-assembled monolayer (SAM) sealing process, it was found that pores with cubic pore side lengths of 1.1 and 3.1 nm coexisted in the OSG film. For the sample without the SAM sealing process, metal (Cu and Mn) atoms diffused from the top Cu/MnN layer into the OSG film and were trapped by the pores. As a result, almost all pore interiors were covered with those metals. For the sample damaged by an Ar/C4F8 plasma etch treatment before the SAM sealing process, SAMs diffused into the OSG film, and they were preferentially trapped by larger pores. The cubic pore side length in these pores containing self-assembled molecules was estimated to be 0.7 nm. Through this work, we have demonstrated that monoenergetic positron beams are a powerful tool for characterizing capped porous films and the trapping of atoms and molecules by pores.

Unique coordination of pyrazine in T[Ni(CN){sub 4}].2pyz with T=Mn, Zn, Cd

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lemus-Santana, A.A.; Rodriguez-Hernandez, J.; Castillo, L.F. del, E-mail: lfelipe@servidor.unam.m

2009-04-15

The materials under study, T[Ni(CN){sub 4}].2pyz with T=Mn, Zn, Cd, were prepared by separation of T[Ni(CN){sub 4}] layers in citrate aqueous solution to allow the intercalation of the pyrazine molecules. The obtained solids were characterized from chemical analyses, X-ray diffraction, infrared, Raman, thermogravimetry, UV-Vis, magnetic and adsorption data. Their crystal structure was solved from ab initio using direct methods and then refined by the Rietveld method. A unique coordination for pyrazine to metal centers at neighboring layers was observed. The pyrazine molecule is found forming a bridge between Ni and T atoms, quite different from the proposed structures for T=Fe,more » Ni where it remains coordinated to two T atoms to form a vertical pillar between neighboring layers. The coordination of pyrazine to both Ni and T atoms minimizes the material free volume and leads to form a hydrophobic framework. On heating the solids remain stable up to 140 deg. C. No CO{sub 2} and H{sub 2} adsorption was observed in the small free spaces of their frameworks. - Graphical abstract: Framework for T[Ni(CN){sub 4}].2pyz with T=Mn, Zn, Cd.« less

Facile method to synthesize dopamine-capped mixed ferrite nanoparticles and their peroxidase-like activity

NASA Astrophysics Data System (ADS)

Mumtaz, Shazia; Wang, Li-Sheng; Abdullah, Muhammad; Zajif Hussain, Syed; Iqbal, Zafar; Rotello, Vincent M.; Hussain, Irshad

2017-03-01

A facile single-step strategy to prepare stable and water-dispersible dopamine-functionalized ultra-small mixed ferrite nanoparticles MFe2O4-DOPA (where M is a bivalent metal atom i.e. Fe, Co Cu, Mn and Ni) at room temperature is described. The nanoparticles formed have narrow size distribution as indicated by their characterization using transmission electron microscopy (TEM) and dynamic light scattering. The surface chemistry of these nanoparticles was probed by FTIR spectroscopy indicating their successful capping with dopamine ligands, which was further confirmed using zetapotential measurements and thermogravimetric analysis. The comparative horseradish peroxidase (HRP)—like activity of these cationic mixed ferrites nanoparticles was studied at pH 4.6 using a negatively-charged 2, 2‧-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) as a chromogenic substrate in the presence of hydrogen peroxide. A time-dependent relative peroxidase-like activity follows the following order CoFe2O4-DOPA  >  MnFe2O4-DOPA  >  CuFe2O4-DOPA  >  NiFe2O4-DOPA  >  Fe3O4-DOPA. This diversity in HRP-like activity may be attributed to the different redox properties of ferrite nanoparticles when doped with M (Fe, Co Cu, Mn and Ni).

Radiation-induced segregation on defect clusters in single-phase concentrated solid-solution alloys

DOE PAGES

Lu, Chenyang; Yang, Taini; Jin, Ke; ...

2017-01-12

A group of single-phase concentrated solid-solution alloys (SP-CSAs), including NiFe, NiCoFe, NiCoFeCr, as well as a high entropy alloy NiCoFeCrMn, was irradiated with 3 MeV Ni 2+ ions at 773 K to a fluence of 5 10 16 ions/cm 2 for the study of radiation response with increasing compositional complexity. Advanced transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS) was used to characterize the dislocation loop distribution and radiation-induced segregation (RIS) on defect clusters in the SP-CSAs. The results show that a higher fraction of faulted loops exists in the more compositionally complex alloys, which indicate that increasingmore » compositional complexity can extend the incubation period and delay loop growth. The RIS behaviors of each element in the SP-CSAs were observed as follows: Ni and Co tend to enrich, but Cr, Fe and Mn prefer to deplete near the defect clusters. RIS level can be significantly suppressed by increasing compositional complexity due to the sluggish atom diffusion. According to molecular static (MS) simulations, disk like segregations may form near the faulted dislocation loops in the SP-CSAs. Segregated elements tend to distribute around the whole faulted loop as a disk rather than only around the edge of the loop.« less

Magnetism and Solid Solution Effects in NiAI (40% AI) Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chain T; Fu, Chong Long; Chisholm, Matthew F

2007-01-01

The solid solution effects of ternary additions of transition elements in intermetallic Ni-40% Al were investigated by both experimental studies and theoretical calculations. Co solute atoms when sitting at Ni sublattice sites do not affect the lattice parameter and hardening behavior of Ni-40Al. On the other hand, Fe, Mn, and Cr solutes, which are mainly on Al sublattice sites, substantially expand the lattice parameter and produce an unusual solid solution softening effect. First-principles calculations predict that these solute atoms with large unfilled d-band electrons develop large magnetic moments and effectively expand the lattice parameter when occupying Al sublattice sites. Themore » theoretical predictions were verified by both electron loss-energy spectroscopy (EELS) analyses and magnetic susceptibility measurements. The observed softening behavior can be explained quantitatively by the replacement of Ni anti-site defects (potent hardeners) by Fe, Mn, and Cr anti-site defects with smaller atom size mismatch between solute and Al atoms. This study has led to the identification of magnetic interaction as an important physical parameter affecting the solid solution hardening in intermetallic alloys containing transition elements.« less

Activation of the manganese(I) tricarbonyl core by selective variation of bidentate ligands (L,L'-Bid = N,N' and N,O donor atom sets) in fac-[Mn(CO)3(L,L'-Bid)(CH3OH)](n) complexes.

PubMed

Twala, T N; Schutte-Smith, M; Roodt, A; Visser, H G

2015-02-21

A range of fac-[Mn(CO)3(L,L'-Bid)(H2O)](n) (L,L'-Bid = neutral or monoanionic bidentate ligands with varied L,L' donor atoms, N,N' and N,O, 1,10-phenanthroline, 2,2'-bipyridine, 2-picolinate, 2,4-quinolinate; n = 0, +1) has been synthesized and the methanol substitution has been investigated for the first time. The complexes were characterized by UV/vis, IR and NMR spectroscopy and X-ray crystallographic studies of the compounds fac-[Mn(CO)3(Bipy)(H2O)][CF3SO3] () and fac-[Mn(CO)3(Phen)(H2O)][CF3SO3] () are reported. A two order-of-magnitude of activation for the methanol substitution is induced as manifested by the second order rate constants with (N,N'-Bid) < (N,O-Bid). Forward and reverse rate and stability constants from slow and stopped-flow UV/vis measurements (k1, M(-1) s(-1); k-1, s(-1); K1, M(-1)) for pyridine as entering nucleophile are as follows: fac-[Mn(CO)3(Phen)(CH3OH)](+) (2.39 ± 5) × 10(-3), (1.5 ± 0.3) × 10(-5), 159 ± 32; fac-[Mn(CO)3(2,4-QuinH)(CH3OH)] (4.5 ± 0.2), (4 ± 1) × 10(-2), 113 ± 29. Activation parameters (ΔH, kJ mol(-1); ΔS, J K(-1) mol(-1)) from Eyring plots for entering nucleophiles as indicated are as follows: fac-[Mn(CO)3(Phen)(CH3OH)](+) (bromide ions) 66.7 ± 0.6, -27 ± 2; (pyridine) 80 ± 3, -25 ± 11; fac-[Mn(CO)3(Pico)(CH3OH)] (bromide ions) 68 ± 2, -24 ± 5. A dissociative interchange mechanism is proposed.

