Magneto-optical properties of biogenic photonic crystals in algae

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

Iwasaka, M., E-mail: iwasaka-m@umin.ac.jp; Japan Science and Technology Agency, PRESTO, 4-1-8 Honcho, Kawaguchi 332-0012 Saitama; Mizukawa, Y.

In the present study, the effects of strong static magnetic fields on the structural colors of the cell covering crystals on a microalgae, coccolithophore, were investigated. The coccolithophore, Emiliania huxleyi, generates a precise assembly of calcite crystals called coccoliths by biomineralization. The coccoliths attached to the cells exhibited structural colors under side light illumination, and the colors underwent dynamic transitions when the magnetic fields were changed between 0 T and 5 T, probably due to diamagnetically induced changes of their inclination under the magnetic fields. The specific light-scattering property of individual coccoliths separated from the cells was also observed. Light scattering frommore » a condensed suspension of coccoliths drastically decreased when magnetic fields of more than 4 T were applied parallel to the direction of observation. The magnetically aligned cell-covering crystals of the coccolithophores exhibited the properties of both a photonic crystal and a minimum micromirror.« less

Magnetic field role on the structure and optical response of photonic crystals based on ferrofluids containing Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} nanoparticles

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

López, J., E-mail: javier.lopez@correounivalle.edu.co; González, Luz E.; Quiñonez, M. F.

2014-05-21

Ferrofluids based on magnetic Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO{sub 4}, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} samples showed superparamagnetic behavior, according to hysteresis loop results. Takingmore » in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferrofluids with the same nanoparticles. Previous experimental results show that a magnetic field applied perpendicular to the ferrofluid plane agglomerates the magnetic nanoparticles in parallel rods to form a hexagonal 2D photonic crystal. We calculated the photonic band structure of photonic crystals by means of the effective refractive index of the magnetic fluid, basing the study on the Maxwell-Garnett theory, finding that the photonic band structure does not present any band gaps under the action of applied magnetic field strengths used in our experimental conditions.« less

Waveguide modes of 1D photonic crystals in a transverse magnetic field

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

Sylgacheva, D. A., E-mail: sylgacheva.darjja@physics.msu.ru; Khokhlov, N. E.; Kalish, A. N.

2016-11-15

We analyze waveguide modes in 1D photonic crystals containing layers magnetized in the plane. It is shown that the magnetooptical nonreciprocity effect emerges in such structures during the propagation of waveguide modes along the layers and perpendicularly to the magnetization. This effect involves a change in the phase velocity of the mode upon reversal of the direction of magnetization. Comparison of the effects in a nonmagnetic photonic crystal with an additional magnetic layer and in a photonic crystal with magnetic layers shows that the magnitude of this effect is several times larger in the former case in spite of themore » fact that the electromagnetic field of the modes in the latter case is localized in magnetic regions more strongly. This is associated with asymmetry of the dielectric layers contacting with the magnetic layer in the former case. This effect is important for controlling waveguide structure modes with the help of an external magnetic field.« less

Optical and magneto-optical properties of one-dimensional magnetized coupled resonator plasma photonic crystals

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

Hamidi, S. M.

2012-01-15

In this paper, the optical and magneto-optical properties of one-dimensional magnetized coupled resonator plasma photonic crystals have been investigated. We use transfer matrix method to solve our magnetized coupled resonator plasma photonic crystals consist of dielectric and magnetized plasma layers. The results of the change in the optical and magneto-optical properties of structure as a result of the alteration in the structural properties such as thickness, plasma frequency and collision frequency, plasma filling factor, number of resonators and dielectric constant of dielectric layers and external magnetic field have been reported. The main feature of this structure is a good magneto-opticalmore » rotation that takes place at the defect modes and the edge of photonic band gap of our proposed optical magnetized plasma waveguide. Our outcomes demonstrate the potential applications of the device for tunable and adjustable filters or reflectors and active magneto-optic in microwave devices under structural parameter and external magnetic field.« less

Magnetic and crystal structures of the honeycomb lattice Na2IrO3 and single layer Sr2IrO4

NASA Astrophysics Data System (ADS)

Ye, Feng

2013-03-01

5 d based iridates have recently attracted great attention due to the large spin-orbit coupling (SOC). It is now recognized that the SOC that competes with other relevant energies, particularly the on-site Coulomb interaction U, and have driven novel electronic and magnetic phases. Combining single crystal neutron and x-ray diffractions, we have investigated the magnetic and crystal structures of the honeycomb lattice Na2IrO3. The system orders magnetically below 18.1 K with Ir4+ ions forming zigzag spin chains within the layered honeycomb network with ordered moment of 0.22 μB /Ir site. Such a configuration sharply contrasts the Neel or stripe states proposed in the Kitaev-Heisenberg model. The structure refinement reveals that the Ir atoms form nearly ideal 2D honeycomb lattice while the IrO6 octahedra experience a trigonal distortion that is critical to the ground state. The results of this study provide much-needed experimental insights into the magnetic and crystal structure crucial to the understanding of the exotic magnetic order and possible topological characteristics in the 5 d-electron based honeycomb lattice. Neutron diffraction experiments are also performed to investigate the magnetic and crystal structure of the single layer iridate Sr2IrO4, where new structural information and spin order are obtained that is not available from previous neutron powder diffraction measurement. This work was sponsored in part by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

Delicate crystal structure changes govern the magnetic properties of 1D coordination polymers based on 3d metal carboxylates.

PubMed

Gavrilenko, Konstantin S; Cador, Olivier; Bernot, Kevin; Rosa, Patrick; Sessoli, Roberta; Golhen, Stéphane; Pavlishchuk, Vitaly V; Ouahab, Lahcène

2008-01-01

Homo- and heterometallic 1D coordination polymers of transition metals (Co II, Mn II, Zn II) have been synthesized by an in-situ ligand generation route. Carboxylato-based complexes [Co(PhCOO)2]n (1 a, 1 b), [Co(p-MePhCOO)2]n (2), [ZnMn(PhCOO)4]n (3), and [CoZn(PhCOO)4]n (4) (PhCOOH=benzoic acid, p-MePhCOOH=p-methylbenzoic acid) have been characterized by chemical analysis, single-crystal X-ray diffraction, and magnetization measurements. The new complexes 2 and 3 crystallize in orthorhombic space groups Pnab and Pcab respectively. Their crystal structures consist of zigzag chains, with alternating M(II) centers in octahedral and tetrahedral positions, which are similar to those of 1 a and 1 b. Compound 4 crystallizes in monoclinic space group P2 1/c and comprises zigzag chains of M II ions in a tetrahedral coordination environment. Magnetic investigations reveal the existence of antiferromagnetic interactions between magnetic centers in the heterometallic complexes 3 and 4, while ferromagnetic interactions operate in homometallic compounds (1 a, 1 b, and 2). Compound 1 b orders ferromagnetically at TC=3.7 K whereas 1 a does not show any magnetic ordering down to 330 mK and displays typical single-chain magnet (SCM) behavior with slowing down of magnetization relaxation below 0.6 K. Single-crystal measurements reveal that the system is easily magnetized in the chain direction for 1 a whereas the chain direction coincides with the hard magnetic axis in 1 b. Despite important similarities, small differences in the molecular and crystal structures of these two compounds lead to this dramatic change in properties.

Magnetic properties of ultrathin tetragonal Heusler D022-Mn3Ge perpendicular-magnetized films

NASA Astrophysics Data System (ADS)

Sugihara, A.; Suzuki, K. Z.; Miyazaki, T.; Mizukami, S.

2015-05-01

We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5-130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the film's plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

Structure symmetry determination and magnetic evolution in Sr 2Ir 1–xRh xO 4

DOE PAGES

Ye, Feng; Wang, Xiaoping; Hoffmann, Christina; ...

2015-11-23

We use single-crystal neutron diffraction to determine the crystal structure symmetry and to study the magnetic evolution in the rhodium doped iridates Sr 2Ir 1–xRh xO 4 (0 ≤ x ≤ 0.16). Throughout this doping range, the crystal structure retains a tetragonal symmetry (space group I4 1/a) with two distinct magnetic Ir sites in the unit cell forming staggered IrO 6 rotation. Upon Rh doping, the magnetic order is suppressed and the magnetic moment of Ir4+ is reduced from 0.21 μ B/Ir for x = 0 to 0.18 μ B/Ir for x = 0.12. As a result, the magnetic structuremore » at x = 0.12 is different from that of the parent compound while the moments remain in the basal plane.« less

Magnetic Properties and Magnetic Phase Diagrams of Trigonal DyNi3Ga9

NASA Astrophysics Data System (ADS)

Ninomiya, Hiroki; Matsumoto, Yuji; Nakamura, Shota; Kono, Yohei; Kittaka, Shunichiro; Sakakibara, Toshiro; Inoue, Katsuya; Ohara, Shigeo

2017-12-01

We report the crystal structure, magnetic properties, and magnetic phase diagrams of single crystalline DyNi3Ga9 studied using X-ray diffraction, electrical resistivity, specific heat, and magnetization measurements. DyNi3Ga9 crystallizes in the chiral structure with space group R32. The dysprosium ions, which are responsible for the magnetism in this compound, form a two-dimensional honeycomb structure on a (0001) plane. We show that DyNi3Ga9 exhibits successive phase transitions at TN = 10 K and T'N = 9 K. The former suggests quadrupolar ordering, and the latter is attributed to the antiferromagnetic order. It is considered that DyNi3Ga9 forms the canted-antiferromagnetic structure below T'N owing to a small hysteresis loop of the low-field magnetization curve. We observe the strong easy-plane anisotropy, and the multiple-metamagnetic transitions with magnetization-plateaus under the field applied along the honeycomb plane. For Hallel [2\\bar{1}\\bar{1}0], the plateau-region arises every 1/6 for saturation magnetization. The magnetic phase diagrams of DyNi3Ga9 are determined for the fields along principal-crystal axes.

Magnetic properties of GdMnO3 nanoparticles embedded in mesoporous silica

NASA Astrophysics Data System (ADS)

Tajiri, Takayuki; Mito, Masaki; Deguchi, Hiroyuki; Kohno, Atsushi

2018-05-01

Perovskite manganite GdMnO3 nanoparticles were synthesized using mesoporous silica as a template, and their magnetic properties and crystal structure were investigated. Powder X-ray diffraction data indicated successful synthesis of the GdMnO3 nanoparticles, with mean particle sizes of 13.9 and 20.9 nm. The lattice constants for the nanoparticles were slightly different from those for the bulk material and varied with the particle size. The magnetic transition temperatures for the nanoparticles were higher than those of the bulk crystal. The synthesized GdMnO3 nanoparticles exhibited superparamagnetic behaviors: The blocking temperature, coercive field, and transition temperature depended on the particle size. Magnetic measurements and crystal structure analysis suggest that the changes in the magnetic properties for GdMnO3 nanoparticles can be attributed to the modulation of the crystallographic structure.

Dielectric, magnetic, and lattice dynamics properties of Y-type hexaferrite Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}Fe{sub 12}O{sub 22}: Comparison of ceramics and single crystals

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

Kamba, S.; Goian, V.; Savinov, M.

2010-05-15

We prepared multiferroic Y-type hexaferrite Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}Fe{sub 12}O{sub 22} ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at T{sub C}=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal.more » Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near T{sub C}. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D{sub 3d}{sup 5} hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.« less

Stability of Magnetically-Suppressed Solutal Convection In Protein Crystal Growth

NASA Technical Reports Server (NTRS)

Leslie, F. W.; Ramachandran, N.

2005-01-01

The effect of convection during the crystallization of proteins is not very well understood. In a gravitational field, convection is caused by crystal sedimentation and by solutal buoyancy induced flow and these can lead to crystal imperfections. While crystallization in microgravity can approach diffusion limited growth conditions (no convection), terrestrially strong magnetic fields can be used to control fluid flow and sedimentation effects. In this work, a theory is presented on the stability of solutal convection of a magnetized fluid in the presence of a magnetic field. The requirements for stability are developed and compared to experiments performed within the bore of a superconducting magnet. The theoretical predictions are in good agreement with the experiments and show solutal convection can be stabilized if the surrounding fluid has larger magnetic susceptibility and the magnetic field has a specific structure. Discussion on the application of the technique to protein crystallization is also provided.

An Overview of Hardware for Protein Crystallization in a Magnetic Field.

PubMed

Yan, Er-Kai; Zhang, Chen-Yan; He, Jin; Yin, Da-Chuan

2016-11-16

Protein crystallization under a magnetic field is an interesting research topic because a magnetic field may provide a special environment to acquire improved quality protein crystals. Because high-quality protein crystals are very useful in high-resolution structure determination using diffraction techniques (X-ray, neutron, and electron diffraction), research using magnetic fields in protein crystallization has attracted substantial interest; some studies have been performed in the past two decades. In this research field, the hardware is especially essential for successful studies because the environment is special and the design and utilization of the research apparatus in such an environment requires special considerations related to the magnetic field. This paper reviews the hardware for protein crystallization (including the magnet systems and the apparatus designed for use in a magnetic field) and progress in this area. Future prospects in this field will also be discussed.

An Overview of Hardware for Protein Crystallization in a Magnetic Field

PubMed Central

Yan, Er-Kai; Zhang, Chen-Yan; He, Jin; Yin, Da-Chuan

2016-01-01

Protein crystallization under a magnetic field is an interesting research topic because a magnetic field may provide a special environment to acquire improved quality protein crystals. Because high-quality protein crystals are very useful in high-resolution structure determination using diffraction techniques (X-ray, neutron, and electron diffraction), research using magnetic fields in protein crystallization has attracted substantial interest; some studies have been performed in the past two decades. In this research field, the hardware is especially essential for successful studies because the environment is special and the design and utilization of the research apparatus in such an environment requires special considerations related to the magnetic field. This paper reviews the hardware for protein crystallization (including the magnet systems and the apparatus designed for use in a magnetic field) and progress in this area. Future prospects in this field will also be discussed. PMID:27854318

Structural, magnetic, magneto-caloric and Mössbauer spectral study of Tb{sub 2}Fe{sub 17} compound synthesized by arc melting

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

Charfeddine, S.; LVMU, Centre National de Recherches en Sciences des Matériaux, Technopole de Borj-Cédria, BP 73 Soliman 8027; Zehani, K.

We have synthesized the intermetallic Tb{sub 2}Fe{sub 17} compound in hexagonal crystal structure by arc-melting without annealing. X-ray diffraction pattern has been refined by Rietveld method. The crystal structure is hexagonal with P6{sub 3}/mmc space group (Th{sub 2}Ni{sub 17}-type). The Mössbauer spectrum of Tb{sub 2}Fe{sub 17} compound has been analyzed with seven magnetic sextets assigned to the inequivalent crystallographic sites. The temperature dependence of magnetization data revealed that Tb{sub 2}Fe{sub 17} exhibits a second-order ferromagnetic to paramagnetic phase transition in the vicinity of Curie temperature (T{sub C}=412 K). The relative cooling power around the magnetic transition and the Arrott plotsmore » are also reported. - Graphical abstract: A 3D surface showing the temperature and applied magnetic field dependencies of the magnetization for Tb{sub 2}Fe{sub 17} compound (left). Rietveld analysis of the XRD pattern (right). Crystal structure for the hexagonal P6{sub 3}/mmc Tb{sub 2}Fe{sub 17} (bottom). Display Omitted - Highlights: • Tb{sub 2}Fe{sub 17} single-phase synthesized by simple arc-melting without any heat treatment. • The crystal structure is hexagonal with P6{sub 3}/mmc space group. • The magnetic entropy change of the sample was determined by Maxwell relation. • Hyperfine parameters, magnetic and magnetocaloric properties were studied.« less

Crystallographic and magnetic structure of the novel compound ErGe 1.83

NASA Astrophysics Data System (ADS)

Oleksyn, O.; Schobinger-Papamantellos, P.; Ritter, C.; de Groot, C. H.; Buschow, K. H. J.

1997-02-01

The crystal structure and the magnetic ordering of the novel orthorhombic compound ErGe 2-x has been studied by neutron powder diffraction and magnetic measurements. The crystal structure belongs to the DyGe 1.85-type (space group Cmc2 1)·ErGe 2-x ( x = 0.17 (2)) orders antiferromagnetically below TN = 6 K and displays a metamagnetic behaviour. The magnetic cell has the same size as the chemical unit cell ( q = 0 ). The magnetic space group is Cmc2 1 (Sh 36173). At T = 1.5 K the magnetic moments of the two erbium sites have the same ordered magnetic moment values of 7.63 (6) μB/Er and are antiferromagnetically coupled leading to an uniaxial structure along the a direction.

Magnetic anisotropy and spin-flop transition of NiWO4 single crystals

NASA Astrophysics Data System (ADS)

Liu, C. B.; He, Z. Z.; Liu, Y. J.; Chen, R.; Shi, M. M.; Zhu, H. P.; Dong, C.; Wang, J. F.

2017-12-01

NiWO4 exhibits a spin chain structure built by magnetic Ni2+ ions, which may be considered as a one dimensional S = 1 system. In this work, large-sized single crystals of NiWO4 were successfully synthesized by a flux method and the crystal quality was confirmed by X-ray diffraction. Magnetic properties of obtained single crystals were studied by means of magnetic susceptibility and high field magnetization along crystallographic axes. The results demonstrate that NiWO4 is highly magnetic anisotropic and possesses a three-dimensional long range ordering below 60 K, where a spin flop transition can be observed at 17.5 T in applied magnetic fields along the magnetic easy axis (c-axis).

Monoclinic crystal structure of α - RuCl 3 and the zigzag antiferromagnetic ground state

DOE PAGES

Johnson, R. D.; Williams, S. C.; Haghighirad, A. A.; ...

2015-12-10

We have proposed the layered honeycomb magnet α - RuCl 3 as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled j eff = 1/2 Ru 3 + magnetic moments. We report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation calculations. We consider several models for the stacking of honeycomb layers and find evidence for a parent crystal structure with a monoclinic unit cell corresponding to a stacking of layers with a unidirectional in-plane offset, with occasional in-plane sliding stacking faults, inmore » contrast with the currently assumed trigonal three-layer stacking periodicity. We also report electronic band-structure calculations for the monoclinic structure, which find support for the applicability of the j eff = 1/2 picture once spin-orbit coupling and electron correlations are included. Of the three nearest-neighbor Ru-Ru bonds that comprise the honeycomb lattice, the monoclinic structure makes the bond parallel to the b axis nonequivalent to the other two, and we propose that the resulting differences in the magnitude of the anisotropic exchange along these bonds could provide a natural mechanism to explain the previously reported spin gap in powder inelastic neutron scattering measurements, in contrast to spin models based on the three-fold symmetric trigonal structure, which predict a gapless spectrum within linear spin wave theory. Our susceptibility measurements on both powders and stacked crystals, as well as magnetic neutron powder diffraction, show a single magnetic transition upon cooling below T N ≈ 13 K. Our analysis of our neutron powder diffraction data provides evidence for zigzag magnetic order in the honeycomb layers with an antiferromagnetic stacking between layers. Magnetization measurements on stacked single crystals in pulsed field up to 60 T show a single transition around 8 T for in-plane fields followed by a gradual, asymptotic approach to magnetization saturation, as characteristic of strongly anisotropic exchange interactions.« less

Effect of structural defects on the magnetic properties of the EuBaCo1.90O5.36 single crystal

NASA Astrophysics Data System (ADS)

Arbuzova, T. I.; Naumov, S. V.; Telegin, S. V.

2018-01-01

The effect of structural defects in cobalt and oxygen sublattices with the constant average oxidation level 3+ of all cobalt ions on the magnetic properties of the EuBaCo1.90O5.36 single crystal has been studied. The magnetic properties of the single crystal and the polycrystalline sample of the corresponding composition are compared in the range T = 200-650 K. The results show that the cobalt-deficient EuBaCo2- x O5.5-δ samples demonstrate a three-dimensional XY ferromagnetic ordering of magnetic sublattices. The values of the effective magnetic moment at T > 480 K indicate the existence of the IS and HS states of Co3+ ions. The large difference of values of μeff of the EuBaCo1.90O5.36 single crystal and polycrystal can be due to that the magnetic ion spins lie in plane ab. The magnetic field directed along plane ab substantially influences the magnetic ordering at T < 300 K.

Anisotropic physical properties of single-crystal U2Rh2Sn in high magnetic fields

NASA Astrophysics Data System (ADS)

Prokeš, K.; Gorbunov, D. I.; Reehuis, M.; Klemke, B.; Gukasov, A.; Uhlířová, K.; Fabrèges, X.; Skourski, Y.; Yokaichiya, F.; Hartwig, S.; Andreev, A. V.

2017-05-01

We report on the crystal and magnetic structures, magnetic, transport, and thermal properties of U2Rh2Sn single crystals studied in part in high magnetic fields up to 58 T. The material adopts a U3Si2 -related tetragonal crystal structure and orders antiferromagnetically below TN=25 K. The antiferromagnetic structure is characterized by a propagation vector k =(00 1/2 ) . The magnetism in U2Rh2Sn is found to be associated mainly with 5 f states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non-negligible magnetic moments also on Rh sites. U moments of 0.50(2) μB are directed along the tetragonal axis while Rh moments of 0.06(4) μB form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above ˜15 K the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the c axis. While for the a axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field-polarized state. A magnetic phase diagram for the field applied along the c axis is presented.

Magnetic and magnetostrictive behavior of Dy 3+ doped CoFe 2O 4 single crystals grown by flux method

NASA Astrophysics Data System (ADS)

Kambale, Rahul C.; Song, K. M.; Won, C. J.; Lee, K. D.; Hur, N.

2012-02-01

We studied the effect of Dy 3+ content on the magnetic properties of cobalt ferrite single crystal. The single crystals of CoFe 1.9Dy 0.1O 4 were grown by the flux method using Na 2B 4O 7.10 H 2O (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction analysis at room temperature confirmed the spinel cubic structure with lattice constant a=8.42 Å of the single crystals. The compositional analysis endorses the presence of constituents Co, Fe and Dy elements after sintering at 1300 °C within the final structure. The magnetic hysteresis measurements at various temperatures viz. 10 K, 100 K, 200 K and 300 K reveal the soft ferrimagnetic nature of the single crystal than that of for pure CoFe 2O 4. The observed saturation magnetization ( Ms) and coercivity ( Hc) are found to be lower than that of pure CoFe 2O 4 single crystal. The magnetostriction ( λ) measurement was carried out along the [001] direction. The magnetic measurements lead to conclude that the present single crystals can be used for magneto-optic recording media.

Structure and magnetic properties of flux grown single crystals of Co3-xFexSn2S2 shandites

NASA Astrophysics Data System (ADS)

Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

2016-01-01

We report a successful single crystal growth of the shandite-type half-metallic ferromagnet Co3Sn2S2, and its Fe-substituted compounds, Co3-xFexSn2S2, by employing the flux method. Although Fe3Sn2S2 is unstable phase, we found that using the self Sn flux enables us to obtain single phase crystals up to x=0.53. The chemical composition of the grown plate-shaped single crystals was examined using wavelength-dispersive X-ray spectroscopy. The shandite structure with R 3 ̅m symmetry was confirmed by powder X-ray diffraction and the crystal structure parameters were refined using the Rietveld method. Magnetization measurements show suppression of the ferromagnetic order upon Fe-substitution , as well as in other substituted systems such as In- and Ni-substituted Co3Sn2S2. The almost identical magnetic phase diagrams of the Fe- and In-substituted compounds indicate that the electron number is dominantly significant to the magnetism in the Co-based shandite.

Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

NASA Astrophysics Data System (ADS)

Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

2002-11-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed. The experiment was conducted both in the presence and absence of a magnetic field gradient. The magnet produces a gradient field of approx. 1 Tesla2/cm. Image analysis of the recorded images indicated an enhanced plume velocity that was of the order of the measurement limit. For this experiment, both the gradient and gravity fields are in the same direction resulting in an enhanced effective gravity that tends to accelerate the observed plume velocity. While the results are not conclusive, pending further tests, it clearly points out the inadequacy of the MSFC magnet for conducting protein crystallization experiments and the need for a stronger magnet. In spacebased experiments, however, where the gravitational effects are small, only a weak magnetic field will be required to control or mitigate the effects of convective contamination.

Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

NASA Technical Reports Server (NTRS)

Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

2002-01-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed. The experiment was conducted both in the presence and absence of a magnetic field gradient. The magnet produces a gradient field of approx. 1 Tesla2/cm. Image analysis of the recorded images indicated an enhanced plume velocity that was of the order of the measurement limit. For this experiment, both the gradient and gravity fields are in the same direction resulting in an enhanced effective gravity that tends to accelerate the observed plume velocity. While the results are not conclusive, pending further tests, it clearly points out the inadequacy of the MSFC magnet for conducting protein crystallization experiments and the need for a stronger magnet. In spacebased experiments, however, where the gravitational effects are small, only a weak magnetic field will be required to control or mitigate the effects of convective contamination.

Structural, mechanical, and magnetic properties of ferrite-austenite mixture in evaporated 304 stainless steel thin films

NASA Astrophysics Data System (ADS)

Merakeb, Noureddine; Messai, Amel; Djelloul, Abdelkader; Ayesh, Ahmad I.

2015-11-01

In this paper, we investigate the structure, composition, magnetic, and mechanical properties of stainless steel thin films formed by thermal evaporation technique. These thin films reveal novel structural and physical properties where they were found to consist of nanocrystals that are ~90 % body-centred cubic crystal structure which holds ferromagnetic properties (α-phase), and ~10 % face-centred cubic crystal structure which is paramagnetic at room temperature (γ-phase). The presence of the above phases was quantified by X-ray diffraction, transmission electron microscopy, and conversion electron Mössbauer spectroscopy. The magnetic properties were evaluated by a superconducting quantum interference device magnetometer, and they confirmed the dual-phase crystal structure of the stainless thin films, where the presence of γ-phase reduced the magnetization of the produced thin films. In addition, the fabricated stainless steel thin films did not contain micro-cracks, and they exhibit a tensile stress of about 1.7 GPa, hardness of 7.5 GPa, and elastic modulus of 104 GPa.

Magnetic order and electronic structure of 5d 3 double perovskite Sr 2ScOsO 6

DOE PAGES

Taylor, A. E.; Morrow, R.; Singh, D. J.; ...

2015-03-01

The magnetic susceptibility, crystal and magnetic structures, and electronic structure of double perovskite Sr 2ScOsO 6 are reported. Using both neutron and x-ray powder diffraction we find that the crystal structure is monoclinic P21/n from 3.5 to 300 K. Magnetization measurements indicate an antiferromagnetic transition at TN=92 K, one of the highest transition temperatures of any double perovskite hosting only one magnetic ion. Type I antiferromagnetic order is determined by neutron powder diffraction, with an Os moment of only 1.6(1) muB, close to half the spin-only value for a crystal field split 5d electron state with t2g^3 ground state. Densitymore » functional calculations show that this reduction is largely the result of strong Os-O hybridization, with spin-orbit coupling responsible for only a ~0.1 muB reduction in the moment.« less

Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides

DOE PAGES

McGuire, Michael A.

2017-04-27

Materials composed of two dimensional layers bonded to one another through weak van der Waals interactions often exhibit strongly anisotropic behaviors and can be cleaved into very thin specimens and sometimes into monolayer crystals. Interest in such materials is driven by the study of low dimensional physics and the design of functional heterostructures. Binary compounds with the compositions MX 2 and MX 3 where M is a metal cation and X is a halogen anion often form such structures. Magnetism can be incorporated by choosing a transition metal with a partially filled d-shell for M, enabling ferroic responses for enhancedmore » functionality. Here we give a brief overview of binary transition metal dihalides and trihalides, summarizing their crystallographic properties and long-range-ordered magnetic structures, focusing on those materials with layered crystal structures and partially filled d-shells required for combining low dimensionality and cleavability with magnetism.« less

Magnetic spherical cores partly coated with periodic mesoporous organosilica single crystals.

PubMed

Li, Jing; Wei, Yong; Li, Wei; Deng, Yonghui; Zhao, Dongyuan

2012-03-07

Core-shell structured materials are of special significance in various applications. Until now, most reported core-shell structures have polycrystalline or amorphous coatings as their shell layers, with popular morphologies of microspheres or quasi-spheres. However, the single crystals, either mesoscale or atomic ones, are still rarely reported as shell layers. If single crystals can be coated on core materials, it would result in a range of new type core-shell structures with various morphologies, and probably more potential applications. In this work, we demonstrate that periodic mesoporous organosilica (PMO) single crystals can partly grow on magnetic microspheres to form incomplete Fe(3)O(4)@nSiO(2)@PMO core-shell materials in aqueous solution, which indeed is the first illustration that mesoporous single-crystal materials can be used as shell layers for preparation of core-shell materials. The achieved materials have advantages of high specific surface areas, good magnetic responses, embedded functional groups and cubic mesopore channels, which might provide them with various application conveniences. We suppose the partial growth is largely decided by the competition between growing tendency of single crystals and the resistances to this tendency. In principle, other single crystals, including a range of atomic single crystals, such as zeolites, are able to be developed into such core-shell structures.

Effect of magnetic field on the phase transition in a dusty plasma

NASA Astrophysics Data System (ADS)

Jaiswal, S.; Hall, T.; LeBlanc, S.; Mukherjee, R.; Thomas, E.

2017-11-01

The formation of a self-consistent crystalline structure is a well-known phenomenon in complex plasmas. In most experiments, the pressure and rf power are the main controlling parameters in determining the phase of the system. We have studied the effect of the externally applied magnetic field on the configuration of plasma crystals, suspended in the sheath of a radio-frequency discharge using the Magnetized Dusty Plasma Experiment device. Experiments are performed at a fixed pressure and rf power where a crystalline structure is formed within a confining ring. The magnetic field is then increased from 0 to 1.28 T. We report on the breakdown of the crystalline structure with the increasing magnetic field. The magnetic field affects the dynamics of the plasma particles and first leads to a rotation of the crystal. At a higher magnetic field, there is a radial variation (shear) in the angular velocity of the moving particles which we believe to lead to the melting of the crystal. This melting is confirmed by evaluating the variation of the pair correlation function as a function of magnetic field.

Bubble and skyrmion crystals in frustrated magnets with easy-axis anisotropy

DOE PAGES

Hayami, Satoru; Lin, Shi-Zeng; Batista, Cristian D.

2016-05-12

We clarify the conditions for the emergence of multiple-Q structures out of lattice and easy-axis spin anisotropy in frustrated magnets. By considering magnets whose exchange interaction has multiple global minima in momentum space, we find that both types of anisotropy stabilize triple-Q orderings. Moderate anisotropy leads to a magnetic field-induced skyrmion crystal, which evolves into a bubble crystal for increasing spatial and spin anisotropy. Finally, the bubble crystal exhibits a quasi-continuous (devil’s staircase) temperature dependent ordering wave-vector, characteristic of the competition between frustrated exchange and strong easy-axis anisotropy.

Crystal structure and magnetism of the FexNi8-xSi3 materials, 0 ≤ x ≤ 8

NASA Astrophysics Data System (ADS)

Gallus, Simone; Haddouch, Mohammed Ait; Chikovani, Mamuka; Perßon, Jörg; Voigt, Jörg; Friese, Karen; Senyshyn, Anatoliy; Grzechnik, Andrzej

2018-02-01

The crystal structure and magnetic properties of the materials FexNi8-xSi3 with 0 ≤ x ≤ 8 have been investigated to estimate any possible magnetocaloric effect and compare it to that in known magnetocalorics. Two structural ranges could be identified in this system by X-ray and neutron diffraction. The structure of the samples with 0 ≤ x ≤ 4 is related to the trigonal structure of Ni31Si12. Doubled c lattice parameters compared to the one in Ni31Si12 are observed in the samples with x = 2 and x = 3. The average structure of Fe2Ni6Si3 has been determined by X-ray single-crystal diffraction. The compounds with the compositions 5 ≤ x ≤ 8 crystallize in cubic Fe3Si-type structure. Magnetic measurements have shown that the compound Fe3Ni5Si3 displays a phase transition close to room temperature. However, its magnetocaloric effect is much smaller than the one in the promising magnetocaloric materials.

Study of Fluid Flow Control In Protein Crystallization Using Strong Magnetic Fields

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F.; Ciszak, E.; Curreri, Peter A. (Technical Monitor)

2002-01-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in 'microgravity', researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined.

Stability of (Fe-Tm-B) amorphous alloys: relaxation and crystallization phenomena

NASA Astrophysics Data System (ADS)

Zemčík, T.

1994-12-01

Fe-Tm-B base (TM=transition metal) amorphous alloys (metallic glasses) are thermodynamically metastable. This limits their use as otherwise favourable materials, e.g. magnetically soft, corrosion resistant and mechanically firm. By analogy of the mechanical strain-stress dependence, at a certain degree of thermal activation the amorphous structure reaches its limiting state where it changes its character and physical properties. Relaxation and early crystallization processes in amorphous alloys, starting already around 100°C, are reviewed involving subsequently stress relief, free volume shrinking, topological and chemical ordering, pre-crystallization phenomena up to partial (primary) crystallization. Two diametrically different examples are demonstrated from among the soft magnetic materials: relaxation and early crystallization processes in the Fe-Co-B metallic glasses and controlled crystallization of amorphous ribbons yielding rather modern nanocrystalline “Finemet” alloys where late relaxation and pre-crystallization phenomena overlap when forming extremely dispersive and fine-grained nanocrystals-in-amorphous-sauce structure. Mössbauer spectroscopy seems to be unique for magnetic and phase analysis of such complicated systems.

Itinerant Antiferromagnetism in FeMnP 0.8Si 0.2

DOE PAGES

Sales, Brian C.; Susner, Michael A.; Conner, Benjamin S.; ...

2015-09-25

Compounds based on the Fe 2P structure have continued to attract interest because of the interplay between itinerant and localized magnetism in a noncentrosymmetric crystal structure, and because of the recent developments of these materials for magnetocaloric applications. We report the growth and characterization of millimeter-sized single crystals of FeMnP 0.8Si 0.2 with the Fe 2P structure. Single-crystal x-ray diffraction, magnetization, resistivity, and Hall and heat capacity data are reported. The crystals exhibit itinerant antiferromagnetic order below 158 K with no hint of ferromagnetic behavior in the magnetization curves and with the spins ordered primarily in the ab plane. Themore » room-temperature resistivity is close to the Ioffe-Regel limit for a metal. Single-crystal x-ray diffraction indicates a strong preference for Mn to occupy the larger pyramidal 3g site. The cation site preference in the as-grown crystals and the antiferromagnetism were not changed after high-temperature anneals and a rapid quench to room temperature« less

Magnetic behavior and spin-lattice coupling in cleavable van der Waals layered CrCl 3 crystals

DOE PAGES

McGuire, Michael A.; Clark, Genevieve; KC, Santosh; ...

2017-06-19

CrCl 3 is a layered insulator that undergoes a crystallographic phase transition below room temperature and orders antiferromagnetically at low temperature. Weak van der Waals bonding between the layers and ferromagnetic in-plane magnetic order make it a promising material for obtaining atomically thin magnets and creating van der Waals heterostructures. In this work we have grown crystals of CrCl 3, revisited the structural and thermodynamic properties of the bulk material, and explored mechanical exfoliation of the crystals. We find two distinct anomalies in the heat capacity at 14 and 17 K confirming that the magnetic order develops in two stagesmore » on cooling, with ferromagnetic correlations forming before long-range antiferromagnetic order develops between them. This scenario is supported by magnetization data. A magnetic phase diagram is constructed from the heat capacity and magnetization results. We also find an anomaly in the magnetic susceptibility at the crystallographic phase transition, indicating some coupling between the magnetism and the lattice. First-principles calculations accounting for van der Waals interactions also indicate spin-lattice coupling, and find multiple nearly degenerate crystallographic and magnetic structures consistent with the experimental observations. Lastly, we demonstrate that monolayer and few-layer CrCl 3 specimens can be produced from the bulk crystals by exfoliation, providing a path for the study of heterostructures and magnetism in ultrathin crystals down to the monolayer limit.« less

Magnetic behavior and spin-lattice coupling in cleavable van der Waals layered CrCl 3 crystals

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

McGuire, Michael A.; Clark, Genevieve; KC, Santosh

CrCl 3 is a layered insulator that undergoes a crystallographic phase transition below room temperature and orders antiferromagnetically at low temperature. Weak van der Waals bonding between the layers and ferromagnetic in-plane magnetic order make it a promising material for obtaining atomically thin magnets and creating van der Waals heterostructures. In this work we have grown crystals of CrCl 3, revisited the structural and thermodynamic properties of the bulk material, and explored mechanical exfoliation of the crystals. We find two distinct anomalies in the heat capacity at 14 and 17 K confirming that the magnetic order develops in two stagesmore » on cooling, with ferromagnetic correlations forming before long-range antiferromagnetic order develops between them. This scenario is supported by magnetization data. A magnetic phase diagram is constructed from the heat capacity and magnetization results. We also find an anomaly in the magnetic susceptibility at the crystallographic phase transition, indicating some coupling between the magnetism and the lattice. First-principles calculations accounting for van der Waals interactions also indicate spin-lattice coupling, and find multiple nearly degenerate crystallographic and magnetic structures consistent with the experimental observations. Lastly, we demonstrate that monolayer and few-layer CrCl 3 specimens can be produced from the bulk crystals by exfoliation, providing a path for the study of heterostructures and magnetism in ultrathin crystals down to the monolayer limit.« less

Crystal structure and magnetism of layered perovskites compound EuBaCuFeO5

NASA Astrophysics Data System (ADS)

Lal, Surender; Mukherjee, K.; Yadav, C. S.

2018-04-01

Layered perovskite compounds have interesting multiferroic properties.YBaCuFeO5 is one of the layered perovskite compounds which have magnetic and dielectric transition above 200 K. The multiferroic properties can be tuned with the replacement of Y with some other rare earth ions. In this manuscript, structural and magnetic properties of layered perovskite compound EuBaCuFeO5 have been investigated. This compound crystallizes in the tetragonal structure with P4mm space group and is iso-structural with YBaCuFeO5. The magnetic transition has been found to shift to 120 K as compared to YBaCuFeO5 which has the transition at 200 K. This shift in the magnetic transition has been ascribed to the decrease in the chemical pressure that relaxes the magnetic moments.

Fe doped Magnetic Nanodiamonds made by Ion Implantation.

PubMed

Chen, ChienHsu; Cho, I C; Jian, Hui-Shan; Niu, H

2017-02-09

Here we present a simple physical method to prepare magnetic nanodiamonds (NDs) using high dose Fe ion-implantation. The Fe atoms are embedded into NDs through Fe ion-implantation and the crystal structure of NDs are recovered by thermal annealing. The results of TEM and Raman examinations indicated the crystal structure of the Fe implanted NDs is recovered completely. The SQUID-VSM measurement shows the Fe-NDs possess room temperature ferromagnetism. That means the Fe atoms are distributed inside the NDs without affecting NDs crystal structure, so the NDs can preserve the original physical and chemical properties of the NDs. In addition, the ion-implantation-introduced magnetic property might make the NDs to become suitable for variety of medical applications.

Fe doped Magnetic Nanodiamonds made by Ion Implantation

NASA Astrophysics Data System (ADS)

Chen, Chienhsu; Cho, I. C.; Jian, Hui-Shan; Niu, H.

2017-02-01

Here we present a simple physical method to prepare magnetic nanodiamonds (NDs) using high dose Fe ion-implantation. The Fe atoms are embedded into NDs through Fe ion-implantation and the crystal structure of NDs are recovered by thermal annealing. The results of TEM and Raman examinations indicated the crystal structure of the Fe implanted NDs is recovered completely. The SQUID-VSM measurement shows the Fe-NDs possess room temperature ferromagnetism. That means the Fe atoms are distributed inside the NDs without affecting NDs crystal structure, so the NDs can preserve the original physical and chemical properties of the NDs. In addition, the ion-implantation-introduced magnetic property might make the NDs to become suitable for variety of medical applications.

Correlations Between Structural and Magnetic Properties of Co2 FeSi Heusler-Alloy Thin Films

NASA Astrophysics Data System (ADS)

Zhu, Weihua; Wu, Di; Zhao, Bingcheng; Zhu, Zhendong; Yang, Xiaodi; Zhang, Zongzhi; Jin, Q. Y.

2017-09-01

The structural and magnetic properties are the most important parameters for practical applications of Co-based Heusler alloys. The correlations between the crystallization degree, chemical order, magnetic coercivity, saturation magnetization (MS ), and in-plane magnetic anisotropies are systematically investigated for Co2FeSi (CFS) films fabricated at different temperatures (TS ). XRD shows that the CFS layer changes progressively from a disordered crystal structure into a chemically disordered A 2 structure and further into a chemically ordered B 2 and even L 21 structures when increasing TS up to 480 °C . Meanwhile, the static angular remanence magnetization curves show a clear transition of magnetic anisotropy from twofold to fourfold symmetry, due to the competition effect between the uniaxial anisotropy field HU and biaxial anisotropy field HB . The HU value is found to be weakly dependent on TS , while HB shows a continuous enhancement at TS>300 °C , implying that the enhancement of the L 21 ordering degree would not weaken the biaxial anisotropy. The varying trend of HB is similar to MS , which can be respectively attributed to the improved crystal structure and chemical order. The anisotropic fields and their variation behaviors determined by a vibrating sample magnetometer are highly consistent with the results by a time-resolved magneto-optical Kerr effect study. Our findings provide a better understanding of the structural ordering and magnetic anisotropy, which will be helpful for designing advanced spintronic devices.

Magnetic phase transitions and magnetic structures in RTxX2, RSn1+xGe1-x and RSn2 compounds

NASA Astrophysics Data System (ADS)

Gil, Alina

2018-02-01

The work presents the review of magnetic properties of the RTxX2, RSn1+xGe1-x and RSn2 compounds. The RTxX2 (where R - rare earth, T - 3d-metal, X - p-electron element: Si, Ge, Sn, and 1 ≥ x > 0) and RSn1+xGe1-x compounds (where x ≈ 0.1) crystallize in the orthorhombic crystal structure of CeNiSi2-type and RSn2 compounds crystallize in ZrSi2-type structure. Both structures are described by the space group Cmcm. The RSn1+xGe1-x compounds seem to be interesting due to the replacement of d-metal to p-electron element. The non-stoichiometric CeNiSi2-type of RTxX2 compounds may be regarded as partially filled ZrSi2-type compounds. The transitions from paramagnetic to antiferromagnetic or ferromagnetic states are observed at low temperatures and there are lots of variants of magnetic structures ranging from simple collinear to the sine-modulated structures with commensurate or incommensurate propagation vector. The comparison of magnetic properties of these compounds may help to find answers to questions concerning mechanisms of interaction between the magnetic moments.

Crystal structure and magnetic properties of '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' containing residual {alpha}-Fe prepared by low-temperature ammonia nitridation

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

Yamashita, S.; Masubuchi, Y.; Nakazawa, Y.

2012-10-15

Slight enhancement of saturation magnetization to 219 A m{sup 2} kg{sup -1} was observed from 199 A m{sup 2} kg{sup -1} for the original {alpha}-Fe on the intermediate nitrided mixture of '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' with residual {alpha}-Fe among the low temperature ammonia nitridation products under 5 T magnetic field at room temperature. The value changed not linearly against the yield as had been expected. Crystal structure refinement indicated that the phase similar to {alpha} Prime Prime -Fe{sub 16}N{sub 2} had deviations on its lattice constants and positional parameters, compared to previously reported values for {alpha} Prime Primemore » -Fe{sub 16}N{sub 2}. Spin-polarized total energy calculations were performed using the projector-augmented wave method as implemented in the Vienna ab-initio simulation package (VASP) to calculate magnetic moment on the refined crystal structure of the intermediate '{alpha} Prime Prime -Fe{sub 16}N{sub 2}'. The calculations supported the observed magnetization enhancement in the intermediate nitridation product. - Graphical abstract: Crystal structural parameters slightly change in the intermediate nitrided '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' from those in {alpha} Prime Prime -Fe{sub 16}N{sub 2} to show the magnetization maxima in the mixture of '{alpha} Prime Prime -Fe{sub 16}N{sub 2}' and the residual {alpha}-F. Highlights: Black-Right-Pointing-Pointer Larger magnetization was observed than the value of Fe{sub 16}N{sub 2} on its intermediate nitrided mixture with residual {alpha}-Fe. Black-Right-Pointing-Pointer The enhancement was related to the crystal structural deviation from Fe{sub 16}N{sub 2} on the intermediate nitride. Black-Right-Pointing-Pointer It was supported by spin-polarized total energy calculation using the deviated structure.« less

Rare-earth metal gallium silicides via the gallium self-flux method. Synthesis, crystal structures, and magnetic properties of RE(Ga 1–xSi x)₂ (RE=Y, La–Nd, Sm, Gd–Yb, Lu)

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

Darone, Gregory M.; Hmiel, Benjamin; Zhang, Jiliang

Fifteen ternary rare-earth metal gallium silicides have been synthesized using molten Ga as a molten flux. They have been structurally characterized by single-crystal and powder X-ray diffraction to form with three different structures—the early to mid-late rare-earth metals RE=La–Nd, Sm, Gd–Ho, Yb and Y form compounds with empirical formulae RE(Ga xSi 1–x)₂ (0.38≤x≤0.63), which crystallize with the tetragonal α-ThSi₂ structure type (space group I4₁/amd, No. 141; Pearson symbol tI12). The compounds of the late rare-earth crystallize with the orthorhombic α-GdSi₂ structure type (space group Imma, No. 74; Pearson symbol oI12), with refined empirical formula REGa xSi 2–x–y (RE=Ho, Er, Tm;more » 0.33≤x≤0.40, 0.10≤y≤0.18). LuGa₀.₃₂₍₁₎Si₁.₄₃₍₁₎ crystallizes with the orthorhombic YbMn₀.₁₇Si₁.₈₃ structure type (space group Cmcm, No. 63; Pearson symbol oC24). Structural trends are reviewed and analyzed; the magnetic susceptibilities of the grown single-crystals are presented. - Graphical abstract: This article details the exploration of the RE–Ga–Si ternary system with the aim to systematically investigate the structural “boundaries” between the α-ThSi₂ and α-GdSi₂-type structures, and studies of the magnetic properties of the newly synthesized single-crystalline materials. Highlights: • Light rare-earth gallium silicides crystallize in α-ThSi₂ structure type. • Heavy rare-earth gallium silicides crystallize in α-GdSi₂ structure type. • LuGaSi crystallizes in a defect variant of the YbMn₀.₁₇Si₁.₈₃ structure type.« less

Synthesis, crystal structure and magnetic properties of the two polymorphs of novel S=1 osmate; Li{sub 4}MgOsO{sub 6}

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

Nguyen, Phoung-Hieu T.; Kemei, Moureen C.; Tan, Malinda S.

2016-10-15

Li{sub 4}MgOsO{sub 6} was synthesized by two different solid-state reaction procedures. The crystal structures were determined by X-ray powder diffraction technique and it was revealed that Li{sub 4}MgOsO{sub 6} crystallizes in two different crystal symmetries in ordered rock salt structure type, namely monoclinic C2/m and orthorhombic Fddd. The unit cell constants for the monoclinic system are a=5.1074(4) Å, b=8.8182(4) Å, c=5.0902(2) Å, and β=109.845(4)° and those of the orthorhombic structure are a=5.8485(1) Å, b=8.3821(1) Å, and c=17.6212(3) Å. In both systems, Os{sup 6+} ions reside exclusively in a specific crystallographic position while Li{sup +} and Mg{sup 2+} ions exhibit mixmore » occupancy. The temperature dependent magnetic susceptibility data for both S=1 osmate systems do not support the occurrence of any magnetic transition down to 2 K. The Curie–Weiss fit to the paramagnetic regime of the magnetic susceptibility data reveal highly negative θ value (−114.81 K and −121.87 K for C2/m and for Fddd systems, respectively), which are indicative of predominant antiferromagnetic (AFM) interactions in both systems. The experimental effective magnetic moment (μ{sub eff}) value for the monoclinic phase is 2.13 μB and that of the orthorhombic system is 2.34 μB. Due to the rather strong AFM interactions and lack of magnetic transition down to 2 K, both of these novel osmates are placed in the class of highly frustrated magnets. Low temperature magnetic susceptibility (below 2 K) and dynamic magnetic properties studies (μsr studies) are in order to better understand the magnetic ground states of these two polymorphs of Li{sub 4}MgOsO{sub 6}. - Graphical abstract: The structural transformation between two modifications of highly frustrated Li{sub 4}MgOsO{sub 6}. - Highlights: • Li4MgOsO{sub 6} was synthesized in two different crystal systems. • The monoclinic variant crystallizes in C2/m space group, while the orthorhombic version forms in Fddd space group. • The Os{sup 6+} ions are fully ordered while Li{sup +} and Mg{sup 2+} are mixed occupied. • These systems are the first Os{sup 6+} compounds in ordered NaCl structure type. • Both compounds exhibit high degree of geometric magnetic frustration.« less

Structural and magnetic characterization of the one-dimensional S = 5/2 antiferromagnetic chain system SrMn(VO 4)(OH)

DOE PAGES

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.; ...

2016-06-06

The descloizite-type compound, SrMn(VO 4)(OH), was synthesized as large single crystals (1-2mm) using a high-temperature high-pressure hydrothermal technique. X-ray single crystal structure analysis reveals that the material crystallizes in the acentric orthorhombic space group of P2 12 12 1 (no. 19), Z = 4. The structure exhibits a one-dimensional feature, with [MnO 4] chains propagating along the a-axis which are interconnected by VO 4 tetrahedra. Raman and infrared spectra were obtained to identify the fundamental vanadate and hydroxide vibrational modes. Magnetization data reveal a broad maximum at approximately 80 K, arising from one-dimensional magnetic correlations with intrachain exchange constant ofmore » J/k B = 9.97(3) K between nearest Mn neighbors and a canted antiferromagnetic behavior below T N = 30 K. Single crystal neutron diffraction at 4 K yielded a magnetic structure solution in the lower symmetry of the magnetic space group P2 1 with two unique chains displaying antiferromagnetically ordered Mn moments oriented nearly perpendicular to the chain axis. Lastly, the presence of the Dzyaloshinskii Moriya antisymmetric exchange interaction leads to a slight canting of the spins and gives rise to a weak ferromagnetic component along the chain direction.« 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.

Single crystal synthesis and magnetism of the Ba Ln 2O 4 family ( Ln = lanthanide)

DOE PAGES

Besara, Tiglet; Lundberg, Matthew S.; Sun, Jifeng; ...