Perovskite-based heterostructures integrating ferromagnetic-insulating La0.1Bi0.9MnO3

NASA Astrophysics Data System (ADS)

Gajek, M.; Bibes, M.; Barthélémy, A.; Varela, M.; Fontcuberta, J.

2005-05-01

We report on the growth of thin films and heterostructures of the ferromagnetic-insulating perovskite La0.1Bi0.9MnO3. We show that the La0.1Bi0.9MnO3 perovskite grows single phased, epitaxially, and with a single out-of-plane orientation either on SrTiO3 substrates or onto strained La2/3Sr1/3MnO3 and SrRuO3 ferromagnetic-metallic buffer layers. We discuss the magnetic properties of the La0.1Bi0.9MnO3 films and heterostructures in view of their possible potential as magnetoelectric or spin-dependent tunneling devices.

Antiferromagnetism in semiconducting SrMn2Sb2 and BaMn2Sb2 single crystals

NASA Astrophysics Data System (ADS)

Sangeetha, N. S.; Smetana, V.; Mudring, A.-V.; Johnston, D. C.

2018-01-01

Crystals of SrMn2Sb2 and BaMn2Sb2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ , heat capacity Cp, and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M (H ) isotherm measurements. SrMn2Sb2 adopts the trigonal CaAl2Si2 -type structure, whereas BaMn2Sb2 crystallizes in the tetragonal ThCr2Si2 -type structure. The ρ (T ) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn2Sb2 and 0.16 eV for BaMn2Sb2 . The χ (T ) and Cp(T ) data reveal antiferromagnetic (AFM) ordering at TN = 110 K for SrMn2Sb2 and 450 K for BaMn2Sb2 . The anisotropic χ (T ≤TN) data also show that the ordered moments in SrMn2Sb2 are aligned in the hexagonal a b plane, whereas the ordered moments in BaMn2Sb2 are aligned collinearly along the tetragonal c axis. The a b -plane M (H ) data for SrMn2Sb2 exhibit a continuous metamagnetic transition at low fields 0

Facile synthesis of graphene-wrapped honeycomb MnO2 nanospheres and their application in supercapacitors.

PubMed

Zhu, Jiayi; He, Junhui

2012-03-01

Graphene-wrapped MnO(2) nanocomposites were first fabricated by coassembly between honeycomb MnO(2) nanospheres and graphene sheets via electrostatic interaction. The materials were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and thermogravimetric analysis. The novel MnO(2)/graphene hybrid materials were used for investigation of electrochemical capacitive behaviors. The hybrid materials displayed enhanced capacitive performance (210 F/g at 0.5 A/g). Additionally, over 82.4% of the initial capacitance was retained after repeating the cyclic voltammetry test for 1000 cycles. The improved electrochemical performance might be attributed to the combination of the pesudocapacitance of MnO(2) nanospheres with the honeycomb-like "opened" structure and good electrical conductivity of graphene sheets. © 2012 American Chemical Society

Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3?xCoxGa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klaer, P.; Jenkins, C.A.; Alijani, V.

2011-05-03

Ferrimagnetic Mn{sub 3-x}Co{sub x}Ga compounds have been investigated by magnetic circular dichroism in x-ray absorption (XMCD). Compounds with x > 0.5 crystallize in the CuHg{sub 2}Ti structure. A tetragonal distortion of the cubic structure occurs for x {le} 0.5. For the cubic phase, magnetometry reveals a linearly increasing magnetization of 2x Bohr magnetons per formula unit obeying the generalized Slater-Pauling rule. XMCD confirms the ferrimagnetic character with Mn atoms occupying two different sublattices with antiparallel spin orientation and different degrees of spin localization and identifies the region 0.6 < x {le} 0.8 as most promising for a high spin polarizationmore » at the Fermi level. Individual Mn moments on inequivalent sites are compared to theoretical predictions.« less

Tuning electronic and magnetic properties of Mn-mullite oxide sub-nanoclusters via MnOn polyhedron units.

PubMed

Li, Hui; Cho, Kyeongjae; Li, Shunfang; Wang, Weichao

2018-06-13

Ternary oxide nano-clusters compared to unary metallic and binary ones potentially exhibit more remarkable properties due to their higher stoichiometric flexibility in addition to cluster size variations. Herein, by combining with the structural searching scheme CALYPSO, we have built a series of Mn-mullite oxide clusters (SmxMnyOz)n {(xyz) = (125); (115); n = 1-4, 8} prior to investigation of their geometric and electronic structures via first-principles calculations. In small size regime (n < 4), (SmxMnyOz)n prefer nonstoichiometric (Sm1Mn1O5)n phases composed of nonmagnetic MnO4 tetrahedrons. When n ≧ 4, the clusters tend to develop as stoichiometric (Sm1Mn2O5)n species, including magnetic MnOn polyhedrons and Mn-Mn dimers, which contribute 3d-orbitals (dz2 and/or dx2-y2) around the Fermi levels. The different magnetic behaviors of nonstoichiometric and stoichiometric species originate from the distinct couplings of MnOn polyhedronal units, wherein Mn atoms experience different ligand fields and thus display different spin states. Such findings enable the tuning of electronic properties and potential applications in heterogeneous catalysis, electrochemical catalysis, and the related fields via engineering cluster size and stoichiometry.

Site-specific ligation of anthracene-1,8-dicarboxylates to an Mn12 core: a route to the controlled functionalisation of single-molecule magnets.

PubMed

Pacchioni, Mirko; Cornia, Andrea; Fabretti, Antonio C; Zobbi, Laura; Bonacchi, Daniele; Caneschi, Andrea; Chastanet, Guillaume; Gatteschi, Dante; Sessoli, Roberta

2004-11-21

A novel single-molecule magnet of the Mn12 family, [Mn12O12(O2CC6H5)8(L)4(H2O)4].8CH2Cl2, has been synthesised by site-specific ligand exchange using a tailor-made dicarboxylate (L2-), which leads to selective occupation of axial binding sites.

Influence of ring size on the cognition-enhancing activity of DM235 and MN19, two potent nootropic drugs.

PubMed

Guandalini, L; Martini, E; Di Cesare Mannelli, L; Dei, S; Manetti, D; Scapecchi, S; Teodori, E; Ghelardini, C; Romanelli, M N

2012-03-01

A series of analogs of DM235 and MN19, characterized by rings with different size, have been prepared and evaluated for their nootropic activity in the mouse passive-avoidance test. It was found that the optimal ring size for the analogs of DM235, showing endocyclic both amidic groups, is 6 or 7 atoms. For the compounds structurally related to MN19, carrying an exocyclic amide group, the piperidine ring is the moiety which gives the most interesting compounds. Copyright © 2012 Elsevier Ltd. All rights reserved.

Magneto-transport in LaTi1-xMnxO3/SrTiO3 oxide heterostructures

NASA Astrophysics Data System (ADS)

Kumar, Pramod; Dogra, Anjana; Budhani, R. C.

2014-04-01

We report the growth of ultrathin film of Mn doped LaTiO3 on TiO2 terminated SrTiO3 (001) substrate by pulsed laser deposition (PLD) and their electrical transport characteristics including magnetoresistance (MR). Though the replacement of Mn in LaTiO3 at the Ti site in dilute limit does not affect the metallic behaviour of films but variation in resistance is observed. Normalised resistance behaviour is explained on the basis of variation in charge carriers and increased interaction between Mn atoms in the system under investigation.

Molecular magnetism of M6 hexagon ring in D(3d) symmetric [(MCl)6(XW9O33)2](12-) (M = Cu(II) and Mn(II), X = Sb(III) and As(III)).