2014-05-27

The series of compounds in the Ba Ln 2O 4 family (Ln = La–Lu, Y) has been synthesized for the first time in single crystalline form, using a molten metal flux. The series crystallizes in the CaV 2O 4 structure type with primitive orthorhombic symmetry (space group Pnma, #62), and a complete structural study of atomic positions, bonds, angles, and distortions across the lanthanide series is presented. With the exception of the Y, La, Eu, and Lu members, magnetic susceptibility measurements were performed between 2 K and 300 K. BaCe 2O 4 and BaYb 2O 4 display large crystal fieldsmore » effects and suppression of magnetic ordering. As a result, all compounds show signs of magnetic frustration due to the trigonal arrangements of the trivalent lanthanide cations in the structure.« less

Magnetic properties of Co 2 2+ Co 1 - x 3+ Fe x 3+ BO5 ( x = 0.10) single crystals with a ludwigite structure

NASA Astrophysics Data System (ADS)

Knyazev, Yu. V.; Kazak, N. V.; Bayukov, O. A.; Platunov, M. S.; Velikanov, D. A.; Bezmaternykh, L. N.; Ivanova, N. B.; Ovchinnikov, S. G.

2017-04-01

The investigation of mixed Co-Fe ludwigite single crystals shows that their magnetic properties are close to the magnetic properties of Fe3BO5 despite the predominance of cobalt ions. The magnetic properties of Co3 - x Fe x BO5 single crystals with x = 0.10 are studied in detail. Magnetometric measurements demonstrate a strong magnetic anisotropy with easy magnetization axis b, and the orbital magnetic moment of cobalt is in a frozen state. The detected temperature dependence of the absorption of Mössbauer spectra allowed us to determine the magnetic ordering temperature, which agrees with the results of magnetization measurements ( T C = 84 K).

Magnetic and structural instabilities in CePd 2Al 2 and LaPd 2Al 2

NASA Astrophysics Data System (ADS)

Chapon, L. C.; Goremychkin, E. A.; Osborn, R.; Rainford, B. D.; Short, S.

2006-05-01

We have investigated the crystal and magnetic structure of the RPd 2Al 2 compounds (R=La, Ce) by neutron powder diffraction (ND) and inelastic neutron scattering (INS). The ND study shows that both compounds undergo a structural phase transition from tetragonal to orthorhombic symmetry at 91.5 K (La) and 13.5 K (Ce). In the case of CePd 2Al 2 the crystal field excitation spectrum, which has an extra peak that cannot be explained by a standard crystal field model, indicates the presence of strong magneto-elastic coupling.

Effect of magnetic field on the phase transition in dusty plasma

NASA Astrophysics Data System (ADS)

Jaiswal, Surabhi; Thomas, Edward; Mukherjee, Rupak

2017-10-01

The formation of self-consistent crystalline structure is a well-known phenomenon in complex plasmas. In most experiments the pressure and rf power are the main controlling parameter in determining the phase of the system. We have studied the effect of externally applied magnetic field on the configuration of plasma crystals, suspended in the sheath of a radio-frequency discharge using the Magnetized Dusty Plasma Experiment (MDPX) device. Experiments are performed at a fixed pressure and rf power where a crystalline structure formed within the confining ring, but ramping the magnetic field up to 1.28 T. We report on the breakdown of the crystalline structure with increasing magnetic field. The magnetic field affects the dynamics of the plasma particles and first leads to a rotation of the crystal. At higher magnetic field, there is a radial variation (shear) in the angular velocity of the moving particles which we believe leads to the melting of the crystal. This melting is confirmed by evaluating the variation of the pair correlation function as a function of magnetic field. This work was supported by the US Dept. of Energy, DE - SC0010485.

Recent Advances in the Understanding of the Influence of Electric and Magnetic Fields on Protein Crystal Growth

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

Pareja-Rivera, Carina; Cuéllar-Cruz, Mayra; Esturau-Escofet, Nuria

Here, in this contribution we use nonconventional methods that help to increase the success rate of a protein crystal growth, and consequently of structural projects using X-ray diffraction techniques. In order to achieve this purpose, this contribution presents new approaches involving more sophisticated techniques of protein crystallization, not just for growing protein crystals of different sizes by using electric fields, but also for controlling crystal size and orientation. Also, this latter was possible through the use of magnetic fields that allow to obtain protein crystals suitable for both high-resolution X-ray and neutron diffraction crystallography where big crystals are required. Thismore » contribution discusses some pros, cons and realities of the role of electromagnetic fields in protein crystallization research, and their effect on protein crystal contacts. Additionally, we discuss the importance of room and low temperatures during data collection. Finally, we also discuss the effect of applying a rather strong magnetic field of 16.5 T, for shorts and long periods of time, on protein crystal growth, and on the 3D structure of two model proteins.« less

Recent Advances in the Understanding of the Influence of Electric and Magnetic Fields on Protein Crystal Growth

DOE PAGES

Pareja-Rivera, Carina; Cuéllar-Cruz, Mayra; Esturau-Escofet, Nuria; ...

2016-12-05

Here, in this contribution we use nonconventional methods that help to increase the success rate of a protein crystal growth, and consequently of structural projects using X-ray diffraction techniques. In order to achieve this purpose, this contribution presents new approaches involving more sophisticated techniques of protein crystallization, not just for growing protein crystals of different sizes by using electric fields, but also for controlling crystal size and orientation. Also, this latter was possible through the use of magnetic fields that allow to obtain protein crystals suitable for both high-resolution X-ray and neutron diffraction crystallography where big crystals are required. Thismore » contribution discusses some pros, cons and realities of the role of electromagnetic fields in protein crystallization research, and their effect on protein crystal contacts. Additionally, we discuss the importance of room and low temperatures during data collection. Finally, we also discuss the effect of applying a rather strong magnetic field of 16.5 T, for shorts and long periods of time, on protein crystal growth, and on the 3D structure of two model proteins.« less

Study of rare earth local moment magnetism and strongly correlated phenomena in various crystal structures

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

Kong, Tai

Benefiting from unique properties of 4f electrons, rare earth based compounds are known for offering a versatile playground for condensed matter physics research as well as industrial applications. This thesis focuses on three specific examples that further explore the rare earth local moment magnetism and strongly correlated phenomena in various crystal structures.

Structure and phase formation behavior and dielectric and magnetic properties of lead iron tantalate-lead zirconate titanate multiferroic ceramics

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

Wongmaneerung, R., E-mail: re_nok@yahoo.com; Tipakontitikul, R.; Jantaratana, P.

2016-03-15

Highlights: • The multiferroic ceramics consisted of PFT and PZT. • Crystal structure changed from cubic to mixedcubic and tetragonal with increasing PZT content. • Dielectric showed the samples underwent a typical relaxor ferroelectric behavior. • Magnetic properties showed very interesting behavior with square saturated magnetic hysteresis loops. - Abstract: Multiferroic (1 − x)Pb(Fe{sub 0.5}Ta{sub 0.5})O{sub 3}–xPb(Zr{sub 0.53}Ti{sub 0.47})O{sub 3} (or PFT–PZT) ceramics were synthesized by solid-state reaction method. The crystal structure and phase formation of the ceramics were examined by X-ray diffraction (XRD). The local structure surrounding Fe and Ti absorbing atoms was investigated by synchrotron X-ray Absorption Near-Edgemore » Structure (XANES) measurement. Dielectric properties were studied as a function of frequency and temperature using a LCR meter. A vibrating sample magnetometer (VSM) was used to determine the magnetic hysteresis loops. XRD study indicated that the crystal structure of the sample changed from pure cubic to mixed cubic and tetragonal with increasing PZT content. XANES measurements showed that the local structure surrounding Fe and Ti ions was similar. Dielectric study showed that the samples underwent a typical relaxor ferroelectric behavior while the magnetic properties showed very interesting behavior with square saturated magnetic hysteresis loops.« less

Low temperature magnetic structure of CeRhIn 5 by neutron diffraction on absorption-optimized samples

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

Fobes, David M.; Bauer, Eric Dietzgen; Thompson, Joe David

Here, two aspects of the ambient pressure magnetic structure of heavy fermion material CeRhIn 5 have remained under some debate since its discovery: whether the structure is indeed an incommensurate helix or a spin density wave, and what is the precise magnitude of the ordered magnetic moment. By using a single crystal sample optimized for hot neutrons to minimize neutron absorption by Rh and In, here we report an ordered moment ofmore » $$m=0.54(2)\\,{{\\mu}_{\\text{B}}}$$. In addition, by using spherical neutron polarimetry measurements on a similar single crystal sample, we have confirmed the helical nature of the magnetic structure, and identified a single chiral domain.« less

Low temperature magnetic structure of CeRhIn 5 by neutron diffraction on absorption-optimized samples

DOE PAGES

Fobes, David M.; Bauer, Eric Dietzgen; Thompson, Joe David; ...

2017-03-28

Here, two aspects of the ambient pressure magnetic structure of heavy fermion material CeRhIn 5 have remained under some debate since its discovery: whether the structure is indeed an incommensurate helix or a spin density wave, and what is the precise magnitude of the ordered magnetic moment. By using a single crystal sample optimized for hot neutrons to minimize neutron absorption by Rh and In, here we report an ordered moment ofmore » $$m=0.54(2)\\,{{\\mu}_{\\text{B}}}$$. In addition, by using spherical neutron polarimetry measurements on a similar single crystal sample, we have confirmed the helical nature of the magnetic structure, and identified a single chiral domain.« less

Growth, structure, morphology, and magnetic properties of Ni ferrite films

PubMed Central

2013-01-01

The morphology, structure, and magnetic properties of nickel ferrite (NiFe2O4) films fabricated by radio frequency magnetron sputtering on Si(111) substrate have been investigated as functions of film thickness. Prepared films that have not undergone post-annealing show the better spinel crystal structure with increasing growth time. Meanwhile, the size of grain also increases, which induces the change of magnetic properties: saturation magnetization increased and coercivity increased at first and then decreased. Note that the sample of 10-nm thickness is the superparamagnetic property. Transmission electron microscopy displays that the film grew with a disorder structure at initial growth, then forms spinel crystal structure as its thickness increases, which is relative to lattice matching between substrate Si and NiFe2O4. PMID:23622034

Growth, structure, morphology, and magnetic properties of Ni ferrite films.

PubMed

Dong, Chunhui; Wang, Gaoxue; Guo, Dangwei; Jiang, Changjun; Xue, Desheng

2013-04-27

The morphology, structure, and magnetic properties of nickel ferrite (NiFe2O4) films fabricated by radio frequency magnetron sputtering on Si(111) substrate have been investigated as functions of film thickness. Prepared films that have not undergone post-annealing show the better spinel crystal structure with increasing growth time. Meanwhile, the size of grain also increases, which induces the change of magnetic properties: saturation magnetization increased and coercivity increased at first and then decreased. Note that the sample of 10-nm thickness is the superparamagnetic property. Transmission electron microscopy displays that the film grew with a disorder structure at initial growth, then forms spinel crystal structure as its thickness increases, which is relative to lattice matching between substrate Si and NiFe2O4.

Changes in magnetic domain structure during twin boundary motion in single crystal Ni-Mn-Ga exhibiting magnetic shape memory effect

NASA Astrophysics Data System (ADS)

Kopecký, V.; Fekete, L.; Perevertov, O.; Heczko, O.

2016-05-01

The complexity of Ni-Mn-Ga single crystal originates from the interplay between ferromagnetic domain structure and ferroelastic twinned microstructure. Magnetic domain structure in the vicinity of single twin boundary was studied using magneto-optical indicator film and magnetic force microscopy technique. The single twin boundary of Type I was formed mechanically and an initial magnetization state in both variants were restored by local application of magnetic field (≈40 kA/m). The differently oriented variants exhibited either stripe or labyrinth magnetic domain pattern in agreement with the uniaxial magnetocrystalline anisotropy of the martensite. The twin boundary was then moved by compressive or tensile stress. The passage of the boundary resulted in the formation of granular or rake domains, respectively. Additionally, the specific magnetic domains pattern projected by twin boundary gradually vanished during twin boundary motion.

Electronic structure and magnetic properties of the strong-rung spin-1 ladder compound Rb3Ni2(NO3)7

NASA Astrophysics Data System (ADS)

Pchelkina, Z. V.; Mazurenko, V. V.; Volkova, O. S.; Deeva, E. B.; Morozov, I. V.; Shutov, V. V.; Troyanov, S. I.; Werner, J.; Koo, C.; Klingeler, R.; Vasiliev, A. N.

2018-04-01

Rb3Ni2(NO3)7 was obtained by crystallization from anhydrous nitric acid solution of rubidium nitrate and nickel nitrate hexahydrate. The crystal structure determined on single crystals implies isolated spin-1 two-leg ladders of Ni2 + ions connected by (NO3)- groups as basic elements. Magnetic susceptibility, specific heat in magnetic fields up to 9 T, magnetization, and high-frequency electron spin resonance studies performed on powder samples show the absence of long-range magnetic order at T ≥2 K. Electronic structure calculations and the detailed analysis of the experimental data enable quantitative estimates of the relevant parameters of the S =1 ladders in Rb3Ni2(NO3)7 . The rung coupling J1=10.16 K, the leg coupling J2=1.5 K, and the Ising-type anisotropy |A |=8.6 K are obtained. The scenario of a valence-bond solidlike quantum ground state realized in the two-leg Ni2 + ladders is further corroborated by model simulations of the magnetic susceptibility.

Crystal and magnetic structure of the La1-xCaxMnO3 compound (0.11⩽x⩽0.175)

NASA Astrophysics Data System (ADS)

Pissas, M.; Margiolaki, I.; Papavassiliou, G.; Stamopoulos, D.; Argyriou, D.

2005-08-01

We studied the crystal and magnetic structure of the La1-xCaxMnO3 compound for (0.11⩽x⩽0.175) using stoichiometric samples. For x<0.13 the system’s ground state is insulating canted antiferromagnetic. For 0.13⩽x⩽0.175 below the Jahn-Teller transition temperature (TJT) the crystal structure undergoes a monoclinic distortion. The crystal structure can be described with P21/c space group which permits two Mn sites. The unit-cell strain parameter s=2(a-c)/(a+c) increases for Ta>b/2) structure.

Dimensional effects on the magnetic domains in planar magnetophotonic crystal waveguides

NASA Astrophysics Data System (ADS)

Huang, Xiaoyue

2007-05-01

The application of photonic crystal technology in magneto-optic media can yield significant improvements in polarization rotation efficiency and optical switching capability and an overall reduction in magneto-optic device dimensions. Resonant photonic crystal structures in planar ferrimagnetic film waveguides are of interest because they may lead to the development of on-chip magneto-optical switches and isolators for photonic device integration. In the present work, two different methods for the fabrication of on-chip waveguide magnetophotonic crystals, through electron beam lithography and focused ion beam milling, are discussed and demonstrated. A high precision photonic measurement system was set up for testing and analysis of the waveguide devices. The results obtained show photonic band gaps with resonant transmission in the gap, and enhanced magneto-optic rotation efficiency. The character of waveguide modes therein, birefringence effects, and structural variation effects were studied extensively and are presented in this thesis. Planar magnetization control produced by manipulation of the magnetic shape anisotropy in the photonic crystal micro-cavity was demonstrated in this work. By introducing strip structures into the resonant cavity formed on magnetic garnet films with in-plane anisotropy, a bi-stable magnetic state and an enhanced magnetic field reversal mechanism were demonstrated. This effect was extensively studied through experimental and micromagnetic simulation analysis of the polarization rotation hysteresis. The results discussed herein show that domain closure loops between the strips limit the magnification of the coercivity in the resonant cavity and that these limitations can be overcome by the formation of isolated single-domain magnetic microstrips in the cavity.

Crystal structure and crystal growth of the polar ferrimagnet CaBaFe4O7

NASA Astrophysics Data System (ADS)

Perry, R. S.; Kurebayashi, H.; Gibbs, A.; Gutmann, M. J.

2018-05-01

Magnetic materials are a cornerstone for developing spintronic devices for the transport of information via magnetic excitations. To date, relatively few materials have been investigated for the purpose of spin transport, mostly due to the paucity of suitable candidates as these materials are often chemically complex and difficult to synthesize. We present the crystal growth and a structure solution on the high-temperature crystal structure of the layered, polar ferrimagnet CaBaFe4O7 , which is a possible new contender for spintronics research. The space group is identified as P 3 by refinement of single crystal and powder neutron diffraction data. At 400 K, the trigonal lattice parameters are a =11.0114 (11 )Å and c =10.330 (3 )Å . The structure is similar to the low-temperature phase with alternating layers of triangular and Kagome-arranged Fe-O tetrahedra. We also present details of the crystal growth by traveling solvent method.

Does the thermal evolution of molecular structures critically affect the magnetic anisotropy?† †Electronic supplementary information (ESI) available. CCDC 1045631–1045633. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc01245g

PubMed Central

Qian, Kang; Baldoví, José J.; Zhang, Yi-Quan; Overgaard, Jacob; Wang, Bing-Wu

2015-01-01

A dysprosium based single-ion magnet is synthesized and characterized by the angular dependence of the single-crystal magnetic susceptibility. Ab initio and effective electrostatic analyses are performed using the molecular structures determined from single crystal X-ray diffraction at 20 K, 100 K and 300 K. Contrary to the common assumption, the results reveal that the structural thermal effects that may affect the energy level scheme and magnetic anisotropy below 100 K are negligible. PMID:29568416

Using Strong Magnetic Fields to Control Solutal Convection

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F. W.

2003-01-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in microgravity , we have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. We postulate that limited convection in a magnetic field will provide the environment for the growth of high quality crystals. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. The paper will report on the experimental results using paramagnetic salts and solutions in magnetic fields and compare them to analytical predictions.

Single crystals of the 96 K superconductor (Hg,Cu)Ba2CuO4+δ: Growth, structure and magnetism

NASA Astrophysics Data System (ADS)

Pelloquin, D.; Hardy, V.; Maignan, A.; Raveau, B.

1997-02-01

Single crystals of the 1201 (n = 1) (Hg,Cu)Ba2CuO4+δ mercury based cuprate have been grown by using a simple process without dry box. The as-synthesized crystals exhibit constant Tc(onset) of 96 K with sharp superconducting transitions. The electron microscopy coupled with EDX analyses evidence a ``1201''-type structure while a mercury deficiency is observed balanced by an excess of copper. The structural refinements based on single-crystal X-ray diffraction data confirm the electron deficiency on the Hg site (0,0,0) and show a splitting of the latter along the c axis correlated to the partial substitution of Cu for Hg. This structural study leads to the following formula Hg0.84Cu0.16Ba2CuO4.19. The magnetic study of a large crystal (1.1 × 0.38 × 0.065 mm3) shows that the (Hg,Cu)-1201 crystals exhibit an irreversibility line higher than that of the 1201 Hg0.8Bi0.2Ba2CuO4+δ crystal (Tc = 75 K). From the reversible magnetization, a λab(0) = 2470 Å value can be extrapolated. Using a 3D-2D decoupling formula, we obtain γ = 29 for the electronic anisotropy of this phase.

Single crystal growth and characterization of kagomé-lattice shandites Co3Sn2-xInxS2

NASA Astrophysics Data System (ADS)

Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

2015-09-01

Single crystals of the shandite-type half metallic ferromagnet Co3Sn2S2, and its In-substituted compounds, Co3Sn2-xInxS2 (0

Ce3 - xMgxCo9 : Transformation of a Pauli Paramagnet into a Strong Permanent Magnet

NASA Astrophysics Data System (ADS)

Lamichhane, Tej N.; Taufour, Valentin; Palasyuk, Andriy; Lin, Qisheng; Bud'ko, Sergey L.; Canfield, Paul C.

2018-02-01

We report on the synthesis of single-crystal and polycrystalline samples of Ce3 -xMgxCo9 solid solution (0 ≤x ≲1.4 ) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6 c site of the CeCo3 structure. Ferromagnetism is induced by Mg substitutions starting as low as x =0.18 and reaching a Curie temperature as high as 450 K for x =1.35 . Measurements on single crystals with x =1.34 and TC=440 K indicate an axial magnetic anisotropy with an anisotropy field of 6 T and a magnetization of 6 μB/f .u . at 300 K. Coercicity is observed in the polycrystalline samples consistent with the observed axial magnetic anisotropy. Our discovery of ferromagnetism with large axial magnetic anisotropy induced by substituting a rare-earth element by Mg is a very promising result in the search of inexpensive permanent-magnet materials and suggests that other nonmagnetic phases, similar to CeCo3 , may also conceal nearby ferromagnetic phases.

Ce 3 - x Mg x Co 9 : Transformation of a Pauli Paramagnet into a Strong Permanent Magnet

DOE PAGES

Lamichhane, Tej N.; Taufour, Valentin; Palasyuk, Andriy; ...

2018-02-23

In this article we report on the synthesis of single-crystal and polycrystalline samples of Ce 3-xMg xCo 9 solid solution (0 ≤ x ≲ 1.4) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6c site of the CeCo 3 structure. Ferromagnetism is induced by Mg substitutions starting as low as x = 0.18 and reaching a Curie temperature as high as 450 K for x = 1.35 . Measurements on single crystals with x = 1.34 and T C = 440 K indicatemore » an axial magnetic anisotropy with an anisotropy field of 6 T and a magnetization of 6 μ B/f.u. at 300 K. Coercicity is observed in the polycrystalline samples consistent with the observed axial magnetic anisotropy. Our discovery of ferromagnetism with large axial magnetic anisotropy induced by substituting a rare-earth element by Mg is a very promising result in the search of inexpensive permanent-magnet materials and suggests that other nonmagnetic phases, similar to CeCo 3, may also conceal nearby ferromagnetic phases.« less

Ce 3 - x Mg x Co 9 : Transformation of a Pauli Paramagnet into a Strong Permanent Magnet

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

Lamichhane, Tej N.; Taufour, Valentin; Palasyuk, Andriy

In this article we report on the synthesis of single-crystal and polycrystalline samples of Ce 3-xMg xCo 9 solid solution (0 ≤ x ≲ 1.4) and characterization of their structural and magnetic properties. The crystal structure remains rhombohedral in the whole composition range and Mg partially replaces Ce in the 6c site of the CeCo 3 structure. Ferromagnetism is induced by Mg substitutions starting as low as x = 0.18 and reaching a Curie temperature as high as 450 K for x = 1.35 . Measurements on single crystals with x = 1.34 and T C = 440 K indicatemore » an axial magnetic anisotropy with an anisotropy field of 6 T and a magnetization of 6 μ B/f.u. at 300 K. Coercicity is observed in the polycrystalline samples consistent with the observed axial magnetic anisotropy. Our discovery of ferromagnetism with large axial magnetic anisotropy induced by substituting a rare-earth element by Mg is a very promising result in the search of inexpensive permanent-magnet materials and suggests that other nonmagnetic phases, similar to CeCo 3, may also conceal nearby ferromagnetic phases.« less

Syntheses, crystal structures and magnetic properties of complexes based on [Ni(L-L)3]2+ complex cations with dimethylderivatives of 2,2‧-bipyridine and TCNQ

NASA Astrophysics Data System (ADS)

Černák, Juraj; Hegedüs, Michal; Váhovská, Lucia; Kuchár, Juraj; Šoltésová, Daniela; Čižmár, Erik; Feher, Alexander; Falvello, L. R.

2018-03-01

From the aqueous-methanolic systems Ni(NO3)2 - LiTCNQ - 5,5‧-dmbpy and Ni(NO3)2 - LiTCNQ - 4,4‧-dmbpy three novel complexes [Ni(5,5‧-dmbpy)3](TCNQ)2 (1), [Ni(4,4‧-dmbpy)3](TCNQ)2 (2) and [Ni(4,4‧-dmbpy)3]2(TCNQ-TCNQ)(TCNQ)2•0.60H2O (3), were isolated in single crystal form. The new compounds were identified using chemical analyses and IR spectroscopy. Single crystal studies of all samples corroborated their compositions and have shown that their ionic structures contain the complex cations [Ni(5,5‧-dmbpy)]2+ (1) or [Ni(4,4‧-dmbpy)]2+ (2 and 3). The anionic parts of the respective crystal structures 1-3 are formed by TCNQṡ- anion-radicals and in 3 also by a σ-dimerized dianion (TCNQ-TCNQ)2- with a C-C distance of 1.663(5) Å. The supramolecular structures are governed by weak hydrogen bonding interactions. The variable-temperature (2-300 K) magnetic studies of 1 and 3 confirmed the presence of magnetically active Ni(II) atoms with S = 1 and TCNQṡ- anion-radicals with S = 1/2 while the (TCNQ-TCNQ)2- dianion is magnetically silent. The magnetic behavior was described by a complex magnetic model assuming strong antiferromagnetic interactions between some TCNQṡ- anion-radicals.

The magnetic properties and structure of the quasi-two-dimensional antiferromagnet CoPS3

NASA Astrophysics Data System (ADS)

Wildes, A. R.; Simonet, V.; Ressouche, E.; Ballou, R.; McIntyre, G. J.

2017-11-01

The magnetic properties and magnetic structure are presented for CoPS3, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Néel temperature of TN ∼120 K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2 K and 300 K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Single-crystal neutron diffraction shows that the magnetic propagation vector is k  =  (0 1 0) with the moments mostly along the {a} axis and with a small component along the {c} axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent 2β = 0.60 +/- 0.01 for T > 0.9~TN .

Reversal of spontaneous magnetization and spontaneous exchange bias for Sm1-xYxCrO3: The effect of Y doping

NASA Astrophysics Data System (ADS)

Zhang, Hongguang; Wang, Jianhua; Xie, Liang; Fu, Dexiang; Guo, Yanyan; Li, Yongtao

2017-11-01

We report the crystal and electronic structures and magnetic properties of non-magnetic Y3+ ion doped SmCrO3 crystals. Structural distortion and electronic structure variation are caused by cation disorder due to Y doping. Although the spin moment of Sm3+ is diluted by nonmagnetic Y ions, spin reorientation continues to exist, and the temperature-dependent magnetization reversal effect and the spontaneous exchange bias effect under zero field cooling are simultaneously induced below Neel temperature. Significantly, the method of doping promotes the achievement of temperature dependent tunable switching of magnetization and sign of a spontaneous exchange bias from positive to negative. Our work provides more tunable ways to the sign reversal of magnetization and exchange bias, which have potential application in designing magnetic random access memory devices, thermomagnetic switches and spin-valve devices.

Effects of wear on structure-sensitive magnetic properties of ceramic ferrite in contact with magnetic tape

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.; Tanaka, K.

1985-01-01

Wear experiments and electron microscopy and diffraction studies were conducted to examine the wear and deformed layers in single-crystal Mn-Zn (ceramic) ferrite magnetic head material in contact with magnetic tape and the effects of that contact on magnetic properties. The crystalline state of the single-crystal magnetic head was changed drastically during the sliding process. A nearly amorphous structure was produced on its wear surface. Deformation in the surficial layer of the magnetic head was a critical factor in readback signal loss above 2.5 dB. The signal output level was reduced as applied normal load was increased. Considerable plastic flow occurred on the magnetic tape surface with sliding, and the signal loss due to the tape wear was approximately 1 dB.

Investigation of a Structural Phase Transition and Magnetic Structure of Na 2BaFe(VO 4) 2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

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

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.

The structural and magnetic properties of a glaserite-type Na 2BaFe(VO 4) 2 compound, featuring a triangular magnetic lattice of Fe 2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal Pmore » $$\\bar{3}$$ m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T s = 288 K). This structural transition involves a tilting of Fe–O–V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na 2BaFe(VO 4) 2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Altogether, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO 6 octahedron.« less

Investigation of a Structural Phase Transition and Magnetic Structure of Na 2BaFe(VO 4) 2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

DOE PAGES

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.; ...

2017-12-07

The structural and magnetic properties of a glaserite-type Na 2BaFe(VO 4) 2 compound, featuring a triangular magnetic lattice of Fe 2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal Pmore » $$\\bar{3}$$ m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T s = 288 K). This structural transition involves a tilting of Fe–O–V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na 2BaFe(VO 4) 2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Altogether, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO 6 octahedron.« less

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

Davaasuren, Bambar; Dashjav, Enkhtsetseg; Kreiner, Guido

The carboferrates RE{sub 15}[Fe{sub 8}C{sub 25}] (RE=Dy, Ho) were prepared from mixtures of the elements by arc-melting followed with subsequent annealing at 1373 K. The crystal structures were determined from single crystal X-ray diffraction data and revealed an isotypic relationship to Er{sub 15}[Fe{sub 8}C{sub 25}] (hP48, P321). The main feature of the crystal structure is given by Fe{sub 6} cluster units characterized by covalent Fe–Fe bonding interactions. {sup 57}Fe Mössbauer spectra of Dy{sub 15}[Fe{sub 8}C{sub 25}] were fitted by three subspectra with relative spectral weights of about 3:3:2 which is in general agreement with the crystal structure. Below 50 K,more » an onset of magnetic hyperfine fields at the three iron sites is observed which is supposed to be caused by dipolar fields arising from neighboring, slowly relaxing Dy magnetic moments. - Graphical abstract: Fe{sub 6}-cluster in the crystal structure of RE{sub 15}[Fe{sub 8}C{sub 25}], RE=Dy, Ho. - Highlights: • New carboferrates RE{sub 15}[Fe{sub 8}C{sub 25}] with RE=Dy, Ho have been synthesized. • The crystal structures were refined using single crystal X-ray data. • An orientational relationship between Fe{sub 6}-clusters and Fe in γ-Fe is outlined. • {sup 57}Fe Mössbauer spectra are in agreement with structural data from X-rays. • Magnetic hyperfine fields below 50 K are explained by dipolar fields from Dy atoms.« less

Magnetic and Crystal Structure of α-RuCl3

NASA Astrophysics Data System (ADS)

Sears, Jennifer

The layered honeycomb material α-RuCl3 has been proposed as a candidate material to show significant bond-dependent Kitaev type interactions. This has prompted several recent studies of magnetism in this material that have found evidence for multiple magnetic transitions in the temperature range of 8-14 K. We will present elastic neutron scattering measurements collected using a co-aligned array of α-RuCl3 crystals, identifying zigzag magnetic order within the honeycomb planes with an ordering temperature of ~8 K. It has been reported that the ordering temperature depends on the c axis periodicity of the layered structure, with ordering temperatures of 8 and 14 K for three and two-layer periodicity respectively. While the in-plane magnetic order has been identified, it is clear that a complete understanding of magnetic ordering and interactions will depend on the three dimensional structure of the crystal. Evidence of a structural transition at ~150 K has been reported and questions remain about the structural details, in particular the stacking of the honeycomb layers. We will present x-ray diffraction measurements investigating the low and high temperature structures and stacking disorder in α-RuCl3. Finally, we will present inelastic neutron scattering measurements of magnetic excitations in this material. Work done in collaboration with K. W. Plumb (Johns Hopkins University), J. P. Clancy, Young-June Kim (University of Toronto), J. Britten (McMaster University), Yu-Sheng Chen (Argonne National Laboratory), Y. Qiu, Y. Zhao, D. Parshall, and J. W. Lynn (NCNR).

Interfacial magnetic coupling in hetero-structure of Fe/double-perovskite NdBaMn2O6 single crystal

NASA Astrophysics Data System (ADS)

Lin, W. C.; Tsai, C. L.; Ogawa, K.; Yamada, S.; Gandhi, Ashish C.; Lin, J. G.

2018-04-01

The interfacial magnetic coupling between metallic Fe and the double-perovskite NdBaMn2O6 single crystal was investigated in the heterostructure of 4-nm Pd/10-nm Fe/NdBaMn2O6. A considerable magnetic coupling effect was observed in the temperature range coincident with the magnetic phase transition of NdBaMn2O6. When the temperature was elevated above 270 K, NdBaMn2O6 transformed from a state of antiferromagnetic fluctuating domains to a superparamagnetism-like (ferromagnetic fluctuation) state with high magnetic susceptibility. Concurrently, the interfacial magnetic coupling between the Fe layer and the NdBaMn2O6 crystal was observed, as indicated by the considerable squareness reduction and coercivity enhancement in the Fe layer. Moreover, the presence of the Fe layer changed the magnetic structure of NdBaMn2O6 from conventional 4-fold symmetry to 2-fold symmetry. These observations offer applicable insights into the mutual magnetic interaction in the heterostructures of metallic ferromagnetism/perovskite materials.

Thermal effect on structural and magnetic properties of Fe78B13Si9 annealed amorphous ribbons

NASA Astrophysics Data System (ADS)

Soltani, Mohamed Larbi; Touares, Abdelhay; Aboki, Tiburce A. M.; Gasser, Jean-Georges

2017-08-01

In the present work, we study the influence of thermal treatments on the magnetic properties of as-quenched and pre-crystallized Fe78Si9B13 after stress relaxation. The crystallization behavior of amorphous and treated Fe78Si9B13 ribbons was revisited. The measurements were carried out by means of Differential Scanning Calorimetry, by X-ray diffraction and by Vibrating Sample Magnetometer, Susceptometer and fluxmeter. Relaxed samples were heated in the resistivity device up to 700°C and annealed near the onset temperature about 420°C for respectively 1, 3, 5, 8 hours. In as-quenched samples, two transition points occur at about 505°C and 564°C but in relaxed sample, the transition points have been found about 552°C and 568°C. Kinetics of crystallization was deduced for all studied samples. Annealing of the as-purchased ribbon shows the occurrence of α-Fe and tetragonal Fe3B resulting from the crystallization of the remaining amorphous phase. The effects on magnetic properties were pointed out by relating the structural evolution of the samples. The magnetic measurements show that annealing change the saturation magnetization and the coercive magnetic field values, hence destroying the good magnetic properties of the material. The heat treatment shows that the crystallization has greatly altered the shape of the cycles and moved the magnetic saturation point of the samples. The effect of treatment on the magneto-crystalline anisotropy is also demonstrated.

X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

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

Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.

2016-07-06

We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu 2Ir 2O 7 and Pr 2Ir 2O 7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu 2Ir 2O 7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa)more » studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu 2Ir 2O 7 and Pr 2Ir 2O 7 using high-resolution Ir L- 3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu 2Ir 2O 7 (found to possess an actual stoichiometry of Eu 2.18Ir 1.82O 7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations« less

Pressure-decoupled magnetic and structural transitions of the parent compound of iron-based 122 superconductors BaFe2As2

PubMed Central

Wu, J. J.; Lin, Jung-Fu; Wang, X. C.; Liu, Q. Q.; Zhu, J. L.; Xiao, Y. M.; Chow, P.; Jin, Changqing

2013-01-01

The recent discovery of iron ferropnictide superconductors has received intensive concern in connection with magnetically involved superconductors. Prominent features of ferropnictide superconductors are becoming apparent: the parent compounds exhibit an antiferromagnetic ordered spin density wave (SDW) state, the magnetic-phase transition is always accompanied by a crystal structural transition, and superconductivity can be induced by suppressing the SDW phase via either chemical doping or applied external pressure to the parent state. These features generated considerable interest in the interplay between magnetism and structure in chemically doped samples, showing crystal structure transitions always precede or coincide with magnetic transition. Pressure-tuned transition, on the other hand, would be more straightforward to superconducting mechanism studies because there are no disorder effects caused by chemical doping; however, remarkably little is known about the interplay in the parent compounds under controlled pressure due to the experimental challenge of in situ measuring both of magnetic and crystal structure evolution at high pressure and low temperatures. Here we show from combined synchrotron Mössbauer and X-ray diffraction at high pressures that the magnetic ordering surprisingly precedes the structural transition at high pressures in the parent compound BaFe2As2, in sharp contrast to the chemical-doping case. The results can be well understood in terms of the spin fluctuations in the emerging nematic phase before the long-range magnetic order that sheds light on understanding how the parent compound evolves from a SDW state to a superconducting phase, a key scientific inquiry of iron-based superconductors. PMID:24101468

Transformation from an easy-plane to an easy-axis antiferromagnetic structure in the mixed rare-earth ferroborates Pr x Y1-x Fe3(BO3)4: magnetic properties and crystal field calculations.

PubMed

Pankrats, A I; Demidov, A A; Ritter, C; Velikanov, D A; Semenov, S V; Tugarinov, V I; Temerov, V L; Gudim, I A

2016-10-05

The magnetic structure of the mixed rare-earth system Pr x Y1-x Fe3(BO3)4 (x  =  0.75, 0.67, 0.55, 0.45, 0.25) was studied via magnetic and resonance measurements. These data evidence the successive spin reorientation from the easy-axis antiferromagnetic structure formed in PrFe3(BO3)4 to the easy-plane one of YFe3(BO3)4 associated with the weakening of the magnetic anisotropy of the Pr subsystem due to its diamagnetic dilution by nonmagnetic Y. This reorientation occurs through the formation of an inclined magnetic structure, as was confirmed by our previous neutron research in the range of x  =  0.67 ÷ 0.45. In the compounds with x  =  0.75 and 0.67 whose magnetic structure is close to the easy-axis one, a two-step spin reorientation takes place in the magnetic field H||c. Such a peculiarity is explained by the formation of an interjacent inclined magnetic structure with magnetic moments of Fe ions located closer to the basal plane than in the initial state, with these intermediate states remaining stable in some ranges of the magnetic field. An approach based on a crystal field model for the Pr(3+) ion and the molecular-field approximation is used to describe the magnetic characteristics of the system Pr x Y1-x Fe3(BO3)4. With the parameters of the d-d and f-d exchange interactions, of the magnetic anisotropy of the iron subsystem and of the crystal field parameters of praseodymium thus determined, it is possible to achieve a good agreement between the experimental and calculated temperature and field dependences of the magnetization curves (up to 90 kOe) and magnetic susceptibilities (2-300 K).

Magnetic properties of dendrimer structures with different coordination numbers: A Monte Carlo study

NASA Astrophysics Data System (ADS)

Masrour, R.; Jabar, A.

2016-11-01

We investigate the magnetic properties of Cayley trees of large molecules with dendrimer structure using Monte Carlo simulations. The thermal magnetization and magnetic susceptibility of a dendrimer structure are given with different coordination numbers, Z=3, 4, 5 and different generations g=3 and 2. The variation of magnetizations with the exchange interactions and crystal fields have been given of this system. The magnetic hysteresis cycles have been established.

Structural, magnetic and magnetocaloric properties of sputtered Gd films

NASA Astrophysics Data System (ADS)

Kumar, N. Pavan; Shaleni, V.; Satyanarayana, L.; Manorama, S. V.; Raja, M. Manivel

2018-05-01

Gd films with different thicknesses varying from 100 nm to 750 nm have been deposited on single crystal Si (100) substrate by ultra high vacuum magnetron sputtering system. X-ray diffraction analysis reveals the crystalline nature and hcp crystal structure of the films. Microstructure investigations have been carried to study the surface morphology of the films. Thermo magnetic studies confirm the magnetic transition of the films and are ˜275 K, close to bulk. Magnetocaloric effect (MCE) has been studied from magnetic isotherms measured around magnetic transition and the maximum isothermal entropy change of 2.0 J/kg-K is achieved for a magnetic field change of 2 T for the 750 nm film. The sputtered Gd films are useful for micro cooling device applications.

Magnetic properties and crystal structure of RENiA1 and UniA1 hydrides.

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

Bordallo, H. N.; Drulis, H.; Havela, L.

1999-08-11

RENiAl (RE = rare-earth metal) and UNiAl compounds crystallizing in the hexagonal ZrNiAl-type structure (space group P{bar 6}2m) can absorb up to 2 and 3 hydrogen (deuterium) atoms per formula unit, respectively. Hydrogenation leads to a notable lattice expansion and modification of magnetic properties. However, the impact of hydrogenation on magnetism is the opposite for 4f- and 5f-materials: TN(T{sub c})is lowered in the case of rare-earth hydrides, while for UNiAlH(D){sub x} it increases by an order of magnitude. Here we present results of magnetic and structure studies performed of these compounds, focusing on the correlation between magnetic and structural variationsmore » and discussing possible reasons of the striking difference in effect of hydrogenation on rare-earth and actinide intermetallics.« less

Three-dimensional magnetophotonic crystals based on artificial opals

NASA Astrophysics Data System (ADS)

Baryshev, A. V.; Kodama, T.; Nishimura, K.; Uchida, H.; Inoue, M.

2004-06-01

We fabricated and experimentally investigated three-dimensional magnetophotonic crystals (3D MPCs) based on artificial opals. Opal samples with three-dimensional dielectric lattices were impregnated with different types of magnetic material. Magnetic and structural properties of 3D MPCs were studied by field emission scanning electron microscopy, x-ray diffraction analysis, and vibrating sample magnetometer. We have shown that magnetic materials synthesized in voids of opal lattices and the composites obtained have typical magnetic properties.

Crystal structure and partial Ising-like magnetic ordering of orthorhombic D y 2 Ti O 5

DOE PAGES

Shamblin, Jacob; Calder, Stuart; Dun, Zhiling; ...

2016-07-12

The structure and magnetic properties of orthorhombic Dy 2TiO 5 have been investigated using x-ray diffraction, neutron diffraction, and alternating current (ac)/direct current (dc) magnetic susceptibility measurements. In this paper, we report a continuous structural distortion below 100 K characterized by negative thermal expansion in the [0 1 0] direction. Neutron diffraction and magnetic susceptibility measurements revealed that two-dimensional (2D) magnetic ordering begins at 3.1 K, which is followed by a three-dimensional magnetic transition at 1.7 K. The magnetic structure has been solved through a representational analysis approach and can be indexed with the propagation vector k = [0 1/2more » 0]. The spin structure corresponds to a coplanar model of interwoven 2D “sheets” extending in the [0 1 0] direction. The local crystal field is different for each Dy 3+ ion (Dy1 and Dy2), one of which possesses strong uniaxial symmetry indicative of Ising-like magnetic ordering. In conclusion, consequently, two succeeding transitions under magnetic field are observed in the ac susceptibility, which are associated with flipping each Dy 3+ spin independently.« less

Countering Solutal Buoyant Convection with High Magnetic Fields

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F. W.

2002-01-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemist, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitant, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in microgravity, we have been able to dramatically effect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. We postulate that limited convection in a magnetic field will provide the environment for the growth of high quality crystals. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. The paper will report on the current status of the investigation and discuss results from the experimental and modeling efforts.

Magnetic Control of Convection during Protein Crystallization

NASA Technical Reports Server (NTRS)

Ramachandran, N.; Leslie, F. W.

2004-01-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular Crystals for diffraction analyses has been the central focus for bio-chemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and Sedimentation as is achieved in "microgravity", we have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, f o d o n of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. We postulate that limited convection in a magnetic field will provide the environment for the growth of high quality crystals. The approach exploits the variation of fluid magnetic susceptibility with counteracts on for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteract terrestrial gravity. The genera1 objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. The paper will report on the experimental results using paramagentic salts and solutions in magnetic fields and compare them to analyticalprctions.

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

Joint refinement model for the spin resolved one-electron reduced density matrix of YTiO3 using magnetic structure factors and magnetic Compton profiles data.

PubMed

Gueddida, Saber; Yan, Zeyin; Kibalin, Iurii; Voufack, Ariste Bolivard; Claiser, Nicolas; Souhassou, Mohamed; Lecomte, Claude; Gillon, Béatrice; Gillet, Jean-Michel

2018-04-28

In this paper, we propose a simple cluster model with limited basis sets to reproduce the unpaired electron distributions in a YTiO 3 ferromagnetic crystal. The spin-resolved one-electron-reduced density matrix is reconstructed simultaneously from theoretical magnetic structure factors and directional magnetic Compton profiles using our joint refinement algorithm. This algorithm is guided by the rescaling of basis functions and the adjustment of the spin population matrix. The resulting spin electron density in both position and momentum spaces from the joint refinement model is in agreement with theoretical and experimental results. Benefits brought from magnetic Compton profiles to the entire spin density matrix are illustrated. We studied the magnetic properties of the YTiO 3 crystal along the Ti-O 1 -Ti bonding. We found that the basis functions are mostly rescaled by means of magnetic Compton profiles, while the molecular occupation numbers are mainly modified by the magnetic structure factors.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

DOE PAGES

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh; ...

2017-04-14

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe 3

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

McGuire, Michael A.; Garlea, V. Ovidiu; KC, Santosh

We have investigated the crystallographic, magnetic, and transport properties of the van der Waals bonded, layered compound CrTe 3 on single-crystal and polycrystalline materials. Furthermore, the crystal structure contains layers made up of lozenge-shaped Cr 4 tetramers. Electrical resistivity measurements show the crystals to be semiconducting, with a temperature dependence consistent with a band gap of 0.3 eV. The magnetic susceptibility exhibits a broad maximum near 300 K characteristic of low dimensional magnetic systems. Weak anomalies are observed in the susceptibility and heat capacity near 55 K, and single-crystal neutron diffraction reveals the onset of long-range antiferromagnetic order at thismore » temperature. Strongly dispersive spin waves are observed in the ordered state. Significant magnetoelastic coupling is indicated by the anomalous temperature dependence of the lattice parameters and is evident in structural optimization in van der Waals density functional theory calculations for different magnetic configurations. The cleavability of the compound is apparent from its handling and is confirmed by first-principles calculations, which predict a cleavage energy 0.5 J / m 2 , similar to graphite. Based on our results, CrTe 3 is identified as a promising compound for studies of low dimensional magnetism in bulk crystals as well as magnetic order in monolayer materials and van der Waals heterostructures.« less

GdPtPb: A noncollinear antiferromagnet with distorted kagome lattice

DOE PAGES

Manni, S.; Bud'ko, Sergey L.; Canfield, Paul C.

2017-08-24

In the spirit of searching for Gd-based, frustrated, rare earth magnets, we have found antiferomagnetism (AF) in GdPtPb, which crystallizes in the ZrNiAl-type structure that has a distorted kagome lattice of Gd triangles. Single crystals were grown and investigated using structural, magnetic, transport, and thermodynamic measurements. GdPtPb orders antiferromagnetically at 15.5 K, arguably with a planar, noncollinear structure. The high temperature magnetic susceptibility data reveal an “anti-frustration” behavior having a frustration parameter, |f| = |Θ|/T N = 0.25, which can be explained by mean field theory within a two-sublattice model. Here, the study of the magnetic phase diagram down tomore » T = 1.8K reveals a change of magnetic structure through a metamagnetic transition at around 20 kOe and the disappearance of the AF ordering near 140 kOe. In total, our work indicates that GdPtPb can serve as an example of a planar, noncollinear AF with a distorted kagome magnetic sublattice.« less

Effect of defects, magnetocrystalline anisotropy, and shape anisotropy on magnetic structure of iron thin films by magnetic force microscopy

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

Xu, Ke; Schreiber, Daniel K.; Li, Yulan

Microstructures of magnetic materials, including defects and crystallographic orientations, are known to strongly influence magnetic domain structures. Measurement techniques such as magnetic force microscopy (MFM) thus allow study of correlations between microstructural and magnetic properties. The present work probes effects of anisotropy and artificial defects on the evolution of domain structure with applied field. Single crystal iron thin films on MgO substrates were milled by Focused Ion Beam (FIB) to create different magnetically isolated squares and rectangles in [110] crystallographic orientations, having their easy axis 45° from the sample edge. To investigate domain wall response on encountering non-magnetic defects, amore » 150 nm diameter hole was created in the center of some samples. By simultaneously varying crystal orientation and shape, both magnetocrystalline anisotropy and shape anisotropy, as well as their interaction, could be studied. Shape anisotropy was found to be important primarily for the longer edge of rectangular samples, which exaggerated the FIB edge effects and provided nucleation sites for spike domains in non-easy axis oriented samples. Center holes acted as pinning sites for domain walls until large applied magnetic fields. The present studies are aimed at deepening the understanding of the propagation of different types of domain walls in the presence of defects and different crystal orientations.« less

Effect of defects, magnetocrystalline anisotropy, and shape anisotropy on magnetic structure of iron thin films by magnetic force microscopy

DOE PAGES

Xu, Ke; Schreiber, Daniel K.; Li, Yulan; ...

2017-02-10

Microstructures of magnetic materials, including defects and crystallographic orientations, are known to strongly influence magnetic domain structures. Measurement techniques such as magnetic force microscopy (MFM) thus allow study of correlations between microstructural and magnetic properties. The present work probes effects of anisotropy and artificial defects on the evolution of domain structure with applied field. Single crystal iron thin films on MgO substrates were milled by Focused Ion Beam (FIB) to create different magnetically isolated squares and rectangles in [110] crystallographic orientations, having their easy axis 45° from the sample edge. To investigate domain wall response on encountering non-magnetic defects, amore » 150 nm diameter hole was created in the center of some samples. By simultaneously varying crystal orientation and shape, both magnetocrystalline anisotropy and shape anisotropy, as well as their interaction, could be studied. Shape anisotropy was found to be important primarily for the longer edge of rectangular samples, which exaggerated the FIB edge effects and provided nucleation sites for spike domains in non-easy axis oriented samples. Center holes acted as pinning sites for domain walls until large applied magnetic fields. The present studies are aimed at deepening the understanding of the propagation of different types of domain walls in the presence of defects and different crystal orientations.« less

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

Wang, Bingnan

Photonic crystals and metamaterials, both composed of artificial structures, are two interesting areas in electromagnetism and optics. New phenomena in photonic crystals and metamaterials are being discovered, including some not found in natural materials. This thesis presents my research work in the two areas. Photonic crystals are periodically arranged artificial structures, mostly made from dielectric materials, with period on the same order of the wavelength of the working electromagnetic wave. The wave propagation in photonic crystals is determined by the Bragg scattering of the periodic structure. Photonic band-gaps can be present for a properly designed photonic crystal. Electromagnetic waves withmore » frequency within the range of the band-gap are suppressed from propagating in the photonic crystal. With surface defects, a photonic crystal could support surface modes that are localized on the surface of the crystal, with mode frequencies within the band-gap. With line defects, a photonic crystal could allow the propagation of electromagnetic waves along the channels. The study of surface modes and waveguiding properties of a 2D photonic crystal will be presented in Chapter 1. Metamaterials are generally composed of artificial structures with sizes one order smaller than the wavelength and can be approximated as effective media. Effective macroscopic parameters such as electric permittivity ϵ, magnetic permeability μ are used to characterize the wave propagation in metamaterials. The fundamental structures of the metamaterials affect strongly their macroscopic properties. By designing the fundamental structures of the metamaterials, the effective parameters can be tuned and different electromagnetic properties can be achieved. One important aspect of metamaterial research is to get artificial magnetism. Metallic split-ring resonators (SRRs) and variants are widely used to build magnetic metamaterials with effective μ < 1 or even μ < 0. Varactor based nonlinear SRRs are built and modeled to study the nonlinearity in magnetic metamaterials and the results will be presented in Chapter 3. Negative refractive index n is one of the major target in the research of metamaterials. Negative n can be obtained with a metamaterial with both ϵ and μ negative. As an alternative, negative index for one of the circularly polarized waves could be achieved with metamaterials having a strong chirality ?. In this case neither ϵ} nor μ negative is required. My work on chiral metamaterials will be presented in Chapter 4.« less

Coupling of Crystal Structure and Magnetism in the Layered, Ferromagnetic Insulator CrI 3

DOE PAGES

McGuire, Michael A.; Dixit, Hemant; Cooper, Valentino R.; ...

2014-12-23

Here, we examine the crystallographic and magnetic properties of single crystals of CrI 3, an easily cleavable, layered and insulating ferromagnet with a Curie temperature of 61 K. Our X-ray diffraction studies reveal a first-order crystallographic phase transition occurring near 210–220 K upon warming, with significant thermal hysteresis. The low-temperature structure is rhombohedral (Rmore » $$\\bar{3}$$, BiI 3-type) and the high-temperature structure is monoclinic (C2/m, AlCl 3-type). Evidence for coupling between the crystallographic and magnetic degrees of freedom in CrI 3 was found; we observed an anomaly in the interlayer spacing at the Curie temperature and an anomaly in the magnetic susceptibility at the structural transition. First-principles calculations reveal the importance of proper treatment of the long-ranged interlayer forces, and van der Waals density functional theory does an excellent job of predicting the crystal structures and their relative stability. Our calculations suggest that the ferromagnetic order found in the bulk material may persist into monolayer form, suggesting that CrI 3 and other chromium trihalides may be promising materials for spintronic and magnetoelectronic research.« less

Phase transition in a multiferroic Ni-Mn-Ga single crystal

NASA Astrophysics Data System (ADS)

Veřtát, P.; Drahokoupil, J.; Perevertov, O.; Heczko, O.

2016-08-01

We studied martensitic phase transformation, crystal structure and twinned microstructure of resulting martensite of a Ni-Mn-Ga single crystal as essential conditions for magnetic shape memory effect. Thermal dependence of electric resistivity, magnetic susceptibility and dilatation measurements were measured to characterise kinetics of the transformation. With the help of XRD analysis and optical microscopy we evaluated the hierarchical twinning microstructure in the 10M martensite.

Magnetoresponsive discoidal photonic crystals toward active color pigments.

PubMed

Lee, Hye Soo; Kim, Ju Hyeon; Lee, Joon-Seok; Sim, Jae Young; Seo, Jung Yoon; Oh, You-Kwan; Yang, Seung-Man; Kim, Shin-Hyun

2014-09-03

Photonic microdisks with a multilayered structure are designed from photocurable suspensions by step-by-step photolithography. In each step of photolithography, either a colloidal photonic crystal or a magnetic-particle-laden layer is stacked over the windows of a photomask. Sequential photolithography enables the creation of multilayered photonic microdisks that have brilliant structural colors that can be switched by an external magnetic field. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photonic-magnonic crystals: Multifunctional periodic structures for magnonic and photonic applications

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

Kłos, J. W., E-mail: klos@amu.edu.pl; Krawczyk, M.; Dadoenkova, Yu. S.

2014-05-07

We investigate the properties of a photonic-magnonic crystal, a complex multifunctional one-dimensional structure with magnonic and photonic band gaps in the GHz and PHz frequency ranges for spin waves and light, respectively. The system consists of periodically distributed dielectric magnetic slabs of yttrium iron garnet and nonmagnetic spacers with an internal structure of alternating TiO{sub 2} and SiO{sub 2} layers which form finite-size dielectric photonic crystals. We show that the spin-wave coupling between the magnetic layers, and thus the formation of the magnonic band structure, necessitates a nonzero in-plane component of the spin-wave wave vector. A more complex structure perceivedmore » by light is evidenced by the photonic miniband structure and the transmission spectra in which we have observed transmission peaks related to the repetition of the magnetic slabs in the frequency ranges corresponding to the photonic band gaps of the TiO{sub 2}/SiO{sub 2} stack. Moreover, we show that these modes split to very high sharp (a few THz wide) subpeaks in the transmittance spectra. The proposed novel multifunctional artificial crystals can have interesting applications and be used for creating common resonant cavities for spin waves and light to enhance the mutual influence between them.« less

Growth, Faraday and inverse Faraday characteristics of Tb₂Ti₂O₇ crystal.

PubMed

Guo, Feiyun; Sun, Yilin; Yang, Xiongsheng; Chen, Xin; Zhao, Bin; Zhuang, Naifeng; Chen, Jianzhong

2016-03-21

Tb₂Ti₂O₇ (TTO) single crystal with dimensions of 20 × 20 × 16 mm³ was grown by the Czochralski method. Rietveld structure refinement of X-ray diffraction (XRD) data confirms that the compound crystallizes in the cubic system with pyrochlore structure. Transmission spectra, Magnetic circular dichroism (MCD) spectra, Faraday and inverse Faraday characteristics of TTO crystal have been measured and analyzed in detail. The results demonstrate that TTO crystal has high transmittance at 700-1400 nm waveband and a larger Verdat constant than that of TGG reported. Magnetic circular dichroism (MCD) spectra showed that the 4f→4f transitions of Tb³⁺ have significant contributions to the magneto-optical activity (MOA). In the time-resolved pump-probe spectroscopy, the rotation signals of the probe beam based on the inverse Faraday effect in magneto-optical crystal were observed at zero time delay, the full width at half maximum of the rotation and ellipticity signals can be as fast as ~500 fs, which indicates that TTO crystal can be a promising material for ultrafast all-optical magnetic switching.

Origin of the magnetoelectric effect in the Cs2FeCl5.D2O compound

NASA Astrophysics Data System (ADS)

Fabelo, Oscar; Rodríguez-Velamazán, J. Alberto; Canadillas-Delgado, Laura; Mazzuca, Lidia; Campo, Javier; Millán, Ángel; Chapon, Laurent C.; Rodríguez-Carvajal, Juan

2017-09-01

Cs2FeCl5.D2O has been identified as a linear magnetoelectric material, although the correlation of this property with the magnetic structures of this compound has not been adequately studied. We have used single-crystal and powder neutron diffraction to obtain detailed information about its nuclear and magnetic structures. From the nuclear structure analysis, we describe the occurrence of a phase transition related to the reorganization of the [FeCl5.D2O] -2 ions and the Cs+ counterion. The magnetic structure was determined at zero magnetic field at 1.8 K using single-crystal diffraction and its temperature evolution was recorded using powder diffraction. The symmetry analysis of the magnetic structure is compatible with the occurrence of the magnetoelectric effect. Moreover, the evolution of the magnetic structure as a function of the external magnetic field has also been studied. The reorientation of the magnetic moments under applied external field along the easy axis (b axis at low temperature) is compatible with the occurrence of a spin-flop transition. The application of a magnetic field below TN compels the magnetic moments to flip from the b axis to the a c plane (with a small induced component along the b axis), for a critical magnetic field of ca. 1.2 T.

Magnetic phase transitions and magnetization reversal in MnRuP

NASA Astrophysics Data System (ADS)

Lampen-Kelley, P.; Mandrus, D.

The ternary phosphide MnRuP is an incommensurate antiferromagnetic metal crystallizing in the non-centrosymmetric Fe2P-type crystal structure. Below the Neel transition at 250 K, MnRuP exhibits hysteretic anomalies in resistivity and magnetic susceptibility curves as the propagation vectors of the spiral spin structure change discontinuously across T1 = 180 K and T2 = 100 K. Temperature-dependent X-ray diffraction data indicate that the first-order spin reorientation occurs in the absence of a structural transition. A strong magnetization reversal (MR) effect is observed upon cooling the system through TN in moderate dc magnetic fields. Positive magnetization is recovered on further cooling through T1 and maintained in subsequent warming curves. The field dependence and training of the MR effect in MnRuP will be discussed in terms of the underlying magnetic structures and compared to anomalous MR observed in vanadate systems. This work is supported by the Gordon and Betty Moore Foundation GBMF4416 and U.S. DOE, Office of Science, BES, Materials Science and Engineering Division.

Intra-Brillouin-zone bandgaps due to periodic misalignment in one-dimensional magnetophotonic crystals

NASA Astrophysics Data System (ADS)

Wang, Fei; Lakhtakia, Akhlesh

2008-01-01

One-dimensional (1D) magnetophotonic crystals (MPCs) can incorporate optical gyrotropy induced by a bias magnetic field, crystalline misalignment, and differential linear birefringence in a single photonic-crystal structure. A 1D MPC whose unit cell contains two layers—one magnetophotonic, the other not—displays intra-Brillouin-zone photonic bandgaps (PBGs) in the Brillouin diagram. While the optical gyrotropy makes the PBG bandwidths tunable by a bias magnetic field, the bicrystalline misalignment modifies and can even trump this magnetic tunability. Magnetic tunability is greatly affected by a proper selection of the two materials; e.g., a large birefringence ratio between the two layers can dramatically enhance the magnetic tunability of the MPC. We also expect our 1D MPCs to be useful for detecting magnetic fields.

Modelling sodium cobaltate by mapping onto magnetic Ising model

NASA Astrophysics Data System (ADS)

Gemperline, Patrick; Morris, David Jonathan Pryce

Fast Ion conductors are a class of crystals that are frequently used as battery materials, especially in smart phones, laptops, and other portable devices. Sodium Cobalt Oxide, NaxCoO2, falls into this class of crystals, but is unique because it possesses the ability to act as a thermoelectric material and a superconductor at different concentrations of Na+. The crystal lattice is mapped onto an Ising Magnetic Spin model and a Monte-Carol Simulation is used to find the most energetically favorable configuration of spins. This spin configuration is mapped back to the crystal lattice resulting in the most stable crystal structure of Sodium Cobalt Oxide at various concentrations. Knowing the atomic structures of the crystals will aid in the research of the materials capabilities and the possible uses of the material commercially. Ohio Supercomputer Center. 1987. Ohio Supercomputer Center. Columbus OH: Ohio Supercomputer Center. and the John Hauck Foundation.

Neutron and X-ray single-crystal diffraction from protein microcrystals via magnetically oriented microcrystal arrays in gels.

PubMed

Tsukui, Shu; Kimura, Fumiko; Kusaka, Katsuhiro; Baba, Seiki; Mizuno, Nobuhiro; Kimura, Tsunehisa

2016-07-01

Protein microcrystals magnetically aligned in D2O hydrogels were subjected to neutron diffraction measurements, and reflections were observed for the first time to a resolution of 3.4 Å from lysozyme microcrystals (∼10 × 10 × 50 µm). This result demonstrated the possibility that magnetically oriented microcrystals consolidated in D2O gels may provide a promising means to obtain single-crystal neutron diffraction from proteins that do not crystallize at the sizes required for neutron diffraction structure determination. In addition, lysozyme microcrystals aligned in H2O hydrogels allowed structure determination at a resolution of 1.76 Å at room temperature by X-ray diffraction. The use of gels has advantages since the microcrystals are measured under hydrated conditions.

Crystal structure and magnetic properties of Mn substituted ludwigite Co 3O 2BO 3

NASA Astrophysics Data System (ADS)

Knyazev, Yu. V.; Ivanova, N. B.; Kazak, N. V.; Platunov, M. S.; Bezmaternykh, L. N.; Velikanov, D. А.; Vasiliev, А. D.; Ovchinnikov, S. G.; Yurkin, G. Yu.

2012-03-01

The needle shape single crystals Co3-x MnxO2BO3 with ludwigite structure have been prepared. According to the X-ray diffraction data the preferable character of distinct crystallographic positions occupation by Mn ions is established. Magnetization field and temperature dependencies are measured. Paramagnetic Curie temperature value Θ=-100 K points out the predominance of antiferromagnetic interactions. Spin-glass magnetic ordering takes the onset at TN=41 K. The crystallographic and magnetic properties of Co3O2BO3:Mn are compared with the same for the isostructural analogs Co3O2BO3 and CoO2BO3:Fe.

Crystal structure and electronic states of Co and Gd ions in a Gd0.4Sr0.6CoO2.85 single crystal

NASA Astrophysics Data System (ADS)

Platunov, M. S.; Dudnikov, V. A.; Orlov, Yu. S.; Kazak, N. V.; Solovyov, L. A.; Zubavichus, Ya. V.; Veligzhanin, A. A.; Dorovatovskii, P. V.; Vereshchagin, S. N.; Shaykhutdinov, K. A.; Ovchinnikov, S. G.

2016-02-01

X-ray diffraction and X-ray absorption near edge structure (XANES) spectra have been measured at the Co K-edge and Gd L 3-edge in GdCoO3 and Gd0.4Sr0.6CoO2.85 cobaltites. The effect of Sr substitution on the crystal structure and electronic and magnetic states of Co3+ ions in a Gd0.4Sr0.6CoO2.85 single crystal has been analyzed. The XANES measurements at the Co K-edge have not showed a noticeable shift of the absorption edge with an increase in the concentration of Sr. This indicates that the effective valence of cobalt does not change. An increase in the intensity of absorption at the Gd L 3-edge is due to an increase in the degree of hybridization of the Gd(5 d) and O(2 p) states. The effect of hole doping on the magnetic properties results in the appearance of the ferromagnetic component and in a significant increase in the magnetic moment.

Unconventional Magnetic Domain Structure in the Ferromagnetic Phase of MnP Single Crystals

NASA Astrophysics Data System (ADS)

Koyama, Tsukasa; Yano, Shin-ichiro; Togawa, Yoshihiko; Kousaka, Yusuke; Mori, Shigeo; Inoue, Katsuya; Kishine, Jun-ichiro; Akimitsu, Jun

2012-04-01

We have studied ferromagnetic (FM) structures in the FM phase of MnP single crystals by low-temperature Lorentz transmission electron microscopy and small-angle electron diffraction analysis. In Lorentz Fresnel micrographs, striped FM domain structures were observed at an external magnetic field less than 10 Oe in specimens with the ab-plane in their plane. From real- and reciprocal-space analyses, it was clearly identified that striped FM domains oriented to the c-axis appear with Bloch-type domain walls in the b-direction and order regularly along the a-axis with a constant separation less than 100 nm. Moreover, the magnetic chirality reverses in alternate FM domain walls. These specific spin configuration of striped FM domains will affect the magnetic phase transition from the FM phase to the proper screw spiral phase at low temperature or to the FAN phase in magnetic fields in MnP.

Synthesis and crystal structure of the solid solution Co3(SeO3)3-x(PO3OH)x(H2O) involving crystallographic split positions of Se4+ and P5+.

PubMed

Zimmermann, Iwan; Johnsson, Mats

2013-10-21

Three new cobalt selenite hydroxo-phosphates laying in the solid solution Co3(SeO3)3-x(PO3OH)x(H2O), with x = 0.8, x = 1.0, and x = 1.2 are reported. Single crystals were obtained by hydrothermal synthesis and the crystal structure was determined by single crystal X-ray diffraction. The structure can be described as a 3D framework having selenite and hydroxo-phosphate groups protruding into channels in the crystal structure. Se(4+) and P(5+) share a split position in the structure so that either SeO3 groups having a stereochemically active lone pair or tetrahedrally coordinated PO3OH groups are present. The OH-group is thus only present when the split position is occupied by P(5+). The crystal water is coordinated to a cobalt atom and TG and IR measurements show that the water and hydroxyl groups leave the structure at unusually high temperatures (>450 °C). Magnetic susceptibility measurements show antiferromagnetic coupling below 16 K and a magnetic moment of 4.02(3) μB per Co atom was observed.

Effect of cooling rate on magnetic domain structure and magnetic properties of Tb0.27Dy0.73Fe1.95 alloys solidified in high magnetic field

NASA Astrophysics Data System (ADS)

Liu, Tie; Dong, Meng; Gao, Pengfei; Xiao, Yubao; Yuan, Yi; Wang, Qiang

2018-05-01

In this work, Tb0.27Dy0.73Fe1.95 alloys were solidified in a high magnetic field of 4.4 T at various cooling rates. Changes in the magnetostriction, crystal orientation, magnetization, and magnetic domain of the solidified alloys were investigated. The application of the magnetic field can induce <111> orientation of (Tb, Dy)Fe2 phase. However, the effect of the magnetic field is strongly dependent on the cooling rate. The alloy solidified at 5 °C/min shows the highest magnetostriction, strongest <111> orientation, best contrast of light and dark in the domain image, and fastest magnetization, and followed in descending order by the alloys solidified at 1.5 °C/min and 60 °C/min. The change in the magnetostriction of the alloys can be attributed to the changes in crystal orientation and magnetic domain structure caused by both the magnetic field and cooling rate.

Crystal structures of tiotropium bromide and its monohydrate in view of combined solid-state nuclear magnetic resonance and gauge-including projector-augmented wave studies.

PubMed

Pindelska, Edyta; Szeleszczuk, Lukasz; Pisklak, Dariusz Maciej; Majka, Zbigniew; Kolodziejski, Waclaw

2015-07-01

Tiotropium bromide is an anticholinergic bronchodilator used in the management of chronic obstructive pulmonary disease. The crystal structures of this compound and its monohydrate have been previously solved and published. However, in this paper, we showed that those structures contain some major errors. Our methodology based on combination of the solid-state nuclear magnetic resonance (NMR) spectroscopy and quantum mechanical gauge-including projector-augmented wave (GIPAW) calculations of NMR shielding constants enabled us to correct those errors and obtain reliable structures of the studied compounds. It has been proved that such approach can be used not only to perform the structural analysis of a drug substance and to identify its polymorphs, but also to verify and optimize already existing crystal structures. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

The role of order-disorder transitions in the quest for molecular multiferroics: structural and magnetic neutron studies of a mixed valence iron(II)-iron(III) formate framework.

PubMed

Cañadillas-Delgado, Laura; Fabelo, Oscar; Rodríguez-Velamazán, J Alberto; Lemée-Cailleau, Marie-Hélène; Mason, Sax A; Pardo, Emilio; Lloret, Francesc; Zhao, Jiong-Peng; Bu, Xian-He; Simonet, Virginie; Colin, Claire V; Rodríguez-Carvajal, Juan

2012-12-05

Neutron diffraction studies have been carried out to shed light on the unprecedented order-disorder phase transition (ca. 155 K) observed in the mixed-valence iron(II)-iron(III) formate framework compound [NH(2)(CH(3))(2)](n)[Fe(III)Fe(II)(HCOO)(6)](n). The crystal structure at 220 K was first determined from Laue diffraction data, then a second refinement at 175 K and the crystal structure determination in the low temperature phase at 45 K were done with data from the monochromatic high resolution single crystal diffractometer D19. The 45 K nuclear structure reveals that the phase transition is associated with the order-disorder of the dimethylammonium counterion that is weakly anchored in the cavities of the [Fe(III)Fe(II)(HCOO)(6)](n) framework. In the low-temperature phase, a change in space group from P31c to R3c occurs, involving a tripling of the c-axis due to the ordering of the dimethylammonium counterion. The occurrence of this nuclear phase transition is associated with an electric transition, from paraelectric to antiferroelectric. A combination of powder and single crystal neutron diffraction measurements below the magnetic order transition (ca. 37 K) has been used to determine unequivocally the magnetic structure of this Néel N-Type ferrimagnet, proving that the ferrimagnetic behavior is due to a noncompensation of the different Fe(II) and Fe(III) magnetic moments.

Hydrothermal synthesis, crystal structure, luminescent and magnetic properties of a new mononuclear GdIII coordination complex

NASA Astrophysics Data System (ADS)

Coban, Mustafa Burak

2018-06-01

A new GdIII coordination complex, {[Gd(2-stp)2(H2O)6].2(4,4'-bipy).4(H2O)}, complex 1, (2-stp = 2-sulfoterephthalate anion and 4,4'-bipy = 4,4'-bipyridine), has been synthesized by hydrothermal method and characterized by elemental analysis, solid state UV-Vis and FT-IR spectroscopy, single-crystal X-ray diffraction, solid state photoluminescence and variable-temperature magnetic measurements. The crystal structure determination shows that GdIII ions are eight coordinated and adopt a distorted square-antiprismatic geometry. Molecules interacting through intra- and intermolecular (O-H⋯O, O-H⋯N) hydrogen bonds in complex 1, give rise to 3D hydrogen bonded structure and the discrete lattice 4,4'-bipy molecules occupy the channel of the 3D structure. π-π stacking interactions also exist 4,4'-bipy-4,4'-bipy and 4,4'-bipy-2-stp molecule rings in 3D structures. Additionally, solid state photoluminescence properties of complex 1 at room temperature have been investigated. Under the excitation of UV light (at 349 nm), the complex 1 exhibited green emissions (at 505 nm) of GdIII ion in the visible region. Furthermore, Variable-temperature magnetic susceptibility and isothermal magnetization as function of external magnetic field studies reveal that complex 1 displays possible antiferromagnetic interaction.

Structural study of quasi-one-dimensional vanadium pyroxene LiVSi{sub 2}O{sub 6} single crystals

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

Ishii, Yuto; Matsushita, Yoshitaka; Oda, Migaku

Single crystals of quasi-one-dimensional vanadium pyroxene LiVSi{sub 2}O{sub 6} were synthesized and the crystal structures at 293 K and 113 K were studied using X-ray diffraction experiments. We found a structural phase transition from the room-temperature crystal structure with space group C2/c to a low-temperature structure with space group P2{sub 1}/c, resulting from a rotational displacement of SiO{sub 4} tetrahedra. The temperature dependence of magnetic susceptibility shows a broad maximum around 116 K, suggesting an opening of the Haldane gap expected for one-dimensional antiferromagnets with S=1. However, an antiferromagnetic long-range order was developed below 24 K, probably caused by amore » weak inter-chain magnetic coupling in the compound. - Graphical abstract: Low temperature crystal structure of LiVSi{sub 2}O{sub 6} and an orbital arrangement within the V-O zig-zag chain along the c-axis. - Highlights: • A low temperature structure of LiVSi{sub 2}O{sub 6} was determined by single crystal X-ray diffraction measurements. • The origin of the structural transition is a rotational displacement of SiO{sub 4} tetrahedra. • The uniform orbital overlap in the V-O zigzag chain makes the system a quasi one-dimensional antiferromagnet.« less

Magnetism and structure of a half-metallic Heusler compound Co-Mn-Cr-Si

NASA Astrophysics Data System (ADS)

Huh, Yung; Joshi, Swarangi; Jain, Sanmati; Pathak, Ojas; Kharel, Parashu

Half metallic ferromagnetic Heusler compounds have a potential in the development of spintronic devices for its high spin polarization at the Fermi level and lattice structure compatibility. Heusler compounds based on cobalt are considered a good candidate for room temperature half-metals due to their high Curie temperature. Co2CrSi is one of such predicted half-metal, but it is meta-stable and difficult to synthesize in the desired crystal structure. We have successfully synthesized a Heusler compound Co2Mn0.5Cr0.5Si by using arc melting and rapid quenching followed by thermal treatment under high vacuum to control any parasitic contamination. Crystal X-ray diffraction pattern shows the samples crystallize in a cubic Heusler structure with some degrees of structural disorder. Curie temperatures of the prepared samples are observed well beyond room temperature near 900 K. Magnetic anomalies present in as-prepared samples are cleared, and its magnetic properties are improved by thermal treatment. This research is supported by Academic and Scholarly Excellence Funds, and Research/Scholarship Support Fund, South Dakota State University.

Epitaxial Ce and the magnetism of single-crystal Ce/Nd superlattices

NASA Astrophysics Data System (ADS)

Clegg, P. S.; Goff, J. P.; McIntyre, G. J.; Ward, R. C.; Wells, M. R.

2003-05-01

The chemical structure of epitaxial γ cerium and the chemical and magnetic structures of cerium/neodymium superlattices have been studied using x-ray and neutron diffraction techniques. The samples were grown using molecular-beam epitaxy, optimized to yield the desired Ce allotropes. The x-ray measurements show that, in the superlattices, both constituents adopt the dhcp structure and that the stacking sequence remains intact down to T˜2 K; these are the first measurements of magnetic ordering in single-crystal dhcp Ce. The magnetic structure of the superlattices with thicker Nd layers exhibit incommensurate order and ferromagnetism on separate sublattices in a similar manner to Nd under applied pressure. The sample with thickest Ce layers has a magnetic structure similar to bulk β Ce, which has commensurate transverse modulation with a propagation wave vector [1/2 0 0] and moments along the hexagonal a direction. These two types of magnetic order appear to be mutually exclusive. γ Ce is the high-temperature fcc phase of Ce, our single-phase epitaxial sample is observed to go through a new, but partial, structural transition not previously seen in the bulk material.

Single crystal growth and anisotropic magnetic properties of HoAl2Ge2

NASA Astrophysics Data System (ADS)

Matin, Md.; Mondal, Rajib; Thamizhavel, A.; Provino, A.; Manfrinetti, P.; Dhar, S. K.

2018-05-01

We have grown a single crystal of HoAl2Ge2, which crystallizes in the hexagonal CaAl2Si2 type structure with Ho ions in the trigonal coordination in the ab plane. The data obtained from the bulk measurement techniques of magnetization, heat capacity and transport reveal that HoAl2Ge2 orders antiferromagnetically at TN ˜6.5 K. The susceptibility below TN and isothermal magnetization at 2 K indicate the ab plane as the easy plane of magnetization. Heat capacity data reveal a prominent Schottky anomaly with a broad peak centered around 25 K, suggesting a relatively low crystal electric field (CEF) splitting. The electrical resistivity reveals the occurrence of a superzone gap below TN. The point charge model of the CEF is applied to the magnetization and the heat capacity data. While a good fit to the paramagnetic susceptibility is obtained, the CEF parameters do not provide a satisfactory fit to the isothermal magnetization at 2 K and the Schottky anomaly.

Complex magnetic order in the kagome ferromagnet Pr3Ru4Al12

NASA Astrophysics Data System (ADS)

Henriques, M. S.; Gorbunov, D. I.; Andreev, A. V.; Fabrèges, X.; Gukasov, A.; Uhlarz, M.; Petříček, V.; Ouladdiaf, B.; Wosnitza, J.

2018-01-01

In the hexagonal crystal structure of Pr3Ru4Al12 , the Pr atoms form a distorted kagome lattice, and their magnetic moments, are subject to competing exchange and anisotropy interactions. We performed magnetization, magnetic-susceptibility, specific-heat, electrical-resistivity, and neutron-scattering measurements. Pr3Ru4Al12 is a uniaxial ferromagnet with TC=39 K that displays a collinear magnetic structure (in the high-temperature range of the magnetically ordered state) for which the only crystallographic position of Pr is split into two sites carrying different magnetic moments. A spin-reorientation phase transition is found at 7 K. Below this temperature, part of the Pr moments rotate towards the basal plane, resulting in a noncollinear magnetic state with a lower magnetic symmetry. We argue that unequal RKKY exchange interactions competing with the crystal electric field lead to a moment instability and qualitatively explain the observed magnetic phases in Pr3Ru4Al12 .

Investigations of surface structural, dynamical, and magnetic properties of systems exhibiting multiferroicity, and topological phases by helium scattering spectroscopies

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

El-Batanouny, Maged

2015-08-03

We propose to investigate the surface structural, dynamics and magnetic properties of the novel class of topological insulator crystals, as well as crystals that exhibit multiferroicity, magnetoelectricity and thermoelectricity. Topological insulators (TIs) are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. These exotic metallic states are formed by topological conditions that also render the electrons travelling on such surfaces insensitive to scattering by impurities. The electronic quasi-particles populating the topological surface state are Dirac fermions; they have a linear dispersion and thus are massless just like photons. We propose to investigate the interaction of these massless Dirac fermions with the massive lattice in the newly discovered crystals, Bi2Se3, Bi2Te3 and Sb2Te3. We shall use inelastic helium beam scattering from surfaces to search for related signatures in surface phonon dispersions mappings that cover the entire surface Brillouin zone of these materials. Our recent investigations of the (001) surface of the multiferroic crystals (Li/Na)Cu2O2 revealed an anomalous surface structural behavior where surface Cumore » $$^{2+}$$ row rise above the surface plane as the crystal was cooled. Subsequent worming revealed the onset of a thermally activated incommensurate surface phase, driven by the elevated rows. We are currently investigating the structure of the magnetic phases in these quasi-one-dimensional magnetic rows. Multiferroics are excellent candidates for large magnetoelectric response. We propose to extend this investigation to the class of delafossites which are also multiferroics and have been investigated as good candidates for thermoelectric power devices. They are also typical triangular lattice antiferromagnets with geometric magnetic frustration that leads to helimagnetic structures.« less

Crystal growth and magnetic properties of equiatomic CeAl

NASA Astrophysics Data System (ADS)

Das, Pranab Kumar; Thamizhavel, A.

2015-03-01

Single crystal of CeAl has been grown by flux method using Ce-Al self-flux. Several needle like single crystals were obtained and the length of the needle corresponds to the [001] crystallographic direction. Powder x-ray diffraction revealed that CeAl crystallizes in orthorhombic CrB-type structure with space group Cmcm (no. 63). The magnetic properties have been investigated by means of magnetic susceptibility, isothermal magnetization, electrical transport, and heat capacity measurements. CeAl is found to order antiferromagnetically with a Neel temperature TN = 10 K. The magnetization data below the ordering temperature reveals two metamagentic transitions for fields less than 20 kOe. From the inverse magnetic susceptibility an effective moment of 2.66 μB/Ce has been estimated, which indicates that Ce is in its trivalent state. Electrical resistivity data clearly shows a sharp drop at 10 K due to the reduction of spin disorder scattering of conduction electrons thus confirming the magnetic ordering. The estimated residual resistivity ratio (RRR) is 33, thus indicating a good quality of the single crystal. The bulk nature of the magnetic ordering is also confirmed by heat capacity data. From the Schottky anomaly of the heat capacity we have estimated the crystal field level splitting energies of the (2J + 1) degenerate ground state as 25 K and 175 K respectively for the fist and second excited states.

Fe/Rh (100) multilayer magnetism probed by x-ray magnetic circular dichroism

NASA Astrophysics Data System (ADS)

Tomaz, M. A.; Ingram, D. C.; Harp, G. R.; Lederman, D.; Mayo, E.; O'brien, W. L.

1997-09-01

We report the layer-averaged magnetic moments of both Fe and Rh in sputtered Fe/Rh (100) multilayer thin films as measured by x-ray magnetic circular dichroism. We observe two distinct regimes in these films. The first is characterized by Rh moments of at least 1μB, Fe moments enhanced as much as 30% above bulk, and a bct crystal structure. The second regime is distinguished by sharp declines of both Fe and Rh moments accompanied by a transition to an fct crystal lattice. The demarcation between the two regions is identified as the layer thickness for which both bct and fct phases first coexist, which we term the critical thickness tcrit. We attribute the change in magnetic behavior to the structural transformation.

Magnetic and optical holonomic manipulation of colloids, structures and topological defects in liquid crystals for characterization of mesoscale self-assembly and dynamics

NASA Astrophysics Data System (ADS)

Varney, Michael C. M.

Colloidal systems find important applications ranging from fabrication of photonic crystals to direct probing of phenomena encountered in atomic crystals and glasses; topics of great interest for physicists exploring a broad range of scientific, industrial and biomedical fields. The ability to accurately control particles of mesoscale size in various liquid host media is usually accomplished through optical trapping methods, which suffer limitations intrinsic to trap laser intensity and force generation. Other limitations are due to colloid properties, such as optical absorptivity, and host properties, such as viscosity, opacity and structure. Therefore, alternative and/or novel methods of colloidal manipulation are of utmost importance in order to advance the state of the art in technical applications and fundamental science. In this thesis, I demonstrate a magnetic-optical holonomic control system to manipulate magnetic and optical colloids in liquid crystals and show that the elastic structure inherent to nematic and cholesteric liquid crystals may be used to assist in tweezing of particles in a manner impossible in other media. Furthermore, I demonstrate the utility of this manipulation in characterizing the structure and microrheology of liquid crystals, and elucidating the energetics and dynamics of colloids interacting with these structures. I also demonstrate the utility of liquid crystal systems as a table top model system to probe topological defects in a manner that may lead to insights into topologically related phenomena in other fields, such as early universe cosmology, sub-atomic and high energy systems, or Skrymionic structures. I explore the interaction of colloid surface anchoring with the structure inherent in cholesteric liquid crystals, and how this affects the periodic dynamics and localization metastability of spherical colloids undergoing a "falling" motion within the sample. These so called "metastable states" cause colloidal dynamics to deviate from Stokes-like behavior at very low Reynolds numbers and is understood by accounting for periodic landscapes of elastic interaction potential between the particle and cholesteric host medium due to surface anchoring. This work extends our understanding of how colloids interact with liquid crystals and topological defects, and introduces a powerful method of colloidal manipulation with many potential applications.

Structure, magnetic, and electrical properties of Zn1-xMnxO material

NASA Astrophysics Data System (ADS)

Sebayang, P.; Hulu, S. F.; Nasruddin, Aryanto, D.; Kurniawan, C.; Subhan, A.; Sudiro, T.; Ginting, M.

2017-07-01

ZnO and MnO2 powder were synthesized using solid state reaction method to produce Zn1-xMnxO materials. Effect of dopant concentrations at the material of Zn1-xMnxO (x = 0.015, 0.02, 0.025) to the change of crystal structure, electrical and magnetic properties was studied. The X-ray diffraction (XRD) result of the samples that were doped with Mn showed a hexagonal wurtzite polycrystalline structure. The addition of Mn dopant resulting the decrease of lattice parameters and peaks intensity. The significant increase of the peak intensity occurred at x = 0.02, which also indicated an increase in the crystal quality of ZnO. The change of the ZnO structure affected the electrical and magnetic properties of the samples.

Low carrier semiconductor like behavior in Lu3Ir4Ge13 single crystal

NASA Astrophysics Data System (ADS)

Kumar, Anil; Matteppanavar, Shidaling; Thamizhavel, A.; Ramakrishnan, S.

2018-04-01

Single crystal of Lu3Ir4Ge13 crystallizing in the Yb3Rh4Sn13-type cubic crystal structure has been grown by Czochralski method in a tetra-arc furnace. In this paper we report on the crystal structure, magnetic and transport properties of Lu3Ir4Ge13. The analysis of the powder x-ray diffraction (XRD) studies revealed that Lu3Ir4Ge13 crystallizes in a cubic structure with the space group Pm-3n, no. 223. The lattice parameter was obtained from the Rietveld refinement of the room temperature XRD data which amounts to 8.904 (3) Å with low R factors. The temperature dependence of the resistivity exhibited semiconductor like behavior till 1.8 K, with a broad hump around 15 - 62 K. This hump was observed in both warming and cooling cycle with a very small hysteresis, it may be due to the existence of structural transition from high - low symmetry. The temperature dependent magnetization data shows the diamagnetic behavior with an anomaly around 70 K, which is well supported by the derivative of resistivity data.

Improving the Quality of Protein Crystals Using Stirring Crystallization

NASA Astrophysics Data System (ADS)

Adachi, Hiroaki; Matsumura, Hiroyoshi; Niino, Ai; Takano, Kazufumi; Kinoshita, Takayoshi; Warizaya, Masaichi; Inoue, Tsuyoshi; Mori, Yusuke; Sasaki, Takatomo

2004-04-01

Recent reports state that a high magnetic field improves the crystal quality of bovine adenosine deaminase (ADA) with an inhibitor [Kinoshita et al.: Acta Cryst. D59 (2003) 1333]. In this paper, we examine the effect of stirring solution on ADA crystallization using a vapor-diffusion technique with rotary and figure-eight motion shakers. The probability of obtaining high-quality crystals is increased with stirring in a figure-eight pattern. Furthermore, rotary stirring greatly increased the probability of obtaining high-quality crystals, however, nucleation time was also increased. The crystal structure with the inhibitor was determined at a high resolution using a crystal obtained from a stirred solution. These results indicate that stirring with simple equipment is as useful as the high magnetic field technique for protein crystallization.

Filling the holes in the CaFe4As3 structure: Synthesis and magnetism of CaCo5As3

NASA Astrophysics Data System (ADS)

Rosa, P. F. S.; Scott, B. L.; Ronning, F.; Bauer, E. D.; Thompson, J. D.

2017-07-01

Here, we investigate single crystals of CaCo5As3 by means of single-crystal x-ray diffraction, microprobe, magnetic susceptibility, heat capacity, and pressure-dependent transport measurements. CaCo5As3 shares the same structure of CaFe4As3 with an additional Co atom filling a lattice vacancy and undergoes a magnetic transition at TM=16 K associated with a frustrated magnetic order. CaCo5As3 displays metallic behavior and its Sommerfeld coefficient (γ =70 mJ/mol K2) indicates a moderate enhancement of electron-electron correlations. Transport data under pressures to 2.5 GPa reveal a suppression of TM at a rate of -0.008 K/GPa. First-principles electronic structure calculations show a complex three-dimensional band structure and magnetic moments that depend on the local environment at each Co site. Our results are compared with previous data on CaFe4As3 and provide a scenario for a magnetically frustrated ground state in this family of compounds.

Electromagnetic response of dielectric nanostructures in liquid crystals

NASA Astrophysics Data System (ADS)

Amanaganti, S.; Chowdhury, D. R.; Ravnik, M.; Dontabhaktuni, J.

2018-02-01

Sub-wavelength periodic metallic nanostructures give rise to very interesting optical phenomena like effective refractive index, perfect absorption, cloaking, etc. However, such metallic structures result in high dissipative losses and hence dielectric nanostructures are being considered increasingly to be an efficient alternative to plasmonic materials. High refractive index (RI) dielectric nanostructures exhibit magnetic and electric resonances simultaneously giving rise to interesting properties like perfect magnetic mirrors, etc. In the present work, we study light-matter interaction of cubic dielectric structures made of very high refractive index material Te in air. We observe a distinct band-like structure in both transmission and reflection spectra resulting from the interaction between magnetic and electric dipolar modes. FDTD simulations using CST software are performed to analyse the different modes excited at the band frequencies. The medium when replaced with liquid crystal gives rise to asymmetry in the band structure emphasizing one of the dominant magnetic modes at resonance frequencies. This will help in achieving a greater control on the excitation of the predominant magnetic dipolar modes at resonance frequencies with applications as perfect magnetic mirrors.

Confined states in photonic-magnonic crystals with complex unit cell

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

Dadoenkova, Yu. S.; Novgorod State University, 173003 Veliky Novgorod; Donetsk Physical and Technical Institute of the National Academy of Sciences of Ukraine, 83114 Donetsk

2016-08-21

We have investigated multifunctional periodic structures in which electromagnetic waves and spin waves can be confined in the same areas. Such simultaneous localization of both sorts of excitations can potentially enhance the interaction between electromagnetic waves and spin waves. The system we considered has a form of one dimensional photonic-magnonic crystal with two types of magnetic layers (thicker and thinner ones) separated by sections of the dielectric photonic crystals. We focused on the electromagnetic defect modes localized in the magnetic layers (areas where spin waves can be excited) and decaying in the sections of conventional (nonmagnetic) photonic crystals. We showedmore » how the change of relative thickness of two types of the magnetic layers can influence on the spectrum of spin waves and electromagnetic defect modes, both localized in magnetic parts of the system.« less

Crystal structure, Raman scattering and magnetic properties of CuCr2-xZrxSe4 and CuCr2-xSnxSe4 selenospinels

NASA Astrophysics Data System (ADS)

Pinto, C.; Galdámez, A.; Barahona, P.; Moris, S.; Peña, O.

2018-06-01

Selenospinels, CuCr2-xMxSe4 (M = Zr and Sn), were synthesized via conventional solid-state reactions. The crystal structure of CuCr1.5Sn0.5Se4, CuCr1.7Sn0.3Se4, CuCr1.5Zr0.5Se4, and CuCr1.8Zr0.2Se4 were determined using single-crystal X-ray diffraction. All the phases crystallized in a cubic spinel-type structure. The chemical compositions of the single-crystals were examined using energy-dispersive X-ray analysis (EDS). Powder X-ray diffraction patterns of CuCr1.3Sn0.7Se4 and CuCr1.7Sn0.3Se4 were consistent with phases belonging to the Fd 3 bar m Space group. An analysis of the vibrational properties on the single-crystals was performed using Raman scattering measurements. The magnetic properties showed a spin glass behavior with increasing Sn content and ferromagnetic order for CuCr1.7Sn0.3Se4.

Temperature-driven Phase Transformation in Y3Co: Neutron Scattering and DFT Studies

NASA Astrophysics Data System (ADS)

Podlesnyak, A.; Ehlers, G.; Cao, H.; Matsuda, M.; Frontzek, M.; Zaharko, O.; Kazantsev, V. A.; Gubkin, A. F.; Baranov, N. V.

2013-03-01

The effects of a crystal structure deformation due to subtle atomic displacements have attracted much attention because they can result in colossal changes of the electronic and magnetic properties of solids. The R3Co binary intermetallic systems exhibit a number of complicated phenomena, including field-induced magnetic phase transitions (R=Er, Ho, Tb), giant magnetoresistance (R=Dy), a substantial magnetocaloric effect (R=Gd) and superconductivity (R=La). Contrary to previous studies that defined the ground state crystal structure of the entire R3Co series as orthorhombic Pnma, we find that Y3Co undergoes a structural phase transition upon cooling around Tc 160K. Density functional theory calculations reveal a dynamical instability of the Pnma structure of Y3Co. Employing inelastic neutron scattering measurements we find a strong damping of the (00 ξ) acoustic phonon mode below the critical temperature Tc. We suggest that some other members of the R3Co series (or even all of them) have ground state crystal symmetry lower than reported Pnma. This raises a question about the true magnetic structures and hence the influence of magnetic properties of the entire R3Co series. The research at ORNL was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

Progressive Transformation between Two Magnetic Ground States for One Crystal Structure of a Chiral Molecular Magnet.

PubMed

Li, Li; Nishihara, Sadafumi; Inoue, Katsuya; Kurmoo, Mohamedally

2016-03-21

We report the exceptional observation of two different magnetic ground states (MGS), spin glass (SG, T(B) = 7 K) and ferrimagnet (FI, T(C) = 18 K), for one crystal structure of [{Mn(II)(D/L-NH2ala)}3{Mn(III)(CN)6}]·3H2O obtained from [Mn(CN)6](3-) and D/L-aminoalanine, in contrast to one MGS for [{Mn(II)(L-NH2ala)}3{Cr(III)(CN)6}]·3H2O. They consist of three Mn(NH2ala) helical chains bridged by M(III)(CN)6 to give the framework with disordered water molecules in channels and between the M(III)(CN)6. Both MGS are characterized by a negative Weiss constant, bifurcation in ZFC-FC magnetizations, blocking of the moments, both components of the ac susceptibilities, and hysteresis. They differ in the critical temperatures, absolute magnetization for 5 Oe FC (lack of spontaneous magnetization for the SG), and the shapes of the hysteresis and coercive fields. While isotropic pressure increases both T(crit) and the magnetizations linearly and reversibly in each case, dehydration progressively transforms the FI into the SG as followed by concerted in situ magnetic measurements and single-crystal diffraction. The relative strengths of the two moderate Mn(III)-CN-Mn(II) antiferromagnetic (J1 and J2), the weak Mn(II)-OCO-Mn(II) (J3), and Dzyaloshinkii-Moriya antisymmetric (DM) interactions generate the two sets of characters. Examination of the bond lengths and angles for several crystals and their corresponding magnetic properties reveals a correlation between the distortion of Mn(III)(CN)6 and the MGS. SG is favored by higher magnetic anisotropy by less distorted Mn(III)(CN)6 in good accordance with the Mn-Cr system. This conclusion is also born out of the magnetization measurements on orientated single crystals with fields parallel and perpendicular to the unique c axis of the hexagonal space group.

Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway.

PubMed

Fernández de Luis, Roberto; Larrea, Edurne S; Orive, Joseba; Lezama, Luis; Arriortua, María I

2016-11-21

The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO 3 )(H 2 O)}(HTae)(Bpy) (H 2 Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4'-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal-organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a two-dimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible structure transformation above 100 °C. Despite the loss of crystallinity, the spectroscopic studies indicate that the main building blocks of the crystal framework are retained after the transformation. The hydrogen-bonding network not only plays a crucial role stabilizing the crystal structure but also is an important pathway for magnetic exchange transmission. In fact, the magnetic susceptibility curves indicate that after the loss of coordinated water molecules, and hence the collapse of the hydrogen-bonding network, the weak anti-ferromagnetic coupling observed in the initial compound is broken. The electron paramagnetic resonance spectra are the consequence of the average signals from Cu(II) with different orientations, indicating that the magnetic coupling is effective between them. In fact, X- and Q-band data are reflecting different situations; the X-band spectra show the characteristics of an exchange g-tensor, while the Q-band signals are coming from both the exchange and the molecular g-tensors.

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

Han, Fei; Wan, Xiangang; Phelan, Daniel

ZrCuSi 2-type CePd 1-xBi 2 crystals were obtained from excess Bi flux. Magnetic susceptibility measurements reveal that CePd 1-xBi 2 is a highly anisotropic antiferromagnet with transition temperature at 6 K, and a magnetic-field-induced metamagnetic transition at 5 T. An enhanced Sommerfeld coefficient of γ of 0.199 J-mol-Ce -1K -2 obtained from specific heat measurements suggests a moderate Kondo effect in CePd 1-xBi 2. In addition to the antiferromagnetic peak the resistivity curve shows a shoulder-like behavior which could be attributed to the presence of Kondo effect and crystal-electric-field effects in this compound. Magnetoresistance and Hall effect measurements suggest anmore » interplay between Kondo and crystal-electric-field effects which reconstructs the Fermi surface topology of CePd 1-xBi 2 around 75 K. Electronic structure calculations reveal the Pd vacancies are important to the magnetic structure and enhance the crystal-electric-field effects which quench the orbital moment of Ce at low temperatures.« less

Crystal, magnetic, calorimetric and electronic structure investigation of GdScGe1-x Sb x compounds

NASA Astrophysics Data System (ADS)

Guillou, F.; Pathak, A. K.; Hackett, T. A.; Paudyal, D.; Mudryk, Y.; Pecharsky, V. K.

2017-12-01

Experimental investigations of crystal structure, magnetism and heat capacity of compounds in the pseudoternary GdScGe-GdScSb system combined with density functional theory projections have been employed to clarify the interplay between the crystal structure and magnetism in this series of RTX materials (R  =  rare-earth, T   =  transition metal and X  =  p-block element). We demonstrate that the CeScSi-type structure adopted by GdScGe and CeFeSi-type structure adopted by GdScSb coexist over a limited range of compositions 0.65 ≤slant x ≤slant 0.9 . Antimony for Ge substitutions in GdScGe result in an anisotropic expansion of the unit cell of the parent that is most pronounced along the c axis. We believe that such expansion acts as the driving force for the instability of the double layer CeScSi-type structure of the parent germanide. Extensive, yet limited Sb substitutions 0 ≤slant x < 0.65 lead to a strong reduction of the Curie temperature compared to the GdScGe parent, but without affecting the saturation magnetization. With a further increase in Sb content, the first compositions showing the presence of the CeFeSi-type structure of the antimonide, x ≈ 0.7 , coincide with the appearance of an antiferromagnetic phase. The application of a finite magnetic field reveals a jump in magnetization toward a fully saturated ferromagnetic state. This antiferro-ferromagnetic transformation is not associated with a sizeable latent heat, as confirmed by heat capacity measurements. The electronic structure calculations for x = 0.75 indicate that the key factor in the conversion from the ferromagnetic CeScSi-type to the antiferromagnetic CeFeSi-type structure is the disappearance of the induced magnetic moments on Sc. For the parent antimonide, heat capacity measurements indicate an additional transition below the main antiferromagnetic transition.

Crystal, magnetic, calorimetric and electronic structure investigation of GdScGe 1–xSb x compounds

DOE PAGES

Guillou, F.; Pathak, A. K.; Hackett, T. A.; ...

2017-11-09

Here, experimental investigations of crystal structure, magnetism and heat capacity of compounds in the pseudoternary GdScGe-GdScSb system combined with density functional theory projections have been employed to clarify the interplay between the crystal structure and magnetism in this series of RTX materials (R = rare-earth,more » $ T$ = transition metal and X = p-block element). We demonstrate that the CeScSi-type structure adopted by GdScGe and CeFeSi-type structure adopted by GdScSb coexist over a limited range of compositions $$0.65 \\leqslant x \\leqslant 0.9$$ . Antimony for Ge substitutions in GdScGe result in an anisotropic expansion of the unit cell of the parent that is most pronounced along the c axis. We believe that such expansion acts as the driving force for the instability of the double layer CeScSi-type structure of the parent germanide. Extensive, yet limited Sb substitutions $$0 \\leqslant x < 0.65$$ lead to a strong reduction of the Curie temperature compared to the GdScGe parent, but without affecting the saturation magnetization. With a further increase in Sb content, the first compositions showing the presence of the CeFeSi-type structure of the antimonide, $$x \\approx 0.7$$ , coincide with the appearance of an antiferromagnetic phase. The application of a finite magnetic field reveals a jump in magnetization toward a fully saturated ferromagnetic state. This antiferro–ferromagnetic transformation is not associated with a sizeable latent heat, as confirmed by heat capacity measurements. The electronic structure calculations for $x = 0.75$ indicate that the key factor in the conversion from the ferromagnetic CeScSi-type to the antiferromagnetic CeFeSi-type structure is the disappearance of the induced magnetic moments on Sc. For the parent antimonide, heat capacity measurements indicate an additional transition below the main antiferromagnetic transition.« less

Crystal, magnetic, calorimetric and electronic structure investigation of GdScGe 1–xSb x compounds

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

Guillou, F.; Pathak, A. K.; Hackett, T. A.