PubMed

Yamase, Toshihiro; Ishikawa, Hirofumi; Abe, Hiroko; Fukaya, Keisuke; Nojiri, Hiroyuki; Takeuchi, Hideo

2012-04-16

Ferromagnetic [n-BuNH(3)](12)[(CuCl)(6)(SbW(9)O(33))(2)]·6H(2)O (1) and antiferromagnetic [n-BuNH(3)](12)[(MnCl)(6)(AsW(9)O(33))(2)]·6H(2)O (4) have been synthesized and structurally and magnetically characterized. Two complexes are structural analogues of [n-BuNH(3)](12)[(CuCl)(6)(AsW(9)O(33))(2)]·6H(2)O (2) and [n-BuNH(3)](12)[(MnCl)(6)(SbW(9)O(33))(2)]·6H(2)O (3) with their ferromagnetic interactions, first reported by us in 2006. (1) When variable temperature (T) direct current (dc) magnetic susceptibility (χ(M)) data are analyzed with the isotropic exchange Hamiltonian for the magnetic exchange interactions, χ(M)T vs T curves fitted by a full matrix diagonalization (for 1) and by the Kambe vector coupling method/Van Vleck's approximation (for 4) yield J = +29.5 and -0.09 cm(-1) and g = 2.3 and 1.9, respectively. These J values were significantly distinguished from +61.0 and +0.14 cm(-1) for 2 and 3, respectively. The magnetization under the pulsed field (up to 10(3) T/s) at 0.5 K exhibits hysteresis loops in the adiabatic process, and the differential magnetization (dM/dB) plots against the pulsed field display peaks characteristic of resonant quantum tunneling of magnetization (QTM) at Zeeman crossed fields, indicating single-molecule magnets for 1-3. High-frequency ESR (HFESR) spectroscopy on polycrystalline samples provides g(∥) = 2.30, g(⊥) = 2.19, and D = -0.147 cm(-1) for 1 (S = 3 ground state), g(∥) = 2.29, g(⊥) = 2.20, and D = -0.145 cm(-1) for 2 (S = 3), and g(∥) = 2.03 and D = -0.007 cm(-1) for 3 (S = 15). An attempt to rationalize the magnetostructural correlation among 1-4, the structurally and magnetically modified D(3d)-symmetric M (=Cu(II) and Mn(II))(6) hexagons sandwiched by two diamagnetic α-B-[XW(9)O(33)](9-) (X = Sb(III) and As(III)) ligands through M-(μ(3)-O)-W linkages, is made. The strongest ferromagnetic coupling for the Cu(6) hexagon of 2, the structure of which approximately provides the Cu(6)(μ(3)-O)(12) cylindrical geometry, is demonstrated by the polarization mechanism based on the point-dipole approximation, which provides a decrease of the ferromagnetic interaction due to the out-of-cylinder deviation of the Cu atoms for 1. The different nature of the magnetic exchange interaction in 3 and 4 is understood by the combined effect of the out-of plane deviation (the largest for 4) of the Mn atoms from the Mn(μ(3)-O)(2)Mn least-squares plane and the antiferromagnetic contribution arising from the large Mn-O-Mn bond angle. The primary contribution to D is discussed in terms of the magnetic dipole-dipole interaction between the electrons located on the magnetic sites in the M(6) hexagon. © 2012 American Chemical Society

Single crystal X- and Q-band EPR spectroscopy of a binuclear Mn(2)(III,IV) complex relevant to the oxygen-evolving complex of photosystem II.

PubMed

Yano, Junko; Sauer, Kenneth; Girerd, Jean-Jacques; Yachandra, Vittal K

2004-06-23

The anisotropic g and hyperfine tensors of the Mn di-micro-oxo complex, [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN, were derived by single-crystal EPR measurements at X- and Q-band frequencies. This is the first simulation of EPR parameters from single-crystal EPR spectra for multinuclear Mn complexes, which are of importance in several metalloenzymes; one of them is the oxygen-evolving complex in photosystem II (PS II). Single-crystal [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN EPR spectra showed distinct resolved (55)Mn hyperfine lines in all crystal orientations, unlike single-crystal EPR spectra of other Mn(2)(III,IV) di-micro-oxo bridged complexes. We measured the EPR spectra in the crystal ab- and bc-planes, and from these spectra we obtained the EPR spectra of the complex along the unique a-, b-, and c-axes of the crystal. The crystal orientation was determined by X-ray diffraction and single-crystal EXAFS (Extended X-ray Absorption Fine Structure) measurements. In this complex, the three crystallographic axes, a, b, and c, are parallel or nearly parallel to the principal molecular axes of Mn(2)(III,IV)O(2)(phen)(4) as shown in the crystallographic data by Stebler et al. (Inorg. Chem. 1986, 25, 4743). This direct relation together with the resolved hyperfine lines significantly simplified the simulation of single-crystal spectra in the three principal directions due to the reduction of free parameters and, thus, allowed us to define the magnetic g and A tensors of the molecule with a high degree of reliability. These parameters were subsequently used to generate the solution EPR spectra at both X- and Q-bands with excellent agreement. The anisotropic g and hyperfine tensors determined by the simulation of the X- and Q-band single-crystal and solution EPR spectra are as follows: g(x) = 1.9887, g(y) = 1.9957, g(z) = 1.9775, and hyperfine coupling constants are A(III)(x) = |171| G, A(III)(y) = |176| G, A(III)(z) = |129| G, A(IV)(x) = |77| G, A(IV)(y) = |74| G, A(IV)(z) = |80| G.

MnO2 nanorods/SiO2 sphere coated on single-wall carbon nanotubes as supercapacitor electrode for high energy storage applications

NASA Astrophysics Data System (ADS)

Iro, Zaharaddeen S.; Subramani, C.; Kesavan, T.; Dash, S. S.; Sasidharan, M.; Sundramoorthy, Ashok K.

2017-12-01

A composite of MnO2/SiO2 sphere was coated on single-wall carbon nanotubes (MnO2/SiO2/SWCNT) using one-pot hydrothermal synthesis method. KMnO4 was used as an oxidizing agent for mild functionalization of single-wall carbon nanotubes (SWCNT), and also as a precursor of MnO2. A comparative study in the presence of SiO2 and SWCNT was carried out using bare MnO2 as a reference. After addition of SiO2, the composite obtained showed an increase in both the specific capacitance and cycle life which can be associated with spherical shape of SiO2 which offered reduction sites for MnO2. With the addition of SWCNT less than 5%, the composite further showed an increase in capacitance and cycle life, this is because of the good conductive nature, excellent mechanical property and chemical stability of SWCNT. The electrochemical behaviour was studied using cyclic voltammetry and galvanostatic charge/discharge method in 1 M Na2SO4 electrolyte. The specific capacitance of MnO2, MnO2/SiO2 and MnO2/SiO2/SWCNT composite is 73.6 F g-1, 108.7 F g-1 and 136 F g-1 at a current density of 1 A g-1, respectively. The MnO2/SiO2/SWCNT energy density was 68 Wh kg-1 with power density of 444.4 W kg-1. The MnO2/SiO2/SWCNT composite retained 88% of its specific capacitance after 500 cycles. We envisage that this hybrid material could be applied for preparation of supercapacitor electrode.

Investigation of the mechanical properties of FeNiCrMnSi high entropy alloy wear resistant

NASA Astrophysics Data System (ADS)

Buluc, G.; Florea, I.; Chelariu, R.; Popescu, G.; Carcea, I.

2016-06-01

In this paper we investigated microstructure, hardness and wear resistance for FeNiCrMnAl, high entropy alloy. The FeNiCrMnSi, high entropy alloy was elaborated in a medium induction furnace, by choosing the silicon, as an alliance element within the equi- atomic high entropy alloy, we managed to obtain a dendritic structure, the formation of intermetallic compounds or separated silicon. The medium hardness value of the investigated alloy was 948.33 HV and the medium value of the friction coefficient was 0.6655 in the first 20 seconds and 0.5425 for 1667 seconds. The volume loss of the high entropy alloy FeNiCrMnSi was 0.0557 mm3.

Antiferromagnetism in semiconducting SrMn 2 Sb 2 and BaMn 2 Sb 2 single crystals

DOE PAGES

Sangeetha, N. S.; Smetana, V.; Mudring, A. -V.; ...