Here, experimental investigations of crystal structure, magnetism and heat capacity of compounds in the pseudoternary GdScGe-GdScSb system combined with density functional theory projections have been employed to clarify the interplay between the crystal structure and magnetism in this series of RTX materials (R = rare-earth,more » $ T$ = transition metal and X = p-block element). We demonstrate that the CeScSi-type structure adopted by GdScGe and CeFeSi-type structure adopted by GdScSb coexist over a limited range of compositions $$0.65 \\leqslant x \\leqslant 0.9$$ . Antimony for Ge substitutions in GdScGe result in an anisotropic expansion of the unit cell of the parent that is most pronounced along the c axis. We believe that such expansion acts as the driving force for the instability of the double layer CeScSi-type structure of the parent germanide. Extensive, yet limited Sb substitutions $$0 \\leqslant x < 0.65$$ lead to a strong reduction of the Curie temperature compared to the GdScGe parent, but without affecting the saturation magnetization. With a further increase in Sb content, the first compositions showing the presence of the CeFeSi-type structure of the antimonide, $$x \\approx 0.7$$ , coincide with the appearance of an antiferromagnetic phase. The application of a finite magnetic field reveals a jump in magnetization toward a fully saturated ferromagnetic state. This antiferro–ferromagnetic transformation is not associated with a sizeable latent heat, as confirmed by heat capacity measurements. The electronic structure calculations for $x = 0.75$ indicate that the key factor in the conversion from the ferromagnetic CeScSi-type to the antiferromagnetic CeFeSi-type structure is the disappearance of the induced magnetic moments on Sc. For the parent antimonide, heat capacity measurements indicate an additional transition below the main antiferromagnetic transition.« less

Exploratory Solid-State Synthesis of Uranium Chalcogenides and Mixed Anion Uranium Chalcogenides

NASA Astrophysics Data System (ADS)

Ward, Matthew David

Several uranium chalcogenides and mixed anion uranium chalcogenides have been synthesized by solid-state synthetic methods. Structural determinations were carried out via single-crystal X-ray diffraction. Some of these compounds have been further characterized by magnetic measurements, optical properties measurements, Raman spectroscopy, resistivity measurements, XANES and XPS. Eight compounds of the composition MU8Q17 were synthesized and characterized by single-crystal X-ray diffraction. All of these compounds crystallize in the CrU8S17 structure type. XANES measurements indicate that ScU8S17 contains Sc3+ and must be charge balanced with some amount of U 3+. Two compounds of the composition ATiU3Te9 crystallize as black rectangular plates. From single-crystal magnetic measurements, CsTiU 3Te9 is consistent with antiferromagnetic coupling between magnetic U atoms. The uranium chalcogenide compounds NiUS3 and Cr4US 8 were synthesized from reaction of the elements in various fluxes. NiUS3 crystallizes in the GdFeO3 structure type. Cr 4US8 crystallizes in the orthorhombic space group D - Pnma and its structure is related to that of Li4UF 8. The compounds Rh2U6S15, Cs 2Ti2U6Se15, and Cs2Cr 2U6Se15 crystallize as black prisms in the cubic space group O-Im3m. Magnetic measurements on Cs 2Cr2U6Se15 give a value for the Weiss temperature, θWeiss, of 57.59 K, indicative of ferromagnetic coupling. Black plates of CsScU(Se2)Se3 were synthesized from the reaction of the elements in a CsCl flux. CsScU(Se2)Se 3 crystallizes in the orthorhombic space group D- Cmcm . Magnetic susceptibility measurements on CsScU(Se2)Se 3 indicate three regions of magnetic response. The uranium double salt Cs5[U2(μ-S 2)2Cl8]I crystallizes as red plates. Cs 5[U2(μ-S2)2Cl 8]I displays optical anisotropy with band gap energies of 1.99 eV and 2.08 eV along the [001] and [100] polarizations. The uranium oxychalcogenides U7O2Se12 and Na2Ba2(UO2)S4 were synthesized by intentional oxygen contamination. The structure of U7O 2Se12 is related to the previously reported U7Q 12. Na2Ba2(UO2)S4 contains isolated uranyl polyhedra in which each uranium atom may be assigned an oxidation state of +6. The four uranium(IV) chlorophosphates, UCl4(POCl3), [U2Cl9][PCl4], UCl3(PO2Cl 2), and U2Cl8(POCl3) were synthesized in an effort to synthesize new novel uranyl sulfides. All are unstable, but UCl4(POCl3) is the thermodynamically favorable phase.

Fragment-Based Electronic Structure Approach for Computing Nuclear Magnetic Resonance Chemical Shifts in Molecular Crystals.

PubMed

Hartman, Joshua D; Beran, Gregory J O

2014-11-11

First-principles chemical shielding tensor predictions play a critical role in studying molecular crystal structures using nuclear magnetic resonance. Fragment-based electronic structure methods have dramatically improved the ability to model molecular crystal structures and energetics using high-level electronic structure methods. Here, a many-body expansion fragment approach is applied to the calculation of chemical shielding tensors in molecular crystals. First, the impact of truncating the many-body expansion at different orders and the role of electrostatic embedding are examined on a series of molecular clusters extracted from molecular crystals. Second, the ability of these techniques to assign three polymorphic forms of the drug sulfanilamide to the corresponding experimental (13)C spectra is assessed. This challenging example requires discriminating among spectra whose (13)C chemical shifts differ by only a few parts per million (ppm) across the different polymorphs. Fragment-based PBE0/6-311+G(2d,p) level chemical shielding predictions correctly assign these three polymorphs and reproduce the sulfanilamide experimental (13)C chemical shifts with 1 ppm accuracy. The results demonstrate that fragment approaches are competitive with the widely used gauge-invariant projector augmented wave (GIPAW) periodic density functional theory calculations.

Crystal Structure and Magnetic Properties of New Cubic Quaternary Compounds RT2Sn2Zn18 (R = La, Ce, Pr, and Nd, and T = Co and Fe)

NASA Astrophysics Data System (ADS)

Isikawa, Yosikazu; Mizushima, Toshio; Ejiri, Jun-ichi; Kitayama, Shiori; Kumagai, Keigou; Kuwai, Tomohiko; Bordet, Pierre; Lejay, Pascal

2015-07-01

The new cubic quaternary intermetallic compounds RT2Sn2Zn18 (R = La, Ce, Pr, and Nd, and T = Co and Fe) were synthesized by the mixture-metal flux method using Zn and Sn. The crystal structure was investigated by powder X-ray diffraction and with a four-circle X-ray diffractometer using single crystals. The space group of the compounds is Fdbar{3}m (No. 227). The rare-earth atom is at the cubic site which is the center of a cage composed of Zn and Sn atoms. The crystal structure is the same as the CeCr2Al20-type crystal structure except the atoms at the 16c site, i.e., the Zn atoms at the 16c site are completely replaced by Sn atoms, indicating that the compounds are crystallographically new ordered quaternary compounds. The lattice parameter a and the physical properties of the magnetic susceptibility χ, the magnetization M, and the specific heat C of these cubic caged compounds were investigated. LaCo2Sn2Zn18 and LaFe2Sn2Zn18 are enhanced Pauli paramagnets that originate from the Co and Fe itinerant 3d electrons. CeCo2Sn2Zn18 and CeFe2Sn2Zn18 are also enhanced Pauli paramagnets that originate from both the 3d electrons and Ce 4f electrons. PrCo2Sn2Zn18 and PrFe2Sn2Zn18 are nonmagnetic materials with huge values of C divided by temperature, which indicates that the ground state of Pr ions is a non-Kramers' doublet. NdCo2Sn2Zn18 and NdFe2Sn2Zn18 are magnetic materials with the Néel temperatures of 1.0 and 3.8 K, respectively. All eight compounds have large magnetic moments of Co/Fe in the paramagnetic temperature region, and thus their magnetic moments are inferred to be magnetically frustrating owing to the pyrochlore lattice in the low-temperature region.

Magneto-structural correlations in rare-earth cobalt pnictides

NASA Astrophysics Data System (ADS)

Thompson, Corey Mitchell

Magnetic materials are used in many applications such as credit cards, hard drives, electric motors, sensors, etc. Although a vast range of magnetic solids is available for these purposes, our ability to improve their efficiency and discover new materials remains paramount to the sustainable progress and economic profitability in many technological areas. The search for magnetic solids with improved performance requires fundamental understanding of correlations between the structural, electronic, and magnetic properties of existing materials, as well as active exploratory synthesis that targets the development of new magnets. Some of the strongest permanent magnets, Nd 2Fe14B, SmCo5, and Sm2Co17, combine transition and rare-earth metals, benefiting from the strong exchange between the 4f and 3d magnetic sublattices. Although these materials have been studied in great detail, the development of novel magnets requires thorough investigation of other 3d-4 f intermetallics, in order to gain further insights into correlations between their crystal structures and magnetic properties. Among many types of intermetallic materials, ternary pnictides RCo 2Pn2 (R = La, Ce, Pr, Nd; Pn = P, As) are of interest because, despite their simple crystal structures, they contain two magnetic sublattices, exchange interactions between which may lead to rich and unprecedented magnetic behavior. Nevertheless, magnetism of these materials was studied only to a limited extent, especially as compared to the extensive studies of their silicide and germanide analogues. The ThCr2Si2 structure type, to which these ternary pnictides belong, is one of the most ubiquitous atomic arrangements encountered among intermetallic compounds. It accounts for over 1000 known intermetallics and has received increased attention due to the recently discovered FeAs-based superconductors. This dissertation is devoted to the investigation of magnetostructural relationships and anomalous magnetic behaviors in rare earth-cobalt pnictides with the ThCr2Si2 structure type, as well as to the development of new synthetic approaches to the preparation of such materials. We use iso- and aliovalent substitutions as effective tools to probe magnetostructural correlations and establish general trends in the magnetic behavior of RCo 2Pn2 phases. The modification of the electronic band structure, which correlates with the changes in the crystal structure of the material, is found to act as the driving force that dictates the magnetic properties of these itinerant systems. We demonstrate how this knowledge can be used effectively to achieve diverse magnetic properties and relate them to specific structural characteristics of materials.

Compositional Tuning, Crystal Growth, and Magnetic Properties of Iron Phosphate Oxide

NASA Astrophysics Data System (ADS)

Tarne, Michael

Iron phosphate oxide, Fe3PO4O 3, is a crystalline solid featuring magnetic Fe3+ ions on a complex lattice composed of closely-spaced triangles. Previous work from our research group on this compound has proposed a helical magnetic structure below T = 163 K attributed to J1 - J2 competing interactions between nearest-neighbor and next-nearest-neighbor iron atoms. This was based on neutron powder diffraction featuring unique broad, flat-topped magnetic reflections due to needle-like magnetic domains. In order to confirm the magnetic structure and origins of frustration, this thesis will expand upon the research focused on this compound. The first chapter focuses on single crystal growth of Fe3PO 4O3. While neutron powder diffraction provides insight to the magnetic structure, powder and domain averaging obfuscate a conclusive structure for Fe3PO4O3 and single crystal neutron scattering is necessary. Due to the incongruency of melting, single crystal growth has proven challenging. A number of techniques including flux growth, slow cooling, and optical floating zone growth were attempted and success has been achieved via heterogenous chemical vapor transport from FePO 4 using ZrCl4 as a transport agent. These crystals are of sufficient size for single crystal measurements on modern neutron diffractometers. Dilution of the magnetic sublattice in frustrated magnets can also provide insight into the nature of competing spin interactions. Dilution of the Fe 3+ lattice in Fe3PO4O3 is accomplished by substituting non-magnetic Ga3+ to form the solid solution series Fe3-xGaxPO4O3 with x = 0, 0.012, 0.06, 0.25, 0.5, 1.0, 1.5. The magnetic susceptibility and neutron powder diffraction data of these compounds are presented. A dramatic decrease of the both the helical pitch length and the domain size is observed with increasing x; for x > 0.5, the compounds lack long range magnetic order. The phases that do exhibit magnetic order show a decrease in helical pitch with increasing x as determined from the magnitude of the magnetic propagation vector. This trend can be qualitatively reproduced by increasing the ratio of J2/ J1 in the Heisenberg model. Intriguingly, the domain size extracted from peak broadening of the magnetic reflections is nearly equal to the pitch length for each value of x, which suggests that the two qualities are linked in this unusual antiferromagnet. The last chapter focuses on the oxyfluoride Fe3PO7-x Fx. Through fluorination using low-temperature chimie douce reactions with polytetrafluoroethylene, the magnetic properties show changes in the magnetic susceptibility, isothermal magnetization, and neutron powder diffraction. The magnetic susceptibility shows a peak near T = 13 K and a zero field cooled/field cooled splitting at T = 78 K. The broad, flat-topped magnetic reflections in the powder neutron diffraction exhibit a decrease in width and increase in intensity. The changes in the neutron powder diffraction suggest an increase in correlation length in the ab plane of the fluorinated compound. Iron phosphate oxide is a unique lattice showing a rich magnetic phase diagram in both the gallium-substituted and fluorinated species. While mean-field interactions are sufficient to describe interactions in the solid solution series Fe3-xGaxPO4O3, the additional magnetic transitions in Fe3PO7-xFx suggest a more complicated set of interactions.

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

Jadav, Mudra; Patel, Rajesh, E-mail: rjp@mkbhavuni.edu.in, E-mail: rpat7@yahoo.co

Here we present a technique using magnetic nanofluid to induce bidispersed suspension of nonmagnetic particles to assemble into colloidal chain, triangle, rectangle, ring-flower configurations. By changing the amplitude and direction of the magnetic field, we could tune the structure of nonmagnetic particles in magnetic nanofluid. The structures are assembled using magneto static interactions between effectively nonmagnetic particles dispersed in magnetizable magnetic nanofluid. The assembly of complex structures out of simple colloidal building blocks is of practical interest in photonic crystals and DNA biosensors.

Electrical, Thermal, and Magnetic Properties of Single Crystal CaMn2O4 Marokite

NASA Astrophysics Data System (ADS)

White, B. D.; Neumeier, J. J.; Souza, J. A.; Chiorescu, C.; Cohn, J. L.

2008-03-01

CaMn2O4 was first described [1] in 1963 as a natural mineral called Marokite. Since its discovery, it has been studied as a minor structural impurity phase in CMR- related CaMnO3 and for its structural similarities to high-pressure phases of spinel-oxide compounds. However, little attention has previously been paid to physical properties beyond its temperature-dependent magnetization. We will present a detailed physical properties study of CaMn2O4 single crystals grown by the optical floating zone method. [2] These measurements, several of which display anisotropy as a result of an orthorhombic crystal structure, include electrical transport, thermal transport, thermal expansion, heat capacity, and magnetization. [1] C. Gaudefroy, G. Jouravsky, F. Permingeat, Bull. Soc. Franc. Min'er. Crist. 86 (1963) 359. [2] B. D. White, C. A. M. dos Santos, J. A. Souza, K. J. McClellan, J. J. Neumeier submitted to J. Cryst. Growth.

Electronic, magnetic, and magnetocrystalline anisotropy properties of light lanthanides

DOE PAGES

Hackett, Timothy A.; Baldwin, D. J.; Paudyal, Durga

2017-05-17

Theoretical understanding of interactions between localized and mobile electrons and the crystal environment in light lanthanides is important because of their key role in much needed magnetic anisotropy in permanent magnet materials that have a great impact in automobile and wind turbine applications. We report electronic, magnetic, and magnetocrystalline properties of these basic light lanthanide elements studied from advanced density functional theory (DFT) calculations. We find that the inclusion of onsite 4f electron correlation and spin orbit coupling within the full-potential band structure is needed to understand the unique magnetocrystalline properties of these light lanthanides. The onsite electron correlation, spinmore » orbit coupling, and full potential for the asphericity of charge densities must be taken into account for the proper treatment of 4f states. We find the variation of total energy as a function of lattice constants that indicate multiple structural phases in Ce contrasting to a single stable structure obtained in other light lanthanides. The 4f orbital magnetic moments are partially quenched as a result of crystalline electric field splitting that leads to magnetocrystalline anisotropy. The charge density plots have similar asphericity and environment in Pr and Nd indicating similar magnetic anisotropy. However, Ce and Sm show completely different asphericity and environment as both orbital moments are significantly quenched. In addition, the Fermi surface structures exemplified in Nd indicate structural stability and unravel a cause of anisotropy. The calculated magnetocrystalline anisotropy energy (MAE) reveals competing c-axis and in-plane anisotropies, and also predicts possibilities of unusual structural deformations in light lanthanides. The uniaxial magnetic anisotropy is obtained in the double hexagonal closed pack structures of the most of the light lanthanides, however, the anisotropy is reduced or turned to planar in the low symmetry structures. As a result, through crystal field calculations we also illustrate the crystal field ground state 4f multiplets of light lanthanides.« less

Electronic, magnetic, and magnetocrystalline anisotropy properties of light lanthanides

NASA Astrophysics Data System (ADS)

Hackett, Timothy A.; Baldwin, D. J.; Paudyal, D.

2017-11-01

Theoretical understanding of interactions between localized and mobile electrons and the crystal environment in light lanthanides is important because of their key role in much needed magnetic anisotropy in permanent magnet materials that have a great impact in automobile and wind turbine applications. We report electronic, magnetic, and magnetocrystalline properties of these basic light lanthanide elements studied from advanced density functional theory (DFT) calculations. We find that the inclusion of onsite 4f electron correlation and spin orbit coupling within the full-potential band structure is needed to understand the unique magnetocrystalline properties of these light lanthanides. The onsite electron correlation, spin orbit coupling, and full potential for the asphericity of charge densities must be taken into account for the proper treatment of 4f states. We find the variation of total energy as a function of lattice constants that indicate multiple structural phases in Ce contrasting to a single stable structure obtained in other light lanthanides. The 4f orbital magnetic moments are partially quenched as a result of crystalline electric field splitting that leads to magnetocrystalline anisotropy. The charge density plots have similar asphericity and environment in Pr and Nd indicating similar magnetic anisotropy. However, Ce and Sm show completely different asphericity and environment as both orbital moments are significantly quenched. In addition, the Fermi surface structures exemplified in Nd indicate structural stability and unravel a cause of anisotropy. The calculated magnetocrystalline anisotropy energy (MAE) reveals competing c-axis and in-plane anisotropies, and also predicts possibilities of unusual structural deformations in light lanthanides. The uniaxial magnetic anisotropy is obtained in the double hexagonal closed pack structures of the most of the light lanthanides, however, the anisotropy is reduced or turned to planar in the low symmetry structures. Through crystal field calculations we also illustrate the crystal field ground state 4f multiplets of light lanthanides.

Electronic, magnetic, and magnetocrystalline anisotropy properties of light lanthanides

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

Hackett, Timothy A.; Baldwin, D. J.; Paudyal, Durga

Theoretical understanding of interactions between localized and mobile electrons and the crystal environment in light lanthanides is important because of their key role in much needed magnetic anisotropy in permanent magnet materials that have a great impact in automobile and wind turbine applications. We report electronic, magnetic, and magnetocrystalline properties of these basic light lanthanide elements studied from advanced density functional theory (DFT) calculations. We find that the inclusion of onsite 4f electron correlation and spin orbit coupling within the full-potential band structure is needed to understand the unique magnetocrystalline properties of these light lanthanides. The onsite electron correlation, spinmore » orbit coupling, and full potential for the asphericity of charge densities must be taken into account for the proper treatment of 4f states. We find the variation of total energy as a function of lattice constants that indicate multiple structural phases in Ce contrasting to a single stable structure obtained in other light lanthanides. The 4f orbital magnetic moments are partially quenched as a result of crystalline electric field splitting that leads to magnetocrystalline anisotropy. The charge density plots have similar asphericity and environment in Pr and Nd indicating similar magnetic anisotropy. However, Ce and Sm show completely different asphericity and environment as both orbital moments are significantly quenched. In addition, the Fermi surface structures exemplified in Nd indicate structural stability and unravel a cause of anisotropy. The calculated magnetocrystalline anisotropy energy (MAE) reveals competing c-axis and in-plane anisotropies, and also predicts possibilities of unusual structural deformations in light lanthanides. The uniaxial magnetic anisotropy is obtained in the double hexagonal closed pack structures of the most of the light lanthanides, however, the anisotropy is reduced or turned to planar in the low symmetry structures. As a result, through crystal field calculations we also illustrate the crystal field ground state 4f multiplets of light lanthanides.« less

Heat capacity, resistivity, and angular dependent magnetization studies of single crystal Nd 1 + ϵ Fe 4 B 4 for ϵ ≈ 1 7

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

Conner, Benjamin S.; Susner, Michael A.; UES Inc., Beavercreek, OH

Advances in crystal growth have allowed for synthesis of large single crystals of Nd 1+ϵFe 4B 4, a well-known phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd 1+ϵFe 4B 4 sample with a distribution of ϵ that skews towards the solubility limit of Nd near ϵ ≈ 17. Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previouslymore » reported values in the Nd 1+ϵFe 4B 4 system. Here, we also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed.« less

Heat capacity, resistivity, and angular dependent magnetization studies of single crystal Nd 1 + ϵ Fe 4 B 4 for ϵ ≈ 1 7

DOE PAGES

Conner, Benjamin S.; Susner, Michael A.; UES Inc., Beavercreek, OH; ...

2017-04-04

Advances in crystal growth have allowed for synthesis of large single crystals of Nd 1+ϵFe 4B 4, a well-known phase with a modulated structure. As a result we are able to report heat capacity and resistivity measurements on a single crystal Nd 1+ϵFe 4B 4 sample with a distribution of ϵ that skews towards the solubility limit of Nd near ϵ ≈ 17. Heat capacity measurements show evidence of crystal field splitting at temperatures higher than the long-range ferromagnetic Curie temperature. Heat capacity, resistivity, and magnetization measurements all confirm a Curie temperature of 7 K which is lower than previouslymore » reported values in the Nd 1+ϵFe 4B 4 system. Here, we also perform measurements of the angular dependence of the magnetization and discover behavior associated with the magnetic anisotropy that is inconsistent with the simple description previously proposed.« less

High-pressure synthesis, crystal structure and magnetic properties of TlCrO3 perovskite.

PubMed

Yi, Wei; Matsushita, Yoshitaka; Katsuya, Yoshio; Yamaura, Kazunari; Tsujimoto, Yoshihiro; Presniakov, Igor A; Sobolev, Alexey V; Glazkova, Yana S; Lekina, Yuliya O; Tsujii, Naohito; Nimori, Shigeki; Takehana, Kanji; Imanaka, Yasutaka; Belik, Alexei A

2015-06-21

TlMO(3) perovskites (M(3+) = transition metals) are exceptional members of trivalent perovskite families because of the strong covalency of Tl(3+)-O bonds. Here we report on the synthesis, crystal structure and properties of TlCrO(3) investigated by Mössbauer spectroscopy, specific heat, dc/ac magnetization and dielectric measurements. TlCrO(3) perovskite is prepared under high pressure (6 GPa) and high temperature (1500 K) conditions. The crystal structure of TlCrO(3) is refined using synchrotron X-ray powder diffraction data: space group Pnma (no. 62), Z = 4 and lattice parameters a = 5.40318(1) Å, b = 7.64699(1) Å and c = 5.30196(1) Å at 293 K. No structural phase transitions are found between 5 and 300 K. TlCrO(3) crystallizes in the GdFeO(3)-type structure similar to other members of the perovskite chromite family, ACrO(3) (A(3+) = Sc, In, Y and La-Lu). The unit cell volume and Cr-O-Cr bond angles of TlCrO(3) are close to those of DyCrO(3); however, the Néel temperature of TlCrO(3) (TN≈ 89 K) is much smaller than that of DyCrO(3) and close to that of InCrO(3). Isothermal magnetization studies show that TlCrO(3) is a fully compensated antiferromagnet similar to ScCrO(3) and InCrO(3), but different from RCrO(3) (R(3+) = Y and La-Lu). Ac and dc magnetization measurements with a fine step of 0.2 K reveal the existence of two Néel temperatures with very close values at T(N2) = 87.0 K and T(N1) = 89.3 K. Magnetic anomalies near T(N2 )are suppressed by static magnetic fields and by 5% iron doping.

Magnetism out of antisite disorder in the J =0 compound Ba2YIrO6

NASA Astrophysics Data System (ADS)

Chen, Q.; Svoboda, C.; Zheng, Q.; Sales, B. C.; Mandrus, D. G.; Zhou, H. D.; Zhou, J.-S.; McComb, D.; Randeria, M.; Trivedi, N.; Yan, J.-Q.

2017-10-01

We systematically investigate the magnetic properties and local structure of Ba2YIrO6 to demonstrate that Y and Ir lattice defects in the form of antiphase boundary or clusters of antisite disorder affect the magnetism observed in this 5 d4 compound. The experimental investigation involved comparison of the magnetic properties and atomic imaging of (1) a slow-cooled crystal, (2) a crystal quenched from 900°C after growth, and (3) a crystal grown using a faster cooling rate during growth than the slow-cooled one. Atomic-scale imaging by scanning transmission electron microscopy (STEM) shows that quenching from 900°C introduces Ir-rich antiphase boundaries in the crystals, and a faster cooling rate during crystal growth leads to clusters of Y and Ir antisite disorder. Compared to the slow-cooled crystals, Ba2YIrO6 crystals with clusters of antisite defects have a larger effective moment and a larger saturation moment, while quenched crystals with Ir-rich antiphase boundary show a slightly suppressed moment. Our DFT and model magnetic Hamiltonian calculations suggest magnetic condensation is unlikely, as the energy to be gained from superexchange is small compared to the spin-orbit gap. However, once Y is replaced by Ir in the antisite disordered region, the picture of local nonmagnetic singlets breaks down and magnetism can be induced. This is because of (a) enhanced interactions due to increased orbital overlap and (b) increased number of orbitals mediating the interactions. Our work highlights the importance of lattice defects in understanding the experimentally observed magnetism in Ba2YIrO6 and other J =0 systems.

Magnetism out of antisite disorder in the J = 0 compound Ba 2 YIrO 6

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

Chen, Qiang; Svoboda, Chris; Zheng, Qiang

Here, we systematically investigate the magnetic properties and local structure of Ba 2YIrO 6 to demonstrate that Y and Ir lattice defects in the form of antiphase boundary or clusters of antisite disorder affect the magnetism observed in this 5d 4 compound. The experimental investigation involved comparison of the magnetic properties and atomic imaging of (1) a slow-cooled crystal, (2) a crystal quenched from 900°C after growth, and (3) a crystal grown using a faster cooling rate during growth than the slow-cooled one. Atomic-scale imaging by scanning transmission electron microscopy (STEM) shows that quenching from 900°C introduces Ir-rich antiphase boundariesmore » in the crystals, and a faster cooling rate during crystal growth leads to clusters of Y and Ir antisite disorder. Compared to the slow-cooled crystals, Ba 2YIrO 6 crystals with clusters of antisite defects have a larger effective moment and a larger saturation moment, while quenched crystals with Ir-rich antiphase boundary show a slightly suppressed moment. Our DFT and model magnetic Hamiltonian calculations suggest magnetic condensation is unlikely, as the energy to be gained from superexchange is small compared to the spin-orbit gap. However, once Y is replaced by Ir in the antisite disordered region, the picture of local nonmagnetic singlets breaks down and magnetism can be induced. This is because of (a) enhanced interactions due to increased orbital overlap and (b) increased number of orbitals mediating the interactions. Our work highlights the importance of lattice defects in understanding the experimentally observed magnetism in Ba 2YIrO 6 and other J = 0 systems.« less

Magnetism out of antisite disorder in the J = 0 compound Ba 2 YIrO 6

DOE PAGES

Chen, Qiang; Svoboda, Chris; Zheng, Qiang; ...

2017-10-18

Here, we systematically investigate the magnetic properties and local structure of Ba 2YIrO 6 to demonstrate that Y and Ir lattice defects in the form of antiphase boundary or clusters of antisite disorder affect the magnetism observed in this 5d 4 compound. The experimental investigation involved comparison of the magnetic properties and atomic imaging of (1) a slow-cooled crystal, (2) a crystal quenched from 900°C after growth, and (3) a crystal grown using a faster cooling rate during growth than the slow-cooled one. Atomic-scale imaging by scanning transmission electron microscopy (STEM) shows that quenching from 900°C introduces Ir-rich antiphase boundariesmore » in the crystals, and a faster cooling rate during crystal growth leads to clusters of Y and Ir antisite disorder. Compared to the slow-cooled crystals, Ba 2YIrO 6 crystals with clusters of antisite defects have a larger effective moment and a larger saturation moment, while quenched crystals with Ir-rich antiphase boundary show a slightly suppressed moment. Our DFT and model magnetic Hamiltonian calculations suggest magnetic condensation is unlikely, as the energy to be gained from superexchange is small compared to the spin-orbit gap. However, once Y is replaced by Ir in the antisite disordered region, the picture of local nonmagnetic singlets breaks down and magnetism can be induced. This is because of (a) enhanced interactions due to increased orbital overlap and (b) increased number of orbitals mediating the interactions. Our work highlights the importance of lattice defects in understanding the experimentally observed magnetism in Ba 2YIrO 6 and other J = 0 systems.« less

Luminescence, magnetic and vibrational properties of novel heterometallic niccolites [(CH3)2NH2][CrIIIMII(HCOO)6] (MII=Zn, Ni, Cu) and [(CH3)2NH2][AlIIIZnII(HCOO)6]:Cr3+

NASA Astrophysics Data System (ADS)

Mączka, Mirosław; Pietraszko, Adam; Pikul, Adam; Hermanowicz, Krzysztof

2016-01-01

We report synthesis of three novel heterometallic MOFs, [(CH3)2NH2][CrIIIMII(HCOO)6] with M=Zn (DMCrZn), Ni (DMCrNi) and Cu (DMCrCu), crystallizing in the niccolite type structure. We also successfully synthesized [(CH3)2NH2][AlCu(HCOO)6] (DMAlCu) and [(CH3)2NH2][AlZn(HCOO)6] doped with 5.8 mol% of Cr3+ (DMAlZn: Cr). X-ray diffraction shows that DMCrZn, DMCrNi and DMAlZn: Cr3+ crystallize in the trigonal structure (space group P 3 bar1c) while DMCrCu and DMAlCu crystallize in the monoclinic structure (space group C2/c). Magnetic investigation of the chromium-based niccolites reveals no magnetic order in DMCrZn and ferromagnetic order in DMCrNi and DMCrCu below 23 and 11 K, respectively. Optical studies show that DMCrZn and DMAlZn: Cr samples exhibit efficient emission typical for chromium ions located at sites of strong crystal field with the Dq/B values 2.62 and 2.67, respectively. We also discuss role of geometrical parameters in stability of the perovskite and niccolite structures.

Inhomogeneous field induced magnetoelectric effect in Mott insulators

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

Boulaevskii, Lev N; Batista, Cristian D

2008-01-01

We consider a Mott insulator like HoMnO{sub 3} whose magnetic lattice is geometrically frustrated and comprises a 3D array of triangular layers with magnetic moments ordered in a 120{sup o} structure. We show that the effect of a uniform magnetic field gradient, {gradient}H, is to redistribute the electronic charge of the magnetically ordered phase leading to a unfirom electric field gradient. The resulting voltage difference between the crystal edges is proportional to the square of the crystal thickness, or inter-edge distance, L. It can reach values of several volts for |{gradient}H| {approx} 0.01 T/cm and L {approx_equal} 1mm, as longmore » as the crystal is free of antiferromagnetic domain walls.« less

Synthesis, crystal structure, and electrical and magnetic properties of BaMo{sub 6}Te{sub 6}: A novel reduced molybdenum telluride containing infinite chains of trans-face shared Mo{sub 6} octahedra

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

Gall, Philippe; Guizouarn, Thierry; Potel, Michel

Powder samples and single crystals of the new ternary compound BaMo{sub 6}Te{sub 6} were obtained by solid state reaction. The structure was determined by single-crystal X-ray diffraction. BaMo{sub 6}Te{sub 6} crystallizes in the hexagonal space group P6{sub 3}/m (No. 176) with unit-cell parameters a=9.3941(2) Å, c=4.5848(1) Å and Z=1. Full-matrix least-squares refinement on F{sup 2} using 452 independent reflections for 17 refinable parameters resulted in R1=0.0208 and wR2=0.0539. The structure consists of one-dimensional infinite chains of trans-face shared Mo{sub 6} octahedra capped by Se atoms. These chains that are running along the c axis are separated from each other bymore » nine-coordinate Ba atoms. Resistivity measurements on a single crystal indicated that the BaMo{sub 6}Te{sub 6} compound is metallic down to 160 K and semiconductor below. Magnetic susceptibility measurements showed that BaMo{sub 6}Te{sub 6} is weakly diamagnetic with no anomaly at the metal–semiconductor transition. - Graphical abstract: We present here the synthesis, the crystal structure, and the electrical and magnetic properties of the new compound BaMo{sub 6}Te{sub 6} containing infinite chains of trans-face shared Mo{sub 6} octahedra. - Highlights: • BaMo{sub 6}Te{sub 6} contains infinite chains of trans-face-sharing Mo{sub 6} octahedra |Mo{sub 6/2}|{sub ∞}{sup 1}. • Synthesis by solid state reaction. • Single-crystal X-ray study. • Continuous metal–nonmetal transition. • Anderson localization.« less

Role of magnetism in superconductivity of BaFe 2As 2: Study of 5d Au-doped crystals

DOE PAGES

Li, Li; Cao, Huibo; McGuire, Michael A.; ...

2015-09-09

We investigate properties of BaFe 2As 2 (122) single crystals upon gold doping, which is the transition metal with the highest atomic weight. The Au substitution into the FeAs-planes of 122 crystal structure (Au-122) is only possible up to a small amount of ~3%. We find that 5d is more effective in reducing magnetism in 122 than its counter 3d Cu, and this relates to superconductivity. We provide evidence of short-range magnetic fluctuations and local lattice inhomogeneities that may prevent strong percolative superconductivity in Ba(Fe 1-xAu x)2As 2.

Photonic band structures of two-dimensional magnetized plasma photonic crystals

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

Qi, L.

By using modified plane wave method, photonic band structures of the transverse electric polarization for two types of two-dimensional magnetized plasma photonic crystals are obtained, and influences of the external magnetic field, plasma density, and dielectric materials on the dispersion curves are studied, respectively. Results show that two areas of flat bands appear in the dispersion curves due to the role of external magnetic field, and the higher frequencies of the up and down flat bands are corresponding to the right-circled and left-circled cutoff frequencies, respectively. Adjusting external magnetic field and plasma density can not only control positions of themore » flat bands, but also can control the location and width of the local gap; increasing relative dielectric constant of the dielectric materials makes omni-direction gaps appear.« less

Anisotropic magnetic structures of the Mn R MnSbO6 high-pressure doubly ordered perovskites (R =La , Pr, and Nd)

NASA Astrophysics Data System (ADS)

Solana-Madruga, Elena; Arévalo-López, Ángel M.; Dos santos-García, Antonio J.; Ritter, Clemens; Cascales, Concepción; Sáez-Puche, Regino; Attfield, J. Paul

2018-04-01

A new type of doubly ordered perovskite (also reported as double double perovskite, DDPv) structure combining columnar and rock-salt orders of the cations at the A and B sites, respectively, was recently found at high pressure for Mn R MnSb O6 (R =La -Sm ). Here we report further magnetic structures of these compounds. M n2 + spins align into antiparallel ferromagnetic sublattices along the x axis for MnLaMnSb O6 , while the magnetic anisotropy of P r3 + magnetic moments induces their preferential order along the z direction for MnPrMnSb O6 . The magnetic structure of MnNdMnSb O6 was reported to show a spin-reorientation transition of M n2 + spins from the z axis towards the x axis driven by the ordering of N d3 + magnetic moments. The crystal-field parameters for P r3 + and N d3 + at the 4 e C2 site of their DDPv structure have been semiempirically estimated and used to derive their energy levels and associated wave functions. The results demonstrate that the spin-reorientation transition in MnNdMnSb O6 arises as a consequence of the crystal-field-induced magnetic anisotropy of N d3 + .

Room-temperature spin-orbit torque in NiMnSb

NASA Astrophysics Data System (ADS)

Ciccarelli, C.; Anderson, L.; Tshitoyan, V.; Ferguson, A. J.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Gayles, J.; Železný, J.; Šmejkal, L.; Yuan, Z.; Sinova, J.; Freimuth, F.; Jungwirth, T.

2016-09-01

Materials that crystallize in diamond-related lattices, with Si and GaAs as their prime examples, are at the foundation of modern electronics. Simultaneously, inversion asymmetries in their crystal structure and relativistic spin-orbit coupling led to discoveries of non-equilibrium spin-polarization phenomena that are now extensively explored as an electrical means for manipulating magnetic moments in a variety of spintronic structures. Current research of these relativistic spin-orbit torques focuses primarily on magnetic transition-metal multilayers. The low-temperature diluted magnetic semiconductor (Ga, Mn)As, in which spin-orbit torques were initially discovered, has so far remained the only example showing the phenomenon among bulk non-centrosymmetric ferromagnets. Here we present a general framework, based on the complete set of crystallographic point groups, for identifying the potential presence and symmetry of spin-orbit torques in non-centrosymmetric crystals. Among the candidate room-temperature ferromagnets we chose to use NiMnSb, which is a member of the broad family of magnetic Heusler compounds. By performing all-electrical ferromagnetic resonance measurements in single-crystal epilayers of NiMnSb we detect room-temperature spin-orbit torques generated by effective fields of the expected symmetry and of a magnitude consistent with our ab initio calculations.

Brownmillerite Ca 2 Co 2 O 5 : Synthesis, Stability, and Re-entrant Single Crystal to Single Crystal Structural Transitions

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

Zhang, Junjie; Zheng, Hong; Malliakas, Christos D.

2014-11-20

We synthesized Ca 2Co 2O 5 in the brownmillerite form using a high-pressure optical-image floating zone furnace, and single crystals with dimensions up to 1.4×0.8×0.5 mm 3 were obtained. At room temperature, Ca 2Co 2O 5 crystallizes as a fully ordered brownmillerite variant in the orthorhombic space group Pcmb (No. 57) with unit cell parameters a=5.28960(10) Å, b=14.9240(2) Å, and c=10.9547(2) Å. Furthermore, with decreasing temperature, it undergoes re-entrant sequence of first-order structural phase transitions (Pcmb→ P2/c11→ P121/m1→ Pcmb) that is unprecedented among brownmillerites, broadening the family of space groups available to these materials and challenging current approaches for sortingmore » the myriad variants of brownmillerite structures. Magnetic susceptibility data indicate antiferromagnetic ordering in Ca 2Co 2O 5 occurs near 240 K, corroborated by neutron powder diffraction. Below 140 K, Ca 2Co 2O 5 shows a weak ferromagnetic component directed primarily along the b axis, and it also exhibits thermal and magnetic history dependence in magnetization.« less

Facile in-situ reduction: Crystal growth and magnetic studies of reduced vanadium (III/IV) silicates CaxLn1-xVSiO5 (Ln = Ce-Nd, Sm-Lu, Y)

NASA Astrophysics Data System (ADS)

Abeysinghe, Dileka; Smith, Mark D.; Morrison, Gregory; Yeon, Jeongho; zur Loye, Hans-Conrad

2018-04-01

A series of lanthanide containing mixed-valent vanadium (III/IV) silicates of the type CaxLn1-xVSiO5 (Ln = Ce-Nd, Sm-Lu, Y) was synthesized as high quality single crystals from a molten chloride eutectic flux, BaCl2/NaCl. Utilizing Ca metal as the reducing agent, an in-situ reduction of V5+ to V3+/4+ as well as of Ce4+ to Ce3+ was achieved. The structures of 14 reported isostructural compounds were determined by single crystal X-ray diffraction. They crystallize in the tilasite (CaMgAsO4F) structure type in the monoclinic space group C2/c. The extended structure contains 1D chains of VO6 octahedra that are connected to each other via SiO4 groups and (Ca/Ln)O7 polyhedra. The magnetic susceptibility and the field dependent magnetization data were measured for CaxLn1-xVSiO5 (Ln = Ce-Nd, Sm, Gd-Lu, Y), and support the existence of antiferromagnetic behavior at low temperatures.

Magnetostructural transition in Fe{sub 5}SiB{sub 2} observed with neutron diffraction

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

Cedervall, Johan, E-mail: johan.cedervall@kemi.uu.se; Kontos, Sofia; Hansen, Thomas C.

2016-03-15

The crystal and magnetic structure of Fe{sub 5}SiB{sub 2} has been studied by a combination of X-ray and neutron diffraction. Also, the magnetocrystalline anisotropy energy constant has been estimated from magnetisation measurements. High quality samples have been prepared using high temperature synthesis and subsequent heat treatment protocols. The crystal structure is tetragonal within the space group I4/mcm and the compound behaves ferromagnetically with a Curie temperature of 760 K. At 172 K a spin reorientation occurs in the compound and the magnetic moments go from aligning along the c-axis (high T) down to the ab-plane (low T). The magnetocrystalline anisotropymore » energy constant has been estimated to 0.3 MJ/m{sup 3} at 300 K. - Highlights: • The crystal and magnetic structure of Fe{sub 5}SiB{sub 2} has been studied by diffraction. • At 172 K a spin reorientation occurs in the compound. • The magnetic moments are aligned along the c-axis at high T. • The magnetic moments are aligned in the ab-plane at low T. • The magnetocrystalline anisotropy energy constant has been estimated to 0.3 MJ/m{sup 3}.« less

On the nature of the reversibility of hydration-dehydration on the crystal structure and magnetism of the ferrimagnet [MnII(enH)(H2O)][CrIII(CN)6].H2O.

PubMed

Yoshida, Yusuke; Inoue, Katsuya; Kurmoo, Mohamedally

2009-01-05

We report the synthesis, crystal structure, and thermal and magnetic properties of the two-dimensional achiral soft ferrimagnet [Mn(II)(enH)(H(2)O)][Cr(III)(CN)(6)].H(2)O (1), en = 1,2-diaminoethane, as well as the recyclability of the dehydration and rehydration and their influence on the crystal structure and its magnetic properties. Unlike [Mn(S-pnH)(H(2)O)][Cr(CN)(6)].H(2)O (2S, pn = 1,2-diaminopropane), which is a chiral (P2(1)2(1)2(1)) enantiopure ferrimagnet (T(C) = 38 K), 1 crystallizes in the achiral orthorhombic Pcmn space group, having a similar two-dimensional square network of Mn-Cr with bridging cyanide, and 1 behaves also as a soft ferrimagnet (T(C) = 42 K). X-ray diffraction experiments on a single crystal of 1 indicate a transformation from a single crystal to an amorphous phase upon dehydrataion and partial recovery of its crystallinity upon rehydration. The dehydrated phase 1-DP exhibits long-range ordering at 75 K to a ferrimagnetic state and coercive field at 2 K of 100 Oe, which are a higher critical temperature and coercive field than for the virgin sample (H(C) = 60 Oe). Thermogravimetric analyses indicate that the crystallinity deteriorates upon hydration-dehydration cycling, with persistence toward the amorphous phase, as also seen by magnetization measurements. This effect is associated with an increase of statistical disorder inherent in the dehydration-rehydration process. X-ray powder diffraction suggests that 1-DP may retain order within the layers but loses coherence in the stacking of the layers.

Crystal structure and properties of tetragonal EuAg{sub 4}In{sub 8} grown by metal flux technique

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

Subbarao, Udumula; Sarkar, Sumanta; Peter, Sebastian C., E-mail: sebastiancp@jncasr.ac.in

The compound EuAg{sub 4}In{sub 8} has been obtained as single crystals in high yield from reactions run in liquid indium. X-ray diffraction on single crystals suggests that EuAg{sub 4}In{sub 8} crystallizes in the CeMn{sub 4}Al{sub 8} structure type, tetragonal space group I4/mmm with lattice constants a=b=9.7937(2) Å and c=5.7492(2) Å. Crystal structure of EuAg{sub 4}In{sub 8} is composed of pseudo Frank–Kasper cages occupied by one europium atom in each ring, which are shared through the corner along the ab plane resulting in a three dimensional network. The magnetic susceptibility of EuAg{sub 4}In{sub 8} was measured in the temperature range 2–300more » K, which obeyed Curie–Weiss law above 50 K. Magnetic moment value calculated from the fitting indicates the presence of divalent europium, which was confirmed by X-ray absorption near edge spectroscopy. Electrical resistivity measurements suggest that EuAg{sub 4}In{sub 8} is metallic in nature with a probable Fermi liquid behavior at low temperature. - Graphical abstract: The tetragonal EuAg{sub 4}In{sub 8} has been grown as single crystals from reactions run in liquid indium. Magnetic and XANES measurements suggest divalent nature of Eu and resistivity measurements suggest metallic nature. - Highlights: • EuAg{sub 4}In{sub 8} phase having tetragonal phase is grown by metal flux technique. • Magnetic and XANES measurements exhibit divalent nature of Eu in EuAg{sub 4}In{sub 8}. • Resistivity measurement suggests metallic nature and probable Fermi liquid behavior.« less

Effect of Sintering Temperature to Physical, Magnetic Properties and Crystal Structure on Permanent Magnet BaFe12O19 Prepared From Mill Scale

NASA Astrophysics Data System (ADS)

Ramlan; Muljadi; Sardjono, Priyo; Gulo, Fakhili; Setiabudidaya, Dedi

2017-07-01

Permanent magnet of Barium hexa Ferrite with formula BaFe12O19 has been made by metallurgy powder method from raw materials : Barium carbonate (BaCO3 E-merck) and Iron Oxide (Fe2O3 from mill scale). Both of raw materials have been mixed with stoichiometry composition by using a ball mill for 24 hours. The fine powder obtained from milling process was formed by using a hydraulic press at pressure 50 MPa and continued with sintering process. The sintering temperature was varied : 1150°C, 1200°C, 1250°C and 1300°C with holding time for 1 hour. The sintered samples were characterized such as : physical properties (bulk density, porosity and shrinkage), magnetic properties (flux density, remanence, coercivity and magnetic saturation) by using VSM and crystal structure by using XRD. According characterization results show that the crystal structure of BaFe12O19 does not change after sintering process, but the grain size tends to increase. The optimum condition is achieved at temperature 1250°C, and at this condition, the sample has characterization such as : bulk density = 4.35 g/cm3, porosity = 1.03% and firing shrinkage = 11.63%, flux density = 681.1 Gauss, remanence (σr) = 20.78 emu/g, coercivity (Hc) = 2058 Oe and magnetic saturation (σs) 45.16 emu/g.

Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4

NASA Astrophysics Data System (ADS)

Carnicom, Elizabeth M.; Klimczuk, Tomasz; von Rohr, Fabian; Winiarski, Michal J.; Kong, Tai; Stolze, Karoline; Xie, Weiwei; Kushwaha, Satya K.; Cava, Robert J.

2017-08-01

The growth and characterization of CePtIn4, stabilized by 10% Zn substitution for In, is reported. The new material is orthorhombic, space group Cmcm (No. 63), with lattice parameters a = 4.51751(4) Å, b = 16.7570(2) Å, and c = 7.36682(8) Å, and the refined crystal composition has 10% of Zn substituted for In, i.e., the crystals are CePt(In0.9Zn0.1)4. Crystals were grown using a self-flux method: only growths containing Zn yielded CePtIn4 crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic temperature-dependent magnetic susceptibilities for single crystals show that Zn-stabilized CePtIn4 orders magnetically at ˜1.9 K. High-temperature Curie-Weiss fits indicate an effective moment of ˜2.49 μB/Ce and a directionally averaged Weiss-temperature of approximately -31 K. Specific heat data shows a peak consistent with the ordering temperature seen in the magnetic susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no superconducting transition down to 0.14 K.

Hydrothermal synthesis and characterization of a two-dimensional piperazinium cobalt–zinc phosphate via a metastable one-dimensional phase

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

Torre-Fernández, Laura; Khainakova, Olena A.; Espina, Aránzazu

2015-05-15

A two-dimensional piperazinium cobalt–zinc phosphate, formulated as (C{sub 4}N{sub 2}H{sub 12}){sub 1.5}(Co{sub 0.6}Zn{sub 0.4}){sub 2}(HPO{sub 4}){sub 2}(PO{sub 4})·H{sub 2}O (2D), was synthesized under hydrothermal conditions. The crystal structure was determined using single-crystal X-ray diffraction data (monoclinic P2{sub 1}/c, a=8.1165(3) Å, b=26.2301(10) Å, c=8.3595(4) Å, and β=110.930(5)°) and the hydrogen atom positions were optimized by DFT calculations. A single-crystal corresponding to one-dimensional metastable phase, (C{sub 4}N{sub 2}H{sub 12})Co{sub 0.3}Zn{sub 0.7}(HPO{sub 4}){sub 2}·H{sub 2}O (1D), was also isolated and the crystal structure was determined (monoclinic P2{sub 1}/c, a=8.9120(6) Å, b=14.0290(1) Å, c=12.2494(5) Å, and β=130.884(6)°). The bulk was characterized by chemical (C–H–N)more » analysis, powder X-ray diffraction (PXRD), powder X-ray thermodiffractometry (HT-XRD), transmission electron microscopy (STEM(DF)-EDX and EFTEM), and thermal analysis (TG/SDTA-MS), including activation energy data of its thermal decomposition. The magnetic susceptibility and magnetization measurements show no magnetic ordering down to 4 K. - Graphical abstract: Hydrothermal synthesis and structural characterization of a two-dimensional piperazinium cobalt–zinc phosphate, (C{sub 4}N{sub 2}H{sub 12}){sub 1.5}(Co{sub 0.6}Zn{sub 0.4}){sub 2}(HPO{sub 4}){sub 2}(PO{sub 4})·H{sub 2}O (2D), have been reported. The crystal structure of a one-dimensional piperazinium cobalt–zinc phosphate, (C{sub 4}N{sub 2}H{sub 12})Co{sub 0.3}Zn{sub 0.7}(HPO{sub 4}){sub 2}·H{sub 2}O (1D) a metastable phase during the hydrothermal synthesis, was also determined. The thermal behavior of 2D compound is strongly dependent on the selected heating rate and the magnetic susceptibility and magnetization measurements show no magnetic ordering down to 4 K. - Highlights: • A 2D piperazinium cobalt–zinc phosphate has been synthesized and characterized. • Crystal structure of 1D metastable phase was also determined. • Thermal behavior of 2D compound is strongly dependent on the selected heating rate. • Magnetic measurements show no magnetic ordering down to 4 K.« less

Phase stability, crystal structure and magnetism in (U1-xNbx)2 Ni21B6 and (UyNb1-y)3Ni20B6

NASA Astrophysics Data System (ADS)

Provino, Alessia; Bhattacharya, Amitava; Dhar, Sudesh K.; Pani, Marcella; Gatti, Flavio; Paudyal, Durga; Manfrinetti, Pietro

Ternary phases with composition T2M21X6 and T3M20X6 (T = transition metal; M = 3 d metal; X = B, C, P) are reported to crystallize with the W2Cr21C6-type and Mg3Ni20B6-type, respectively (ternary ordered derivatives of the cubic Cr23C6-type, cF116). They attract interest due to their refractory, mechanical, and peculiar magnetic properties. Literature data on these compounds only concern apparently stoichiometric 2:21:6 and 3:20:6 phases. Often only nominal composition has been reported, with few structural refinements and no measurements of physical properties. Lack of detailed stoichiometry and crystallographic data does not allow sufficient understanding of the crystal chemistry and properties of these compounds. We studied stability, crystal structure and magnetism of (U1-xNbx)2 Ni21B6 and (UyNb1-y)3Ni20B6; stable phases are U2Ni21B6 and Nb3Ni20B6, as also confirmed by theoretical calculations. The two pristine compounds solubilize Nb and U, respectively, up to a given extent. The substitution of U by Nb leads to a structural change from the W2Cr21C6- to the Mg3Ni20B6-type. While U2Ni21B6 is a Pauli paramagnet (itinerant non-magnetic state of U-5 f electrons), in agreement with literature, magnetization data for (UyNb1-y)3 Ni20B6 show itinerant ferromagnetism with TC >300 K.

Local spin density functional investigations of a manganite with perovskite-type derived structures

NASA Astrophysics Data System (ADS)

Matar, S. F.; Studer, F.; Siberchicot, B.; Subramanian, M. A.; Demazeau, G.; Etourneau, J.

1998-11-01

The electronic and magnetic structures of the perovskite CaMnO3 are self-consistently calculated assuming two crystal structures at the same formula unit volume within the local spin density functional theory and the augmented spherical wave (ASW) method. From the comparisons of energy differences between the different magnetic states the ground state configuration is an insulator with G-type ordering. This result together with the magnitudes of the magnetic moments are in agreement with experiment. The influence of mixing between Mn and O is found spin dependent from the analysis of the crystal orbital overlap population (COOP) which enable to describe the chemical bond. The calculations underline a feature of a half metallic ferromagnet which could be connected with the colossal magnetoresistance (CMR) property of related compounds.

Preparation, Crystal Structure, Dielectric Properties, and Magnetic Behavior of Ba 2Fe 2Ti 4O 13

NASA Astrophysics Data System (ADS)

Vanderah, T. A.; Huang, Q.; Wong-Ng, W.; Chakoumakos, B. C.; Goldfarb, R. B.; Geyer, R. G.; Baker-Jarvis, J.; Roth, R. S.; Santoro, A.

1995-11-01

The preparation, crystal structure, dielectric properties, and magnetic behavior of the new compound Ba2Fe2Ti4O13 are reported. Structural studies carried out by single-crystal X-ray diffraction and neutron powder diffraction show that this phase is isostructural with K2Ti6O13 and Ba2ZnTi5O13 (C2/m (No. 12); a = 15.216(1), b = 3.8979(3), c = 9.1350(6) Å, β = 98.460(7)°; V = 535.90(8) Å3; Z = 2). The cations Fe3+ and Ti4+ are partially ordered among distorted octahedral sites with Ba2+ occupying eleven-coordinated polyhedra. Ba2Fe2Ti4O13 exhibits TE0 resonance near 10 GHz with a dielectric constant of ∼28 and a dielectric loss tangent of 2 × 10-3. The compound displays complex paramagnetic behavior with marked field dependence; the magnetization at 80 kA/m is several orders of magnitude smaller than that of most ferrites. Spin-glass effects have not been observed; however, weak collective interactions are clearly present. No magnetic ordering has been detected by neutron diffraction down to 13 K.

Antiferromagnetism in EuCu 2As 2 and EuCu 1.82Sb 2 single crystals

DOE PAGES

Anand, V. K.; Johnston, D. C.

2015-05-07

Single crystals of EuCu 2As 2 and EuCu 2Sb 2 were grown from CuAs and CuSb self-flux, respectively. The crystallographic, magnetic, thermal, and electronic transport properties of the single crystals were investigated by room-temperature x-ray diffraction (XRD), magnetic susceptibility χ versus temperature T, isothermal magnetization M versus magnetic field H, specific heat C p(T), and electrical resistivity ρ(T) measurements. EuCu 2As 2 crystallizes in the body-centered tetragonal ThCr 2Si 2-type structure (space group I4/mmm), whereas EuCu 2Sb 2 crystallizes in the related primitive tetragonal CaBe 2Ge 2-type structure (space group P4/nmm). The energy-dispersive x-ray spectroscopy and XRD data for themore » EuCu 2Sb 2 crystals showed the presence of vacancies on the Cu sites, yielding the actual composition EuCu 1.82Sb 2. The ρ(T) and C p(T) data reveal metallic character for both EuCu 2As 2 and EuCu 1.82Sb 2. Antiferromagnetic (AFM) ordering is indicated from the χ(T),C p(T), and ρ(T) data for both EuCu 2As 2 (T N = 17.5 K) and EuCu 1.82Sb 2 (T N = 5.1 K). In EuCu 1.82Sb 2, the ordered-state χ(T) and M(H) data suggest either a collinear A-type AFM ordering of Eu +2 spins S = 7/2 or a planar noncollinear AFM structure, with the ordered moments oriented in the tetragonal ab plane in either case. This ordered-moment orientation for the A-type AFM is consistent with calculations with magnetic dipole interactions. As a result, the anisotropic χ(T) and isothermal M(H) data for EuCu 2As 2, also containing Eu +2 spins S = 7/2, strongly deviate from the predictions of molecular field theory for collinear AFM ordering and the AFM structure appears to be both noncollinear and noncoplanar.« less

Structure of new Hg0.75V0.25Ba2CuO4+δ superconducting single crystals.Effect of overdoping on the magnetization second peak

NASA Astrophysics Data System (ADS)

Villard, G.; Pelloquin, D.; Maignan, A.

1998-10-01

Superconducting crystals (Tc=88 K) of the `1201' mercury cuprate have been grown by using vanadium as stabilizer of the (HgOδ) mercury layer. Its shortened c-axis parameter, c=9.345 Å, is linked to the substitution of small VO4 tetrahedra for HgO2 stick deduced from the structural study. The regular layer stacking is confirmed by high resolution microscopy, and cationic analysis coupled to an electron microscope leads to the average formula Hg0.75V0.25Ba2CuO4+δ for these overdoped crystals in good agreement with the structural refinements. One of the major result of the structural part is the mobility of oxygens located at the [BaO]∞ layer level. The superconducting properties of crystals with typical 800×500×10 μm3 dimensions have been investigated by magnetic measurements. Well-marked fishtail features are exhibited on their M(H) curves. The corresponding second peak line differs from that of optimized 1201 crystals demonstrating the important consequences on the superconducting properties of the vanadium for mercury substitution.

Observation of a commensurate array of flux chains in tilted flux lattices in Bi-Sr-Ca-Cu-O single crystals

NASA Astrophysics Data System (ADS)

Bolle, C. A.; Gammel, P. L.; Grier, D. G.; Murray, C. A.; Bishop, D. J.; Mitzi, D. B.; Kapitulnik, A.

1991-01-01

We report the observation of a novel flux-lattice structure, a commensurate array of flux-line chains. Our experiments consist of the magnetic decoration of the flux lattices in single crystals of Ba-Sr-Ca-Cu-O where the magnetic field is applied at an angle with respect to the conducting planes. For a narrow range of angles, the equilibrium structure is one with uniformly spaced chains with a higher line density of vortices than the background lattice. Our observations are in qualitative agreement with theories which suggest that, in strongly anisotropic materials the vortices develop an attractive interaction in tilted magnetic fields.

Yb7Ni4InGe12: a quaternary compound having mixed valent Yb atoms grown from indium flux.

PubMed

Subbarao, Udumula; Jana, Rajkumar; Chondroudi, Maria; Balasubramanian, Mahalingam; Kanatzidis, Mercouri G; Peter, Sebastian C

2015-03-28

The new intermetallic compound Yb7Ni4InGe12 was obtained as large silver needle shaped single crystals from reactive indium flux. Single crystal X-ray diffraction suggests that Yb7Ni4InGe12 crystallizes in the Yb7Co4InGe12 structure type, and tetragonal space group P4/m and lattice constants are a = b = 10.291(2) Å and c = 4.1460(8) Å. The crystal structure of Yb7Ni4InGe12 consists of columnar units of three different types of channels filled with the Yb atoms. The crystal structure of Yb7Ni4InGe12 is closely related to Yb5Ni4Ge10. The effective magnetic moment obtained from the magnetic susceptibility measurements in the temperature range 200-300 K is 3.66μB/Yb suggests mixed/intermediate valence behavior of ytterbium atoms. X-ray absorption near edge spectroscopy (XANES) confirms that Yb7Ni4InGe12 exhibits mixed valence.

Growth and structural characterization of single crystals of the magnetic superconductor Ru1-xSr2-yGd1+yCu2+xO8-δ (RuGd-1212) obtained by the partial melting technique

NASA Astrophysics Data System (ADS)

Yamaki, K.; Bamba, Y.; Mochiku, T.; Funahashi, S.; Matsushita, Y.; Irie, A.

2018-05-01

In this study, cubic single crystals of the magnetic superconductor Ru1-xSr2-yGd1+yCu2+xO8-δ (RuGd-1212) with typical dimensions of 100-150 μm in length were grown by the partial melting technique. Multiple 00l reflections were first observed by XRD measurements of the bulk RuGd-1212 single crystals. The resistivity of the obtained crystals was roughly estimated to be ∼24-80 mΩ cm and no superconducting transition was observed down to 4.2 K. From the XRD measurements and refinement of the crystal structure, it was apparent that the Ru and Sr sites of the single-crystal RuGd-1212 were partially substituted by Cu and Gd, respectively. Oxygen defects were found to be minor (δ ≈ 0.1). The lattice parameters a and c of the single crystals were found to be larger and smaller, respectively, than those of a polycrystalline sample.

Spin-glass polyamorphism induced by a magnetic field in LaMnO3 single crystal

NASA Astrophysics Data System (ADS)

Eremenko, V. V.; Sirenko, V. A.; Baran, A.; Čižmár, E.; Feher, A.

2018-05-01

We present experimental evidence of field-driven transition in spin-glass state, similar to pressure-induced transition between amorphous phases in structural and metallic glasses, attributed to the polyamorphism phenomena. Cusp in temperature dependences of ac magnetic susceptibility of weakly disordered LaMnO3 single crystal is registered below the temperature of magnetic ordering. Frequency dependence of the cusp temperature proves its spin-glass origin. The transition induced by a magnetic field in spin-glass state, is manifested by peculiarity in dependence of cusp temperature on applied magnetic field. Field dependent maximum of heat capacity is observed in the same magnetic field and temperature range.

Magnetic field controlled floating-zone single crystal growth of intermetallic compounds

NASA Astrophysics Data System (ADS)

Hermann, R.; Gerbeth, G.; Priede, J.

2013-03-01

Radio-frequency (RF) floating zone single crystal growth is an important technique for the preparation of single bulk crystals. The advantage of the floating-zone method is the crucible-free growth of single crystals of reactive materials with high melting points. The strong heat diffusion on the surface, as well as the melt convection in the molten zone due to induction heating, often leads to an undesired solid-liquid interface geometry with a concave (towards the solid phase) outer rim. These concave parts aggravate the single crystal growth over the full cross-section. A two-phase stirrer was developed at IFW Dresden in order to avoid the problems connected with these concave parts. It acts as a magnetic field pump and changes the typical double vortex structure to a single roll structure, thus pushing hot melt into the regions where the concave parts may arise. The current in the secondary coil is induced by the primary coil, and the capacitor and the resistance of the secondary circuit are adjusted to get a stable 90 degree phase-shift between the coil currents. Single crystal growth of industrial relevant RuAl and TiAl intermetallic compounds was performed based on the material parameters and using the adjusted two-phase stirrer. Very recently, the magnetic system was applied to the crystal growth of biocompatible TiNb alloys and antiferromagnetic Heusler MnSi compounds.

New structure type in the mixed-valent compound YbCu4Ga8.

PubMed

Subbarao, Udumula; Gutmann, Matthias J; Peter, Sebastian C

2013-02-18

The new compound YbCu(4)Ga(8) was obtained as large single crystals in high yield from reactions run in liquid gallium. Preliminary investigations suggest that YbCu(4)Ga(8) crystallizes in the CeMn(4)Al(8) structure type, tetragonal space group I4/mmm, and lattice constants are a = b = 8.6529(4) Å and c = 5.3976(11) Å. However, a detailed single-crystal XRD revealed a tripling of the c axis and crystallizing in a new structure type with lattice constants of a = b = 8.6529(4) Å and c = 15.465(1) Å. The structural model was further confirmed by neutron diffraction measurements on high-quality single crystal. The crystal structure of YbCu(4)Ga(8) is composed of pseudo-Frank-Kasper cages occupying one ytterbium atom in each ring which are shared through the corner along the ab plane, resulting in a three-dimensional network. The magnetic susceptibility of YbCu(4)Ga(8) investigated in the temperature range 2-300 K showed Curie-Weiss law behavior above 100 K, and the experimentally measured magnetic moment indicates mixed-valent ytterbium. Electrical resistivity measurements show the metallic nature of the compound. At low temperatures, variation of ρ as a function of T indicates a possible Fermi-liquid state at low temperatures.

Low Temperature Magnetic Ordering of the Magnetic Ionic Plastic Crystal, Choline[FeCl4

NASA Astrophysics Data System (ADS)

de Pedro, I.; García-Saiz, A.; Andreica, D.; Fernández Barquín, L.; Fernández-Díaz, M. T.; Blanco, J. A.; Amato, A.; Rodríguez Fernández, J.

2015-11-01

We report on the nature of the low temperature magnetic ordering of a magnetic ionic plastic crystal, Choline[FeCl4]. This investigation was carried out using heat capacity measurements, neutron diffraction experiments and muon spin relaxation (μSR) spectroscopy. The calorimetric measurements show the onset of an unusual magnetic ordering below 4 K with a possible second magnetic phase transition below 2 K. Low temperature neutron diffraction data reveal a three dimensional antiferromagnetic ordering at 2 K compatible with the previous magnetometry results. The analysis of μSR spectra indicates a magnetic phase transition below 2.2 K. At 1.6 K, the analysis of the shape of the μSR spectra suggests the existence of an additional magnetic phase with features of a possible incommensurate magnetic structure.

Solid-State Molecular Nanomagnet Inclusion into a Magnetic Metal-Organic Framework: Interplay of the Magnetic Properties.

PubMed

Mon, Marta; Pascual-Álvarez, Alejandro; Grancha, Thais; Cano, Joan; Ferrando-Soria, Jesús; Lloret, Francesc; Gascon, Jorge; Pasán, Jorge; Armentano, Donatella; Pardo, Emilio

2016-01-11

Single-ion magnets (SIMs) are the smallest possible magnetic devices and are a controllable, bottom-up approach to nanoscale magnetism with potential applications in quantum computing and high-density information storage. In this work, we take advantage of the promising, but yet insufficiently explored, solid-state chemistry of metal-organic frameworks (MOFs) to report the single-crystal to single-crystal inclusion of such molecular nanomagnets within the pores of a magnetic MOF. The resulting host-guest supramolecular aggregate is used as a playground in the first in-depth study on the interplay between the internal magnetic field created by the long-range magnetic ordering of the structured MOF and the slow magnetic relaxation of the SIM. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ionothermal synthesis, crystal structure, and magnetic study of Co2PO4OH isostructural with caminite.

PubMed

Wang, Guangmei; Valldor, Martin; Spielberg, Eike T; Mudring, Anja-Verena

2014-03-17

A new framework cobalt(II) hydroxyl phosphate, Co2PO4OH, was prepared by ionothermal synthesis using 1-butyl-4-methyl-pyridinium hexafluorophosphate as the ionic liquid. As the formation of Co2PO4F competes in the synthesis, the synthesis conditions have to be judiciously chosen to obtain well-crystallized, single phase Co2PO4OH. Single-crystal X-ray diffraction analyses reveal Co2PO4OH crystallizes with space group I41/amd (a = b = 5.2713(7) Å, c = 12.907(3) Å, V = 358.63(10) Å(3), and Z = 4). Astonishingly, it does not crystallize isotypically with Co2PO4F but rather isotypically with the hydroxyl minerals caminite Mg1.33[SO4(OH)0.66(H2O)0.33] and lipscombite Fe(2–y)PO4(OH) (0 ≤ y ≤ 2/3). Phosphate tetrahedra groups interconnect four rod-packed face-sharing ∞(1){CoO(6/2)} octahedra chains to form a three-dimensional framework structure. The compound Co2PO4OH was further characterized by powder X-ray diffraction, Fourier transform–infrared, and ultraviolet–visible spectroscopy, confirming the discussed structure. The magnetic measurement reveals that Co2PO4OH undergoes a magnetic transition and presents at low temperatures a canted antiferromagnetic spin order in the ground state.

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.

Structural phase transition of magnetic [Ni(dmit)2]- salts induced by supramolecular cation structures of (M+)([12]crown-4)2.

PubMed

Akutagawa, Tomoyuki; Motokizawa, Takeshi; Matsuura, Kazumasa; Nishihara, Sadafumi; Noro, Shin-ichiro; Nakamura, Takayoshi

2006-03-30

Sandwich-type supramolecular cation structures of (M(+))([12]crown-4)(2) complexes (M(+) = Li(+), Na(+), K(+), and Rb(+)) were introduced as countercations to the [Ni(dmit)(2)](-) anion, which bears an S = (1)/(2) spin, to form novel magnetic crystals (dmit(2-) = 2-thione-1,3-dithiole-4,5-dithiolate). The zigzag arrangement of Li(+)([12]crown-4)(2) cations in Li(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salt induced weak intermolecular interactions of [Ni(dmit)(2)](-) dimers, whose magnetic spins were isolated from each other. The molecular arrangements of cations and anions in M(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salts (M(+) = Na(+), K(+), and Rb(+)) were isostructural to each other. In the case of Na(+)([12]crown-4)(2)[Ni(dmit)(2)](-), the space group C2/m changed to C2/c with a lowering in temperature from 298 to 100 K. This structural change occurred at 222.5 K as a first-order phase transition. The space group C2/m (T = 298 K) in the salt K(+)([12]crown-4)(2)[Ni(dmit)(2)](-) also changed to C2/c (T = 100 K), which transition occurred at 270 K. Crystal structural analyses at 298 and 100 K revealed changes in both supramolecular cation conformation and [Ni(dmit)(2)](-) anion arrangements. The transition from C2/m to C2/c crystals generated a dipole moment in the Na(+)([12]crown-4)(2) and K(+)([12]crown-4)(2) structures, which were reconstructed to cancel the net dipole moment of the C2/c crystals. These cation transformations led to changes in intermolecular interactions between the [Ni(dmit)(2)](-) anions via structural rearrangements. The crystal structure of C2/c was stabilized in Rb(+)([12]crown-4)(2)[Ni(dmit)(2)](-) at 298 K. The [Ni(dmit)(2)](-) configuration in these salts with the C2/c space group was a one-dimensional uniform chain, which showed the temperature-dependent magnetic susceptibility of a one-dimensional linear Heisenberg antiferromagnetic chain.

Nonreciprocal optical isolation via graphene based photonic crystals

NASA Astrophysics Data System (ADS)

Roshan Entezar, S.; Karimi Habil, M.

2018-03-01

The transmission properties of a one-dimensional photonic crystal containing graphene mono-layers are studied using the transfer matrix method. It is shown that the structure can be used as a polarization-selective nonreciprocal device which discriminates between the two circularly polarized waves with different handedness impinging in the same direction. This structure may be utilized in designing optical isolators for the circularly polarized waves due to the gyrotropic behavior of the graphene mono-layers under the perpendicularly applied external magnetic field. Moreover, the effect of an external magnetic field and the chemical potential of the graphene mono-layers on the band gap of the structure are investigated.

Phase-field-crystal model for magnetocrystalline interactions in isotropic ferromagnetic solids

NASA Astrophysics Data System (ADS)

Faghihi, Niloufar; Provatas, Nikolas; Elder, K. R.; Grant, Martin; Karttunen, Mikko

2013-09-01

An isotropic magnetoelastic phase-field-crystal model to study the relation between morphological structure and magnetic properties of pure ferromagnetic solids is introduced. Analytic calculations in two dimensions were used to determine the phase diagram and obtain the relationship between elastic strains and magnetization. Time-dependent numerical simulations in two dimensions were used to demonstrate the effect of grain boundaries on the formation of magnetic domains. It was shown that the grain boundaries act as nucleating sites for domains of reverse magnetization. Finally, we derive a relation for coercivity versus grain misorientation in the isotropic limit.

The structural and magnetic phase transitions in a ``parent'' Fe pnictide compound

NASA Astrophysics Data System (ADS)

Ni, Ni; Allred, Jared; Cao, Huibo; Tian, Wei; Liu, Lian; Cho, Kyuil; Krogstad, Matthew; Ma, Jie; Taddei, Keith; Tanatar, Makariy; Prozorov, Ruslan; Matsuda, Masaaki; Rosenkranz, Stephan; Uemura, Yasutomo; Jiang, Shan

2015-03-01

We will present transport, thermodynamic, synchrotron X-ray, neutron diffraction, μSR, ARPES and polarized optical image measurements on the ``parent'' compound of the 112 high Tc superconducting Fe pnictide family. Structural and magnetic phase transitions are revealed. Detailed magnetic structure was solved by single crystal neutron diffraction. We will discuss the similarity and difference of these transitions comparing to the parent compounds of other Fe pnictide superconductors.

Magnetic and electrical properties of Nd7Pt3 studied on single crystals

NASA Astrophysics Data System (ADS)

Tsutaoka, Takanori; Ueda, Koyo; Matsushita, Takuya

2018-07-01

Magnetic and electrical properties of Nd7Pt3 with the Th7Fe3 type hexagonal structure have been studied on single crystals by measuring magnetization, magnetic susceptibility and electrical resistivity. Nd7Pt3 possesses a ferromagnetic state below TC = 38 K; a canted antiferromagnetic state takes place at Tt2 = 34 K. Another magnetic phase transition has also been observed at Tt1 = 25 K. The magnetization curve along the a- and b-axes at 2 K shows anomalous first-order irreversible behavior. The direction of the magnetic moment in the canted state can be tilted from the c-plane. Electrical resistivity measurement results show metallic property; three anomalies were observed at Tt1, Tt2 and TC, respectively.

Spin dynamics, electronic, and thermal transport properties of two-dimensional CrPS4 single crystal

NASA Astrophysics Data System (ADS)

Pei, Q. L.; Luo, X.; Lin, G. T.; Song, J. Y.; Hu, L.; Zou, Y. M.; Yu, L.; Tong, W.; Song, W. H.; Lu, W. J.; Sun, Y. P.

2016-01-01

2-Dimensional (2D) CrPS4 single crystals have been grown by the chemical vapor transport method. The crystallographic, magnetic, electronic, and thermal transport properties of the single crystals were investigated by the room-temperature X-ray diffraction, electrical resistivity ρ(T), specific heat CP(T), and the electronic spin response (ESR) measurements. CrPS4 crystals crystallize into a monoclinic structure. The electrical resistivity ρ(T) shows a semiconducting behavior with an energy gap Ea = 0.166 eV. The antiferromagnetic transition temperature is about TN = 36 K. The spin flipping induced by the applied magnetic field is observed along the c axis. The magnetic phase diagram of CrPS4 single crystal has been discussed. The extracted magnetic entropy at TN is about 10.8 J/mol K, which is consistent with the theoretical value R ln(2S + 1) for S = 3/2 of the Cr3+ ion. Based on the mean-field theory, the magnetic exchange constants J1 and Jc corresponding to the interactions of the intralayer and between layers are about 0.143 meV and -0.955 meV are obtained based on the fitting of the susceptibility above TN, which agree with the results obtained from the ESR measurements. With the help of the strain for tuning the magnetic properties, monolayer CrPS4 may be a promising candidate to explore 2D magnetic semiconductors.

ThMn12-type phases for magnets with low rare-earth content: Crystal-field analysis of the full magnetization process.

PubMed

Tereshina, I S; Kostyuchenko, N V; Tereshina-Chitrova, E A; Skourski, Y; Doerr, M; Pelevin, I A; Zvezdin, A K; Paukov, M; Havela, L; Drulis, H

2018-02-26

Rare-earth (R)-iron alloys are a backbone of permanent magnets. Recent increase in price of rare earths has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. For this reason strong magnets with the ThMn 12  type of structure came into focus. Functional properties of R(Fe,T) 12 (T-element stabilizes the structure) compounds or their interstitially modified derivatives, R(Fe,T) 12 -X (X is an atom of hydrogen or nitrogen) are determined by the crystal-electric-field (CEF) and exchange interaction (EI) parameters. We have calculated the parameters using high-field magnetization data. We choose the ferrimagnetic Tm-containing compounds, which are most sensitive to magnetic field and demonstrate that TmFe 11 Ti-H reaches the ferromagnetic state in the magnetic field of 52 T. Knowledge of exact CEF and EI parameters and their variation in the compounds modified by the interstitial atoms is a cornerstone of the quest for hard magnetic materials with low rare-earth content.

Melting of anisotropic colloidal crystals in two dimensions

NASA Astrophysics Data System (ADS)

Eisenmann, C.; Keim, P.; Gasser, U.; Maret, G.

2004-09-01

The crystal structure and melting transition of two-dimensional colloids interacting via an anisotropic magnetic dipole-dipole potential are studied. Anisotropy is achieved by tilting the external magnetic field inducing the dipole moments of the colloidal particles away from the direction perpendicular to the particle plane. We find a centred rectangular lattice and a two-step melting similar to the phase transitions of the corresponding isotropic crystals via a quasi-hexatic phase. The latter is broadened compared to the hexatic phase for isotropic interaction potential due to strengthening of orientational order.

Mild hydrothermal crystal growth of new uranium(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30}: Structures, optical and magnetic properties

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

Yeon, Jeongho; Smith, Mark D.; Tapp, Joshua

Two new uranium(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} (1) and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30} (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 UF{sub 9} and MF{sub 6} (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)F{sub 6} octahedra and sodium ions, whereas the small hexagonal cavities include M(II) and sodium ions on a mixed-occupied site.more » Magnetic susceptibility measurements yielded effective magnetic moments of 8.36 and 11.6 µ{sub B} 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. - Graphical abstract: Two new quaternary U(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30}, were crystallized via an in situ reduction step of U(VI) to U(IV) under mild hydrothermal conditions. The compounds show complex crystal structures based on the 3-D building block of U{sub 6}F{sub 30}. Magnetic property measurements revealed that the U(IV) exhibits a nonmagnetic singlet ground state at low temperature with a spin gap. - Highlights: • Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30} have been synthesized and characterized. • The U(IV) fluorides exhibit complex three-dimensional crystal structures. • The optical properties were investigated. • Magnetic susceptibility data were collected.« less

Evidence for single-chain magnet behavior in a Mn(III)-Ni(II) chain designed with high spin magnetic units: a route to high temperature metastable magnets.

PubMed

Clérac, Rodolphe; Miyasaka, Hitoshi; Yamashita, Masahiro; Coulon, Claude

2002-10-30

We herein present the synthesis, crystal structure, and magnetic properties of a new heterometallic chain of MnIII and NiII ions, [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (saltmen2- = N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate) and pao- = pyridine-2-aldoximate). The crystal structure of 1 was investigated by X-ray crystallographic analysis: compound 1 crystallized in monoclinic, space group C2/c (No. 15) with a = 21.140(3) A, b = 15.975(1) A, c = 18.6212(4) A, beta = 98.0586(4) degrees , V = 6226.5(7) A3, and Z = 4. This compound consists of two fragments, the out-of-plane dimer [Mn2(saltmen)2]2+ as a coordination acceptor building block and the neutral mononuclear unit [Ni(pao)2(py)2] as a coordination donor building block, forming an alternating chain having the repeating unit [-Mn-(O)2-Mn-ON-Ni-NO-]n. In the crystal structure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of 10.39 A and with the absence of interchain pi overlaps between organic ligands. These features ensure a good magnetic isolation of the chains. The dc and ac magnetic measurements were performed on both the polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility of this one-dimensional compound was successfully described in a mean field approximation as an assembly of trimers (Mn...Ni...Mn) with a NiII...MnIII antiferromagnetic interaction (J = -21 K) connected through a ferromagnetic MnIII...MnIII interaction (J'). However, the mean field theory fails to describe the magnetic behavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between 5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading to the same value of J'. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In the same range of temperature, combined ac and dc measurements show a slow relaxation of the magnetization. This result indicates the presence of a metastable state without magnetic long-range order. This material is the first experimental design of a heterometallic chain with ST = 3 magnetic units showing a "single-chain magnet" behavior predicted in 1963 by R. J. Glauber for an Ising one-dimensional system. This work opens new perspectives for one-dimensional systems to obtain high temperature metastable magnets by combining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.

On the edge of periodicity: Unconventional magnetism of Gd 117Co 56.4Sn 114.3

DOE PAGES

Liu, J.; Mudryk, Yaroslav; Ryan, D. H.; ...

2017-08-04

Magnetization measurements reveal the onset of magnetic ordering at T C = 65 K followed by three additional magnetic anomalies at T 1 = 47 K, T 2 = 28 K, and T 3 = 11 K in Gd 117Co 56.4Sn 114.3 – a compound with a giant cubic unit cell that crystallizes in the Dy 117Co 56Sn 112 structure type with space group Fm3¯m and lattice parameter a = 30.186 Å. The magnetic ordering temperature increases with applied magnetic field; however, the analysis of magnetic data indicates that antiferromagnetic interactions also play a role in the ground state. ACmore » magnetic susceptibility confirms multiple magnetic anomalies and shows minor frequency dependence. The local magnetic ordering below 60 K is supported by the Mössbauer spectroscopy. A single broad anomaly is detected at T 3 in the heat capacity; we suggest that magnetic domains form below this temperature. Furthermore, these data highlight unique features of magnetism in this and, potentially, other rare-earth intermetallics crystallizing with giant unit-cells where the exchange correlation lengths are much shorter when compared to the periodicity of the crystal lattice.« less

Magneto-optical Kerr effect of a Ni2.00Mn1.16Ga0.84 single crystal across austenite and intermartensite transitions

NASA Astrophysics Data System (ADS)

Fikáček, Jan; Heczko, Oleg; Kopecký, Vít; Kaštil, Jiří; Honolka, Jan

2018-04-01

We carried out magneto-optical Kerr effect (MOKE) and magnetization measurements on a single crystal of Ni2.00Mn1.16Ga0.84, which is a magnetic shape memory material with application potential for actuator devices or for energy recuperation. Up to the time of our study, there had been reports of MOKE measurements in polar geometry. Against earlier predictions, we show that surface magnetic states of the martensite and the austenite can be also probed efficiently via longitudinal MOKE. A single-variant magnetic state prepared at room temperature is characterized by square-shaped ferromagnetic hysteresis loops yielding coercive fields, which are key material properties for future applications. Temperature dependencies of Kerr rotation were found to be linearly proportional to magnetization for martensitic phases. After passing through an inter-martensitic structural transition below room temperature in zero magnetic field, the coercive fields are more than doubled in comparison with the room temperature values. Above room temperature where an austenite structure is formed, MOKE signals are dominated by quadratic contributions and the magnitude of Kerr rotation drops due to changes in the electronic and magnetic domains structure.

Interplay between crystal and magnetic structures in YFe{sub 2}(H{sub α}D{sub 1−α}){sub 4.2} compounds studied by neutron diffraction

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

Paul-Boncour, V., E-mail: paulbon@icmpe.cnrs.fr; Guillot, M.; Isnard, O.

We report a detailed magnetic structure investigation of YFe{sub 2}(H{sub α}D{sub 1−α}){sub 4.2} (α=0, 0.64, 1) compounds presenting a strong (H,D) isotope effect by neutron diffraction and Mössbauer spectroscopy analysis. They crystallize in the same monoclinic structure (Pc space group) with 8 inequivalent Fe sites having different H(D) environment. At low temperature, the compounds are ferromagnetic (FM) and show an easy magnetization axis perpendicular to the b axis and only slightly tilted away from the c axis. Upon heating, they display a first order transition from a ferromagnetic towards an antiferromagnetic (AFM) structure at T{sub M0} which is sensitive tomore » the H/D isotope nature. The AFM cell is described by doubling the crystal cell along the monoclinic b axis. It presents an unusual coexistence of non magnetic Fe layer sandwiched by two thicker ferromagnetic Fe layers which are antiparallel to each other. This FM-AFM transition is driven by the loss of ordered moment on one Fe site (Fe7) through an itinerant electron metamagnetic (IEM) behaviour. The key role of the Fe7 position is assigned to both its hydrogen rich atomic environment and its geometric position. Above T{sub M0} a field induced metamagnetic transition is observed from the AFM towards the FM structure accompanied by a cell volume increase. Both thermal and magnetic field dependence of the magnetic structure are found strongly related to the anisotropic cell distortion induced by (H,D) order in interstitial sites. - Graphical abstract: Representation of the FM-AFM magnetic structures of YFe{sub 2}D{sub 4.2} deuteride. - Highlights: • YFe{sub 2}(H,D){sub 4.2} compounds undergoes a isotope sensitive FM-AFM transition at T{sub M0}. • The FM structure is formed of Fe moments perpendicular to the monoclinic b axis. • AFM structure is formed by antiparallel Fe layers separated by non-magnetic Fe layer. • One Fe site among eight loses its moment at T{sub M0} due to larger Fe–H bonding. • Magnetic properties are driven by the monoclinic distortion induced by D order.« less

The influence of the concentration of Sr ions on the crystal and magnetic structures of Ba{sub 2} –{sub x}Sr{sub x}FeMoO{sub 6} double perovskites (x = 0–1.6)

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

Turchenko, V. A., E-mail: turchenko@jinr.ru; Kalanda, N. A.; Kovalev, L. V.

2017-01-15

The crystal and magnetic structures of a solid solution of double perovskite Ba{sub 2–} {sub x}Sr{sub x}FeMoO{sub 6} (x = 0–1.6) have been investigated by neutron diffraction. The high-resolution diffraction patterns have provided precise information about the changes in the crystal and magnetic structures with an increase in the strontium content and data on the behavior of the sample microstructure. Replacement of barium with strontium leads to a change in the lattice symmetry from cubic (x = 0, sp. gr. Fm3̄m)) to tetragonal (x = 0.4, sp. gr. I4/m). At x = 1.0, the symmetry is either tetragonal (sp. gr.more » I4/m) or orthorhombic (sp. gr. Fmmm), and at x = 1.6 the symmetry becomes again tetragonal (sp. gr. I4/m). The values of the Curie temperature and microstrain increase with an increase in the strontium content.« less

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications

NASA Astrophysics Data System (ADS)

Elilarassi, R.; Chandrasekaran, G.

2017-11-01

In the present investigation, diluted magnetic semiconductor (Zn1-xFexO) nanoparticles with different doping concentrations (x = 0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet-visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature.

Vortex lattice structures in YNi{sub 2}B{sub 2}C

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

Yethiraj, M.; Paul, D.M.; Tomy, C.V.

The authors observe a flux lattice with square symmetry in the superconductor YNi{sub 2}B{sub 2}C when the applied field is parallel to the c-axis of the crystal. A square lattice observed previously in the isostructural magnetic analog ErNi{sub 2}B{sub 2}C was attributed to the interaction between magnetic order in that system and the flux lattice. Since the Y-based compound does not order magnetically, it is clear that the structure of the flux lattice is unrelated to magnetic order. In fact, they show that the flux lines have a square cross-section when the applied field is parallel to the c-axis ofmore » the crystal, since the measured penetration depth along the 100 crystal direction is larger than the penetration depth along the 110 by approximately 60%. This is the likely reason for the square symmetry of the lattice. Although they find considerable disorder in the arrangement of the flux lines at 2.5T, no melting of the vortex lattice was observed.« less

Vortex lattice structures in YNi{sub 2}B{sub 2}C

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

Yethiraj, M.; Paul, D.M.; Tomy, C.V.

We observe a flux lattice with square symmetry in the superconductor YNi{sub 2}B{sub 2}C when the applied field is parallel to the c-axis of the crystal. A square lattice observed previously in the isostructural magnetic analog ErNi{sub 2}B{sub 2}C was attributed to the interaction between magnetic order in that system and the flux lattice. Since the Y-based compound does not order magnetically, it is clear that the structure of the flux lattice is unrelated to magnetic order. In fact, we show that the flux lines have a square cross-section when the applied field is parallel to the c-axis of themore » crystal, since the measured penetration depth along the 110 crystal direction is smaller than the penetration depth along the 100 by approximately 30%. This causes the square symmetry of the lattice. Although we find considerable disorder in the arrangement of the flux lines at 2.5T, no melting of the vortex lattice was observed.« less

Magnetic and thermal properties of amorphous TbFeCo alloy films

NASA Astrophysics Data System (ADS)

Wang, Ke; Dong, Shuo; Huang, Ya; Qiu, Yuzhen

2017-07-01

Amorphous TbFeCo material with perpendicular magnetic anisotropy is currently attracting more attention for potential applications in spintronic devices and logic memories. We systematically investigate magnetic, structural, thermal, optical and electrical properties of TbFeCo alloy films. It shows out-of-plane easy axis of the films turns into in-plane orientation after annealing. Significant increase in saturation magnetization in the temperature range between 400 and 450 °C is revealed by thermomagnetic measurements. The occurrence of crystallization and oxidation at high temperatures is confirmed by X-ray diffraction measurements. Pronounced changes in optical reflectance and sheet resistance are observed with temperature, in line with structural relaxation and change. The activation barriers for crystallization and oxidation are determined to be 1.01 eV and 0.83 eV, respectively, for FeCo-rich and Tb-rich samples. Better thermal stability against crystallization and oxidation is demonstrated in the FeCo-rich sample than the Tb-rich type. Our results provide some useful information for the alloy used in device fabrication.

Anisotropic antiferromagnetic order in the spin-orbit coupled trigonal-lattice Ca2Sr2IrO6

NASA Astrophysics Data System (ADS)

Sheng, Jieming; Ye, Feng; Hoffmann, Christina; Cooper, Valentino R.; Okamoto, Satoshi; Terzic, Jasminka; Zheng, Hao; Zhao, Hengdi; Cao, G.

2018-06-01

We used single-crystal x-ray and neutron diffraction to investigate the crystal and magnetic structures of trigonal lattice iridate Ca2Sr2IrO6 . The crystal structure is determined to be R 3 ¯ with two distinct Ir sites. The system exhibits long-range antiferromagnetic order below TN=13.1 K. The magnetic wave vector is identified as (0,0.5,1) with ferromagnetic coupling along the a axis and antiferromagnetic correlation along the b axis. Spins align dominantly within the basal plane along the [1,2,0] direction and tilt 34∘ toward the c axis. The ordered moment is 0.66(3) μB/Ir, larger than other iridates where iridium ions form corner- or edge-sharing IrO6 octahedral networks. The tilting angle is reduced to ≈19∘ when a magnetic field of 4.9 T is applied along the c axis. Density functional theory calculations confirm that the experimentally determined magnetic configuration is the most probable ground state with an insulating gap ˜0.5 eV.

Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium

USGS Publications Warehouse

Sparks, N.H.C.; Mann, S.; Bazylinski, D.A.; Lovley, D.R.; Jannasch, H.W.; Frankel, R.B.

1990-01-01

Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57Fe Mo??ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 ?? 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of {110} faces which are capped and truncated by {111} end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization. ?? 1990.

Magnetic order of Nd 5 Pb 3 single crystals

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

Yan, Jiaqiang; Ochi, Masayuki; Cao, Huibo B.

We report millimeter-sized Nd 5Pb 3 single crystals grown out of a Nd–Co flux. We experimentally study the magnetic order of Nd 5Pb 3 single crystals by measuring the anisotropic magnetic properties, electrical resistivity under high pressure up to 8 GPa, specific heat, and neutron single crystal diffraction. Two successive magnetic orders are observed at T N1 = 44 K and T N2 = 8 K. The magnetic cells can be described with a propagation vector $k=(0.5, 0, 0)$ . Cooling below T N1, Nd1 and Nd3 order forming ferromagnetic stripes along the b-axis, and the ferromagnetic stripes are coupledmore » antiferromagnetically along the a-axis for the $k=(0.5, 0, 0)$ magnetic domain. Cooling below T N2, Nd2 orders antiferromagnetically to nearby Nd3 ions. All ordered moments align along the crystallographic c-axis. The magnetic order at T N1 is accompanied by a quick drop of electrical resistivity upon cooling and a lambda-type anomaly in the temperature dependence of specific heat. At T N2, no anomaly was observed in electrical resistivity but there is a weak feature in specific heat. The resistivity measurements under hydrostatic pressures up to 8 GPa suggest a possible phase transition around 6 GPa. Our first-principles band structure calculations show that Nd 5Pb 3 has the same electronic structure as does Y 5Si 3 which has been reported to be a one-dimensional electride with anionic electrons that do not belong to any atom. Our study suggests that R 5Pb 3 (R = rare earth) can be a materials playground for the study of magnetic electrides. To conclude, this deserves further study after experimental confirmation of the presence of anionic electrons.« less

Magnetic order of Nd 5 Pb 3 single crystals

DOE PAGES

Yan, Jiaqiang; Ochi, Masayuki; Cao, Huibo B.; ...

2018-03-02

We report millimeter-sized Nd 5Pb 3 single crystals grown out of a Nd–Co flux. We experimentally study the magnetic order of Nd 5Pb 3 single crystals by measuring the anisotropic magnetic properties, electrical resistivity under high pressure up to 8 GPa, specific heat, and neutron single crystal diffraction. Two successive magnetic orders are observed at T N1 = 44 K and T N2 = 8 K. The magnetic cells can be described with a propagation vector $k=(0.5, 0, 0)$ . Cooling below T N1, Nd1 and Nd3 order forming ferromagnetic stripes along the b-axis, and the ferromagnetic stripes are coupledmore » antiferromagnetically along the a-axis for the $k=(0.5, 0, 0)$ magnetic domain. Cooling below T N2, Nd2 orders antiferromagnetically to nearby Nd3 ions. All ordered moments align along the crystallographic c-axis. The magnetic order at T N1 is accompanied by a quick drop of electrical resistivity upon cooling and a lambda-type anomaly in the temperature dependence of specific heat. At T N2, no anomaly was observed in electrical resistivity but there is a weak feature in specific heat. The resistivity measurements under hydrostatic pressures up to 8 GPa suggest a possible phase transition around 6 GPa. Our first-principles band structure calculations show that Nd 5Pb 3 has the same electronic structure as does Y 5Si 3 which has been reported to be a one-dimensional electride with anionic electrons that do not belong to any atom. Our study suggests that R 5Pb 3 (R = rare earth) can be a materials playground for the study of magnetic electrides. To conclude, this deserves further study after experimental confirmation of the presence of anionic electrons.« less

Crystal growth, structure determination and magnetism of a new m=3, n=1 member of the A3 n+3 mA' nB3 m+ nO 9 m+6 n family of oxides: 12R-Ba 12Rh 9.25Ir 1.75O 33

NASA Astrophysics Data System (ADS)

Stitzer, Katharine E.; El Abed, Ahmed; Darriet, Jacques; zur Loye, Hans-Conrad

2004-04-01

Single crystals of a new Ba-Rh-Ir-O oxide were grown from a molten potassium carbonate flux. The new compound, Ba 12Rh 9.25Ir 1.75O 33, is structurally related to the 2H-hexagonal perovskite structure and contains pseudo one-dimensional chains of alternating units of ten face-sharing (Rh/Ir)O 6 octahedra and one (Rh/Ir)O 6 trigonal prism. The magnetic susceptibility of Ba 12Rh 9.25Ir 1.75O 33 is featureless, indicating the absence of magnetic order. The oxide is a semiconductor with a room temperature resistance of 280 Ω.

Site selectivity on chalcogen atoms in superconducting La(O,F)BiSSe

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

Tanaka, Masashi, E-mail: Tanaka.Masashi@nims.go.jp; Matsushita, Yoshitaka; Fujioka, Masaya

2015-03-16

Single crystals of La(O,F)BiSSe were grown by using a CsCl flux method. Single crystal X-ray structural analysis reveals that the crystal structure is isostructural to the BiS{sub 2}- or BiSe{sub 2}-based compounds crystallizing with space group P4/nmm (lattice parameters a = 4.1110(2) Å, c = 13.6010(7) Å). However, the S atoms are selectively occupied at the apical site of the Bi-SSe pyramids in the superconducting layer. The single crystals show a superconducting transition at around 4.2 K in the magnetic susceptibility and resistivity measurements. The superconducting anisotropic parameter is determined to be 34–35 from its upper critical magnetic field. The anisotropy is in the same range withmore » that of other members of the La(O,F)BiCh{sub 2} (Ch = S, Se) family under ambient pressure.« less

Swinging Symmetry, Multiple Structural Phase Transitions, and Versatile Physical Properties in RECuGa3 (RE = La-Nd, Sm-Gd).

PubMed

Subbarao, Udumula; Rayaprol, Sudhindra; Dally, Rebecca; Graf, Michael J; Peter, Sebastian C

2016-01-19

The compounds RECuGa3 (RE = La-Nd, Sm-Gd) were synthesized by various techniques. Preliminary X-ray diffraction (XRD) analyses at room temperature suggested that the compounds crystallize in the tetragonal system with either the centrosymmetric space group I4/mmm (BaAl4 type) or the non-centrosymmetric space group I4mm (BaNiSn3 type). Detailed single-crystal XRD, neutron diffraction, and synchrotron XRD studies of selected compounds confirmed the non-centrosymmetric BaNiSn3 structure type at room temperature with space group I4mm. Temperature-dependent single-crystal XRD, powder XRD, and synchrotron beamline measurements showed a structural transition between centro- and non-centrosymmetry followed by a phase transition to the Rb5Hg19 type (space group I4/m) above 400 K and another transition to the Cu3Au structure type (space group Pm3̅m) above 700 K. Combined single-crystal and synchrotron powder XRD studies of PrCuGa3 at high temperatures revealed structural transitions at higher temperatures, highlighting the closeness of the BaNiSn3 structure to other structure types not known to the RECuGa3 family. The crystal structure of RECuGa3 is composed of eight capped hexagonal prism cages [RE4Cu4Ga12] occupying one rare-earth atom in each ring, which are shared through the edge of Cu and Ga atoms along the ab plane, resulting in a three-dimensional network. Resistivity and magnetization measurements demonstrated that all of these compounds undergo magnetic ordering at temperatures between 1.8 and 80 K, apart from the Pr and La compounds: the former remains paramagnetic down to 0.3 K, while superconductivity was observed in the La compound at T = 1 K. It is not clear whether this is intrinsic or due to filamentary Ga present in the sample. The divalent nature of Eu in EuCuGa3 was confirmed by magnetization measurements and X-ray absorption near edge spectroscopy and is further supported by the crystal structure analysis.

Effect of Sr doping on structural and magnetic behavior of SmBa1-xSrxCo2O5+δ (x = 0 and 1)

NASA Astrophysics Data System (ADS)

Kumari, Archana; Dhanasekhar, C.; Das, A. K.

2018-05-01

Layered double perovskite, SmBa1-xSrxCo2O5+δ (x = 0, δ = 0.5 and x = 1, δ = 1) samples were prepared by solid state reaction method. X-ray diffraction studies show that the SmBaCo2O5.5 sample crystallizes in the orthorhombic crystal structure with Pmmm space group, whereas SmSrCo2O6 sample crystallizes in the orthorhombic crystal structure with Pnma space group. The temperature dependent magnetization of the SmBaCo2O5.5 sample shows a paramagnetic (PM)-ferromagnetic (FM) and a FM-antiferromagnetic (AFM) transitions at TC = 267 K and TN = 221 K, respectively. In contrast, the SmSrCo2O6 sample shows a PM-FM transition at TC = 175 K. According to Goodenough-Kanamori-Anderson rules, the ferromagnetic behavior in SmSrCo2O6 can be understood from the super exchange interaction between the intermediate spin Co3+ and low spin Co4+ via O2- (IS Co3+ -O2- - LS Co4+). The change in magnetic entropy (ΔSMmax) is found to be maximum for the SmSrCo2O6 sample.

Crystal structure, thermochromic and magnetic properties of organic-inorganic hybrid compound: (C7H7N2S)2CuCl4

NASA Astrophysics Data System (ADS)

Vishwakarma, Ashok K.; Kumari, Reema; Ghalsasi, Prasanna S.; Arulsamy, Navamoney

2017-08-01

The synthesis, thermal analysis, crystal structure and magnetic properties of (2-aminobenzothiazolium)2CuCl4, organic-inorganic hybrid compound, have been described. The compound crystallizes in the monoclinic space group P21/c with two formula units in a unit cell of dimensions a = 6.9522(4) Å, b = 9.6979(4) Å, c = 13.9633(6) Å, β = 97.849(3)° and volume 930.83(8) Å3 at 150(2) K. The structure consists of isolated nearly square planer [CuC14]2- units, with somewhat longer than normal Cusbnd Cl bond lengths [Cusbnd Cl (average) = 2.2711 Å]. The magnetic measurements of (2-aminobenzothiazolium)2CuCl4 using SQUID magnetometer show paramagnetic nature of the compound. Thermal measurements (TG-DTA and DSC) on this compound showed reversible phase transition at 83 °C. This transition is accompanied by the reversible change in colour of the prismatic crystal from green to dark brown, thermochromic behaviour. Temperature dependent EPR measurements on powdered sample ascertain change in coordination sphere around Cu(II) with shift in g|| = 2.150 and g⊥ = 2.071 at room temperature, typical of square planar, to g|| = 2.201 and g⊥ = 2.182 at 170 °C, typical of distorted tetrahedral geometry.

Structure and magnetic properties of Ce₃(Ni/Al/Ga)₁₁—A new phase with the La₃Al₁₁ structure type

DOE PAGES

Janka, Oliver; Shang, Tian; Baumbach, Ryan E.; ...