2018-01-03

Here, crystals of SrMn 2Sb 2 and BaMn 2Sb 2 were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ, heat capacity C p, and magnetic susceptibility χ measurements versus temperature T, and magnetization versus field M(H) isotherm measurements. SrMn 2Sb 2 adopts the trigonal CaAl 2Si 2-type structure, whereas BaMn 2Sb 2 crystallizes in the tetragonal ThCr 2Si 2-type structure. The ρ(T) data indicate semiconducting behaviors for both compounds with activation energies of ≳0.35 eV for SrMn 2Sb 2 and 0.16 eV for BaMn 2Sb 2. The χ(T) andmore » C p(T) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2Sb 2 and 450 K for BaMn 2Sb 2. The anisotropic χ(T≤T N) data also show that the ordered moments in SrMn 2Sb 2 are aligned in the hexagonal ab plane, whereas the ordered moments in BaMn 2Sb 2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H) data for SrMn 2Sb 2 exhibit a continuous metamagnetic transition at low fields 02Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ(T) and C p(T) data for both SrMn 2Sb 2 and BaMn 2Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl 2Si 2 and ThCr 2Si 2 crystal structures show that the T N values for the CaAl 2Si 2-type compounds are much smaller than those for the ThCr 2Si 2-type materials.« less

Manganese(IV) Oxide Production by Acremonium sp. Strain KR21-2 and Extracellular Mn(II) Oxidase Activity

PubMed Central

Miyata, Naoyuki; Tani, Yukinori; Maruo, Kanako; Tsuno, Hiroshi; Sakata, Masahiro; Iwahori, Keisuke

2006-01-01

Ascomycetes that can deposit Mn(III, IV) oxides are widespread in aquatic and soil environments, yet the mechanism(s) involved in Mn oxide deposition remains unclear. A Mn(II)-oxidizing ascomycete, Acremonium sp. strain KR21-2, produced a Mn oxide phase with filamentous nanostructures. X-ray absorption near-edge structure (XANES) spectroscopy showed that the Mn phase was primarily Mn(IV). We purified to homogeneity a laccase-like enzyme with Mn(II) oxidase activity from cultures of strain KR21-2. The purified enzyme oxidized Mn(II) to yield suspended Mn particles; XANES spectra indicated that Mn(II) had been converted to Mn(IV). The pH optimum for Mn(II) oxidation was 7.0, and the apparent half-saturation constant was 0.20 mM. The enzyme oxidized ABTS [2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] (pH optimum, 5.5; Km, 1.2 mM) and contained two copper atoms per molecule. Moreover, the N-terminal amino acid sequence (residues 3 to 25) was 61% identical with the corresponding sequence of an Acremonium polyphenol oxidase and 57% identical with that of a Myrothecium bilirubin oxidase. These results provide the first evidence that a fungal multicopper oxidase can convert Mn(II) to Mn(IV) oxide. The present study reinforces the notion of the contribution of multicopper oxidase to microbially mediated precipitation of Mn oxides and suggests that Acremonium sp. strain KR21-2 is a good model for understanding the oxidation of Mn in diverse ascomycetes. PMID:17021194

Environmentally friendly gamma-MnO2 hexagon-based nanoarchitectures: structural understanding and their energy-saving applications.

PubMed

Wu, Changzheng; Xie, Wei; Zhang, Miao; Bai, Liangfei; Yang, Jinlong; Xie, Yi

2009-01-01

Although about 200,000 metric tons of gamma-MnO(2) are used annually worldwide for industrial applications, the gamma-MnO(2) structure is still known to possess a highly ambiguous crystal lattice. To better understand the gamma-MnO(2) atomic structure, hexagon-based nanoarchitectures were successfully synthesized and used to elucidate its internal structure for the present work. The structural analysis results, obtained from the hexagon-based nanoarchitectures, clearly show the coexistence of akhtenskite (epsilon-MnO(2)), pyrolusite (beta-MnO(2)), and ramsdellite in the so-called gamma-MnO(2) phase and verified the heterogeneous phase assembly of the gamma-MnO(2) state, which violates the well-known "De Wolff" model and derivative models, but partially accords with Heuer's results. Furthermore, heterogeneous gamma-MnO(2) assembly was found to be a metastable structure under hydrothermal conditions, and the individual components of the heterogeneous gamma-MnO(2) system have structural similarities and a high lattice matches with pyrolusite (beta-MnO(2)). The as-obtained gamma-MnO(2) nanoarchitectures are nontoxic and environmentally friendly, and the application of such nanoarchitectures as support matrices successfully mitigates the common problems for phase-change materials of inorganic salts, such as phase separation and supercooling-effects, thereby showing prospect in energy-saving applications in future "smart-house" systems.

Direct Electrothermal Atomic Absorption Determination of Trace Elements in Body Fluids (Review)

NASA Astrophysics Data System (ADS)

Zacharia, A. N.; Arabadji, M. V.; Chebotarev, A. N.

2017-03-01

This review is focused on the state and development of tendencies of electrothermal atomic absorption spectroscopy over the last 25 years (from 1990 to 2016) in the direct determination of Cu, Zn, Pb, Cd, Mn, Se, As, Cr, Co, Ni, Al, and Hg in body fluids such as blood, urine, saliva, and breast milk.

Formation of self-organized Mn3O4 nanoinclusions in LaMnO3 films

NASA Astrophysics Data System (ADS)

Pomar, Alberto; Konstantinović, Zorica; Bagués, Nuria; Roqueta, Jaume; López-Mir, Laura; Balcells, Lluis; Frontera, Carlos; Mestres, Narcis; Gutiérrez-Llorente, Araceli; Šćepanović, Maja; Lazarević, Nenad; Popović, Zoran; Sandiumenge, Felip; Martínez, Benjamín; Santiso, José

2016-09-01

We present a single-step route to generate ordered nanocomposite thin films of secondary phase inclusions (Mn3O4) in a pristine perovskite matrix (LaMnO3) by taking advantage of the complex phase diagram of manganese oxides. We observed that in samples grown under vacuum growth conditions from a single LaMnO3 stoichiometric target by Pulsed Laser Deposition, the most favourable mechanism to accommodate Mn2+ cations is the spontaneous segregation of self-assembled wedge-like Mn3O4 ferrimagnetic inclusions inside a LaMnO3 matrix that still preserves its orthorhombic structure and its antiferromagnetic bulk-like behaviour. A detailed analysis on the formation of the self-assembled nanocomposite films evidences that Mn3O4 inclusions exhibit an epitaxial relationship with the surrounding matrix that it may be explained in terms of a distorted cubic spinel with slight ( 9º) c-axis tilting. Furthermore, a Ruddlesden-Popper La2MnO4 phase, helping to the stoichiometry balance, has been identified close to the interface with the substrate. We show that ferrimagnetic Mn3O4 columns influence the magnetic and transport properties of the nanocomposite by increasing its coercive field and by creating local areas with enhanced conductivity in the vicinity of the inclusions.

Synthesis, crystal structure, and properties of KSbO{sub 3}-type Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Manrong; Retuerto, Maria; Bok Go, Yong