2015-03-01

Single crystals of Ce₃(Ni/Al/Ga)₁₁ were obtained from an Al flux reaction. Single crystals of the title compound crystallizing in the orthorhombic space group Immm (No. 71, Z = 2) with a = 436.38(14), b = 1004.5(3) and c = 1293.4(4) pm. This is a standardized unit cell of the previously published La₃Al₁₁ structure type. Wavelength dispersive microprobe provides the composition of Ce₃.₁₁₍₁₎Ni₀.₀₃₍₁₎Al₈.₉₅₍₁₎Ga₁.₉₀₍₁₎. Single crystal refinement provides the composition Ce₃Ni₀.₀₈Al₉.₁₃Ga₁.₇₈ with substitution of the Ni and Ga on the Al1 and Al4 sites with the Al2 and Al3 solely occupied by Al. Magnetic susceptibility measurements reveal antiferromagnetic ordering with T Nmore » = 4.8 K and there is no evidence for a ferromagnetic ordering that has been reported for Ce₃Al₁₁. The effective magnetic moment was found to be μ eff = 1.9μB/Ce, which is lower than the expected value for trivalent Ce (2.54μB/Ce).« less

Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Crx(Rh1-yRuy)7-xB3 (x=0.88-1; y=0-1) with Th7Fe3-type structure

NASA Astrophysics Data System (ADS)

Misse, Patrick R. N.; Mbarki, Mohammed; Fokwa, Boniface P. T.

2012-08-01

Powder samples and single crystals of the new complex boride series Crx(Rh1-yRuy)7-xB3 (x=0.88-1; y=0-1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region.

Transport and magnetic properties of HITPERM alloys

NASA Astrophysics Data System (ADS)

Pekala, K.; Latuch, J.; Pekala, M.; Skorvanek, I.; Jaskiewicz, P.

2003-02-01

Nanocrystalline HITPERM alloys Fe44.6Co43.3X7.4B3.7Cu1 (X = Nb, Zr, Hf) prepared by crystallization of amorphous precursors are studied by magnetization and electrical resistivity measurements for the first time. Structural and magnetic components of the electrical resistivity are separated. The electrical resistivity of the nanocrystalline α' (FeCo) phase calculated using the Maxwell Garnett relation proves strong electron scattering on the grain boundaries. The temperature variation of the crystalline fraction during the first crystallization stage is calculated for the Hf based alloy.

Short review of high-pressure crystal growth and magnetic and electrical properties of solid-state osmium oxides

NASA Astrophysics Data System (ADS)

Yamaura, Kazunari

2016-04-01

High-pressure crystal growth and synthesis of selected solid-state osmium oxides, many of which are perovskite-related types, are briefly reviewed, and their magnetic and electrical properties are introduced. Crystals of the osmium oxides, including NaOsO3, LiOsO3, and Na2OsO4, were successfully grown under high-pressure and high-temperature conditions at 6 GPa in the presence of an appropriate amount of flux in a belt-type apparatus. The unexpected discovery of a magnetic metal-insulator transition in NaOsO3, a ferroelectric-like transition in LiOsO3, and high-temperature ferrimagnetism driven by a local structural distortion in Ca2FeOsO6 may represent unique features of the osmium oxides. The high-pressure and high-temperature synthesis and crystal growth has played a central role in the development of solid-state osmium oxides and the elucidation of their magnetic and electronic properties toward possible use in multifunctional devices.

Topological transformations of Hopf solitons in chiral ferromagnets and liquid crystals.

PubMed

Tai, Jung-Shen B; Ackerman, Paul J; Smalyukh, Ivan I

2018-01-30

Liquid crystals are widely known for their facile responses to external fields, which forms a basis of the modern information display technology. However, switching of molecular alignment field configurations typically involves topologically trivial structures, although singular line and point defects often appear as short-lived transient states. Here, we demonstrate electric and magnetic switching of nonsingular solitonic structures in chiral nematic and ferromagnetic liquid crystals. These topological soliton structures are characterized by Hopf indices, integers corresponding to the numbers of times that closed-loop-like spatial regions (dubbed "preimages") of two different single orientations of rod-like molecules or magnetization are linked with each other. We show that both dielectric and ferromagnetic response of the studied material systems allow for stabilizing a host of topological solitons with different Hopf indices. The field transformations during such switching are continuous when Hopf indices remain unchanged, even when involving transformations of preimages, but discontinuous otherwise.

Solitons in Crystalline Processes; Statistical thermodynamics of structural phase transitions and mesoscopic disorder

NASA Astrophysics Data System (ADS)

Fujimoto, Minoru

2017-11-01

Solitons in Crystalline Processes is an introduction to the statistical thermodynamics of phase transitions in crystallized solids. This book is written as an introductory treatise with respect to the soliton concept, from structural transitions where the crystal symmetry changes, to magnets and superconductors, describing the role of nonlinear excitations in detail.

Surface Modification and Nanojunction Fabrication with Molecular Metal Wires

DTIC Science & Technology

2012-12-21

single - crystal X-ray diffraction studies of 2 and 3. Both the single - crystal structural data of 2 and 3 and the spectroscopic/voltammetric data...structure, magnetic properties, and single -molecule conductance of two new trinuclear metal string complexes, [Ni3(dzp)4(NCS)2] (2) and [ Co3 (dzp)4(NCS...modifying the crystallization conditions. The [s- Co3 (dpa)4(Cl)2] contains a symmetrical tricobalt framework with identical Co–Co bond lengths (2.34 Å

Metal–organic coordination architectures of tetrazole heterocycle ligands bearing acetate groups: Synthesis, characterization and magnetic properties

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

Hu, Bo-Wen, E-mail: bowenhu@hit.edu.cn; Zheng, Xiang-Yu; Ding, Cheng

2015-12-15

Two new coordination complexes with tetrazole heterocycle ligands bearing acetate groups, [Co(L){sub 2}]{sub n} (1) and [Co{sub 3}(L){sub 4}(N{sub 3}){sub 2}·2MeOH]{sub n} (2) (L=tetrazole-1-acetate) have been synthesized and structurally characterized. Single crystal structure analysis shows that the cobalt-complex 1 has the 3D 3,6-connected (4{sup 2}.6){sub 2}(4{sup 4}.6{sup 2}.8{sup 8}.10)-ant topology. By introducing azide in this system, complex 2 forms the 2D network containing the [Co{sub 3}] units. And the magnetic properties of 1 and 2 have been studied. - Graphical abstract: The synthesis, crystal structure, and magnetic properties of the new coordination complexes with tetrazole heterocycle ligands bearing acetate groupsmore » are reported. - Highlights: • Two novel Cobalt(II) complexes with tetrazole acetate ligands were synthesized. • The magnetic properties of two complexes were studied. • Azide as co-ligand resulted in different structures and magnetic properties. • The new coordination mode of tetrazole acetate ligand was obtained.« less

Tunable magnetic properties and magnetocaloric effect of off-stoichiometric LaMnO3 nanoparticles

NASA Astrophysics Data System (ADS)

Tola, P. S.; Kim, H. S.; Kim, D. H.; Phan, T. L.; Rhyee, J. S.; Shon, W. H.; Yang, D. S.; Manh, D. H.; Lee, B. W.

2017-12-01

The crystal and electronic structures and the magnetic and magnetocaloric properties of off-stoichiometric LaMnO3 nanoparticles (NPs) with various particle sizes D = 20-100 nm were studied. The Rietveld refinement revealed that all NPs were crystallized in the rhombohedral structure, with varied structural parameters dependent on D. Magnetization (M) measurements indicated a considerable difference between zero-field-cooled and field-cooled magnetizations at temperatures below ferromagnetic-paramagnetic (FM-PM) phase transition, particularly for the samples with D = 25-40 nm. These results are ascribed to spin-glass-like behaviors and magnetic inhomogeneity. We also found the possibility of tuning the FM-PM phase transition temperature (TC) from 77 to 262 K, which is dependent on both D and W (the eg-electron bandwidth). Under an applied field of H = 50 kOe, the absolute maximum magnetic entropy change that achieved around TC can be improved from 4.02 J kg-1 K-1 for D = 40 nm to 6.36 Jṡ kg-1ṡ K-1 for D = 100 nm, corresponding to the relative-cooling-power values of 241-245 Jṡ kg-1. We also analyzed the data of M and magnetic entropy change based on theoretical models to further understand the magnetic property and phase-transition type of the NP samples.

Magnetic and structural properties of yellow europium oxide compound and Eu(OH){sub 3}

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

Lee, Dongwook, E-mail: dongwookleedl324@gmail.com; Seo, Jiwon, E-mail: jiwonseo@yonsei.ac.kr; Valladares, Luis de los Santos

A new material based on a yellow europium oxide compound was prepared from europium oxide in a high vacuum environment. The structural and magnetic properties of the material were investigated. Owing to the absence of a crystal structure, the material exhibited a disordered magnetic behavior. In a reaction with deionized (DI) water without applied heat, the compound assumed a white color as soon as the DI water reached the powder, and the structure became polycrystalline Eu(OH){sub 3}. The magnetic properties, such as the thermal hysteresis, disappeared after the reaction with DI water, and the magnetic susceptibility of the yellow oxidemore » compound weakened. The magnetic properties of Eu(OH){sub 3} were also examined. Although Eu{sup 3+} is present in Eu(OH){sub 3}, a high magnetic moment due to the crystal field effect was observed. - Graphical abstract: (top left) Optical image of the yellow europium oxide compound. (top right) Optical image of the product of DI water and yellow europium oxide. (bottom) Magnetization curves as a function of temperature measured in various magnetic field. - Highlights: • We prepared a new material based on a yellow europium oxide compound from europium oxide. • We characterized the magnetic properties of the material which exhibits a disordered magnetic behavior such as thermal hysteresis. • The compound turned white (Eu(OH){sub 3}) as soon as the DI water reached the powder. • The thermal hysteresis disappeared after the reaction with DI water and the magnetic susceptibility of the yellow oxide compound weakened.« less

Structure and magnetic properties of Fe-Co-B alloy thin films prepared on cubic (001) single-crystal substrates

NASA Astrophysics Data System (ADS)

Ohtake, Mitsuru; Serizawa, Kana; Futamoto, Masaaki; Kirino, Fumiyoshi; Inaba, Nobuyuki

2018-04-01

Fe70Co30 and (Fe70Co30)0.95B5 (at. %) alloy films of 5 nm thickness are prepared by sputtering on cubic (001) oxide substrates at 200 °C. The lattice mismatch between film and substrate is varied from -4.2%, 0%, to +3.5% by employing MgO, MgAl2O4, and SrTiO3 substrates, respectively. Fe70Co30 and (Fe70Co30)0.95B5 single-crystal films with bcc structure grow epitaxially on all the substrates in the orientation relationship of (001)[110]film || (001)[100]substrate. The in-plane and out-of-plane lattice constants, a and c, are in agreement within small differences ranging between +1.1% and -0.9% with the value of bulk bcc-Fe70Co30 crystal, even though there exist the lattice mismatches of -4.2% and +3.5%. The result indicates that misfit dislocations are introduced around the film/substrate interface when films are deposited on MgO and SrTiO3 substrates. The single-crystal films show in-plane magnetic anisotropies with the easy magnetization direction of bcc[100], which are reflecting the magnetocrystalline anisotropy of bulk Fe70Co30 crystal.

Magnetostructural Properties of Colossal Magnetoresistance Manganites Under External Magnetic Fields and Uniaxial Pressure

NASA Astrophysics Data System (ADS)

Kaplan, Michael; Zimmerman, George

2002-03-01

In the colossal magnetoresistance manganites the transport and magnetostructural properties are tightly connected [1,2]. Many magnetic field induced structural phase transitions and anomalous magnetoacoustical properties continue to be discovered in various manganite derivatives. Nevertheless the mechanism of structural transitions and microscopic theory of corresponding anomalous properties are still to be completely understood. Here we present a microscopic model of magnetic field and uniaxial pressure induced structural phase transitions in lightly doped manganites. The model is based on the cooperative Jahn-Teller effect which takes into account the Mn3+-ground doublet and excited triplet electronic states. Numerous calculations for different orientation magnetic field suggest the explanations of the origin of the structural transitions and of the measured magnetostriction data. The calculations for the two-sublattice antiferrodistortive crystals under uniaxial pressure support the idea of metaelasticity - a property typical for Jahn-Teller antiferroelastics. 1.Y. Tokura, ed. Colossal Magnetoresistance Oxides. Gordon & Breach, London, 2000. 2.M. Kaplan, G. Zimmerman, eds. Vibronic Interactions: Jahn-Teller Effect in Crystal and Molecules. NATO Science Series, Dordrecht/Boston/London, 2001

Magnetic domains and defects in ferromagnetic liquid crystal colloids realized with optical patterning

NASA Astrophysics Data System (ADS)

Hess, Andrew; Liu, Qingkun; Smalyukh, Ivan

A promising approach in designing composite materials with unusual physical behavior combines solid nanostructures and orientationally ordered soft matter at the mesoscale. Such composites not only inherit properties of their constituents but also can exhibit emergent behavior, such as ferromagnetic ordering of colloidal metal nanoparticles forming mesoscopic magnetization domains when dispersed in a nematic liquid crystal. Here we demonstrate the optical patterning of domain structures and topological defects in such ferromagnetic liquid crystal colloids which allows for altering their response to magnetic fields. Our findings reveal the nature of the defects in this soft matter system which is different as compared to non-polar nematic and ferromagnetic systems alike. This research was supported by the NSF Grant DMR-1420736.

Synthesis and Physical Properties of the Oxofluoride Cu2(SeO3)F2.

PubMed

Mitoudi-Vagourdi, Eleni; Papawassiliou, Wassilios; Müllner, Silvia; Jaworski, Aleksander; Pell, Andrew J; Lemmens, Peter; Kremer, Reinhard K; Johnsson, Mats

2018-04-16

Single crystals of the new compound Cu 2 (SeO 3 )F 2 were successfully synthesized via a hydrothermal method, and the crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma with the unit cell parameters a = 7.066(4) Å, b = 9.590(4) Å, and c = 5.563(3) Å. Cu 2 (SeO 3 )F 2 is isostructural with the previously described compounds Co 2 TeO 3 F 2 and CoSeO 3 F 2 . The crystal structure comprises a framework of corner- and edge-sharing distorted [CuO 3 F 3 ] octahedra, within which [SeO 3 ] trigonal pyramids are present in voids and are connected to [CuO 3 F 3 ] octahedra by corner sharing. The presence of a single local environment in both the 19 F and 77 Se solid-state MAS NMR spectra supports the hypothesis that O and F do not mix at the same crystallographic positions. Also the specific phonon modes observed with Raman scattering support the coordination around the cations. At high temperatures the magnetic susceptibility follows the Curie-Weiss law with Curie temperature of Θ = -173(2) K and an effective magnetic moment of μ eff ∼ 2.2 μ B . Antiferromagnetic ordering below ∼44 K is indicated by a peak in the magnetic susceptibility. A second though smaller peak at ∼16 K is tentatively ascribed to a magnetic reorientation transition. Both transitions are also confirmed by heat capacity measurements. Raman scattering experiments propose a structural phase instability in the temperature range 6-50 K based on phonon anomalies. Further changes in the Raman shift of modes at ∼46 K and ∼16 K arise from transitions of the magnetic lattice in accordance with the susceptibility and heat capacity measurements.

Possible Itinerant Moment Contributions to the Magnetic Excitations in Gd, Studied by Neutron Spectroscopy

NASA Astrophysics Data System (ADS)

Granroth, G. E.; Aczel, A. A.; Fernandez-Baca, J. A.; Nagler, S. E.

2013-03-01

Many experimental features in magnetic superconductors are also present when these complex materials are in the normal state. Therefore studies of simpler itinerant magnets may help provide understanding of these phenomena. We chose to study Gd as it is has an ~ 0 . 6μB itinerant moment in addition to a ~ 7 . 0μB localized moment. The SEQUOIA spectrometer, at the Spallation Neutron Source at Oak Ridge National Laboratory, was used in fine resolution mode with Ei=50 meV neutrons, to measure the magnetic excitations in a 12 gm 160Gd single crystal. The crystal was mounted with the h 0 l plane horizontal and rotated around the vertical axis to map out the excitations. The measured magnetic structure factor for the acoustic modes in the hh 0 direction has an intensity step at h ~ 0 . 3 . Electronic band structure calculations (W. M. Temmerman and P. A. Sterne, J. Phys: Condes. Matter,2, 5529 (1990)) show this Q position to be near several band crossings of the Fermi surface. A detailed analysis, including instrumental resolution, is presented to clarify any relationship between the magnetic structure factor and the electronic band structure. This work was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Synthesis, crystal structure, and magnetic properties of two-dimensional divalent metal glutarate/dipyridylamine coordination polymers, with a single crystal-to-single crystal transformation in the copper derivative

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

Montney, Matthew R.; Supkowski, Ronald M.; Staples, Richard J.

Hydrothermal reaction of divalent metal chlorides with glutaric acid and 4,4'-dipyridylamine (dpa) has afforded an isostructural family of coordination polymers with formulation [M(glu)(dpa)]{sub n} (M=Co (1), Ni (2), Cu (3); glu=glutarate). Square pyramidal coordination is seen in 1-3, with semi-ligation of a sixth donor to produce a '5+1' extended coordination sphere. Neighboring metal atoms are linked into 1D [M(glu)]{sub n} neutral chains through chelating/monodentate bridging glutarate moieties with a syn-anti binding mode, and semi-chelation of the pendant carboxylate oxygen. These chains further connect into 2D layers through dipodal dpa ligands. Neighboring layers stack into the pseudo 3D crystal structure ofmore » 1-3 through supramolecular hydrogen bonding between dpa amine units and the semi-chelated glutarate oxygen atoms. The variable temperature magnetic behavior of 1-3 was explored and modeled as infinite 1D Heisenberg chains. Notably, complex 3 undergoes a thermally induced single crystal-to-single crystal transformation between centric and acentric space groups, with a conformationally disordered unilayer structure at 293 K and an ordered bilayer structure at 173 K. All materials were further characterized via infrared spectroscopy and elemental and thermogravimetric analyses. - Graphical abstract: The coordination polymers [M(glu)(dpa)]{sub n} (M=Co (1), Ni (2), Cu (3); glu=glutarate, dpa=4,4'-dipyridylamine) exhibit 2D layer structures based on 1D [M(glu)]{sub n} chains linked through dpa tethers. Antiferromagnetic coupling is observed for 2 and 3, while ferromagnetism is predominant in 1. Compound 3 undergoes a thermally induced single crystal-to-single crystal transformation from an acentric to a centrosymmetric space group.« less

Mapping the magnetic and crystal structure in cobalt nanowires

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

Cantu-Valle, Jesus; Betancourt, Israel; Sanchez, John E.

2015-07-14

Using off-axis electron holography under Lorentz microscopy conditions to experimentally determine the magnetization distribution in individual cobalt (Co) nanowires, and scanning precession-electron diffraction to obtain their crystalline orientation phase map, allowed us to directly visualize with high accuracy the effect of crystallographic texture on the magnetization of nanowires. The influence of grain boundaries and disorientations on the magnetic structure is correlated on the basis of micromagnetic analysis in order to establish the detailed relationship between magnetic and crystalline structure. This approach demonstrates the applicability of the method employed and provides further understanding on the effect of crystalline structure on magneticmore » properties at the nanometric scale.« less

Magnetic and thermal behavior of a family of compositionally related zero-dimensional fluorides

NASA Astrophysics Data System (ADS)

Felder, Justin B.; Smith, Mark D.; Sefat, Athena; zur Loye, Hans-Conrad

2018-07-01

The mild hydrothermal crystal growth technique has been leveraged to synthesize four new zero-dimensional transition metal fluorides. Their structures were determined by single crystal X-ray diffraction and confirmed by powder X-ray diffraction. The thermal, optical, and magnetic properties were investigated and the presence of thermal polymorphism and antiferromagnetism were observed. In addition, the potential application of these materials as precursors for advanced functional materials was explored.

Nature of the magnetic ground state in the mixed valence compound CeRuSn: a single-crystal study.

PubMed

Fikáček, J; Prokleška, J; Prchal, J; Custers, J; Sechovský, V

2013-10-16

We report on detailed low-temperature measurements of the magnetization, the specific heat and the electrical resistivity on high-quality CeRuSn single crystals. The compound orders antiferromagnetically at T(N) = 2.8 K with the Ce(3+) ions locked within the a-c plane of the monoclinic structure. Magnetization shows that below T(N) CeRuSn undergoes a metamagnetic transition when applying a magnetic field of 1.5 and 0.8 T along the a- and c-axis, respectively. This transition manifests in a tremendous negative jump of ~25% in the magnetoresistance. The value of the saturated magnetization along the easy magnetization direction (c-axis) and the magnetic entropy above T(N) derived from specific heat data correspond to the scenario of only one third of the Ce ions in the compound being trivalent and carrying a stable Ce(3+) magnetic moment, whereas the other two thirds of the Ce ions are in a nonmagnetic tetravalent and/or mixed valence state. This is consistent with the low-temperature CeRuSn crystal structure i.e., a superstructure consisting of three unit cells of the CeCoAl type piled up along the c-axis, and in which the Ce(3+) ions are characterized by large distances from the Ru ligands while the Ce-Ru distances of the other Ce ions are much shorter causing a strong 4f-ligand hybridization and hence leading to tetravalent and/or mixed valence Ce ions.

Magnetic and photocatalytic studies on Zn1-xMgxFe2O4 nanocolloids synthesized by solvothermal reflux method.

PubMed

Manohar, A; Krishnamoorthi, C

2017-12-01

Biocompatible magnetic semiconductor Zn 1-x Mg x Fe 2 O 4 (x=0, 0.1, 0.3, 0.5 & 0.7) nanoparticles of around 10nm diameter were synthesized by solvothermal reflux method. The method produces well separated and narrow size distributed nanoparticles. Crystal structure, morphology, particles surface properties, surfactant quantity, colloidal stability, magnetic properties and photocatalytic properties of the synthesized nanoparticles were studied. Different characterizations confirmed that all compounds were single crystals and superparamagnetic at room temperature. Saturation mass magnetization (M s =57.5emu/g) enhances with substituent Mg 2+ concentration due to promotion of mixed spinel (normal and inverse) structure. Photocatalytic activity of all synthesized magnetic semiconductor nanoparticles were studied through methylene blue degradation. The degradation of 98% methylene blue was observed on 60 min irradiation of light. It is observed that photocatalytic activity slightly enhances with substituent Mg 2+ concentration. The synthesized biocompatible magnetic semiconductor nanoparticles can be utilized as photocatalysts and could also be recycled and separated by applying an external magnetic field. Copyright © 2017 Elsevier B.V. All rights reserved.

Magnetic structures and excitations in CePd2(Al,Ga)2 series: Development of the "vibron" states

NASA Astrophysics Data System (ADS)

Klicpera, M.; Boehm, M.; Doležal, P.; Mutka, H.; Koza, M. M.; Rols, S.; Adroja, D. T.; Puente Orench, I.; Rodríguez-Carvajal, J.; Javorský, P.

2017-02-01

CePd2Al2 -xGax compounds crystallizing in the tetragonal CaBe2Ge2 -type structure (space group P 4 /n m m ) and undergoing a structural phase transition to an orthorhombic structure (C m m e ) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector k ⃗=(δx,1/2 +δy,0 ) with δx=0.06 and δy=0.04 . The magnetic moments order antiferromagnetically within the a b planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) μB/Ce3 +. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector k1⃗=(1/2 ,1/2 ,0 ) , and the second one propagates with k2⃗=(0 ,1/2 ,0 ) . The magnetic moments of both components are aligned along the same direction—the orthorhombic [100] direction—and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors k1⃗ and k2⃗ describe also the magnetic structure of substituted CePd2Al2 -xGax compounds, except the one with x =0.1 .CePd2Al1.9Ga0.1 with magnetic structure described by k ⃗ and k1⃗ stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2 , while only two crystal field (CF) excitations are expected from the splitting of ground state J =5/2 of the Ce3 + ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2 . A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd2Ga2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd2Al2 -xGax series is discussed and crystal field parameters determined.

Complex structures of different CaFe2As2 samples

PubMed Central

Saparov, Bayrammurad; Cantoni, Claudia; Pan, Minghu; Hogan, Thomas C.; II, William Ratcliff; Wilson, Stephen D.; Fritsch, Katharina; Gaulin, Bruce D.; Sefat, Athena S.

2014-01-01

The interplay between magnetism and crystal structures in three CaFe2As2 samples is studied. For the nonmagnetic quenched crystals, different crystalline domains with varying lattice parameters are found, and three phases (orthorhombic, tetragonal, and collapsed tetragonal) coexist between TS = 95 K and 45 K. Annealing of the quenched crystals at 350°C leads to a strain relief through a large (~1.3%) expansion of the c-parameter and a small (~0.2%) contraction of the a-parameter, and to local ~0.2 Å displacements at the atomic-level. This annealing procedure results in the most homogeneous crystals for which the antiferromagnetic and orthorhombic phase transitions occur at TN/TS = 168(1) K. In the 700°C-annealed crystal, an intermediate strain regime takes place, with tetragonal and orthorhombic structural phases coexisting between 80 to 120 K. The origin of such strong shifts in the transition temperatures are tied to structural parameters. Importantly, with annealing, an increase in the Fe-As length leads to more localized Fe electrons and higher local magnetic moments on Fe ions. Synergistic contribution of other structural parameters, including a decrease in the Fe-Fe distance, and a dramatic increase of the c-parameter, which enhances the Fermi surface nesting in CaFe2As2, are also discussed. PMID:24844399

Synthesis, crystal structure and study of magnetocaloric effect and single molecular magnetic behaviour in discrete lanthanide complexes.

PubMed

Adhikary, Amit; Sheikh, Javeed Ahmad; Biswas, Soumava; Konar, Sanjit

2014-06-28

The synthesis, crystal structure and magnetic properties of four polynuclear lanthanide coordination complexes having molecular formulae, [Gd3(2)(1)L(H2O)8(Cl)](Cl)4·10H2O (1), [Dy3L(2)(1)(H2O)9](Cl)5·6H2O (2) [Gd6L(2)(2)(HCO2)4(μ3-OH)4(DMF)6(H2O)2](Cl)2·4H2O (3) and [Dy6L(2)(2)(HCO2)4(μ3-OH)4(DMF)6(H2O)2](Cl)2·4H2O (4) (where H2L(1) = bis[(2-pyridyl)methylene]pyridine-2,6-dicarbohydrazide and H4L(2) = bis[2-hydroxy-benzylidene]pyridine-2,6-dicarbohydrazide) are reported. Structural investigation by X-ray crystallography reveals similar structural features for complexes 1 and 2 and they exhibit butterfly like shapes of the molecules. Non-covalent interactions between the molecules create double helical arrangements for both molecules. Complexes 3 and 4 are isostructural and the core structures feature four distorted hemi-cubanes connected by vertex sharing. Magnetic studies unveil significant magnetic entropy changes for complexes 1, 3 and slow relaxation of magnetization for both dysprosium analogues 2 and 4.

Determination of bulk domain structure and magnetization processes in bcc ferromagnetic alloys: Analysis of magnetostriction in F e83G a17

NASA Astrophysics Data System (ADS)

He, Yangkun; Coey, J. M. D.; Schaefer, Rudolf; Jiang, Chengbao

2018-01-01

The ground state of macroscopic samples of magnetically ordered materials is a domain state because of magnetostatic energy or entropy, yet we have limited experimental means for imaging the bulk domain structure and the magnetization process directly. The common methods available reveal the domains at the surface or in electron- or x-ray transparent lamellae, not those in the bulk. The magnetization curve just reflects the vector sum of the moments of all the domains in the sample, but magnetostriction curves are more informative. They are strongly influenced by the domain structure in the unmagnetized state and its evolution during the magnetization process in an applied field. Here we report a method of determining the bulk domain structure in a cubic magnetostrictive material by combining magneto-optic Kerr microscopy with magnetostriction and magnetization measurements on single crystals as a function of applied field. We analyze the magnetostriction of F e83G a17 crystals in terms of a domain structure that is greatly influenced by sample shape and heat treatment. Saturation magnetostriction measurements are used to determine the fraction of domains orientated along the three 〈100 〉 axes in the initial state. Domain wall motion and rotation process have characteristic signatures in the magnetostriction curves, including those associated with the Δ E effect and domain rotation through a 〈110 〉 auxetic direction.

Influence of Al substitution on magnetism and adsorption properties of hematite

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

Cao, Shanshan; Kang, Feifei; Yang, Xin

2015-08-15

A series of Al-substituted hematite was prepared. The structures and properties of as-prepared samples were characterized by various techniques. The magnetic property of the samples was determined and the adsorption of three dyes Acid Blue 74, Methylene Blue and Phenol Red onto the samples was investigated. The results showed that Al incorporation into the crystal structure of hematite occurs via isomorphous ionic substitution of Al for Fe. With increasing Al content, the particle size of samples decreases, the magnetization increases and the remanent magnetization remains unchanged. The coercivity of the samples increases with Al substitution up to n{sub Al}/n{sub Fe}more » 0.03, and then decreases as Al content further increases. Compared with Al-free hematite, Al-substituted samples exhibit better adsorption ability to all of the three dyes. The adsorption rates of the three dyes on the surface of Al substituted samples depend on the structure of dye, pH and Al content in hematite. - Graphical abstract: Effect of Al on the structure, magnetic properties and adsorption performance of hematite was investigated. - Highlights: • A series of Al-substituted α-Fe{sub 2}O{sub 3} was prepared. • Effect of Al content on the crystal structure and magnetic property of hematite was investigated. • Al-substituted hematite exhibits better adsorption ability than hematite.« less

Magnetic properties of magnetic bilayer Kekulene structure: A Monte Carlo study

NASA Astrophysics Data System (ADS)

Jabar, A.; Masrour, R.

2018-06-01

In the present work, we have studied the magnetic properties of magnetic bilayer Kekulene structure with mixed spin-5/2 and spin-2 Ising model using Monte Carlo study. The magnetic phase diagrams of mixed spins Ising model have been given. The thermal total, partial magnetization and magnetic susceptibilities of the mixed spin-5/2 and spin-2 Ising model on a magnetic bilayer Kekulene structure are obtained. The transition temperature has been deduced. The effect of crystal field and exchange interactions on the this bilayers has been studied. The partial and total magnetic hysteresis cycles of the mixed spin-5/2 and spin-2 Ising model on a magnetic bilayer Kekulene structure have been given. The superparamagnetism behavior is observed in magnetic bilayer Kekulene structure. The magnetic coercive field decreases with increasing the exchange interactions between σ-σ and temperatures values and increases with increasing the absolute value of exchange interactions between σ-S. The multiple hysteresis behavior appears.

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

Gil, D.M.; Osiry, H.; Pomiro, F.

The hydrogen bond and π-π stacking are two non-covalent interactions able to support cooperative magnetic ordering between paramagnetic centers. This contribution reports the crystal structure and related magnetic properties for VO[Fe(CN){sub 5}NO]·2H{sub 2}O, which has a layered structure. This solid crystallizes with an orthorhombic unit cell, in the Pna2{sub 1} space group, with cell parameters a=14.1804(2), b=10.4935(1), c=7.1722(8) Å and four molecules per unit cell (Z=4). Its crystal structure was solved and refined from powder X-ray diffraction data. Neighboring layers remain linked through a network of hydrogen bonds involving a water molecule coordinated to the axial position for the Vmore » atom and the unbridged axial NO and CN ligands. An uncoordinated water molecule is found forming a triple bridge between these last two ligands and the coordinated water molecule. The magnetic measurements, recorded down to 2 K, shows a ferromagnetic interaction between V atoms located at neighboring layers, with a Curie-Weiss constant of 3.14 K. Such ferromagnetic behavior was interpreted as resulting from a superexchange interaction through the network of strong OH····O{sub H2O}, OH····N{sub CN}, and OH····O{sub NO} hydrogen bonds that connects neighboring layers. The interaction within the layer must be of antiferromagnetic nature and it was detected close to 2 K. - Graphical abstract: Coordination environment for the metals in vanadyl (II) nitroprusside dihydrate. Display Omitted - Highlights: • Crystal structure of vanadyl nitroprusside dehydrate. • Network of hydrogen bonds. • Magnetic interactions through a network of hydrogen bonds. • Layered transition metal nitroprussides.« less

Canted antiferromagnetism in phase-pure CuMnSb

NASA Astrophysics Data System (ADS)

Regnat, A.; Bauer, A.; Senyshyn, A.; Meven, M.; Hradil, K.; Jorba, P.; Nemkovski, K.; Pedersen, B.; Georgii, R.; Gottlieb-Schönmeyer, S.; Pfleiderer, C.

2018-05-01

We report the low-temperature properties of phase-pure single crystals of the half-Heusler compound CuMnSb grown by means of optical float zoning. The magnetization, specific heat, electrical resistivity, and Hall effect of our single crystals exhibit an antiferromagnetic transition at TN=55 K and a second anomaly at a temperature T*≈34 K. Powder and single-crystal neutron diffraction establish an ordered magnetic moment of (3.9 ±0.1 ) μB/f .u . , consistent with the effective moment inferred from the Curie-Weiss dependence of the susceptibility. Below TN, the Mn sublattice displays commensurate type-II antiferromagnetic order with propagation vectors and magnetic moments along <111 > (magnetic space group R [I ]3 c ). Surprisingly, below T*, the moments tilt away from <111 > by a finite angle δ ≈11∘ , forming a canted antiferromagnetic structure without uniform magnetization consistent with magnetic space group C [B ]c . Our results establish that type-II antiferromagnetism is not the zero-temperature magnetic ground state of CuMnSb as may be expected of the face-centered cubic Mn sublattice.

Metal Flux Growth, Structural Relations, and Physical Properties of EuCu2Ge2 and Eu3T2In9 (T = Cu and Ag).

PubMed

Subbarao, Udumula; Roy, Soumyabrata; Sarma, Saurav Ch; Sarkar, Sumanta; Mishra, Vidyanshu; Khulbe, Yatish; Peter, Sebastian C

2016-10-17

Single crystals (SCs) of the compounds Eu 3 Ag 2 In 9 and EuCu 2 Ge 2 were synthesized through the reactions run in liquid indium. Eu 3 Ag 2 In 9 crystallizes in the La 3 Al 11 structure type [orthorhombic space group (SG) Immm] with the lattice parameters: a = 4.8370(1) Å, b = 10.6078(3) Å, and c = 13.9195(4) Å. EuCu 2 Ge 2 crystallizes in the tetragonal ThCr 2 Si 2 structure type (SG I4/mmm) with the lattice parameters: a = b = 4.2218(1) Å, and c = 10.3394(5) Å. The crystal structure of Eu 3 Ag 2 In 9 is comprised of edge-shared hexagonal rings consisting of indium. The one-dimensional chains of In 6 rings are shared through the edges, which are further interconnected with other six-membered rings forming a three-dimensional (3D) stable crystal structure along the bc plane. The crystal structure of EuCu 2 Ge 2 can be explained as the complex [CuGe] (2+δ)- polyanionic network embedded with Eu ions. These polyanionic networks present in the crystal structure of EuCu 2 Ge 2 are shared through the edges of the 011 plane containing Cu and Ge atoms, resulting in a 3D network. The structural relationship between Eu 3 T 2 In 9 and EuCu 2 Ge 2 has been discussed in detail, and we conclude that Eu 3 T 2 In 9 is the metal deficient variant of EuCu 2 Ge 2 . The magnetic susceptibilities of Eu 3 T 2 In 9 (T = Cu and Ag) and EuCu 2 Ge 2 were measured between 2 and 300 K. In all cases, magnetic susceptibility data followed Curie-Weiss law above 150 K. Magnetic moment values obtained from the measurements indicate the probable mixed/intermediate valent behavior of the europium atoms, which was further confirmed by X-ray absorption studies and bond distances around the Eu atoms. Electrical resistivity measurements suggest that Eu 3 T 2 In 9 and EuCu 2 Ge 2 are metallic in nature.

Effect of doping with nickel ions on the structural state of a zinc oxide crystal

NASA Astrophysics Data System (ADS)

Dubinin, S. F.; Sokolov, V. I.; Parkhomenko, V. D.; Maksimov, V. I.; Gruzdev, N. B.

2009-10-01

The fine structure of a hexagonal zinc oxide crystal doped with nickel ions of the composition Zn1 - x Ni x O has been studied using neutron diffraction and magnetic measurements. It is established that even at very low doping levels ( x = 0.0004), the crystal undergoes local distortions in basal planes of the initial hexagonal lattice. The local distortions are assumed to be sources of the formation of ferromagnetism in compounds of this class.

Structural and magnetic transitions in spinel FeM n 2 O 4 single crystals

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

Nepal, Roshan; Zhang, Qiang; Dai, Samuel

Materials that form the spinel structure are known to exhibit geometric frustration, which can lead to magnetic frustration as well. Through magnetization and neutron diffraction measurements, we find that FeMn 2O 4 undergoes one structural and two magnetic transitions. The structural transition occurs at T s ~595K from cubic at high temperatures to tetragonal at low temperatures. Here, two magnetic transitions are ferrimagnetic at T FI–1 ~373K and T FI–2 ~50K, respectively. Further investigation of the specific heat, thermal conductivity, and Seebeck coefficient confirms both magnetic transitions. Of particular interest is that there is a significant magnetic contribution to themore » low-temperature specific heat and thermal conductivity, providing a unique system to study heat transport by magnetic excitations.« less

Structural and magnetic transitions in spinel FeM n 2 O 4 single crystals

DOE PAGES

Nepal, Roshan; Zhang, Qiang; Dai, Samuel; ...

2018-01-11

Materials that form the spinel structure are known to exhibit geometric frustration, which can lead to magnetic frustration as well. Through magnetization and neutron diffraction measurements, we find that FeMn 2O 4 undergoes one structural and two magnetic transitions. The structural transition occurs at T s ~595K from cubic at high temperatures to tetragonal at low temperatures. Here, two magnetic transitions are ferrimagnetic at T FI–1 ~373K and T FI–2 ~50K, respectively. Further investigation of the specific heat, thermal conductivity, and Seebeck coefficient confirms both magnetic transitions. Of particular interest is that there is a significant magnetic contribution to themore » low-temperature specific heat and thermal conductivity, providing a unique system to study heat transport by magnetic excitations.« less

Antiferromagnetic Kondo lattice in the layered compound CePd 1 - x Bi 2 and comparison to the superconductor LaPd 1 - x Bi 2

DOE PAGES

Han, Fei; Wan, Xiangang; Phelan, Daniel; ...

2015-07-13

ZrCuSi 2-type CePd 1-xBi 2 crystals were obtained from excess Bi flux. Magnetic susceptibility measurements reveal that CePd 1-xBi 2 is a highly anisotropic antiferromagnet with transition temperature at 6 K, and a magnetic-field-induced metamagnetic transition at 5 T. An enhanced Sommerfeld coefficient of γ of 0.199 J-mol-Ce -1K -2 obtained from specific heat measurements suggests a moderate Kondo effect in CePd 1-xBi 2. In addition to the antiferromagnetic peak the resistivity curve shows a shoulder-like behavior which could be attributed to the presence of Kondo effect and crystal-electric-field effects in this compound. Magnetoresistance and Hall effect measurements suggest anmore » interplay between Kondo and crystal-electric-field effects which reconstructs the Fermi surface topology of CePd 1-xBi 2 around 75 K. Electronic structure calculations reveal the Pd vacancies are important to the magnetic structure and enhance the crystal-electric-field effects which quench the orbital moment of Ce at low temperatures.« less

Thermal response, catalytic activity, and color change of the first hybrid vanadate containing Bpe guest molecules.

PubMed

Fernández de Luis, Roberto; Urtiaga, M Karmele; Mesa, José L; Larrea, Edurne S; Iglesias, Marta; Rojo, Teófilo; Arriortua, María I

2013-03-04

Four isomorphic compounds with formula [{Co2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoBpe 1; [{CoNi(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoNiBpe 2; [{Co0.6Ni1.4(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiCoBpe 3; and [{Ni2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiBpe 4, have been obtained by hydrothermal synthesis. The crystal structures of CoBpe 1 and NiBpe 4 were determined by single-crystal X-ray diffraction (XRD). The Rietveld refinement of CoNiBpe 2 and NiCoBpe 3 XRD patterns confirms that those are isomorphic. The compounds crystallize in the P1̅ space group, exhibiting a crystal structure constructed from inorganic layers pillared by Bpe ligands. The crystal structure contains intralayer and interlayer channels, in which the crystallization water molecules and Bpe guest molecules, respectively, are located. The solvent molecules establish a hydrogen bonding network with the coordinated water molecules. Thermodiffractometric and thermogravimetric studies showed that the loss of crystallization and coordinated water molecules takes place at different temperatures, giving rise to crystal structure transformations that involve important reduction of the interlayer distance, and strong reduction of crystallinity. The IR, Raman, and UV-vis spectra of the as-synthesized and heated compounds confirm that the structural building blocks and octahedral coordination environment of the metal centers are maintained after the structural transformations. The color change and reversibility of the water molecules uptake/removal were tested showing that the initial color is not completely recovered when the compounds are heated at temperatures higher than 200 °C. The thermal evolution of the magnetic susceptibility indicates one-dimensional antiferromagnetic coupling of the metal centers at high temperatures. For NiCoBpe 3 and NiBpe 4 compounds magnetic ordering is established at low temperatures, as can be judged by the maxima observed in the magnetic susceptibilities. CoNiBpe 2 was proved as catalyst being active for cyanosilylation reactions of aldehydes.

{sup 45}Sc Solid State NMR studies of the silicides ScTSi (T=Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt)

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

Harmening, Thomas; Eckert, Hellmut, E-mail: eckerth@uni-muenster.de; Fehse, Constanze M.

The silicides ScTSi (T=Fe, Co, Ni, Cu, Ru, Rh, Pd, Ir, Pt) were synthesized by arc-melting and characterized by X-ray powder diffraction. The structures of ScCoSi, ScRuSi, ScPdSi, and ScIrSi were refined from single crystal diffractometer data. These silicides crystallize with the TiNiSi type, space group Pnma. No systematic influences of the {sup 45}Sc isotropic magnetic shift and nuclear electric quadrupolar coupling parameters on various structural distortion parameters calculated from the crystal structure data can be detected. {sup 45}Sc MAS-NMR data suggest systematic trends in the local electronic structure probed by the scandium atoms: both the electric field gradients andmore » the isotropic magnetic shifts relative to a 0.2 M aqueous Sc(NO{sub 3}){sub 3} solution decrease with increasing valence electron concentration and within each T group the isotropic magnetic shift decreases monotonically with increasing atomic number. The {sup 45}Sc nuclear electric quadrupolar coupling constants are generally well reproduced by quantum mechanical electric field gradient calculations using the WIEN2k code. Highlights: Black-Right-Pointing-Pointer Arc-melting synthesis of silicides ScTSi. Black-Right-Pointing-Pointer Single crystal X-ray data of ScCoSi, ScRuSi, ScPdSi, and ScIrSi. Black-Right-Pointing-Pointer {sup 45}Sc solid state NMR of silicides ScTSi.« less

Magnetic and Structural Characterization of Fe-Ga Using Kerr Microscopy and Neutron Scattering

DTIC Science & Technology

2010-01-01

117 4.6 Schematic of triple axes single crystal neutron diffractometer (left). TriCS intrument at Paul Scherrer Institut, Switzerland (right...Therefore, USANS data is one-dimensional. 4.3.3 Single Crystal Neutron Diffraction The single crystal neutron diffractometer, TriCS at Paul Scherrer...crystal neutron diffractometer (left). TriCS intrument at Paul Scherrer Institut, Switzerland (right) [106] 4.4 Unpolarized SANS In this section, SANS

Laser MBE-grown CoFeB epitaxial layers on MgO: Surface morphology, crystal structure, and magnetic properties

NASA Astrophysics Data System (ADS)

Kaveev, Andrey K.; Bursian, Viktor E.; Krichevtsov, Boris B.; Mashkov, Konstantin V.; Suturin, Sergey M.; Volkov, Mikhail P.; Tabuchi, Masao; Sokolov, Nikolai S.

2018-01-01

Epitaxial layers of CoFeB were grown on MgO by means of laser molecular beam epitaxy using C o40F e40B20 target. The growth was combined with in situ structural characterization by three-dimensional reciprocal space mapping obtained from reflection high energy electron diffraction (RHEED) data. High-temperature single stage growth regime was adopted to fabricate CoFeB layers. As confirmed by the atomic force microscopy, the surface of CoFeB layers consists of closely spaced nanometer sized islands with dimensions dependent on the growth temperature. As shown by RHEED and XRD analysis, the CoFeB layers grown at high-temperature on MgO(001) possess body centered cubic (bcc) crystal structure with the lattice constant a =2.87 Å close to that of the C o75F e25 alloy. It was further shown that following the same high-temperature growth technique the MgO/CoFeB/MgO(001) heterostructures can be fabricated with top and bottom MgO layers of the same crystallographic orientation. The CoFeB layers were also grown on the GaN(0001) substrates using MgO(111) as a buffer layer. In this case, the CoFeB layers crystallize in bcc crystal structure with the (111) axis perpendicular to the substrate surface. The magnetic properties of the CoFeB/MgO (001) heterostructures have been investigated by measuring magnetization curves with a vibrating sample magnetometer as well as by performing magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR) studies. FMR spectra were obtained for the variety of the magnetic field directions and typically consisted of a single relatively narrow resonance line. The magnetization orientations and the resonance conditions were calculated in the framework of a standard magnetic energy minimization procedure involving a single K1 c cubic term for the magnetocrystalline anisotropy. This allows a fairly accurate description of the angular dependences of the resonance fields—both in-plane and out-of-plane. It was shown that CoFeB layers exhibit in-plane fourth-order magnetic anisotropy. A two-step magnetization reversal model has been adopted for the CoFeB layers based on the VSM measurement analysis. Magnetization reversal studies performed by polar MOKE indicate that the magnetization lies in-plane in absence of magnetic field. Observed magnetic field dependences of reflected light ellipticity in geometry of longitudinal Kerr effect give convincing evidence for contribution of quadratic in magnetization terms in the dielectric tensor and clearly show the in-plane magnetization rotation.

Crystal structures and magnetic properties of two-dimensional antiferromagnets Co{sub 1-x}Zn{sub x}TeMoO{sub 6}

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

Doi, Yoshihiro, E-mail: doi@sci.hokudai.ac.j; Suzuki, Ryo; Hinatsu, Yukio

2009-12-15

Crystal structures and magnetic properties of metal telluromolybdates Co{sub 1-x}Zn{sub x}TeMoO{sub 6} (x=0.0, 0.1,...,0.9) are reported. All the compounds have an orthorhombic structure with space group P2{sub 1}2{sub 1}2 and a charge configuration of M{sup 2+}Te{sup 4+}Mo{sup 6+}O{sub 6}. In this structure, M ions form a pseudo-two-dimensional lattice in the ab plane. Their magnetic susceptibility measurements have been performed in the temperature range between 1.8 and 300 K. The end member CoTeMoO{sub 6} shows a magnetic transition at 24.4 K. The transition temperature for solid solutions rapidly decreases with increasing x and this transition disappears between x=0.4 and 0.5, whichmore » is corresponding to the percolation limit for the square-planer lattice. From the magnetization, specific heat, and powder neutron diffraction measurements, it is found that the magnetic transition observed in the CoTeMoO{sub 6} is a canted antiferromagnetic ordering of Co{sup 2+} ions. The antiferromagnetic component of the ordered magnetic moment (3.12(3)mu{sub B} at 10 K) is along the b-axis. In addition, there exists a small ferromagnetic component (0.28(3)mu{sub B}) along the a-axis. - Graphical abstract: The metal telluromolybdates Co{sub 1-x}Zn{sub x}TeMoO{sub 6} have an orthorhombic structure with space group P2{sub 1}2{sub 1}2. In this structure, M ions form a pseudo-square-planer lattice in the ab plane. These compounds show a low-dimensional magnetism reflecting this structural feature. The magnetic transition observed in the CoTeMoO{sub 6} is a canted antiferromagnetic ordering of Co{sup 2+} ions, and the figure is the magnetic structure.« less

Magnetic phase dependence of the anomalous Hall effect in Mn 3Sn single crystals

DOE PAGES

Sung, Nakheon H.; Ronning, Filip; Thompson, Joe David; ...

2018-03-29

Thermodynamic and transport properties are reported on single crystals of the hexagonal antiferromagnet Mn 3Sn grown by the Sn flux technique. Magnetization measurements reveal two magnetic phase transitions at T 1 = 275 K and T 2 = 200 K, below the antiferromagnetic phase transition at T N ≈ 420 K. The Hall conductivity in zero magnetic field is suppressed dramatically from 4.7 Ω -1 cm -1 to near zero below T 1, coincident with the vanishing of the weak ferromagnetic moment. Finally, this illustrates that the large anomalous Hall effect arising from the Berry curvature can be switched onmore » and off by a subtle change in the symmetry of the magnetic structure near room temperature.« less

Magnetic phase dependence of the anomalous Hall effect in Mn 3Sn single crystals

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

Sung, Nakheon H.; Ronning, Filip; Thompson, Joe David

Thermodynamic and transport properties are reported on single crystals of the hexagonal antiferromagnet Mn 3Sn grown by the Sn flux technique. Magnetization measurements reveal two magnetic phase transitions at T 1 = 275 K and T 2 = 200 K, below the antiferromagnetic phase transition at T N ≈ 420 K. The Hall conductivity in zero magnetic field is suppressed dramatically from 4.7 Ω -1 cm -1 to near zero below T 1, coincident with the vanishing of the weak ferromagnetic moment. Finally, this illustrates that the large anomalous Hall effect arising from the Berry curvature can be switched onmore » and off by a subtle change in the symmetry of the magnetic structure near room temperature.« less

Magnetic phase dependence of the anomalous Hall effect in Mn3Sn single crystals

NASA Astrophysics Data System (ADS)

Sung, N. H.; Ronning, F.; Thompson, J. D.; Bauer, E. D.

2018-03-01

Thermodynamic and transport properties are reported on single crystals of the hexagonal antiferromagnet Mn3Sn grown by the Sn flux technique. Magnetization measurements reveal two magnetic phase transitions at T1 = 275 K and T2 = 200 K, below the antiferromagnetic phase transition at TN ≈ 420 K. The Hall conductivity in zero magnetic field is suppressed dramatically from 4.7 Ω-1 cm-1 to near zero below T1, coincident with the vanishing of the weak ferromagnetic moment. This illustrates that the large anomalous Hall effect arising from the Berry curvature can be switched on and off by a subtle change in the symmetry of the magnetic structure near room temperature.