2013-01-15

Single crystals of Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11} were prepared from NaCl+KCl flux. This compound adopts KSbO{sub 3}-type crystal structure as evidenced by electron and single crystal X-ray diffraction analysis. The three-dimensional channel structure is formed by corner-sharing octahedral (Mn{sub 0.63}Te{sub 0.37}){sub 2}O{sub 10} dimers and two identical (Bi1){sub 4}(Bi2){sub 2} interpenetrating lattices. The intra-dimer Mn/Te-Mn/Te distances in Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11} are short and are consistent with weak metal-metal interactions. The mixed oxidation state of manganese and the edge-sharing octahedral features are confirmed by X-ray near edge absorption spectroscopy measurements, which indicate Bi{sub 3}(Mn{sup III}{sub 1.1}Mn{sup IV}{sub 0.8})Te{supmore » VI}{sub 1.1}O{sub 11} with 57.7% Mn{sup 3+} and 42.3% Mn{sup 4+}. The partial substitution of Te for Mn perturbs long-range magnetic interactions, thereby destroying the ferromagnetic ordering found in Bi{sub 3}Mn{sub 3}O{sub 11} (T{sub C}=150 K). - Graphical abstract: Single crystal of Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11} was grown from NaCl+KCl binary flux, suggesting that the high pressure Bi{sub 3}Mn{sub 3}O{sub 11} phase can be stabilized by partial substitution of Mn by Te at ambient pressure. Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11} adopts a typical three dimensional KSbO{sub 3}-type crystal structure with three interpenetrating lattices and weak intra-dimmer metal-metal interaction caused by the d electrons of Mn. The edge-shared (Mn{sub 0.63}Te{sub 0.37}){sub 2}O{sub 10} octahedral dimer and mixed oxidation state of manganese (Bi{sub 3}(Mn{sup III}{sub 1.1}Mn{sup IV}{sub 0.8})Te{sup VI}{sub 1.1}O{sub 11} with 57.7% Mn{sup 3+} and 42.3% Mn{sup 4+}) features were evidenced by X-ray absorption near edge spectroscopy. Compared with Bi{sub 3}Mn{sub 3}O{sub 11}, the Te substituted Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11} relaxes the crystal structure, but destroys the long-range magnetic ordering and gives short-range magnetic ordering below 5 K. Highlights: Black-Right-Pointing-Pointer High pressure Bi{sub 3}Mn{sub 3}O{sub 11} is stabilized by partial Te substitution at ambient pressure. Black-Right-Pointing-Pointer New KSbO{sub 3}-type Bi{sub 3}Mn{sub 1.9}Te{sub 1.1}O{sub 11} single crystal was grown from binary flux. Black-Right-Pointing-Pointer The presence of mixed oxidation state of manganese is evidenced by XANES study. Black-Right-Pointing-Pointer The Te-substitution destroys the long-range magnetic ordering and relaxes the structure.« less

Manganese accumulation in hair and teeth as a biomarker of manganese exposure and neurotoxicity in rats.

PubMed

Liang, Guiqiang; Zhang, Li'e; Ma, Shuyan; Lv, Yingnan; Qin, Huiyan; Huang, Xiaowei; Qing, Li; Li, Qin; Chen, Kangcheng; Xiong, Feng; Ma, Yifei; Nong, Jie; Yang, Xiaobo; Zou, Yunfeng

2016-06-01

Manganese (Mn) is an essential trace element to humans. However, excessive Mn causes cognitive impairment resulting from injury to the central nervous system within the hippocampus. No ideal biomarker is currently available for evaluating Mn exposure and associated neurotoxicity in the body. Hence, this study used Mn levels in the serum (MnS), teeth (MnT), and hair (MnH) as biomarkers for evaluating the association between Mn exposure and cognitive impairment in Mn-treated rats. A total of 32 male Sprague-Dawley rats were randomly divided into four groups, received 0, 5, 10, and 20 mg/(kg day) of MnCl2·4H2O for 5 days a week for 18 weeks, respectively. Lifetime Mn cumulative dose (LMCD) was used to evaluate external Mn exposure. Hippocampus, serum, teeth, and hair specimens were collected from the rats for Mn determination by graphite furnace atomic absorption spectrometry. Learning and memory functions were assessed using the Morris water maze test. Results showed that chronic Mn exposure increased the hippocampus (MnHip), MnS, MnT, and MnH levels, as well as impaired learning and memory function in rats. MnHip, MnT, and MnH levels were positively correlated with LMCD (r = 0.759, r = 0.925, and r = 0.908, respectively; p < 0.05), escape latency (r = 0.862, r = 0.716, and r = 0.814, respectively; p < 0.05), and the number of platform crossings (r = -0.734, r = -0.514, and r = -0.566, respectively; p < 0.05). No association was observed between MnS levels and the number of platform crossings (r = -0.286, p > 0.05). Thus, MnT and MnH detected long-term low-dose Mn exposure. These parameters can be reliable biomarkers for Mn exposure and associated neurotoxicity in Mn-treated rats.

Graphene oxide electrocatalyst on MnO2 air cathode as an efficient electron pump for enhanced oxygen reduction in alkaline solution

NASA Astrophysics Data System (ADS)

Basirun, Wan Jeffrey; Sookhakian, Mehran; Baradaran, Saeid; Endut, Zulkarnain; Mahmoudian, Mohammad Reza; Ebadi, Mehdi; Yousefi, Ramin; Ghadimi, Hanieh; Ahmed, Sohail

2015-03-01

Graphene oxide (GO) was deposited on the surface of a MnO2 air cathode by thermal evaporation at 50°C from a GO colloidal suspension. Fourier transformed infrared spectroscopy and field emission scanning electron microscopy confirmed the presence of GO on the MnO2 air cathode (GO-MnO2). Voltammetry and chrono-amperometry showed increased currents for the oxygen reduction reaction (ORR) in 6 M KOH solution for GO-MnO2 compared to the MnO2 cathode. The GO-MnO2 was used as an air cathode in an alkaline tin-air cell and produced a maximum power density of 13 mW cm-2, in contrast to MnO2, which produced a maximum power density of 9.2 mW cm-2. The electrochemical impedance spectroscopy results suggest that the chemical step for the ORR is the rate determining step, as proposed earlier by different researchers. It is suggested that the presence of GO and electrochemically reduced graphene oxide (ERGO) on the MnO2 surface are responsible for the increased rate of this step, whereby GO and ERGO accelerate the process of electron donation to the MnO2 and to adsorbed oxygen atoms.

Simple Map with Low MN Perturbation for a Single-Null Divertor Tokamak with Constant Width of Stochastic Layer

NASA Astrophysics Data System (ADS)

Verma, Arun; Smith, Terry; Punjabi, Alkesh; Boozer, Allen

1996-11-01

In this work, we investigate the effects of low MN perturbations in a single-null divertor tokamak with stochastic scrape-off layer. The unperturbed magnetic topology of a single-null divertor tokamak is represented by Simple Map (Punjabi A, Verma A and Boozer A, Phys Rev Lett), 69, 3322 (1992) and J Plasma Phys, 52, 91 (1994). We choose the combinations of the map parameter k, and the strength of the low MN perturbation such that the width of stochastic layer remains unchanged. We give detailed results on the effects of low MN perturbation on the magnetic topology of the stochastic layer and on the footprint of field lines on the divertor plate given the constraint of constant width of the stochastic layer. The low MN perturbations occur naturally and therefore their effects are of considerable importance in tokamak divertor physics. This work is supported by US DOE OFES. Use of CRAY at HU and at NERSC is gratefully acknowledged.

Magnetic avalanches in manganese-acetate, "magnetic deflagration"

NASA Astrophysics Data System (ADS)

Suzuki, Yoko

Mn12-acetate, first synthesized in 1980 by Lis, is one example of a class of many molecules called single molecule magnets (SMMs) or molecular nanomagnets. These molecules have several atomic spins strongly coupled together within each molecule. They exhibit interesting quantum mechanical phenomena at low temperatures such as quantum tunneling of magnetization, which was first found with Mn12-acetate in 1996 by Friedman, et al. , and Berry phase oscillations which were measured in Fe8 (another SMM) in 1999 by Wernsdorfer, et al. In addition to possible application as memory storage and qubits for quantum computers, these systems provide the means for studies of mesoscopic physics as well as the interactions of the molecules with their environment, such as phonon, photon, nuclear spin, intermolecular dipole, and exchange interactions. Mn12-acetate has twelve Mn ions magnetically coupled in the center of the molecule yielding a giant spin of S = 10 at low temperature. It also has a large uniaxial anisotropy of 65 K. Below 3 K, magnetization curves show strong hysteresis due to the anisotropy barrier. At thesis temperatures, the spin relaxes through the barrier by quantum tunneling of magnetization, which produces regularly-spaced multiple resonant steps in the hysteresis curve. Magnetic avalanches, first detected by Paulsen et al., also occur for some samples only at low temperature, leading to a very fast single-step reversal of the full magnetization, which clearly differs from relaxation by tunneling. In this thesis, I present the results of detailed experimental studies of two aspects of magnetic avalanche phenomenon: "conditions for the triggering of avalanches" and "propagation of the avalanche front". In the first study, we find the magnetic fields at which avalanches occur are stochastically distributed in a particular range of fields. For the second study, we conducted local time-resolved measurements. The results indicate the magnetization avalanches spread as a narrow interface that propagate through the crystal at a constant velocity which is roughly two orders of magnitude smaller than the speed of sound in solids. We argue this phenomenon is closely analogous to the propagation of a flame front(deflagration) through a flammable chemical substance.

Thermal expansion of monogermanides of 3d-metals

NASA Astrophysics Data System (ADS)

Valkovskiy, G. A.; Altynbaev, E. V.; Kuchugura, M. D.; Yashina, E. G.; Sukhanov, A. S.; Dyadkin, V. A.; Tsvyashchenko, A. V.; Sidorov, V. A.; Fomicheva, L. N.; Bykova, E.; Ovsyannikov, S. V.; Chernyshov, D. Yu; Grigoriev, S. V.

2016-09-01

Temperature dependent powder and single-crystal synchrotron diffraction, specific heat, magnetic susceptibility and small-angle neutron scattering experiments have revealed an anomalous response of MnGe. The anomaly becomes smeared out with decreasing Mn content in Mn1-x Co x Ge and Mn1-x Fe x Ge solid solutions. Mn spin state instability is discussed as a possible candidate for the observed effects.

Using complimentary microscopy methods to examine Ni-Mn-Si-precipitates in highly-irradiated reactor pressure vessel steels

DOE PAGES

Edmondson, P. D.; Parish, C. M.; Nanstad, R. K.

2017-05-29

Nano-scale Ni-Mn-Si-rich precipitates formed in a reactor pressure vessel steel under high neutron fluence have been characterized using highly complimentary atom probe tomography (APT) and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS) combined with STEM-EDS modeling. Using these techniques in a synergistic manner to overcome the well-known trajectory aberrations in APT data, the average upper limit Fe concentration within the precipitates was found to be ~6 at.%. Using this knowledge, accurate compositions of the precipitates was determined and it was found that the spread of precipitate compositions was large, but mostly centered around the Γ2-and G-phases. The usemore » of STEM-EDS also allowed for larger areas to be examined, and segregation of minor solutes was observed to occur on grain boundaries, along with Ni-Mn-Si-rich precipitates that were smaller in size than those in the matrix. Solute segregation at the grain boundaries is proposed to occur through a radiation induced segregation or radiation enhanced diffusion mechanism due to the presence of a denuded zone about the grain boundary. It is also proposed that the reduced precipitate size at the grain boundaries is due to the structure of the grain boundary. The lack of Ni-Mn-Si precipitates observed in larger Mo-rich precipitates is also discussed, and the absence of the minor solutes required to form the Ni-Mn-Si precipitates results in the lack of nucleation. This is in contrast to cementite phases in which Ni-Mn-Si precipitates have been seen to be formed. It was also determined through this work that the exclusion of all the Fe ions during atom probe analysis is a reasonable approximation.« less

Polar fluctuations in Mn substituted KTaO{sub 3} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Axelsson, Anna-Karin; Pan Yuya; Valant, Matjaz

2010-09-15

Polar fluctuations were found in KTaO{sub 3} when K{sup +} was substituted with Mn{sup 2+} on the A-site. The temperature dependence of the real part of the dielectric permittivity of (K{sub 1-2x}Mn{sub x{open_square}x})TaO{sub 3} ceramics (x=0-0.05) shows a diffuse maximum between 50-100 K in the frequency range 10{sup 2}-10{sup 6} Hz, shifting to higher temperature with increasing frequency and Mn content. The results are analyzed using a modified Curie-Weiss law, the Cole-Cole equation and the Arrhenius law. Here it is suggested that the observed relaxor-type dielectric behavior is attributed to the formation of electric dipoles originating from two distinct sources;more » one from an atomic off-center position when Mn{sup 2+} substitutes for K{sup +} and one from the anion deficiencies formed by these aliovalent substitutions.« less

Excitations and magnetization density distribution in the dilute ferromagnetic semiconductor Yb 14 MnSb 11

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stone, M. B.; Garlea, V. O.; Gillon, B.

2017-01-23

One rare example of a Kondo lattice compound with ferromagnetic dominated RKKY interactions is Ybmore » $$_{14}$$MnSb$$_{11}$$. As a ferromagnetic semiconductor with $$T_c \\approx 53$$~K, it is also a potential compound for exploration of spintronic devices. This material is furthermore one of the most efficient high temperature thermoelectrics. We describe measurements which answer remaining questions regarding the energy scales of the exchange interactions, the valence and the magnetization density distribution in this system. We also find that the system consists of RKKY exchange coupled Mn$$^{2+}$$ sites with nearest and next nearest exchange interactions dominating the magnetic spectrum with no significant magnetization density localized on other atomic sites. The extended spread of a negative magnetization around each of the Mn ions supports a Kondo screening cloud scenario for Yb$$_{14}$$MnSb$$_{11}$$.« less

Band structure modification of the thermoelectric Heusler-phase TiFe2Sn via Mn substitution.

PubMed

Zou, Tianhua; Jia, Tiantian; Xie, Wenjie; Zhang, Yongsheng; Widenmeyer, Marc; Xiao, Xingxing; Weidenkaff, Anke

2017-07-19

Doping (or substitution)-induced modification of the electronic structure to increase the electronic density of states (eDOS) near the Fermi level is considered as an effective strategy to enhance the Seebeck coefficient, and may consequently boost the thermoelectric performance. Through density-functional theory calculations of Mn-substituted TiFe 2-x Mn x Sn compounds, we demonstrate that the d-states of the substituted Mn atoms induce a strong resonant level near the Fermi energy. Our experimental results are in good agreement with the calculations. They show that Mn substitution results in a large increase of the Seebeck coefficient, arising from an enhanced eDOS in Heusler compounds. The results prove that a proper substitution position and element selection can increase the eDOS, leading to a higher Seebeck coefficient and thermoelectric performance of ecofriendly materials.

The effect of calcination temperature on the formation and magnetic properties of ZnMn2O4 spinel

NASA Astrophysics Data System (ADS)

Hermanto, B.; Ciswandi; Afriani, F.; Aryanto, D.; Sudiro, T.

2018-03-01

The spinel based on transition-metal oxides has a typical composition of AB2O4. In this study, the ZnMn2O4 spinel was synthesized using a powder metallurgy technique. The Zn and Mn metallic powders with an atomic ratio of 1:2 were mechanically alloyed for 3 hours in aqueous solution. The mixed powder was then calcined in a muffle furnace at elevated temperature of 400, 500 and 600 °C. The X-ray Diffractometer (XRD) was used to evaluate the formation of a ZnMn2O4 spinel structure. The magnetic properties of the sample at varying calcination temperatures were characterized by a Vibrating Sample Magnetometer (VSM). The results show that the fraction of ZnMn2O4 spinel formation increases with the increase of calcination temperature. The calcination temperature also affects the magnetic properties of the samples.

Structures and stability of metal-doped Ge nM (n = 9, 10) clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua

The lowest-energy structures of neutral and cationic Ge nM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge 9 and Ge 10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge n clusters. However, the neutral and cationic FeGe 9,10,MnGe 9,10 and Ge 10Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge n clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge 9,10Fe and Ge 9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Binding effects of Mn²⁺ and Zn²⁺ ions on the vibrational properties of guanine-cytosine base pairs in the Watson-Crick and Hoogsteen configurations.

PubMed

Morari, Cristian; Bogdan, Diana; Muntean, Cristina M

2012-11-01

The binding effects of Mn²⁺ and Zn²⁺ ions on the vibrational properties of guanine-cytosine base pairs have been performed using density functional theory investigations. The calculations were carried out on Watson-Crick and Hoogsteen configurations of the base pairs. We have found, that in Watson-Crick configuration, the metal is coordinated to N7 atom of guanine while, in the case of Hoogsteen configuration, the coordination is at N3 atom of guanine. We have pointed out the vibrational bands that can be used to detect the presence of metallic ions in the Watson-Crick and Hoogsteen structures. Our results show that the vibrational amplitudes of metallic atoms are strong for wavenumbers lower than 600 cm⁻¹. Also, we predict that the distinction between Watson-Crick and Hoogsteen configurations can be seen around 85, 170 and 310 cm⁻¹.

Structures and stability of metal-doped Ge nM (n = 9, 10) clusters

DOE PAGES

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua; ...