Magneto-crystalline anisotropy of NdFe0.9Mn0.1O3 single crystal

NASA Astrophysics Data System (ADS)

Mihalik, Marián; Mihalik, Matúš; Zentková, Mária; Uhlířová, Klára; Kratochvílová, Marie; Roupcová, Pavla

2018-05-01

Our present study on oriented single crystal revealed huge magneto-crystalline anisotropy with respect to principal crystallographic axes, even several magnetic transitions were observed below TN = 748 K (c-axis) at 700 K (a-axis) as well 657 K (b-axis). The spin reorientation of magnetic moment takes place in very narrow temperature range between 135 K and 125 K and is attributed to vanishing of ferromagnetic component aligned along b-axis. Measurements of magnetic isotherms trace the development of ferromagnetic component and revealed the intermediate temperature range between 120 K and 20 K which is characterised by zero ferromagnetic components in any principal crystal direction. The ferromagnetic component develops consecutive at low temperature below 20 K along a-axis. Our study indicates completely different magnetic structure of NdFe0.9Mn0.1O3 below 135 K in comparison with NdFeO3.

Paramagnetic resonance and susceptibility of ilmenite, FeTiO3 crystal

NASA Technical Reports Server (NTRS)

Mcdonald, P. F.; Parasiris, A.; Pandey, R. K.; Gries, B. L.; Kirk, W. P.

1991-01-01

Large high-purity single crystals of FeTiO3 with ilmenite structure have been grown from a stoichiometric melt of Fe2O3 and TiO2 under an inert atmosphere using the modified Czochralski technique. Susceptibility and X-band paramagnetic resonance studies have been performed. Susceptibility measurements indicate a Neel temperature of about 59 K. The paramagnetic resonance spectrum for magnetic field perpendicular to the crystal c axis consists of a portion of a single, very intense approximately Lorentzian absorption line with its peak at about 600 G and half width at half maximum almost 1200 G. The absorption extends to zero magnetic field. For magnetic field approximately parallel to the c axis, the paramagnetic absorption is much smaller and may be considered a superposition of two approximately Lorentzian line shapes. The magnetic resonance measurements indicate a weak temperature dependence and large angular anisotropy.

Rapid liquid phase sintered Mn doped BiFeO3 ceramics with enhanced polarization and weak magnetization

NASA Astrophysics Data System (ADS)

Kumar, Manoj; Yadav, K. L.

2007-12-01

Single-phase BiFe1-xMnxO3 multiferroic ceramics have been synthesized by rapid liquid phase sintering method to study the influence of Mn substitution on their crystal structure, dielectric, magnetic, and ferroelectric behaviors. From XRD analysis it is seen that Mn substitution does not affect the crystal structure of the BiFe1-xMnxO3 system. An enhancement in magnetization was observed for BiFe1-xMnxO3 ceramics. However, the ferooelectric hysteresis loops were not really saturated, we observed a spontaneous polarization of 10.23μC /cm2 under the applied field of 42kV/cm and remanent polarization of 3.99μC/cm2 for x =0.3 ceramic.

Electronic Structure and Magnetic Interactions in the Radical Salt [BEDT-TTF]2[CuCl4].

PubMed

Calzado, Carmen J; Rodríguez-García, Bárbara; Galán Mascarós, José Ramón; Hernández, Norge Cruz

2018-06-07

The magnetic behavior and electric properties of the hybrid radical salt [BEDT-TTF] 2 [CuCl 4 ] have been revisited through extended experimental analyses and DDCI and periodic DFT plane waves calculations. Single crystal X-ray diffraction data have been collected at different temperatures, discovering a phase transition occurring in the 250-300 K range. The calculations indicate the presence of intradimer, interdimer, and organic-inorganic π-d interactions in the crystal, a magnetic pattern much more complex than the Bleaney-Bowers model initially assigned to this material. Although this simple model was good enough to reproduce the magnetic susceptibility data, our calculations demonstrate that the actual magnetic structure is significantly more intricate, with alternating antiferromagnetic 1D chains of the organic BEDT-TTF + radical, connected through weak antiferromagnetic interactions with the CuCl 4 2- ions. Combination of experiment and theory allowed us to unambiguously determine and quantify the leading magnetic interactions in the system. The density-of-states curves confirm the semiconductor nature of the system and the dominant organic contribution of the valence and conduction band edges. This general and combined approach appears to be fundamental in order to properly understand the magnetic structure of these complex materials, where experimental data can actually be fitted from a variety of models and parameters.

Single crystal EPR study at 95 GHz of a large Fe based molecular nanomagnet: toward the structuring of magnetic nanoparticle properties.

PubMed

Castelli, L; Fittipaldi, M; Powell, A K; Gatteschi, D; Sorace, L

2011-08-28

A W-band single-crystal EPR study has been performed on a molecular cluster comprising 19 iron(III) ions bridged by oxo- hydroxide ions, Fe(19), in order to investigate magnetic nanosystems with a behavior in between the one of Magnetic NanoParticles (MNP) and that of Single Molecule Magnets (SMM). The Fe(19) has a disk-like shape: a planar Fe(7) core with a brucite (Mg(OH)(2)) structure enclosed in a "shell" of 12 Fe(III) ions. EPR and magnetic measurements revealed an S = 35/2 ground state with an S = 33/2 excited state lying ∼ 8 K above. The presence of other low-lying excited states was also envisaged. Rhombic Zero Field Splitting (ZFS) tensors were determined, the easy axes lying in the Fe(19) plane for both the multiplets. At particular temperatures and orientations, a partially resolved fine structure could be observed which could not be distinguished in powder spectra, due to orientation disorder. The similarities of the EPR behavior of Fe(19) and MNP, together with the accuracy of single crystal analysis, helped to shed light on spectral features observed in MNP spectra, that is a sharp line at g = 2 and a low intensity transition at g = 4. Moreover, a theoretical analysis has been used to estimate the contribution to the total magnetic anisotropy of core and surface; this latter is crucial in determining the easy axis-type anisotropy, alike that of MNP surface. This journal is © The Royal Society of Chemistry 2011

Lanthanide contraction effect on crystal structures, magnetic, and dielectric properties in ordered double perovskites LnPbCoSbO{sub 6} (Ln = La, Pr, Nd)

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

Han, L.; Yao, C. G.; Meng, J. L.

The crystal structures, magnetic, and dielectric properties for the ordered double perovskites LnPbCoSbO{sub 6} (Ln = La, Pr, Nd) have been investigated. The crystal structure has been solved by Rietveld refinements of X-ray diffraction data in the monoclinic space group P2{sub 1}/n (No. 14). The Co{sup 2+} and Sb{sup 5+} ions are almost fully ordered over the B-site, and the octahedral framework displays significant tilting distortion according to the Glazer's tilt system a{sup –}a{sup –}c{sup +}. As the result of lanthanide contraction from La{sup 3+} to Nd{sup 3+}, the B-site sublattice distortions become stronger accompanying with the reduction of themore » tolerance factor and coordination number. The magnetization measurements show an antiferromagnetic ordering with large effective magnetic moments (μ{sub eff}) suggesting that the orbital component is significant. The maximum values of isothermal magnetization increase with the decrease in radii of rare earth ions, which is attributed to the weakening of antiferromagnetic interaction via Co{sup 2+}–O–Sb{sup 5+}–O–Co{sup 2+} paths. The dielectric constants present frequency dependence and monotonically decrease with the ionic radii reduction from La{sup 3+} to Nd{sup 3+} due to the suppression of electron transfer. These results indicate that the magnetic and dielectric properties can be tuned by controlling the degree of lattice distortion, which is realized by introducing different Ln{sup 3+} ions at the A-site.« less

Rational design of azide-bridged bimetallic complexes. Crystal structure and magnetic properties of Fe(III)MFe(III) (M = Ni(II) and Cu(II)) trinuclear species.

PubMed

Colacio, Enrique; Costes, Jean-Pierre; Domínguez-Vera, José M; Maimoun, Ikram Ben; Suárez-Varela, José

2005-01-28

The first examples of azide-bridged bimetallic trinuclear complexes ([M(cyclam)][FeL(N3)(mu1,5-N3)]2) (H2L = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene) have been structurally and magnetically characterized.

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications.

PubMed

Elilarassi, R; Chandrasekaran, G

2017-11-05

In the present investigation, diluted magnetic semiconductor (Zn 1-x Fe x O) nanoparticles with different doping concentrations (x=0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet-visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe 3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature. Copyright © 2017 Elsevier B.V. All rights reserved.

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

Osiry, H.; Cano, A.; Lemus-Santana, A.A.

This contribution discusses the intercalation of imidazole and its 2-ethyl derivative, and pyridine in 2D copper nitroprusside. In the interlayer region, neighboring molecules remain interacting throu gh their dipole and quadrupole moments, which supports the solid 3D crystal structure. The crystal structure of this series of intercalation compounds was solved and refined from powder X-ray diffraction patterns complemented with spectroscopic information. The intermolecular interactions were studied from the refined crystal structures and low temperature magnetic measurements. Due to strong attractive forces between neighboring molecules, the resulting π–π cloud overlapping enables the ferromagnetic coupling between metal centers on neighboring layers, which wasmore » actually observed for the solids containing imidazole and pyridine as intercalated molecules. For these two solids, the magnetic data were properly described with a model of six neighbors. For the solid containing 2-ethylimidazole and for 2D copper nitroprusside, a model of four neighbors in a plane is sufficient to obtain a reliable data fitting. - Highlights: • Intercalation of organic molecules in 2D copper (II) nitroprusside. • Molecular properties of intercalation compounds of 2D copper (II) nitroprusside. • Magnetic properties of hybrid inorganic–organic solids. • Hybrid inorganic–organic 3D framework.« less

Magnetic microbes: Bacterial magnetite biomineralization

DOE PAGES

Prozorov, Tanya

2015-09-14

Magnetotactic bacteria are a diverse group of prokaryotes with the ability to orient and migrate along the magnetic field lines in search for a preferred oxygen concentration in chemically stratified water columns and sediments. These microorganisms produce magnetosomes, the intracellular nanometer-sized magnetic crystals surrounded by a phospholipid bilayer membrane, typically organized in chains. Magnetosomes have nearly perfect crystal structures with narrow size distribution and species-specific morphologies, leading to well-defined magnetic properties. As a result, the magnetite biomineralization in these organisms is of fundamental interest to diverse disciplines, from biotechnology to astrobiology. As a result, this article highlights recent advances inmore » the understanding of the bacterial magnetite biomineralization.« less

Crystal growth and magnetic properties of spinel (Co,Mn)3O4

NASA Astrophysics Data System (ADS)

Kang, Sun Hee; Kim, Ill Won; Jeong, Yoon Hee; Koo, Tae Yeong

2012-04-01

Single crystals of cubic and tetragonal spinel Co3-xMnxO4 (x=1.0 and 1.5) were successfully grown using a solvent evaporation method with PbF2 flux. Single crystals in octahedral shape with a size of about 4 mm on edge were obtained from 100 cm3 Pt crucibles. Ferrimagnetic transitions were detected at 170 K and 160 K from the measurements of temperature dependent magnetization and specific heat of Co2MnO4 and Co1.5Mn1.5O4, respectively. Low temperature field-dependent magnetization curves give a strong indication of the non-collinear spin structure, offering an insulating Co3-xMnxO4 system as a possible candidate for examining the multiferroicity.

Magnetically induced ferroelectricity in Bi2CuO4

NASA Astrophysics Data System (ADS)

Zhao, L.; Guo, H.; Schmidt, W.; Nemkovski, K.; Mostovoy, M.; Komarek, A. C.

2017-08-01

The tetragonal copper oxide Bi2CuO4 has an unusual crystal structure with a three-dimensional network of well separated CuO4 plaquettes. The spin structure of Bi2CuO4 in the magnetically ordered state below TN˜43 K remains controversial. Here we present the results of detailed studies of specific heat, magnetic, and dielectric properties of Bi2CuO4 single crystals grown by the floating zone technique, combined with the polarized neutron scattering and high-resolution x-ray measurements. Down to 3.5 K our polarized neutron scattering measurements reveal ordered magnetic Cu moments which are aligned within the a b plane. Below the onset of the long range antiferromagnetic ordering we observe an electric polarization induced by an applied magnetic field, which indicates inversion symmetry breaking by the ordered state of Cu spins. For the magnetic field applied perpendicular to the tetragonal axis, the spin-induced ferroelectricity is explained in terms of the linear magnetoelectric effect that occurs in a metastable magnetic state. A relatively small electric polarization induced by the field parallel to the tetragonal axis may indicate a more complex magnetic ordering in Bi2CuO4 .

2Flux growth and characterization of Ce-substituted Nd 2 Fe 14 B single crystals

DOE PAGES

Susner, Michael A.; Conner, Benjamin S.; Saparov, Bayrammurad I.; ...

2016-10-27

Single crystals of (Nd 1-xCe x) 2Fe 14B are grown out of Fe-(Nd,Ce) flux. Chemical and structural analysis of the crystals indicate that (Nd 1-xCe x) 2Fe 14B forms a solid solution until at least x = 0.38 with a Vegard-like variation of the lattice constants with x. Refinements of single crystal neutron diffraction data indicate that Ce has a slight site preference (7:3) for the 4g rare earth site over the 4f site. Magnetization measurements at 300 K show only small decreases with increasing Ce content in saturation magnetization (M s) and anisotropy field (H A), and Curie temperaturemore » (T C). First principles calculations are carried out to understand the effect of Ce substitution on the electronic and magnetic properties. For a multitude of applications, it is expected that the advantage of incorporating lower-cost and more abundant Ce will outweigh the small adverse effects on magnetic properties. In conclusion, Ce-substituted Nd 2Fe 14B is therefore a potential high-performance permanent magnet material with substantially reduced Nd content.« less

Anisotropic magnetic properties of the KMo4O6

NASA Astrophysics Data System (ADS)

Andrade, M.; Maffei, M. L.; Dos Santos, C. A. M.; Ferreira, B.; Sartori, A. F.

2012-02-01

Electrical resistivity measurements in the tetragonal KMo4O6 single crystals show a metal-insulator transition (MIT) near 100K. Magnetization measurements as a function of temperature show no evidence of magnetic ordering at this MIT [1]. Single crystals of KMo4O6 were obtained by electrolysis of a melt with a molar ratio of K2MoO4:MoO3 = 6:1. The process were carried out at 930 C with a current of 20-25mA for 52h in argon atmosphere. After that, electrodes were removed from the melt alloying the crystals to cool down to room temperature rapidly. Scanning Electron Microscopy (SEM) showed that the black single crystals were grown on the platinum cathode. Typical dimensions of the single crystals are 1x0.2x0.2mm^3. X-ray diffractometry confirmed that the single crystals have KMo4O6 tetragonal crystalline structure with space group P4. Magnetization measurements were performed parallel and perpendicular to the c-axis from 2 to 300K. The results show anisotropic behavior between both directions. Furthermore, the temperature independence of the magnetization at high temperature and the upturn at low temperature are observed in agreement with previous results [1]. MxH curves measured at several temperatures show nonlinear behavior and a small magnetic ordering. The magnetic ordering seems to be related to the MIT near 100K. This material is based upon support by FAPESP (2009/14524-6 and 2009/54001-6) and CNPq/NSF (490182/2009-7). M. Andrade is CAPES fellow and C.A.M. dos Santos is CNPq fellow. [4pt] [1] K. V. Ramanujachary et al., J. Sol. State Chem.102 (1993) 69.

Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor

DOE PAGES

Meier, William R.; Ding, Qing-Ping; Kreyssig, Andreas; ...

2018-02-09

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-doped and Co-doped CaKFe 4As 4 based on thermodynamic, transport, structural and local magneticmore » probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe 4As 4 structure. Thus, our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.« less

Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor

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

Meier, William R.; Ding, Qing-Ping; Kreyssig, Andreas

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-doped and Co-doped CaKFe 4As 4 based on thermodynamic, transport, structural and local magneticmore » probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe 4As 4 structure. Thus, our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.« less

RNi2B2C (R = Ho, Dy, Tb and Pr) single crystals grown by the cold copper crucible method

NASA Astrophysics Data System (ADS)

Durán, A.; Munoz, E.; Bernès, S.; Escudero, R.

2000-08-01

Single crystals of RNi2B2C (R = Ho, Dy, Tb, Pr) have been grown on cold copper crucibles in a high-frequency induction furnace. As a result, shiny metallic and brittle platelike single crystals were obtained. They were examined by x-ray and scanning electron microscopy with WDX/EDX for local composition analysis and show a very good crystallographic structure and compositions. Resistivity and dc magnetic measurements were performed to study superconducting and magnetic properties. Besides known electronic properties of the RNi2B2C family, we report for the first time results for PrNi2B2C single crystals successfully obtained by this technique.

Desolvation-Driven 100-Fold Slow-down of Tunneling Relaxation Rate in Co(II)-Dy(III) Single-Molecule Magnets through a Single-Crystal-to-Single-Crystal Process

NASA Astrophysics Data System (ADS)

Liu, Jun-Liang; Wu, Jie-Yi; Huang, Guo-Zhang; Chen, Yan-Cong; Jia, Jian-Hua; Ungur, Liviu; Chibotaru, Liviu F.; Chen, Xiao-Ming; Tong, Ming-Liang

2015-11-01

Single-molecule magnets (SMMs) are regarded as a class of promising materials for spintronic and ultrahigh-density storage devices. Tuning the magnetic dynamics of single-molecule magnets is a crucial challenge for chemists. Lanthanide ions are not only highly magnetically anisotropic but also highly sensitive to the changes in the coordination environments. We developed a feasible approach to understand parts of the magneto-structure correlations and propose to regulate the relaxation behaviors via rational design. A series of Co(II)-Dy(III)-Co(II) complexes were obtained using in situ synthesis; in this system of complexes, the relaxation dynamics can be greatly improved, accompanied with desolvation, via single-crystal to single-crystal transformation. The effective energy barrier can be increased from 293 cm-1 (422 K) to 416 cm-1 (600 K), and the tunneling relaxation time can be grown from 8.5 × 10-4 s to 7.4 × 10-2 s. These remarkable improvements are due to the change in the coordination environments of Dy(III) and Co(II). Ab initio calculations were performed to better understand the magnetic dynamics.

Structural and magnetic characterization of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} nanoparticles prepared via a facile microwave-assisted method

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

Moradi, J., E-mail: j_moradi@yahoo.com; Ghazi, M.E.; Ehsani, M.H., E-mail: mhe_ehsani@yahoo.com

2014-07-01

Nanoparticles of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSMO) with different particle sizes are synthesized by a very fast, inexpensive, reproducible, and environmentally friendly method: the microwave irradiation of the corresponding mixture of nitrates. The structural and magnetic properties of the samples are investigated by the X-Ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and magnetic (DC magnetization and AC susceptibility) measurements. The XRD study coupled with the Rietveld refinement show that all samples crystallize in a rhombohedral structure with the space group of R−3C. The FT-IR spectroscopy and FE-SEM images indicate formationmore » of the perovskite structure of LSMO. The DC magnetization measurements confirm the decrease in the particle size effects on the magnetic properties, e.g. reduction in the ferromagnetic (FM) moment and increase in the surface spin disorder. Magnetic dynamics of the samples studied by AC magnetic susceptibility shows that the magnetic behavior of the nanometer-sized samples is well-described by the Vogel-Fulcher and critical slowing down laws. Strong interaction between magnetic nanoparticles of LSMO was detected by fitting the experimental data with the mentioned models. - Graphical abstract: Temperature dependence of the magnetization M(T) was measured in the zero-field-cooling (ZFC) and field-cooling (FC) modes at the applied magnetic field of 100 Oe for the La{sub 0.8}Sr{sub 0.2}MnO{sub 3} with different size prepared via a facile microwave-assisted method. - Highlights: • Nanoparticles of La{sub 0.8}Sr{sub 0.2}MnO{sub 3} were synthesized by the microwave irradiation process. • The structural studies show that all samples crystallize in a rhombohedral structure with space group of R−3C. • The DC magnetic studies confirm tuning of the magnetic properties due to the particle size effects. • Magnetic dynamic studied by AC magnetic susceptibility indicate strong interaction between magnetic nanoparticles.« less

Magnetic and electric control of multiferroic properties in monodomain crystals of BiFeO3

NASA Astrophysics Data System (ADS)

Tokunaga, Masashi

One of the important goals for multiferroics is to develop the non-volatile magnetic memories that can be controlled by electric fields with low power consumption. Among numbers of multiferroic materials, BiFeO3 has been the most extensively studied because of its substantial ferroelectric polarization and magnetic order up to above room temperature. Recent high field experiments on monodomain crystals of BiFeO3 revealed the existence of additional electric polarization normal to the three-fold rotational axis. This transverse component is coupled with the cycloidal magnetic domain, and hence, can be controlled by external magnetic fields. Application of electric fields normal to the trigonal axis modifies volume fraction of these multiferroic domains, which involves change in resistance of the sample, namely exhibits the bipolar resistive memory effect. In this talk, I will introduce the effects of magnetic and electric fields on magnetoelectric and structural properties observed in monodomain crystals of BiFeO3. This work was supported by JSPS Grant Number 16K05413 and by a research Grant from The Murata Science Foundation.

Magnetic and Ferroelectric Anisotropy in Multiferroic FeVO4

NASA Astrophysics Data System (ADS)

Abdelhamid, Ehab; Dixit, Ambesh; Kimura, Kenta; Kimura, Tsuyoshi; Jayakumar, Onattu; Naik, Vaman; Naik, Ratna; Lawes, Gavin; Nadgorny, Boris

FeVO4 has been studied as a model system for understanding the magnetoelectric interaction mechanisms in low symmetry multiferroics. Triclinic FeVO4 is characterized by two antiferromagnetic phase transitions, occurring at TN 1 = 22 K and TN 2 = 15 K, with the latter transition signaling a break in the space inversion symmetry, accompanied by the development of a non-collinear magnetic order which induces ferroelectricity. Earlier measurements on polycrystalline FeVO4 doped with magnetic (Cr and Mn) as well as non magnetic (Zn) dopants indicate the stability of the two antiferromagnetic transition temperatures. In this work, single crystals of both undoped and doped FeVO4 were grown from flux. To track the changes in lattice parameters induced by changing the doping concentration (measured by EDAX), XRD and Raman spectra were obtained. By recording the magnetization along two different crystal orientations, we were able to confirm the easy magnetic axis in this structure. Finally, we obtain the crystal's ferroelectric polarization along two different directions in an attempt to further understand the mechanism responsible for the ferroelectric transition. This work is supported by the NSF under DMR-1306449.

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.

Honeycombs of triangles and magnetic frustration in SrL{sub 2}O{sub 4} (L=Gd, Dy, Ho, Er, Tm, and Yb)

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

Karunadasa, H.; Regan, K.A.; Cava, R.J.

2005-04-01

The crystal structures, magnetic order, and susceptibility have been investigated for magnetically frustrated SrDy{sub 2}O{sub 4}, SrHo{sub 2}O{sub 4}, SrEr{sub 2}O{sub 4}, SrTm{sub 2}O{sub 4}, and SrYb{sub 2}O{sub 4}. Powder neutron-diffraction structural refinements reveal columns of LO{sub 6} octahedra that run along one crystallographic direction, with Sr-O polyhedra in the interstices. The lanthanide sublattice displays multiple triangular interconnections: one-dimensional strings form the backbones of four types of chains of lanthanide triangles sharing edges arranged in a honeycomb pattern. This crystal structure produces strong geometric frustration for the magnetic system that is evidenced in both magnetic susceptibility and neutron-scattering data atmore » low temperatures. The susceptibility measurements for the series, including SrGd{sub 2}O{sub 4} for which data are also reported, lack the sharp features characteristic of three-dimensional long-range magnetic ordering. Metamagnetic behavior is observed in the magnetization vs applied field data at 1.8 K for the cases of L=Dy, Er, and Ho. Magnetic neutron-scattering studies for the Dy and Er materials show only very broad magnetic scattering at low temperatures, while the Ho system exhibits long-range two-dimensional order. Any magnetic scattering in the Tm and Yb compounds, if present, was too weak to be detected in these measurements.« less

Exotic magnetic structures in high-pressure synthesized perovskites

NASA Astrophysics Data System (ADS)

Manuel, Pascal; Khalyavin, Dmitry; Ding, Lei; Yi, Wei; Kumagai, Yu; Oba, Fumiyasu; Orlandi, Fabio; Belik, Alexei

We present a neutron powder diffraction study of the crystal and magnetic structures of the high-pressure stabilized perovskite phases of TlMnO3, ScCrO3, InCrO3 and TlCrO3. These compounds exhibit original magnetic structures compared to other members of their respective manganite and orthochromite families with TlMnO3 also displaying unusual orbital ordering pattern. For both systems, we rationalise the structures through a combination of group theory and first principle calculations. We also highlight the dominant mechanism controlling the spin direction as being the single ion anisotropy.

Molecular packing and magnetic properties of lithium naphthalocyanine crystals: hollow channels enabling permeability and paramagnetic sensitivity to molecular oxygen

PubMed Central

Pandian, Ramasamy P.; Dolgos, Michelle; Marginean, Camelia; Woodward, Patrick M.; Hammel, P. Chris; Manoharan, Periakaruppan T.; Kuppusamy, Periannan

2009-01-01

The synthesis, structural framework, magnetic and oxygen-sensing properties of a lithium naphthalocyanine (LiNc) radical probe are presented. LiNc was synthesized in the form of a microcrystalline powder using a chemical method and characterized by electron paramagnetic resonance (EPR) spectroscopy, magnetic susceptibility, powder X-ray diffraction analysis, and mass spectrometry. X-Ray powder diffraction studies revealed a structural framework that possesses long, hollow channels running parallel to the packing direction. The channels measured approximately 5.0 × 5.4 Å2 in the two-dimensional plane perpendicular to the length of the channel, enabling diffusion of oxygen molecules (2.9 × 3.9 Å2) through the channel. The powdered LiNc exhibited a single, sharp EPR line under anoxic conditions, with a peak-to-peak linewidth of 630 mG at room temperature. The linewidth was sensitive to surrounding molecular oxygen, showing a linear increase in pO2 with an oxygen sensitivity of 31.2 mG per mmHg. The LiNc microcrystals can be further prepared as nano-sized crystals without the loss of its high oxygen-sensing properties. The thermal variation of the magnetic properties of LiNc, such as the EPR linewidth, EPR intensity and magnetic susceptibility revealed the existence of two different temperature regimes of magnetic coupling and hence differing columnar packing, both being one-dimensional antiferromagnetic chains but with differing magnitudes of exchange coupling constants. At a temperature of ∼50 K, LiNc crystals undergo a reversible phase transition. The high degree of oxygen-sensitivity of micro- and nano-sized crystals of LiNc, combined with excellent stability, should enable precise and accurate measurements of oxygen concentration in biological systems using EPR spectroscopy. PMID:19809598

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

Wasielewski, M.R.; Gast, P.; Norris, J.R.

Photoexcitation of the reaction center protein from purple photosynthetic bacteria results in rapid (< 5 ps) formation of a radical pair, P/sup F/ composed of an oxidized bacteriochlorophyll a dimer, P/sup +/ and a reduced bacteriopheophytin a, I/sup -/. The recent crystallization of the reaction center protein from R. viridis enables us to use magnetic resonance to obtain structural information about the reaction center relatively rapidly. We have grown large numbers of R. viridis reaction center crystals and have determined the orientation of the triplet axis system of the primary donor to within + 1 degree as well as amore » number of magnetically non-equivalent donor sites in the crystal.« less

Dimensionality Effects in FeGe 2 Nanowires: Enhanced Anisotropic Magnetization and Anomalous Electrical Transport

DOE PAGES

Mandrus, D.; Gai, Zheng; Ward, Thomas Zac; ...

2017-08-02

Here, we report the synthesis of single-crystal iron germanium nanowires via chemical vapor deposition without the assistance of any catalysts. The assembly of single-crystal FeGe 2 nanowires with tetragonal C16 crystal structure shows anisotropic magnetic behavior along the radial direction or the growth axial direction, with both antiferromagnetic and ferromagnetic orders. Single FeGe 2 nanowire devices were fabricated using e-beam lithography. Electronic transport measurement in these devices show two resistivity anomalies near 250 K and 200 K which are likely signatures of the two spin density wave states in FeGe 2.

Dimensionality Effects in FeGe 2 Nanowires: Enhanced Anisotropic Magnetization and Anomalous Electrical Transport

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

Mandrus, D.; Gai, Zheng; Ward, Thomas Zac

Here, we report the synthesis of single-crystal iron germanium nanowires via chemical vapor deposition without the assistance of any catalysts. The assembly of single-crystal FeGe 2 nanowires with tetragonal C16 crystal structure shows anisotropic magnetic behavior along the radial direction or the growth axial direction, with both antiferromagnetic and ferromagnetic orders. Single FeGe 2 nanowire devices were fabricated using e-beam lithography. Electronic transport measurement in these devices show two resistivity anomalies near 250 K and 200 K which are likely signatures of the two spin density wave states in FeGe 2.

Defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

NASA Astrophysics Data System (ADS)

Li, Dong-Xiang; Qin, Xiu-Bo; Zheng, Li-Rong; Li, Yu-Xiao; Cao, Xing-Zhong; Li, Zhuo-Xin; Yang, Jing; Wang, Bao-Yi

2013-03-01

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane. By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+—VO defect complexes (or clusters) have been identified in annealed crystals at a high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. In addition, excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.

Anisotropic mean-square displacements in two-dimensional colloidal crystals of tilted dipoles

NASA Astrophysics Data System (ADS)

Froltsov, V. A.; Likos, C. N.; Löwen, H.; Eisenmann, C.; Gasser, U.; Keim, P.; Maret, G.

2005-03-01

Superparamagnetic colloidal particles confined to a flat horizontal air-water interface in an external magnetic field, which is tilted relative to the interface, form anisotropic two-dimensional crystals resulting from their mutual dipole-dipole interactions. Using real-space experiments and harmonic lattice theory we explore the mean-square displacements of the particles in the directions parallel and perpendicular to the in-plane component of the external magnetic field as a function of the tilt angle. We find that the anisotropy of the mean-square displacement behaves nonmonotonically as a function of the tilt angle and does not correlate with the structural anisotropy of the crystal.

Neutron diffraction, specific heat and magnetization studies on Nd{sub 2}CuTiO{sub 6}

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

Rayaprol, S., E-mail: sudhindra@csr.res.in; Kaushik, S. D.; Kumar, Naresh

2016-05-23

Structural and physical properties of a double-perovskite compound, Nd{sub 2}CuTiO{sub 6} have been studied using neutron diffraction, magnetization and specific heat measurements. The compound crystallizes in an orthorhombic structure in space group Pnma. The interesting observation we make here is that, though no long range magnetic order is observed between 2 and 300 K, the low temperature specific heat and magnetic susceptibility behavior exhibits non-Fermi liquid like behavior in this insulating compound. The magnetization and specific heat data are presented and discussed in light of these observations.

Porous silicon photonic crystals as hosts for polymers, biopolymers, and magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Li, Yang Yang

This thesis describes the construction of one-dimensional photonic crystals of porous silicon by electrochemically etching and the use of these materials as hosts for polymers, biopolymers, and magnetic nanoparticles. The spectral features of the photonic crystals derive from a porosity gradient that is determined by the electrochemical etching parameters. Since the photonic crystals are constructed of a porous material, they can serve as hosts for other materials. The first chapter of the thesis provides an introduction to porous Si, templating techniques and the use of porous materials for controlled release of drugs. This latter section is added because much of the thesis work addresses the application of porous Si hosts for controlled release of drugs. In the second chapter, it is shown that the spectral properties of the porous Si photonic crystal template can be transferred to a variety of organic and biopolymers. It is demonstrated that these castings can be used as vapor sensors and as self-reporting, bioresorbable materials. If the template is not removed, porous Si polymer composites are formed. The third chapter discussed that by spray-coating a fine mist of polymer solution onto the porous Si film, robust and smooth micron-sized cylindrical photonic crystals suitable for bioassays can be prepared. The fourth chapter focuses on using porous Si photonic crystals as a host for magnetic nanoparticles. The magnetic nanoparticles in this work are found to adhere to the surface of the porous Si film as well to infiltrate the pore structure. In a demonstration of optical switching that may be useful for information display applications, flipping between the colored to dark sides by application of a magnetic field is found to occur at rates of as large as 175 Hz. As the host for soluble molecular species, porous Si photonic crystals can be impregnated from solution. The aggregates that form upon evaporation of solvent are found to scatter light from the resonant optical structure over a large solid angle. The spectrum of the scattered light provides a convenient means of monitoring the temporal release characteristics of the guest material. An application of the phenomenon is demonstrated for release of a drug (caffeine) into aqueous solution from a porous Si photonic crystal.

Structural and magnetic studies of half-metallic Heusler alloy Cr2CoSi nanoparticle synthesized by mechanical-alloying method

NASA Astrophysics Data System (ADS)

Saravanan, G.; Asvini, V.; Kalaiezhily, R. K.; Ravichandran, K.

2018-05-01

Heusler Alloy based Cr2CoSi nanoparticles were synthesized by using ball milling. X-ray diffractions studies were used to characterize the crystal structure of Cr2CoSi nanoparticles and magnetic properties were studied using VSM. XRD data analysis confirms the Heusler alloy phase showing the L21 structure. Magnetic properties are measured for synthesized samples having coercivity Hc = 389 Oe, with high saturation magnetization value Ms = 8.64 emu/g and remenance value Mr = 2.93 emu/g. Synthesized Heusler alloy Cr2CoSi nanoparticles can be potential materials for use in Spin polarized based spin sensors, spin devices, magnetic sensors and transducer applications.

Multiple-decker phthalocyaninato dinuclear lanthanoid(III) single-molecule magnets with dual-magnetic relaxation processes.

PubMed

Katoh, Keiichi; Horii, Yoji; Yasuda, Nobuhiro; Wernsdorfer, Wolfgang; Toriumi, Koshiro; Breedlove, Brian K; Yamashita, Masahiro

2012-11-28

The SMM behaviour of dinuclear Ln(III)-Pc multiple-decker complexes (Ln = Tb(3+) and Dy(3+)) with energy barriers and slow-relaxation behaviour were explained by using X-ray crystallography and static and dynamic susceptibility measurements. In particular, interactions among the 4f electrons of several dinuclear Ln(III)-Pc type SMMs have never been discussed on the basis of the crystal structure. For dinuclear Tb(III)-Pc complexes, a dual magnetic relaxation process was observed. The relaxation processes are due to the anisotropic centres. Our results clearly show that the two Tb(3+) ion sites are equivalent and are consistent with the crystal structure. On the other hand, the mononuclear Tb(III)-Pc complex exhibited only a single magnetic relaxation process. This is clear evidence that the magnetic relaxation mechanism depends heavily on the dipole-dipole (f-f) interactions between the Tb(3+) ions in the dinuclear systems. Furthermore, the SMM behaviour of dinuclear Dy(III)-Pc type SMMs with smaller energy barriers compared with that of Tb(III)-Pc and slow-relaxation behaviour was explained. Dinuclear Dy(III)-Pc SMMs exhibited single-component magnetic relaxation behaviour. The results indicate that the magnetic relaxation properties of dinuclear Ln(III)-Pc multiple-decker complexes are affected by the local molecular symmetry and are extremely sensitive to tiny distortions in the coordination geometry. In other words, the spatial arrangement of the Ln(3+) ions (f-f interactions) in the crystal is important. Our work shows that the SMM properties can be fine-tuned by introducing weak intermolecular magnetic interactions in a controlled SMM spatial arrangement.

Influence of the Ligand Field on the Slow Relaxation of Magnetization of Unsymmetrical Monomeric Lanthanide Complexes: Synthesis and Theoretical Studies.

PubMed

Upadhyay, Apoorva; Vignesh, Kuduva R; Das, Chinmoy; Singh, Saurabh Kumar; Rajaraman, Gopalan; Shanmugam, Maheswaran

2017-11-20

A series of monomeric lanthanide Schiff base complexes with the molecular formulas [Ce(HL) 3 (NO 3 ) 3 ] (1) and [Ln(HL) 2 (NO 3 ) 3 ], where Ln III = Tb (2), Ho (3), Er (4), and Lu (5), were isolated and characterized by single-crystal X-ray diffraction (XRD). Single-crystal XRD reveals that, except for 1, all complexes possess two crystallographically distinct molecules within the unit cell. Both of these crystallographically distinct molecules possess the same molecular formula, but the orientation of the coordinating ligand distinctly differs from those in complexes 2-5. Alternating-current magnetic susceptibility measurement reveals that complexes 1-3 exhibit slow relaxation of magnetization in the presence of an optimum external magnetic field. In contrast to 1-3, complex 4 shows a blockade of magnetization in the absence of an external magnetic field, a signature characteristic of a single-ion magnet (SIM). The distinct magnetic behavior observed in 4 compared to other complexes is correlated to the suitable ligand field around a prolate Er III ion. Although the ligand field stabilizes an easy axis of anisotropy, quantum tunnelling of magnetization (QTM) is still predominant in 4 because of the low symmetry of the complex. The combination of low symmetry and an unsuitable ligand-field environment in complexes 1-3 triggers faster magnetization relaxation; hence, these complexes exhibit field-induced SIM behavior. In order to understand the electronic structures of complexes 1-4 and the distinct magnetic behavior observed, ab initio calculations were performed. Using the crystal structure of the complexes, magnetic susceptibility data were computed for all of the complexes. The computed susceptibility and magnetization are in good agreement with the experimental magnetic data [χ M T(T) and M(H)] and this offers confidence on the reliability of the extracted parameters. A tentative mechanism of magnetization relaxation observed in these complexes is also discussed in detail.

Analysis of Crystal Structure of Fe3O4 Thin Films Based on Iron Sand Growth by Spin Coating Method

NASA Astrophysics Data System (ADS)

Rianto, D.; Yulfriska, N.; Murti, F.; Hidayati, H.; Ramli, R.

2018-04-01

Recently, iron sand used as one of base materials in the steel industry. However, the content of iron sand can be used as starting materials in sensor technology in the form of thin films. In this paper, we report the analysis of crystal structure of magnetite thin film based on iron sand from Tiram’s Beach. The magnetic content of sand separated by a permanent magnet, then it was milled at 30 hours milling time. In order to increase the purity of magnetite, it washed after milling using aquades under magnetic separation by a magnet permanent. The thin film has been prepared using iron (III) nitrate by sol–gel technique. The precursor is resulted by dissolving magnetite in oxalic acid and nitric acid. Then, solution of iron (III) nitrate dissolved in ethylene glycol was applied on glass substrates by spin coating. The X-Ray Diffraction is operated thin film characterization. The structure of magnetite has been studied based on X-Ray Peaks that correspond to magnetite content of thin films.

Magnetic impurity effect on charge and magnetic order in doped La1.5Ca0.5CoO4

NASA Astrophysics Data System (ADS)

Horigane, K.; Hiraka, H.; Tomiyasu, K.; Ohoyama, K.; Louca, D.; Yamada, K.

2012-02-01

Neutron scattering experiments were performed on single crystals of magnetic impurity doped cobalt oxides La1.5Ca0.5CoO4 to characterize the charge and spin orders. We newly found contrasting impurity effects. Two types of magnetic peaks are observed at q = (0.5,0,L) with L = half-integer and integer in La1.5Ca0.5CoO4, while magnetic peak at L = half-integer (integer) was only observed in Mn (Fe)-substituted sample. Although Mn and Fe impurities degrade charge and magnetic order, Cr impurity stabilizes the ordering at x = 0.5. Based on the crystal structural analysis of Cr doped sample, we found that the excess oxygen and change of octahedron around Co3+ were realized in Cr doped sample.

Magnetic order of Nd5Pb3 single crystals

NASA Astrophysics Data System (ADS)

Yan, J.-Q.; Ochi, M.; Cao, H. B.; Saparov, B.; Cheng, J.-G.; Uwatoko, Y.; Arita, R.; Sales, B. C.; Mandrus, D. G.

2018-04-01

We report millimeter-sized Nd5Pb3 single crystals grown out of a Nd-Co flux. We experimentally study the magnetic order of Nd5Pb3 single crystals by measuring the anisotropic magnetic properties, electrical resistivity under high pressure up to 8 GPa, specific heat, and neutron single crystal diffraction. Two successive magnetic orders are observed at T N1  =  44 K and T N2  =  8 K. The magnetic cells can be described with a propagation vector k=(0.5, 0, 0) . Cooling below T N1, Nd1 and Nd3 order forming ferromagnetic stripes along the b-axis, and the ferromagnetic stripes are coupled antiferromagnetically along the a-axis for the k=(0.5, 0, 0) magnetic domain. Cooling below T N2, Nd2 orders antiferromagnetically to nearby Nd3 ions. All ordered moments align along the crystallographic c-axis. The magnetic order at T N1 is accompanied by a quick drop of electrical resistivity upon cooling and a lambda-type anomaly in the temperature dependence of specific heat. At T N2, no anomaly was observed in electrical resistivity but there is a weak feature in specific heat. The resistivity measurements under hydrostatic pressures up to 8 GPa suggest a possible phase transition around 6 GPa. Our first-principles band structure calculations show that Nd5Pb3 has the same electronic structure as does Y5Si3 which has been reported to be a one-dimensional electride with anionic electrons that do not belong to any atom. Our study suggests that R 5Pb3 (R  =  rare earth) can be a materials playground for the study of magnetic electrides. This deserves further study after experimental confirmation of the presence of anionic electrons.

Magnetic order of Nd5Pb3 single crystals.

PubMed

Yan, J-Q; Ochi, M; Cao, H B; Saparov, B; Cheng, J-G; Uwatoko, Y; Arita, R; Sales, B C; Mandrus, D G

2018-04-04

We report millimeter-sized Nd 5 Pb 3 single crystals grown out of a Nd-Co flux. We experimentally study the magnetic order of Nd 5 Pb 3 single crystals by measuring the anisotropic magnetic properties, electrical resistivity under high pressure up to 8 GPa, specific heat, and neutron single crystal diffraction. Two successive magnetic orders are observed at T N1   =  44 K and T N2   =  8 K. The magnetic cells can be described with a propagation vector [Formula: see text]. Cooling below T N1 , Nd1 and Nd3 order forming ferromagnetic stripes along the b-axis, and the ferromagnetic stripes are coupled antiferromagnetically along the a-axis for the [Formula: see text] magnetic domain. Cooling below T N2 , Nd2 orders antiferromagnetically to nearby Nd3 ions. All ordered moments align along the crystallographic c-axis. The magnetic order at T N1 is accompanied by a quick drop of electrical resistivity upon cooling and a lambda-type anomaly in the temperature dependence of specific heat. At T N2 , no anomaly was observed in electrical resistivity but there is a weak feature in specific heat. The resistivity measurements under hydrostatic pressures up to 8 GPa suggest a possible phase transition around 6 GPa. Our first-principles band structure calculations show that Nd 5 Pb 3 has the same electronic structure as does Y 5 Si 3 which has been reported to be a one-dimensional electride with anionic electrons that do not belong to any atom. Our study suggests that R 5 Pb 3 (R  =  rare earth) can be a materials playground for the study of magnetic electrides. This deserves further study after experimental confirmation of the presence of anionic electrons.

Novel Co(III)/Co(II) mixed valence compound [Co(bapen)Br2]2[CoBr4] (bapen = N,N‧-bis(3-aminopropyl)ethane-1,2-diamine): Synthesis, crystal structure and magnetic properties

NASA Astrophysics Data System (ADS)

Smolko, Lukáš; Černák, Juraj; Kuchár, Juraj; Miklovič, Jozef; Boča, Roman

2016-09-01

Green crystals of Co(III)/Co(II) mixed valence compound [Co(bapen)Br2]2[CoBr4] (bapen = N,N‧-bis(3-aminopropyl)ethane-1,2-diamine) were isolated from the aqueous system CoBr2 - bapen - HBr, crystallographically studied and characterized by elemental analysis and IR spectroscopy. Its ionic crystal structure is built up of [Co(bapen)Br2]+ cations and [CoBr4]2- anions. The Co(III) central atoms within the complex cations are hexacoordinated (donor set trans-N4Br2) with bromido ligands placed in the axial positions. The Co(II) atoms exhibit distorted tetrahedral coordination. Beside ionic forces weak Nsbnd H⋯Br intermolecular hydrogen bonding interactions contribute to the stability of the structure. Temperature variable magnetic measurements confirm the S = 3/2 behavior with the zero-field splitting of an intermediate strength: D/hc = 8.7 cm-1.

Synthesis, crystal structure, characterizations and magnetic study of a novel two-dimensional iron fluoride

NASA Astrophysics Data System (ADS)

Bouketaya, Sabrine; Smida, Mouna; Abdelbaky, Mohammed S. M.; Dammak, Mohamed; García-Granda, Santiago

2018-06-01

A new hybrid compound formulated as [Fe3F8(H2O)2](Am2TAZ)2 (Am2TAZ= 3,5-diamino-1,2,4-triazole) was prepared under hydrothermal conditions. The crystal structure was solved by single-crystal X-ray diffraction and the bulk was characterized by thermal analyses (TG-MS), vibrational spectroscopy (FTIR, Raman), Ultraviolet-visible spectroscopy (UV-Vis), and scanning electron microscopy (SEM-EDX). It crystallizes in the triclinic system space group P 1 ̅ with unit cell parameters a= 7.100(2) Å, b= 7.658(2) Å, c= 8.321(2) Å, α = 107.330(20)°, β = 111.842(18)°, γ = 93.049(17)°, Z = 1 and V= 394.01(17) Å3. The studied X-ray crystal structure shows the two oxidation states for iron atoms (Fe2+, Fe3+) and generates a 2D inorganic network, built up of inorganic layers constructed from infinite inorganic chains running along a axis. In fact, these chains are connected via (Fe3+(3)F6) octahedral. OW-H…F and N-H…F hydrogen bonds, making up the whole 3D network, are strongly linked in the layers. Magnetization measurements were performed, exhibiting the paramagnetic feature of the studied compound above 150 K.

High-temperature magnetostructural transition in van der Waals-layered α - MoCl 3

DOE PAGES

McGuire, Michael A.; Yan, Jiaqiang; Lampen-Kelley, Paula; ...

2017-11-07

Here, the crystallographic and magnetic properties of the cleavable 4d 3 transition metal compound α–MoCl 3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagneticmore » at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.« less

High-temperature magnetostructural transition in van der Waals-layered α -MoCl3

NASA Astrophysics Data System (ADS)

McGuire, Michael A.; Yan, Jiaqiang; Lampen-Kelley, Paula; May, Andrew F.; Cooper, Valentino R.; Lindsay, Lucas; Puretzky, Alexander; Liang, Liangbo; KC, Santosh; Cakmak, Ercan; Calder, Stuart; Sales, Brian C.

2017-11-01

The crystallographic and magnetic properties of the cleavable 4 d3 transition metal compound α -MoCl3 are reported, with a focus on the behavior above room temperature. Crystals were grown by chemical vapor transport and characterized using temperature dependent x-ray diffraction, Raman spectroscopy, and magnetization measurements. A structural phase transition occurs near 585 K, at which the Mo-Mo dimers present at room temperature are broken. A nearly regular honeycomb net of Mo is observed above the transition, and an optical phonon associated with the dimerization instability is identified in the Raman data and in first-principles calculations. The crystals are diamagnetic at room temperature in the dimerized state, and the magnetic susceptibility increases sharply at the structural transition. Moderately strong paramagnetism in the high-temperature structure indicates the presence of local moments on Mo. This is consistent with results of spin-polarized density functional theory calculations using the low- and high-temperature structures. Above the magnetostructural phase transition the magnetic susceptibility continues to increase gradually up to the maximum measurement temperature of 780 K, with a temperature dependence that suggests two-dimensional antiferromagnetic correlations.

Structure and soft magnetic properties of Fe-Si-B-P-Cu nanocrystalline alloys with minor Mn addition

NASA Astrophysics Data System (ADS)

Jia, Xingjie; Li, Yanhui; Wu, Licheng; Zhang, Wei

2018-05-01

Addition of minor Mn effectively improves the amorphous-forming ability and thermal stability of the Fe85Si2B8P4Cu1 alloy. With increasing the Mn content from 0 to 3 at.%, the critical thickness for amorphous formation and onset temperature of the primary crystallization increase from 14 μm and 659 K to 27 μm and 668 K, respectively. The fine nanocrystalline structure with α-Fe grains in size (D) of < 20 nm was obtained for the annealed amorphous alloys, which show excellent soft magnetic properties. The alloying of Mn reduces the coercivity (Hc) by decreasing the D value and widens the optimum annealing temperature range for obtaining low Hc, although the saturation magnetic flux density (Bs) is decreased slightly. The Fe83Mn2Si2B8P4Cu1 nanocrystalline alloy possesses fine structure with a D of ˜17.5 nm, and exhibits a high Bs of ˜1.75 T and a low Hc of ˜5.9 A/m. The mechanism related to the alloying effects on the structure and magnetic properties was discussed in term of the crystallization activation energy.

Magnetic structure of the ferromagnetic new ternary silicide Nd5CoSi2.

PubMed

Mayer, C; Gaudin, E; Gorsse, S; Porcher, F; André, G; Chevalier, B

2012-04-04

Nd(5)CoSi(2) was obtained from the elements by arc-melting followed by annealing at 883 K. Its investigation by single-crystal x-ray and neutron powder diffraction shows that this ternary silicide crystallizes as Nd(5)Si(3) in a tetragonal structure deriving from the Cr(5)B(3)-type (I4/mcm space group; a = 7.7472(2) and c = 13.5981(5) Å as unit cell parameters). The structural refinements confirm the mixed occupancy on the 8h site between Si and Co atoms, as already observed for Gd(5)CoSi(2). Magnetization and specific heat measurements reveal a ferromagnetic behavior below T(C) = 55 K for Nd(5)CoSi(2). This magnetic ordering is further evidenced by neutron powder diffraction investigation revealing between 1.8 K and T(C) a canted ferromagnetic structure in the direction of the c-axis described by a propagation vector k = (0 0 0). At 1.8 K, the two Nd(3+) ions carry ordered magnetic moments equal respectively to 1.67(7) and 2.37(7) μ(B) for Nd1 and Nd2; these two moments exhibit a canting angle of θ = 4.3(6)°. This magnetic structure presents some similarities with that reported for Nd(5)Si(3). © 2012 IOP Publishing Ltd

Intermolecular shielding contributions studied by modeling the 13C chemical-shift tensors of organic single crystals with plane waves

PubMed Central

Johnston, Jessica C.; Iuliucci, Robbie J.; Facelli, Julio C.; Fitzgerald, George; Mueller, Karl T.