2015-06-26

The lowest-energy structures of neutral and cationic Ge nM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge 9 and Ge 10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Ge n clusters. However, the neutral and cationic FeGe 9,10,MnGe 9,10 and Ge 10Al are cage-like withmore » the metal atom encapsulated inside. Such cage-like transition metal doped Ge n clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge 9,10Fe and Ge 9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.« less

Structures and stability of metal-doped GenM (n = 9, 10) clusters

NASA Astrophysics Data System (ADS)

Qin, Wei; Lu, Wen-Cai; Xia, Lin-Hua; Zhao, Li-Zhen; Zang, Qing-Jun; Wang, C. Z.; Ho, K. M.

2015-06-01

The lowest-energy structures of neutral and cationic GenM (n = 9, 10; M = Si, Li, Mg, Al, Fe, Mn, Pb, Au, Ag, Yb, Pm and Dy) clusters were studied by genetic algorithm (GA) and first-principles calculations. The calculation results show that doping of the metal atoms and Si into Ge9 and Ge10 clusters is energetically favorable. Most of the metal-doped Ge cluster structures can be viewed as adding or substituting metal atom on the surface of the corresponding ground-state Gen clusters. However, the neutral and cationic FeGe9,10,MnGe9,10 and Ge10Al are cage-like with the metal atom encapsulated inside. Such cage-like transition metal doped Gen clusters are shown to have higher adsorption energy and thermal stability. Our calculation results suggest that Ge9,10Fe and Ge9Si would be used as building blocks in cluster-assembled nanomaterials because of their high stabilities.

Copper and manganese complexes based on 1,4-naphthalene dicarboxylic acid ligand and its derivative: Syntheses, crystal structures, and magnetic properties

NASA Astrophysics Data System (ADS)

Xing, Yubo; Liu, Yuqi; Xue, Xiaofei; Wang, Xinying; Li, Wei

2018-02-01

Three new metal-organic coordination polymers, {[Mn2(1,4-NDC)2 (C2H5OH) (DMF) (H2O)]·CH3OH}n(1), {[Mn(III)(1,4-NDC)(C2H5O)][Mn(II)(1,4-NDC)(DMF)(H2O)]}n(2) and {[Cu2(C13H9O4)4(H2O)2]}n(3) based on1,4-H2NDC and its derivative were hydrothermally synthesized (1,4-H2NDC = 1,4-naphthalene-dicarboxylic acid, C13H10O4 = 4-methyl formate-1-naphthalenecarboxylic acid), and characterized by techniques of single crystal X-ray diffraction, infrared spectra (IR), elemental analysis, powder X-ray diffraction(PXRD) and variable-temperature magnetic susceptibility measurements. X-ray crystal structure analyses reveal that complexes 1 and 2 show a same 3,5-connected fsc 3D topology network with the Schlȁfli symbol of {4·6·8}{4·66·83}. But, the valence of some Mn atom in complex 2 take place transition from the +II oxidation state to the +III oxidation state, which may be the effect of the different solvent ratio. In complex 3, the Cu⋯Cu distance of 2.620(13) Å is significantly shorter than the sum of the van der Waals radii of Cu (1.40 Å), resulting in a strong ferromagnetic interaction between the Cu(II) centers. Furthermore, the temperature-dependent magnetic susceptibility measurements exhibit overall antiferromagnetic interactions between manganese ions for complexes 1 and 2, and a strong ferromagnetic interaction between the Cu(II) centers for complex 3.

High-resolution synchrotron x-ray powder diffraction study of the incommensurate modulation in the martensite phase of Ni2MnGa: Evidence for nearly 7M modulation and phason broadening

NASA Astrophysics Data System (ADS)

Singh, Sanjay; Petricek, V.; Rajput, Parasmani; Hill, Adrian H.; Suard, E.; Barman, S. R.; Pandey, Dhananjai

2014-07-01

The modulated structure of the martensite phase of Ni2MnGa is revisited using high-resolution synchrotron x-ray powder diffraction measurements, which reveal higher-order satellite reflections up to the third order and phason broadening of the satellite peaks. The structure refinement, using the (3+1) dimensional superspace group approach, shows that the modulated structure of Ni2MnGa can be described by orthorhombic superspace group Immm(00γ)s00 with lattice parameters a=4.218 61(2)Å,b=5.546 96(3)Å, and c=4.187 63(2) Å, and an incommensurate modulation wave vector q =0.43160(3)c*=(3/7+δ)c*, where δ =0.00303(3) is the degree of incommensuration of the modulated structure. Additional satellite peak broadening, which could not be accounted for in terms of the anisotropic strain broadening based on a lattice parameter distribution, has been modeled in terms of phasons using fourth-rank covariant strain-tensor representation for incommensurate structures. The simulation of single-crystal diffraction patterns from the refined structural parameters unambiguously reveals a rational approximant structure with 7M modulation. The inhomogeneous displacement of different atomic sites on account of incommensurate modulation and the presence of phason broadening clearly rule out the adaptive phase model proposed recently by Kaufmann et al. [S. Kaufmann, U. K. Rößler, O. Heczko, M. Wuttig, J. Buschbeck, L. Schultz, and S. Fähler, Phys. Rev. Lett. 104, 145702 (2010), 10.1103/PhysRevLett.104.145702] and suggest that the modulation in Ni2MnGa originates from soft-mode phonons.

Temperature and electric-field induced phase transition behavior and electrical properties of [001]-oriented 0.23Pb(In1/2Nb1/2)O3-0.47Pb(Mg1/3Nb2/3)O3-0.3PbTiO3-Mn single crystals

NASA Astrophysics Data System (ADS)

Zhang, Zhang; Chen, Jianwei; Xu, Jialin; Li, Xiaobing; Luo, Haosu

2017-12-01

The temperature and electric-field induced phase transition behavior and dielectric, piezoelectric, and ferroelectric properties of [001]-oriented 0.23Pb(In1/2Nb1/2)O3-0.47Pb(Mg1/3Nb2/3)O3-0.3PbTiO3-Mn (PIMNT-Mn) single crystals were investigated. Dielectric performance analysis and temperature-dependent Raman spectra show three apparent ferroelectric phase transition temperatures around 120 °C(TR-M),145 °C(TM-T), and 170 °C(TT-C), respectively. In addition, the temperature dependence of the relative Raman intensities of Lorentzian peaks indicates the poled PIMNT-Mn single crystals exhibit rhombohedral(R) → monoclinic(M) → tetragonal(T) → cubic(C) phase transition path. The electrical properties of the PIMNT-Mn single crystals such as the longitudinal electrostrictive coefficient (Q), the converse piezoelectric constant (d33), and the maximum strain value (Smax%) have changed abnormally around the phase transition temperatures (TR-M and TM-T).

Heterometallic [Mn5-Ln4] single-molecule magnets with high anisotropy barriers.

PubMed

Mereacre, Valeriu; Ako, Ayuk M; Clérac, Rodolphe; Wernsdorfer, Wolfgang; Hewitt, Ian J; Anson, Christopher E; Powell, Annie K

2008-01-01

The reaction of [Mn6O2(Piv)(10)(4-Me-py)(2.5)(PivH)(1.5)] (1) (py: pyridine, Piv: pivilate) with N-methyldiethanolamine (mdeaH2) and Ln(NO3)3 x 6 H2O in MeCN leads to a series of nonanuclear compounds [Mn5Ln4(O)6(mdea)2(mdeaH)2(Piv)6(NO3)4(H2O)2]2 MeCN (Ln=Tb(III) (2), Dy(III) (3), Ho(III) (4), Y(III) (5)). Single-crystal X-ray diffraction shows that compounds 2-5 are isostructural, with the central core composed of two distorted {Mn(IV)Mn(III)Ln2O4} cubanes sharing a Mn(IV) vertex, representing a new heterometallic 3d-4f motif for this class of ligand. The four new compounds display single-molecule magnet (SMM) behaviour, which is modulated by the lanthanide ion used. Moreover, the values found for Delta(eff) and tau(o) for 3 of 38.6 K and 3.0 x 10(-9) s respectively reveal that the complex 3 exhibits the highest energy barrier recorded so far for 3d-4f SMMs. The slow relaxation of the magnetisation for 3 was confirmed by mu-SQUID measurements on an oriented single crystal and the observation of M versus H hysteresis loops below 1.9 K.

Role of ligands in permanganate oxidation of organics.

PubMed

Jiang, Jin; Pang, Su-Yan; Ma, Jun

2010-06-01

We previously demonstrated that several ligands such as phosphate, pyrophosphate, EDTA, and humic acid could significantly enhance permanganate oxidation of triclosan (one phenolic biocide), which was explained by the contribution of ligand-stabilized reactive manganese intermediates in situ formed upon permanganate reduction. To further understand the underlying mechanism, we comparatively investigated the influence of ligands on permanganate oxidation of bisphenol A (BPA, one phenolic endocrine-disrupting chemical), carbamazepine (CBZ, a pharmaceutical containing the olefinic group), and methyl p-tolyl sulfoxide (TMSO, a typical oxygen-atom acceptor). Selected ligands exerted oxidation enhancement for BPA but had negligible influence for CBZ and TMSO. This was mainly attributed to the effects of identified Mn(III) complexes, which would otherwise disproportionate spontaneously in the absence of ligands. The one-electron oxidant Mn(III) species exhibited no reactivity toward CBZ and TMSO for which the two-electron oxygen donation may be the primary oxidation mechanism but readily oxidized BPA. The latter case was a function of pH, the complexing ligand, and the molar [Mn(III)]:[ligand] ratio, generally consistent with the patterns of ligand-affected permanganate oxidation. Moreover, the combination of the one-electron reduction of Mn(III) (Mn(III) + e(-) -->Mn(II)) and the Mn(VII)/Mn(II) reaction in excess ligands (Mn(VII) + 4Mn(II) ----> (ligands) 5Mn(III)) suggested a catalytic role of the Mn(III)/Mn(II) pair in permanganate oxidation of some phenolics in the presence of ligands.

Synthesis and characterization of single-phase Mn-doped ZnO

NASA Astrophysics Data System (ADS)

Chattopadhyay, S.; Dutta, S.; Banerjee, A.; Jana, D.; Bandyopadhyay, S.; Chattopadhyay, S.; Sarkar, A.

2009-05-01

Different samples of Zn 1-xMn xO series have been prepared using conventional solid-state sintering method. We identified up to what extent doping will enable us to synthesize single-phase polycrystalline Mn-doped ZnO sample, which is one of the prerequisites for dilute magnetic semiconductor, and we have analyzed its some other physical aspects. In synthesizing the samples, proportion of Mn varies from 1 to 5 at%. However, the milling time varied (6, 12, 24, 48 and 96 h) only for 2 at% Mn-doped samples while for other samples (1, 3, 4 and 5 at% Mn doped) the milling time has been fixed to 96 h. Room-temperature X-ray diffraction (XRD) data reveal that all of the prepared samples up to 3 at% of Mn doping exhibit wurtzite-type structure, and no segregation of Mn and/or its oxides has been found. The 4 at% Mn-doped samples show a weak peak of ZnMn 2O 4 apart from the other usual peaks of ZnO and the intensity of this impurity peak has been further increased for 5 at% of Mn doping. So beyond 3 at% doping, single-phase behavior is destroyed. Band gap for all the 2 at% Mn-doped samples has been estimated to be between 3.21 and 3.19 eV and the reason for this low band gap values has been explained through the grain boundary trapping model. The room-temperature resistivity measurement shows an increase of resistivity up to 48 h of milling and with further milling it saturates. The defect state of these samples has been investigated using the positron annihilation lifetime (PAL) spectroscopy technique. Here all the relevant lifetime parameters of positron i.e. free annihilation ( τ1) at defect site ( τ2) and average ( τav) increases with milling time.

Reduced expression of PARK2 in manganese-exposed smelting workers.

PubMed

Fan, Ximin; Luo, Ying; Fan, Qiyuan; Zheng, Wei

2017-09-01

Manganese (Mn) is widely used in modern industries. Occupational exposure to Mn is known to cause clinical syndromes similar, but not identical to, Parkinson's disease. This human cohort study was designed to investigate if workers exposed to Mn altered the PARK2 gene expression, leading to Mn-induced neurotoxicity. Workers (n=26) occupationally exposed to Mn were recruited from a Mn-iron (Fe) alloy smelter, and control workers (n=20) without Mn-exposure were from an Fe smelter from Zunyi City in China. Subjects were matched with socioeconomic status and background for environmental factors. Metal concentrations were determined by atomic absorption spectrophotometry (AAS). Total RNA from the blood samples was isolated and analyzed by RT-PCR to quantify PARK2. The data showed that Mn concentrations in plasma, red blood cell (RBC) and saliva, and the cumulative Mn-exposure were about 2.2, 2.0, 1.7 and 3.0 fold higher, respectively, in Mn-exposed workers than those in control subjects (p<0.01). The expression of PARK2 in Mn-exposed workers was significantly decreased by 42% as compared to controls (p<0.01). Linear regression analysis further established that the expression of PARK2 mRNA was inversely correlated with Mn levels in plasma, RBC and saliva, as well as the cumulative Mn exposure (p<0.01). Taken together, it seems likely that Mn exposure among smelters may lead to a reduced expression of PARK2, which may partly explain the Mn-induced Parkinsonian disorder. Copyright © 2017 Elsevier B.V. All rights reserved.

The EPR study of Mn(2+) ion doped DADT single crystal produced under high pressure and temperature.

PubMed

Ceylan, Ümit; Tapramaz, Recep

2016-01-05

An EPR study on Cu(2+) and VO(2+) doped di ammonium d-tartrate single crystals has been reported in previous papers, but the same host did not accept Mn(2+) ion at the same reaction conditions in previous trials. In this study EPR study of Mn(2+) ion doped di ammonium d tartrate single crystal, (DADT) [(NH4)2C4H4O6], produced in a reactor under high pressure and high temperature. The electronic transitions were determined by the optical absorption spectrum. Hyperfine splitting and g values of the Mn(2+) ion forming a complex in the lattice were measured from experimental spectra and spin-spin dipolar splitting parameters D and E were found by the spectrum simulation techniques. Copyright © 2015 Elsevier B.V. All rights reserved.

Study of the electronic structure and half-metallicity of CaMnO3/BaTiO3 superlattice

NASA Astrophysics Data System (ADS)

Wang, Kai; Jiang, Wei; Chen, Jun-Nan; Huang, Jian-Qi

2016-09-01

In this paper, the electronic structure, magnetic properties and half-metallicity of the CaMnO3/BaTiO3 superlattice are investigated by employing the first-principle calculation based on density functional theory within the GGA or GGA + U exchange-correlation functional. The CaMnO3/BaTiO3 superlattice is constructed by the cubic CaMnO3 and the tetragonal ferroelectric BaTiO3 growing alternately along (0 0 1) direction. The cubic CaMnO3 presents a robust half-metallicity and a metastable ferromagnetic phase. Its magnetic moment is an integral number of 3.000 μB per unit cell. However, the CaMnO3/BaTiO3 superlattice has a stable ferromagnetic phase, for which the magnetic moment is 12.000 μB per unit cell. It also retains the robust half-metallicity which mainly results from the strong hybridization between Mn and O atoms. The results show that the constructed CaMnO3/BaTiO3 superlattice exhibits superior magnetoelectric properties. It may provide a theoretical reference for the design and preparation of new multiferroic materials.

Mn2- x Y x (MoO4)3 Phosphor Excited by UV GaN-Based Light-Emitting Diode for White Emission

NASA Astrophysics Data System (ADS)

Chen, Lung-Chien; Tseng, Zong-Liang; Hsu, Ting-Chun; Yang, Shengyi; Chen, Yuan-Bin

2017-04-01

One option for low-cost white light-emitting diodes (LEDs) is the combination of a near-ultraviolet (UV) LED chip (382 nm) and a single phosphor. Such Mn2- x Y x (MoO4)3 single phosphors have been fabricated by a simple solid-state reaction route and their emission color tuned by controlling the Mn doping amount. The chromaticity coordinates of the white light emitted by the UV GaN LED with the MnY(MoO4)3 phosphor were x = 0.5204 and y = 0.4050 [correlated color temperature (CCT) = 7958 K].