2009-01-01

In order to predict accurately the chemical shift of NMR-active nuclei in solid phase systems, magnetic shielding calculations must be capable of considering the complete lattice structure. Here we assess the accuracy of the density functional theory gauge-including projector augmented wave method, which uses pseudopotentials to approximate the nodal structure of the core electrons, to determine the magnetic properties of crystals by predicting the full chemical-shift tensors of all 13C nuclides in 14 organic single crystals from which experimental tensors have previously been reported. Plane-wave methods use periodic boundary conditions to incorporate the lattice structure, providing a substantial improvement for modeling the chemical shifts in hydrogen-bonded systems. Principal tensor components can now be predicted to an accuracy that approaches the typical experimental uncertainty. Moreover, methods that include the full solid-phase structure enable geometry optimizations to be performed on the input structures prior to calculation of the shielding. Improvement after optimization is noted here even when neutron diffraction data are used for determining the initial structures. After geometry optimization, the isotropic shift can be predicted to within 1 ppm. PMID:19831448

Synthesis, Structure, and Complex Magnetism of MIr 2In 8 (M = Eu, Sr)

DOE PAGES

Calta, Nicholas P.; L. Bud’ko, Sergey; Rodriguez, Alexandra P.; ...

2016-03-07

In this paper, we report the synthesis, crystal structure, and physical properties of two new polar intermetallic compounds, EuIr 2In 8 and SrIr 2In 8. Both were synthesized in good yield using In metal as a reactive flux medium, enabling the growth of large crystals for physical property measurements. They crystallize in the orthorhombic space group Pbam with the CeFe 2Al 8 structure type, which is sometimes also referred to as the CaCo 2Al 8 structure type. The two analogues have unit cell parameters of a = 13.847(3) Å, b = 16.118(3) Å, and c = 4.3885(9) Å for Mmore » = Eu and a = 13.847(3) Å, b = 16.113(3) Å, and c = 4.3962(9) Å for M = Sr at room temperature. SrIr 2In 8 is a diamagnetic metal with no local magnetic moments on either the Sr or Ir sites, and the diamagnetic contribution from core electrons overwhelms the expected Pauli paramagnetism normally seen in intermetallic compounds. Magnetism in EuIr 2In 8 is dominated by the local Eu moments, which order antiferromagnetically at 5 K in low applied fields. Increasing the field strength depresses the magnetic ordering temperature and also induces a spin reorientation at lower temperature, indicating complex competing magnetic interactions. Finally, low-temperature heat capacity measurements show a significant enhancement of the Sommerfeld coefficient in EuIr 2In 8 relative to that in SrIr 2In 8, with estimated values of γ = 118(3) and 18.0(2) mJ mol –1 K –2, respectively.« less

Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2

NASA Astrophysics Data System (ADS)

May, Andrew; Calder, Stuart; Parker, David; Sales, Brian; McGuire, Michael

CuFe2Ge2 has been identified as a system with competing magnetic ground states that are strongly coupled to the crystal lattice and easily manipulated by temperature or applied magnetic field. Powder neutron diffraction data reveal the emergence of antiferromagnetic (AFM) order near TN = 175 K, as well as a transition into an incommensurate AFM spin structure below approximately 125 K. Together with refined moments of approximately 1 Bohr magneton per iron, the incommensurate structure supports an itinerant picture of magnetism in CuFe2Ge2, which is consistent with theoretical calculations. Bulk magnetization measurements suggest that the spin structures are easily manipulated with an applied field, which further demonstrates the near-degeneracy of different magnetic configurations. Interestingly, the thermal expansion is found to be very anisotropic, and the c lattice parameter has anomalous temperature dependence near TN. These results show that the ground state of CuFe2Ge2 is easily manipulated by external forces, making it a potential parent compound for a rich phase diagram of emergent phenomena. Research supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and Scientific User Facilities Division.

Structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kanzyuba, Vasily; Dong, Sining; Liu, Xinyu; Li, Xiang; Rouvimov, Sergei; Okuno, Hanako; Mariette, Henri; Zhang, Xueqiang; Ptasinska, Sylwia; Tracy, Brian D.; Smith, David J.; Dobrowolska, Margaret; Furdyna, Jacek K.

2017-02-01

We describe the structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy on GaAs (111) substrates, as revealed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. When the Mn concentration is increased, the lattice of the ternary (Sn,Mn)Se films evolves quasi-coherently from a SnSe2 two-dimensional (2D) crystal structure into a more complex quasi-2D lattice rearrangement, ultimately transforming into the magnetically concentrated antiferromagnetic MnSe 3D rock-salt structure as Mn approaches 50 at. % of this material. These structural transformations are expected to underlie the evolution of magnetic properties of this ternary system reported earlier in the literature.

Study of crystal-field interaction in magnetic frustrated lead pyrochlore Gd2Pb2O7

NASA Astrophysics Data System (ADS)

Swarnakar, D.; Jana, Y. M.

2018-05-01

A fine tuning between the crystal field and the molecular field to adopt unique ground state in frustrated magnetic R2M2O7 pyrochlores structures is made by the variation of chemical pressure at R-site caused by substitution of nonmagnetic cation of M-site. Existence of larger cation at M-site increases the lattice parameter or nearest-neighbor bond distance between magnetic R-spins, and causes subtle changes to the local oxygen environment surrounding each R-ion, thereby reduces the chemical pressure at R-site which leads to a dramatic change in the crystal-field and molecular field. To investigate the effect of chemical pressure, the experimental results of powder magnetic susceptibility and isothermal magnetization of the frustrated compound Gd2Pb2O7 containing largest cation, e.g. lead (Pb), at M4+-sites were simulated and analyzed employing a D3d crystal-field (CF) and anisotropic molecular field at R-sites in the self- consistent mean-field approach. The second-ordered axial parameter B20 and total CF splitting of the ground multiplet Gd-ion in Gd2Pb2O7 are 477 cm-1 and 4.8 cm-1 respectively which are the lowest among their isomorphous counterparts, implying reduced effect of the crystal-field at Gd site in Gd2Pb2O7.

Magnetic structures of REPdBi half-Heusler bismuthides (RE = Gd, Tb, Dy, Ho, Er)

NASA Astrophysics Data System (ADS)

Pavlosiuk, Orest; Fabreges, Xavier; Gukasov, Arsen; Meven, Martin; Kaczorowski, Dariusz; Wiśniewski, Piotr

2018-05-01

We present results of neutron diffraction on single crystals of several equiatomic ternary compounds of rare-earth elements with palladium and bismuth, crystallizing with cubic MgAgAs-type structure (half-Heusler phases). Band structure calculations showed that many members of that family possess electronic band inversion, which may lead to occurrence of topological insulator or topological semimetal. But even for the compounds without intrinsic band inversion another way of topologically non-trivial state realization, through a specific antiferromagnetic order, has been theoretically proposed. Our results show that the antiferromagnetic structures of all studied bismuthides are characterized by the propagation vector, allowing for antiferromagnetic topological insulator state. Therefore, the antiferromagnetic representatives of half-Heusler family are excellent candidates for extended investigations of coexistence of superconductivity, magnetic order and non-trivial topology of electronic states.

Synthesis, crystal structure and magnetic properties of a novel tetranuclear oxo-bridged iron(III) butterfly

NASA Astrophysics Data System (ADS)

Arizaga, Livia; Gancheff, Jorge S.; Faccio, Ricardo; Cañón-Mancisidor, Walter; González, Ricardo; Kremer, Carlos; Chiozzone, Raúl

2014-01-01

A novel carboxylate/picolinate oxo-bridged iron(III) cluster, namely [Na2(H2O)8][Fe4(μ-O)2(O2CPh)7(pic)2]2·2H2O (1) where pic = picolinate, has been obtained by reacting "basic iron benzoate" [Fe3O(O2CPh)6(H2O)3](O2CPh) with sodium picolinate in acetonitrile. The compound has been characterized by elemental analysis and IR spectroscopy and its crystal structure has been determined by single-crystal X-ray diffraction.

New Polymorph Form of Dexamethasone Acetate.

PubMed

Silva, Ronaldo Pedro da; Ambrósio, Mateus Felipe Schuchter; Piovesan, Luciana Almeida; Freitas, Maria Clara Ramalho; Aguiar, Daniel Lima Marques de; Horta, Bruno Araújo Cautiero; Epprecht, Eugenio Kahn; San Gil, Rosane Aguiar da Silva; Visentin, Lorenzo do Canto

2018-02-01

A new monohydrated polymorph of dexamethasone acetate was crystallized and its crystal structure characterized. The different analytical techniques used for describing its structural and vibrational properties were: single crystal and polycrystal X-ray diffraction, solid state nuclear magnetic resonance, infrared spectroscopy. A Hirshfeld surface analysis was carried out through self-arrangement cemented by H-bonds observed in this new polymorph. This new polymorph form appeared because of self-arrangement via classical hydrogen bonds around the water molecule. Copyright © 2018 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Preparation of Scandium-Doped, Textured, M-Type Barium Ferrite via a Wet Magnetizing Orientation Process

NASA Astrophysics Data System (ADS)

Wang, Yu; Liu, Yingli; Zhang, Huaiwu; Li, Jie; Gao, Liwen; Chen, Daming; Chen, Yong

2018-02-01

In this paper, a wet magnetizing orientation process was applied to synthesize c-axis-textured, M-type barium ferrite (BaFe12O19 or BaM), which is widely used to produce hard magnetic materials. To modify the magnetic properties of the BaM ferrite and make it suitable for certain operating frequencies, Sc3+ was substituted into Fe3+ sites of the BaM crystal structure. A BaSc x Fe12- x O19 ferrite with a typical relative density of ˜ 75% was successfully obtained. We used x-ray diffraction, scanning electronic microscopy, and a vibrating sample magnetometer to obtain phase information, detail of the microstructure, and magnetic properties of the BaSc x Fe12- x O19, respectively. The composition BaSc x Fe12- x O19 ( x = 0.1) featured a superior squareness ratio of ˜ 67% and a saturation magnetization ( M S) of ˜ 5300 Gauss in magnetic hysteresis loop measurements. These features match well with requirements for self-biased passive devices. Moreover, the site preference of Sc3+ in the hexagonal crystal structure was investigated.

Properties of pure single crystals of actinide compounds

NASA Astrophysics Data System (ADS)

Vogt, O.

1989-07-01

Actinide research started with substances of poor quality and a multitude of "unexplainable" results mostly found on powder samples of doubtful quality exerted some pressure on the crystal growers. As an example we may mention the measurements on UP. Type I antiferromagnetism was found below 123 K by neutron diffraction experiments on powdered samples. At 23 K another transition becomes apparent in susceptibility measurements. The change of the magnetic moments associated with this transition remained unexplained. It was only after the discovery of multi k structures in other actinide compounds that the need was seen to perform even inelastic neutron diffraction experiments on single crystals so that finally the true nature of the transition in UP could be revealed. NpAs is another illustrative example for the fact that sometimes it takes decades to get a clear understanding for things even so simple as macroscopic magnetic properties. The main reason for the need of single crystals is certainly the anisotropy of the magnetic moment encountered in all actinide compounds. Self-heating effects may prevent research on big crystals or might call for isotopic purity of certain samples.

Artificial crystals with 3d metal and palladium particles subjected to high-temperature heat treatment

NASA Astrophysics Data System (ADS)

Rinkevich, A. B.; Nemytova, O. V.; Perov, D. V.; Samoylovich, M. I.; Kuznetsov, E. A.

2018-04-01

High-temperature heat treatment has valuable impact on the structure and physical properties of artificial crystals with 3d metal and palladium particles. Artificial crystals are obtained by means of introduction of particles into the interspherical voids of opal matrices. The magnetic properties are studied at the temperatures ranging from 2 to 300 K and in fields up to 350 kOe. Microwave properties are investigated in the millimeter frequency range. The complex dielectric permittivity of several nanocomposites is measured. The influence of heat treatment up to 960 °C on the structure of artificial crystals is clarified.

Electronic structures and magnetic/optical properties of metal phthalocyanine complexes

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

Baba, Shintaro; Suzuki, Atsushi, E-mail: suzuki@mat.usp.ac.jp; Oku, Takeo

2016-02-01

Electronic structures and magnetic / optical properties of metal phthalocyanine complexes were studied by quantum calculations using density functional theory. Effects of central metal and expansion of π orbital on aromatic ring as conjugation system on the electronic structures, magnetic, optical properties and vibration modes of infrared and Raman spectra of metal phthalocyanines were investigated. Electron and charge density distribution and energy levels near frontier orbital and excited states were influenced by the deformed structures varied with central metal and charge. The magnetic parameters of chemical shifts in {sup 13}C-nuclear magnetic resonance ({sup 13}C-NMR), principle g-tensor, A-tensor, V-tensor of electricmore » field gradient and asymmetry parameters derived from the deformed structures with magnetic interaction of nuclear quadruple interaction based on electron and charge density distribution with a bias of charge near ligand under crystal field.« less

The origin of transverse anisotropy in axially symmetric single molecule magnets.

PubMed

Barra, Anne-Laure; Caneschi, Andrea; Cornia, Andrea; Gatteschi, Dante; Gorini, Lapo; Heiniger, Leo-Philipp; Sessoli, Roberta; Sorace, Lorenzo

2007-09-05

Single-crystal high-frequency electron paramagnetic resonance spectroscopy has been employed on a truly axial single molecule magnet of formula [Mn(12)O(12)(tBu-CH(2)CO(2))16(CH(3)OH)4].CH(3)OH to investigate the origin of the transverse magnetic anisotropy, a crucial parameter that rules the quantum tunneling of the magnetization. The crystal structure, including the absolute structure of the crystal used for EPR experiments, has been fully determined and found to belong to I4 tetragonal space group. The angular dependence of the resonance fields in the crystallographic ab plane shows the presence of high-order tetragonal anisotropy and strong dependence on the MS sublevels with the second-highest-field transition being angular independent. This was rationalized including competing fourth- and sixth-order transverse parameters in a giant spin Hamiltonian which describes the magnetic anisotropy in the ground S = 10 spin state of the cluster. To establish the origin of these anisotropy terms, the experimental results have been further analyzed using a simplified multispin Hamiltonian which takes into account the exchange interactions and the single ion magnetic anisotropy of the Mn(III) centers. It has been possible to establish magnetostructural correlations with spin Hamiltonian parameters up to the sixth order. Transverse anisotropy in axial single molecule magnets was found to originate from the multispin nature of the system and from the breakdown of the strong exchange approximation. The tilting of the single-ion easy axes of magnetization with respect to the 4-fold molecular axis of the cluster plays the major role in determining the transverse anisotropy. Counterintuitively, the projections of the single ion easy axes on the ab plane correspond to hard axes of magnetization.

Magnetocrystalline anisotropy of cementite pseudo single crystal fabricated under a rotating magnetic field

NASA Astrophysics Data System (ADS)

Yamamoto, Sukeyoshi; Terai, Tomoyuki; Fukuda, Takashi; Sato, Kazunori; Kakeshita, Tomoyuki; Horii, Shigeru; Ito, Mikio; Yonemura, Mitsuharu

2018-04-01

We have fabricated a pseudo single crystal of cementite under a rotating magnetic field and investigated its easy and hard axes of magnetization, and determined its magnetocrystalline anisotropy energy. The obtained results are as follows: the hard and easy axes of cementite are the a- and c-axes of the orthorhombic structure with the space group Pnma, respectively. The hard axis observed experimentally was in good agreement with that obtained by an ab initio calculation; however, such consistency was not observed for the easy axis. The magnetocrystalline anisotropy energy was determined as 334 ± 20 kJ/m3 at 5 K.

Enhanced magnetocaloric properties and critical behavior of (Fe0.72Cr0.28)3Al alloys for near room temperature cooling

NASA Astrophysics Data System (ADS)

Sharma, V.; Maheshwar Repaka, D. V.; Chaudhary, V.; Ramanujan, R. V.

2017-04-01

Magnetic cooling is an environmentally friendly, energy efficient, thermal management technology relying on high performance magnetocaloric materials (MCM). Current research has focused on low cost, corrosion resistant, rare earth (RE) free MCMs. We report the structural and magnetocaloric properties of novel, low cost, RE free, iron based (Fe0.72Cr0.28)3Al alloys. The arc melted buttons and melt spun ribbons possessed the L21 crystal structure and B2 crystal structure, respectively. A notable enhancement of 33% in isothermal entropy change (-ΔS m) and 25% increase in relative cooling power (RCP) for the ribbons compared to the buttons can be attributed to higher structural disorder in the Fe-Cr and Fe-Al sub-lattices of the B2 structure. The critical behavior was investigated using modified Arrott plots, the Kouvel-Fisher plot and the critical isotherm technique; the critical exponents were found to correspond to the short-range order 3D Heisenberg model. The field and temperature dependent magnetization curves of (Fe0.72Cr0.28)3Al alloys revealed their soft magnetic nature with negligible hysteresis. Thus, these alloys possess promising performance attributes for near room temperature magnetic cooling applications.

Mixed valence transition metal 2D-oxides: Comparison between delafossite and crednerite compounds

NASA Astrophysics Data System (ADS)

Martin, Christine; Poienar, Maria

2017-08-01

Transition metal oxides offer large opportunities to study relationships between structures and properties. Indeed these compounds crystallize in numerous frameworks corresponding to different dimensionalities and, accordingly, show a huge variety of properties (as high Tc superconductivity, colossal magnetoresistivity, multiferroicity..). The control of the oxidation state of the transition metal, via the monitoring of the oxygen content, is of prime importance to understand and optimize the properties, due to the strong coupling that exists between the lattice and the charges and spins of the transition metals. In this large playground for chemists, we reinvestigated several 2D-compounds derived from delafossite structure. Considering this paper as a very short review, we report here the results obtained on CuMO2 compounds (with M = Cr, Mn or Mn+Cu) by using a combination of techniques, as X-ray, neutrons and/or electrons diffraction on poly-crystals for structural characterisations that are correlated with electrical and/or magnetic properties. The complementarity of studies is also addressed by the synthesis and characterization of single crystals in addition to poly-crystals. Moreover the comparison of the structures of similar Cr and Mn based oxides highlights the crucial role of the Jahn-Teller effect of trivalent manganese to lift the degeneracy, which is responsible of the magnetic frustration in CuCrO2.

Tuning the ground state of the Kondo lattice in UT Bi2 (T = Ag, Au) single crystals

NASA Astrophysics Data System (ADS)

Rosa, Priscila; Luo, Yongkang; Pagliuso, Pascoal; Bauer, Eric; Thompson, Joe; Fisk, Zachary

2015-03-01

Motivated by the interesting magnetic anisotropy found in the Ce-based heavy fermion family Ce TX2 (T = transition metal, X = pnictogen), here we study the novel U-based parent compounds U TBi2 (T = Ag, Au) by combining magnetization, electrical resistivity, and heat-capacity measurements. The single crystals, synthesized by the self-flux method, also crystallize in the tetragonal HfCuSi2-type structure (space group P4/nmm). Interestingly, although UAgBi2 is a low- γ antiferromagnet below TN = 181 K, UAuBi2 is a moderately heavy uniaxial ferromagnet below Tc = 22 K. Nevertheless, both compounds display the easy-magnetization direction along the c-axis and a large magnetocrystalline anisotropy. Our results point out to an incoherent Kondo behaviour in the paramagnetic state and an intricate competition between crystal field effects and two anisotropic exchange interactions, which lead to the remarkable difference in the observed ground states.

Impact of structural symmetry on magnetization properties in SrCo0.95Mn0.05O3 prepared by sol-gel method

NASA Astrophysics Data System (ADS)

Kumar, Amit; Meenakshi, Mahto, Rabindra Nath

2018-04-01

We have investigated magnetization properties of the sol-gel prepared SrCo0.95Mn0.05O3 (SCMO) sample with respect to change in structural symmetry. The X-ray diffraction patterns show the crystal structure changes from nH-hexagonal, showing trigonal symmetry (SCMO1), to 2H-hexagonal phase (SCMO2). The trigonal crystal symmetry was obtained at lower annealing temperature (less than 1100 °C), however, the 2H-hexagonal symmetry was obtained at higher annealing temperature. The crystallite size calculated using Debye Scherer formula is found to be ˜ 46 nm and ˜ 33 nm for SCMO1 and SCMO2 samples respectively. The temperature dependence zero field cooled (MZFC) and field cooled (MFC) magnetization curves measured under the applied magnetic field of 500 Oe show magnetic reversibility for the SCMO1 sample. However, MZFC and MFC curves in hexagonal phase show magnetic irreversibility with onset temperature, Tirr ˜ 150 K, exhibits weak ferromagnetic ordering. The temperature variation of magnetization in paramagnetic region was analyzed by following Curie-Weiss law fitting. The χ-1(T) curve shows complete linear behavior with single slope for SCMO1 sample, whereas, the SCMO2 curve exhibit the linear behavior with two distinct slopes. Interestingly the sample in hexagonal phase shows small hysteresis loop at 2 K and 100 K respectively.

Iridium double perovskite Sr2YIrO6 : A combined structural and specific heat study

NASA Astrophysics Data System (ADS)

Corredor, L. T.; Aslan-Cansever, G.; Sturza, M.; Manna, Kaustuv; Maljuk, A.; Gass, S.; Dey, T.; Wolter, A. U. B.; Kataeva, Olga; Zimmermann, A.; Geyer, M.; Blum, C. G. F.; Wurmehl, S.; Büchner, B.

2017-02-01

Recently, the iridate double perovskite Sr2YIrO6 has attracted considerable attention due to the report of unexpected magnetism in this Ir5 + (5 d4 ) material, in which according to the Jeff model, a nonmagnetic ground state is expected. However, in recent works on polycrystalline samples of the series Ba2 -xSrxYIrO6 no indication of magnetic transitions have been found. We present a structural, magnetic, and thermodynamic characterization of Sr2YIrO6 single crystals, with emphasis on the temperature and magnetic field dependence of the specific heat. As determined by x-ray diffraction, the Sr2YIrO6 single crystals have a cubic structure, with space group F m 3 ¯m . In agreement with the expected nonmagnetic ground state of Ir5 + (5d 4 ) in Sr2YIrO6 , no magnetic transition is observed down to 430 mK. Moreover, our results suggest that the low-temperature anomaly observed in the specific heat is not related to the onset of long-range magnetic order. Instead, it is identified as a Schottky anomaly caused by paramagnetic impurities present in the sample, of the order of n ˜0.5 (2 )% . These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.

Fe-Cluster Compounds of Chalcogenides: Candidates for Rare-Earth-Free Permanent Magnet and Magnetic Nodal-Line Topological Material.

PubMed

Zhao, Xin; Wang, Cai-Zhuang; Kim, Minsung; Ho, Kai-Ming

2017-12-04

Fe-cluster-based crystal structures are predicted for chalcogenides Fe 3 X 4 (X = S, Se, Te) using an adaptive genetic algorithm. Topologically different from the well-studied layered structures of iron chalcogenides, the newly predicted structures consist of Fe clusters that are either separated by the chalcogen atoms or connected via sharing of the vertex Fe atoms. Using first-principles calculations, we demonstrate that these structures have competitive or even lower formation energies than the experimentally synthesized Fe 3 X 4 compounds and exhibit interesting magnetic and electronic properties. In particular, we show that Fe 3 Te 4 can be a good candidate as a rare-earth-free permanent magnet and Fe 3 S 4 can be a magnetic nodal-line topological material.

XANES study of Fe-implanted strontium titanate

NASA Astrophysics Data System (ADS)

Lobacheva, O.; Goncharova, L. V.; Chavarha, M.; Sham, T. K.

2014-03-01

Properties of strontium titanate SrTiO3 (STO) depend to a great extent on the substitutional dopants and defects of crystal structure. The ion beam implantation method was used for doping STO (001) crystals with Fe at different doses. Implanted samples were then annealed at 350°C in oxygen to induce recrystallization and remove oxygen vacancies produced during ion implantation process. The effect of Fe doping and post-implantation annealing was studied by X-ray Absorption Near Edge Spectroscopy (XANES) method and Superconducting Quantum Interference Device (SQUID). XANES allowed to monitor the change in structure of STO crystals and in the local environment of Fe following the implantation and annealing steps. SQUID measurements revealed correlation between magnetic moment and Fe implantation dose. Ferromagnetic hysteresis was observed on selected Fe-implanted STO at 5 K. The observed magnetic properties can be correlated with the several Fe oxide phases in addition to the presence of O/Ti vacancies.

Ab-initio study of pressure evolution of structural, mechanical and magnetic properties of cementite (Fe3C) phase

NASA Astrophysics Data System (ADS)

Gorai, S.; Ghosh, P. S.; Bhattacharya, C.; Arya, A.

2018-04-01

The pressure evolution of phase stability, structural and mechanical properties of Fe3C in ferro-magnetic (FM) and high pressure non magnetic (NM) phase is investigated from first principle calculations. The 2nd order FM to NM phase transition of Fe3C is identified around 60 GPa. Pressure (or density) variation of sound velocities from our ab-initio calculated single crystal elastic constants are determined to predict these parameters at Earth's outer core pressure.

Crystal structure and magnetic properties of a copper(II)-octacyanotungstate(V) bimetallic complex coordinated with macrocyclic ligand

NASA Astrophysics Data System (ADS)

Yuan, Ai-Hua; Liu, Wen-Yan; Zhou, Hu.; Chen, Ying-Ying; Shen, Xiao-Ping

2009-02-01

A new cyanide-bridged heterobimetallic assembly based on octacyanotungstate(V) as building block, {[Cu II(L)] 3[W V(CN) 8] 2}·[Cu II(L)·2H 2O]·(ClO 4) 2·4H 2O 1 (L = 3,10-dipropyl-1,3,5,8,10,12-hexaazacyclotetradecane), has been prepared and characterized. X-ray single-crystal analysis reveals that 1 displays a two-dimensional structure with corrugated sheets, in which the 12-membered rings are the basic building units. Magnetic studies reveal that 1 displays a ferromagnetic interaction between Cu II and W V through cyano bridges.

Structure and magnetic properties of Co-Ni-Mn alloy coatings (part 2)

NASA Astrophysics Data System (ADS)

Schmidt, V. V.; Zhikhareva, I. G.; Smirnova, N. V.; Shchipanov, V. P.

2018-03-01

Using the method of high-frequency alternating current (HFAC), based on the preliminary model forecasting of the ratio of metal ions in the electrolyte and the phase composition of the coating, Co-Ni-Mn alloy precipitates with the specified magnetic properties are obtained. It is shown that precipitation with a hexagonal close-packed α-Co phase has the highest coercive force. The presence of a free phase in a small amount (2.1 - 2.6% of weight) of Mn increases the ferromagnetic properties of films due to the domain structures with a poorly defecting α-Mn crystal lattice. The adjustable amount of the amorphous Co(OH)2 phase provides the nanostructure dimensions of the crystals.

Thickness-modulated anisotropic ferromagnetism in Fe-doped epitaxial HfO2 thin films

NASA Astrophysics Data System (ADS)

Liu, Wenlong; Liu, Ming; Zhang, Ruyi; Ma, Rong; Wang, Hong

2017-10-01

Epitaxial tetragonal Fe-doped Hf0.95Fe0.05O2 (FHO) thin films with various thicknesses were deposited on (001)-oriented NdCaAlO4 (NCAO) substrates by using a pulsed laser deposition (PLD) system. The crystal structure and epitaxial nature of the FHO thin films were confirmed by typical x-ray diffraction (XRD) θ-2θ scan and reciprocal space mapping (RSM). The results indicate that two sets of lattice sites exist with two different crystal orientations [(001) and (100)] in the thicker FHO thin films. Further, the intensity of the (100) direction increases with the increase in thicknesses, which should have a significant effect on the anisotropic magnetization of the FHO thin films. Meanwhile, all the FHO thin films possess a tetragonal phase structure. An anisotropy behavior in magnetization has been observed in the FHO thin films. The anisotropic magnetization of the FHO thin films is slowly weakened as the thickness increases. Meanwhile, the saturation magnetization (Ms) of both in-plane and out-of-plane decreases with the increase in the thickness. The change in the anisotropic magnetization and Ms is attributed to the crystal lattice and the variation in the valence of Fe ions. These results indicate that the thickness-modulated anisotropic ferromagnetism of the tetragonal FHO epitaxial thin films is of potential use for the integration of metal-oxide semiconductors with spintronics.

DFT study on the crystal, electronic and magnetic structures of tantalum based double perovskite oxides Ba2MTaO6 (M = Cr, Mn, Fe) via GGA and GGA + U

NASA Astrophysics Data System (ADS)

Saad, H.-E.; Musa, M.; Elhag, Ahmed

2018-06-01

In this paper, we study the crystal, electronic and magnetic structures of three tantalum based double perovskite oxides Ba2MTaO6 (M = Cr, Mn, Fe). All calculations were performed using the full-potential linear augmented plane-wave (PF-LAPW) method based on the first-principles density functional theory (DFT). For the exchange correlation potential, the generalized gradient approximation (GGA) and GGA plus on-site Coulomb parameter (GGA + U) were employed. The structural optimization reveals that the three compounds are stable in cubic structure (space group Fm-3m; tilt system a0a0a0). The band structure, density of states (DOS), charge density and spin magnetic moments were calculated and analyzed in details. By analysis the band structure and DOS, Ba2MTaO6 exhibits an insulating behavior (M = Cr, Fe) and a half-metallic (HM) nature (M = Mn). GGA + U method yields quite accurate results for the band-gap (Eg) as compared with GGA. We found that all three compounds have stable ferromagnetic (FM) ground state within GGA and GGA + U calculations. The M3+ (3d) ions contribute the majority in the total spin magnetic-moments, while, the empty T5+ (5d) ions carry very small induced magnetic moment via the M (3d)-O (2p)-Ta (5d) hybridization.

Order-disorder structural phase transition and magnetocaloric effect in organic-inorganic halide hybrid (C2H5NH3)2CoCl4

NASA Astrophysics Data System (ADS)

Sen, Abhijit; Roy, Soumyabrata; Peter, Sebastian C.; Paul, Arpita; Waghmare, Umesh V.; Sundaresan, A.

2018-02-01

We report a detailed experimental and theoretical investigation of structural, optical, magnetic and magnetothermal properties of single crystals of a new organic-inorganic hybrid (C2H5NH3)2CoCl4. Grown by slow evaporation method at room temperature, the compound crystallizes in centrosymmetric orthorhombic structure (Pnma) which undergoes a reversible phase transition at 235/241 K (cooling/heating) to noncentrosymmetric P212121 space group symmetry associated with order-disorder transformation of carbon atoms of the ammonium cations as well as molecular rearrangement. Electronic absorption spectra of the compound are typical of geometrically distorted [CoCl4]2- tetrahedra having spin-orbit coupling effect. The isolated nature of [CoCl4]2- tetrahedra in the crystal reflect in paramagnetic behaviour of the compound. Interestingly, field induced spin flipping behaviour is observed at low temperature. First principles density functional calculations reveal weak magnetic interaction among cobalt spins with ferromagnetic state being the ground state. The entropy change associated with the spin flipping has been experimentally estimated by magnetic and heat capacity measurements which has a maximum value of 16 J Kg-1 K-1 at 2.5 K under 7 T magnetic field. To the best of our knowledge, this is the first report on magnetocaloric effect observed in an organic-inorganic halide compound. The estimated value is sizable and is comparable to that of well-known transition metal molecular cluster magnets Mn12 or Fe14. The overall findings promise to enlighten new routes to design and constitute multifunctional organic-inorganic halide materials.

Surface defect free growth of a spin dimer TlCuCl{sub 3} compound crystals and investigations on its optical and magnetic properties

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

Ryu, Gihun, E-mail: G.Ryu@fkf.mpg.de; Son, Kwanghyo

A defect-free high quality single crystal of spin dimer TlCuCl{sub 3} compound is firstly synthesized at the optimal growth temperature using the vertical Bridgman method. In this study, we clearly found that the cupric chloride is easily decomposed into the Cl{sup −} deficient composition at ≥470 °C. The Cl{sup −}- related gas phase at the high temperature region also always gives rise to a pinhole-like surface defect at the surface of crystal. Therefore, we clearly verified an exotic anisotropic magnetic behavior (anisotropic ratio of M{sub b}/M{sub (201)} at 2 K, 7 T=10) using the defect-free TlCuCl{sub 3} crystals in thismore » three-dimensional spin dimer TlCuCl{sub 3} compound, relatively stronger magnetic ordering in the H//b than that of H//(201) direction at above the transition magnetic field. - Graphical abstract: A single crystal of spin dimer TlCuCl{sub 3} compound with a defect free is successfully synthesized on the basis of TG/DTA result. We newly found that this cupric chloride compound is easily decomposed into the Cl{sup −} deficient composition at ≥470 °C and Cl{sup −} related gas phases also give rise to the defects like a pinhole on the surface of TlCuCl{sub 3} crystal. Using the crystals with a surface defect free, we also clearly verified the crystal structure of spin dimer TlCuCl{sub 3} compound.« less

Coupling between crystal structure and magnetism in transition-metal oxides

NASA Astrophysics Data System (ADS)

Barton, Phillip Thomas

Transition-metal oxides exhibit a fascinating array of phenomena ranging from superconductivity to negative thermal expansion to catalysis. This dissertation focuses on magnetism, which is integral to engineering applications such as data storage, electric motors/generators, and transformers. The investigative approach follows structure-property relationships from materials science and draws on intuition from solid-state chemistry. The interplay between crystal structure and magnetic properties is studied experimentally in order to enhance the understanding of magnetostructural coupling mechanisms and provide insight into avenues for tuning behavior. A combination of diffraction and physical property measurements were used to study structural and magnetic phase transitions as a function of chemical composition, temperature, and magnetic field. The systems examined are of importance in Li-ion battery electrochemistry, condensed-matter physics, solid-state chemistry, and p-type transparent conducting oxides. The materials were prepared by solid-state reaction of powder reagents at high temperatures for periods lasting tens of hours. The first project discussed is of a solid solution between NiO, a correlated insulator, and LiNiO2, a layered battery cathode. Despite the deceptive structural and compositional simplicity of this system, a complete understanding of its complex magnetic properties has remained elusive. This study shows that nanoscale domains of chemical order form at intermediate compositions, creating interfaces between antiferromagnetism and ferrimagnetism that give rise to magnetic exchange bias. A simple model of the magnetism is presented along with a comprehensive phase diagram. The second set of investigations focus on the Ge-Co-O system where the spin-orbit coupling of Co(II) plays a significant role. GeCo2O 4 is reported to exhibit unusual magnetic behavior that arises from Ising spin in its spinel crystal structure. Studies by variable-temperature synchrotron X-ray diffraction reveal a magnetostructural transition and capacitance measurements show evidence for magnetodielectric behavior. The above work uncovered a Co10Ge3O16 phase that had a known structure but whose physical properties were largely uncharacterized. This project examined its metamagnetic properties using detailed magnetometry experiments. Upon the application of a magnetic field, this material goes through a first-order phase transition from a noncollinear antiferromagnet to an unknown ferrimagnetic state. Lastly, this thesis explored the chemical dilution of magnetism in some perovskite and delafossite solid solutions. In the perovskite structure, compositions intermediate to the endmembers SrRuO3, a ferromagnetic metal, and LaRhO3, a diamagnetic semiconductor, were investigated. While the magnetism of this system is poised between localized and itinerant behavior, a compositionally-driven metal to insulator transition, revealed by electrical resistivity measurements, did not strongly impact the magnetic properties. Instead, both octahedral tilting and magnetic dilution had strong effects, and comparison of this characterization to Sr1-- x CaxRuO3 reinforces the important role of structural distortions in determining magnetic ground state. The final materials studied were of composition CuAl1-- xCrxO2 (0 < x < 1) in the delafossite structure. The primary interest was the geometric frustration of antiferromagnetism in CuCrO 2 and significant short-range correlations were observed above TN. The analysis found that reducing the number of degenerate states through Al substitution did not enhance magnetic ordering because of the weakening of magnetic exchange.

A new oxytelluride: Perovskite and CsCl intergrowth in Ba 3Yb 2O 5Te

DOE PAGES

Whalen, J. B.; Besara, T.; Vasquez, R.; ...

2013-04-27

The new oxytelluride Ba 3Yb 2O 5Te was obtained from an alkaline earth flux. Ba3Yb2O5Te crystallizes in the tetragonal space group P4/ mmm (#123), with a=4.3615(3) Å and c=11.7596(11) angstrom, Z=1. The structure combines two distinct building blocks, a Ba 2Yb 2O 5 perovskite-like double layer with square bipyramidal coordination of the ytterbium ions, and a CsCl-type BaTe layer. Short range magnetic order is apparent at below 5 K, with the magnetic behavior above this temperature dominated by crystal field effects. The structure may be considered as an analog to the Ruddlesden-Popper phases, where the NaCl-type layer has been replacedmore » by the CsCl-type layer. Finally, the two-dimensional magnetic behavior is expected based on the highly anisotropic nature of the structure.« less

Magnetism and anisotropy of Ir5+ based double perovskites Sr2CoIrO6andSr2FeIrO6

NASA Astrophysics Data System (ADS)

Terzic, Jasminka; Yuan, S. J.; Song, W. H.; Aswartham, S.; Cao, G.

2015-03-01

We report on structural, thermodynamic and transport study of single-crystal double perovskites Sr2CoIrO6andSr2FeIrO6.TheisostructuralSr2CoIrO6andSr2FeIrO6 feature a cubic crystal structure with pentavalent Ir5+(5d4) which are anticipated to have J =0 singlet ground states in the strong spin-orbit coupling limit. Here we observe magnetic coupling between 5d and 3d (Co, Fe) elements, which result in antiferromagnetic order at high temperatures in both double perovskites. Of the two, Sr2CoIrO6 displays antiferromagnetic metallic behavior with a pronounced magnetic anisotropy; in sharp contrast, the isostructural Sr2FeIrO6 exhibits an antiferroamagnetic, insulating ground state without discernible magnetic anisotropy. The data will be discussed and presented with comparisons drawn with similar systems. This work was supported by NSF via Grant DMR 1265162.

Seminar on "MAGNETISM"

NASA Astrophysics Data System (ADS)

Lander, Gerard H.

1998-12-01

During the course of this seminar we had 4 presentations by people who had participated in the earlier poster session. The speakers and titles were: (1) U. Gasser (PSI, Switzerland): "Dimer splitting in RxY1-xNi2B2C". High resolution inelastic work done on polycrystalline samples at the IRIS spectrometer at ISIS and determining the exchange interactions in these superconducting materials. (2) B. Roessli (PSI, Switzerland): "Enhancement of magnetic fluctuations in UPd2Al3 below Tc". High resolution work done on single crystals at the cold source IN14 triple axis spectrometer at the ILL and also involving polarisation analysis. (3) P. Wisniewski (Wroclaw, Poland): "Magnetic structures in U3X4-type uranium pnictides - neutron diffraction studies". Elastic scattering experiments done at Saclay on single crystals with both polarised and unpolarised neutrons. (4) A. Schneidewind (TU Dresden): "Investigation of magnetic structures of NdCu2 by synchrotron x-ray scattering". Work done at the ID20 diffractometer at the ESRF and involving resonant and non-resonant scattering, as well as polarisation analysis…

Crystal Structure and Antiferromagnetic Ordering of Quasi-2D [Cu(HF2)(pyz)2]TaF6 (pyz=pyrazine)

NASA Astrophysics Data System (ADS)

Manson, J. L.; Schlueter, J. A.; McDonald, R. D.; Singleton, J.

2010-04-01

The crystal structure of the title compound was determined by X-ray diffraction at 90 and 295 K. Copper(II) ions are coordinated to four bridging pyz ligands to form square layers in the ab-plane. Bridging HF2- ligands join the layers together along the c-axis to afford a tetragonal, three-dimensional (3D) framework that contains TaF6- anions in every cavity. At 295 K, the pyz rings lie exactly perpendicular to the layers and cooling to 90 K induces a canting of those rings. Magnetically, the compound exhibits 2D antiferromagnetic correlations within the 2D layers with an exchange interaction of -13.1(1) K. Weak interlayer interactions, as mediated by Cu-F-H-F-Cu, leads to long-range magnetic order below 4.2 K. Pulsed-field magnetization data at 0.5 K show a concave curvature with increasing B and reveal a saturation magnetization at 35.4 T.

Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography

NASA Astrophysics Data System (ADS)

Albisetti, E.; Petti, D.; Pancaldi, M.; Madami, M.; Tacchi, S.; Curtis, J.; King, W. P.; Papp, A.; Csaba, G.; Porod, W.; Vavassori, P.; Riedo, E.; Bertacco, R.

2016-06-01

The search for novel tools to control magnetism at the nanoscale is crucial for the development of new paradigms in optics, electronics and spintronics. So far, the fabrication of magnetic nanostructures has been achieved mainly through irreversible structural or chemical modifications. Here, we propose a new concept for creating reconfigurable magnetic nanopatterns by crafting, at the nanoscale, the magnetic anisotropy landscape of a ferromagnetic layer exchange-coupled to an antiferromagnetic layer. By performing localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are reversibly patterned without modifying the film chemistry and topography. This opens unforeseen possibilities for the development of novel metamaterials with finely tuned magnetic properties, such as reconfigurable magneto-plasmonic and magnonic crystals. In this context, we experimentally demonstrate spatially controlled spin wave excitation and propagation in magnetic structures patterned with the proposed method.

Nanopatterning reconfigurable magnetic landscapes via thermally assisted scanning probe lithography.

PubMed

Albisetti, E; Petti, D; Pancaldi, M; Madami, M; Tacchi, S; Curtis, J; King, W P; Papp, A; Csaba, G; Porod, W; Vavassori, P; Riedo, E; Bertacco, R

2016-06-01

The search for novel tools to control magnetism at the nanoscale is crucial for the development of new paradigms in optics, electronics and spintronics. So far, the fabrication of magnetic nanostructures has been achieved mainly through irreversible structural or chemical modifications. Here, we propose a new concept for creating reconfigurable magnetic nanopatterns by crafting, at the nanoscale, the magnetic anisotropy landscape of a ferromagnetic layer exchange-coupled to an antiferromagnetic layer. By performing localized field cooling with the hot tip of a scanning probe microscope, magnetic structures, with arbitrarily oriented magnetization and tunable unidirectional anisotropy, are reversibly patterned without modifying the film chemistry and topography. This opens unforeseen possibilities for the development of novel metamaterials with finely tuned magnetic properties, such as reconfigurable magneto-plasmonic and magnonic crystals. In this context, we experimentally demonstrate spatially controlled spin wave excitation and propagation in magnetic structures patterned with the proposed method.

Synthesis, crystal structure, and magnetic properties of quaternary iron selenides: Ba{sub 2}FePnSe{sub 5} (Pn=Sb, Bi)

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

Wang, Jian; Greenfield, Joshua T.; Kovnir, Kirill

Two new barium iron pnictide–selenides, Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5}, were synthesized by a high-temperature solid-state route and their crystal structures were determined using single crystal X-ray diffraction. Both compounds are isomorphic to the high pressure phase Ba{sub 3}FeS{sub 5} and crystallize in the orthorhombic space group Pnma (No. 62) with cell parameters of a=12.603(2)/12.619(2) Å, b=9.106(1)/9.183(1) Å, c=9.145(1)/9.123(1) Å and Z=4 for Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5}, respectively. According to differential scanning calorimetry, Ba{sub 2}FePnSe{sub 5} compounds exhibit high thermal stability and melt congruently at 1055(5) K (Pn=Sb) and 1105(5) K (Pn=Bi). Magnetic characterizations revealmore » strong antiferromagnetic nearest-neighbor interactions in both compounds resulting in an antiferromagnetic ordering at 58(1) K for Ba{sub 2}FeSbSe{sub 5} and 79(2) K for Ba{sub 2}FeBiSe{sub 5}. The magnetic interactions between Fe{sup 3+} centers, which are at least 6 Å apart from each other, are mediated by superexchange interactions. - Graphical abstract: In Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5} the magnetic interactions between Fe{sup 3+} centers, which are at least 6 Å apart from each other, are mediated by superexchange interactions. - Highlights: • New compounds Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5} have been synthesized. • The crystal structure was determined by single crystal X-ray diffraction. • Both compounds melt congruently at temperatures above 1000 K. • Ba{sub 2}FeSbSe{sub 5} and Ba{sub 2}FeBiSe{sub 5} exhibit AFM ordering at 58 K (Sb) and 70 K (Bi). • Magnetic exchange between Fe{sup 3+} is mediated by either Se–Sb(Bi)–Se or Se–Ba–Se bridges.« less

Observation of steric hindrance effect controlling crystal packing structures and physical properties in three new isomeric nitronyl nitroxide radicals

NASA Astrophysics Data System (ADS)

Zhao, Hai-Rong; Sun, Jia-Sen; Sui, Yun-Xia; Ren, Xiao-Ming; Yao, Bin-Qian; Shen, Lin-Jiang; Meng, Qing-Jin

2009-07-01

Three isomeric nitronyl nitroxide radical compounds, 2-[ n-( N-benzyl)pyridinium]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide bromide ( n = 2, 3 and 4 for 1, 2 and 3, respectively), have been synthesized and structurally characterized. The influence of steric hindrance on the molecular packing structures and physical properties has been observed. In the radical 1, such steric hindrance leads to a folding conformation of the imidazoline and benzene rings and the intramolecular C-H…π interaction between the methyl group and the benzene ring. There is no such effect in 2 and 3. In crystal of 2, there are the intermolecular C-H…π between methyl groups and benzene ring and intermolecular π…π stacking interaction between pyridine and benzene rings. Crystal of 2 with a chiral space group P2 12 12 1 shows the SHG response about 0.4 times as that of urea. In crystal of 3, there are three symmetry-independent radical molecules, which form an unusually six-membered supramolecular ring via intermolecular O…π interactions. For the solid sample of 3, the X-band EPR exhibits an axially symmetric signal and magnetic susceptibility data suggest intermolecular antiferromagnetic (AFM) coupling interactions and very weak intermolecular ferromagnetic (FM) coupling interactions which is more likely caused by magnetic anisotropy, while measurements of both 1 and 2 show isotropic X-band EPR signals and simple Currie-Weiss magnetic behavior.

SdsA polymorph isolation and improvement of their crystal quality using nonconventional crystallization techniques

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

De la Mora, Eugenio; Flores-Hernández, Edith; Jakoncic, Jean

SdsA, a sodium dodecyl sulfate hydrolase, from Pseudomonas aeruginosa was crystallized in three different crystal polymorphs and their three-dimensional structure was determined. The different polymorphs present different crystal packing habits. One of the polymorphs suggests the existence of a tetramer, an oligomeric state not observed previously, while the crystal packing of the remaining two polymorphs obstructs the active site entrance but stabilizes flexible regions of the protein. Nonconventional crystallization methods that minimize convection, such as counterdiffusion in polyvinyl alcohol gel coupled with the influence of a 500 MHz (10.2 T) magnetic field, were necessary to isolate the poorest diffracting polymorphmore » and increase its internal order to determine its structure by X-ray diffraction. In conclusion, the results obtained show the effectiveness of nonconventional crystallographic methods to isolate different crystal polymorphs.« less

Evolution of magnetic properties and microstructure of Hf2Co11B alloys

DOE PAGES

McGuire, Michael A.; Rios, Orlando

2015-02-05

Amorphous Hf 2Co 11B alloys produced by melt-spinning have been crystallized by annealing at 500-800 °C, and the products have been investigated using magnetization measurements, x-ray diffraction, and scanning electron microscopy. The results reveal the evolution of the phase fractions, microstructure, and magnetic properties with both annealing temperature and time. Crystallization of the phase denoted HfCo 7, which is associated with the development of coercivity, occurs slowly at 500 °C. Annealing at intermediate temperatures produces mixed phase samples containing some of the HfCo 7 phase with the highest values of remanent magnetization and coercivity. The equilibrium structure at 800 °Cmore » contains HfCo3B 2, Hf 6Co 23 and Co, and displays soft ferromagnetism. Maximum values for the remanent magnetization, intrinsic coercivity, and magnetic energy product among the samples are approximately 5.2 kG, 2.0 kOe, and 3.1 MGOe, respectively, which indicates that the significantly higher values observed in crystalline, melt-spun Hf 2Co 11B ribbons are a consequence of the non-equilibrium solidification during the melt-spinning process. Application of high magnetic fields during annealing is observed to strongly affect the microstructural evolution, which may provide access to higher performance materials in Zr/Hf-Co hard ferromagnets. The crystal structure of HfCo 7 and the related Zr analogues is unknown, and without knowledge of atomic positions powder diffraction cannot distinguish among proposed unit cells and symmetries found in the literature.« less

Crystal structure optimisation using an auxiliary equation of state

NASA Astrophysics Data System (ADS)

Jackson, Adam J.; Skelton, Jonathan M.; Hendon, Christopher H.; Butler, Keith T.; Walsh, Aron

2015-11-01

Standard procedures for local crystal-structure optimisation involve numerous energy and force calculations. It is common to calculate an energy-volume curve, fitting an equation of state around the equilibrium cell volume. This is a computationally intensive process, in particular, for low-symmetry crystal structures where each isochoric optimisation involves energy minimisation over many degrees of freedom. Such procedures can be prohibitive for non-local exchange-correlation functionals or other "beyond" density functional theory electronic structure techniques, particularly where analytical gradients are not available. We present a simple approach for efficient optimisation of crystal structures based on a known equation of state. The equilibrium volume can be predicted from one single-point calculation and refined with successive calculations if required. The approach is validated for PbS, PbTe, ZnS, and ZnTe using nine density functionals and applied to the quaternary semiconductor Cu2ZnSnS4 and the magnetic metal-organic framework HKUST-1.

Phase transition studied by 7Li nuclear magnetic resonance in LiXSO4 (X = K, Rb, Cs and NH4) single crystals

NASA Astrophysics Data System (ADS)

Lim, Ae Ran; Choh, Sung Ho; Jeong, Se-Young

2000-11-01

The temperature dependences of 7Li nuclear magnetic resonance in LiXSO4 (X = K, Rb, Cs, and NH4) single crystals grown by the slow evaporation method have been investigated by employing a Bruker FT NMR spectrometer. From the experimental data, the nuclear quadrupole constant, the asymmetry parameter and the principal axes of the EFG tensor were determined, and the results were compared with the crystal structure. The temperature dependences of the quadrupole parameters were explained with a single torsional mode of the Li-O bond by the Bayer theory. All the LiO4 tetrahedra in four different crystals showed torsional motion about the X-axis of the EFG tensor. Based on these results, the differences in atomic weight of X in the LiXSO4 single crystals are responsible for the differences in the torsional angular frequencies.

The formation, structure and physical properties of M(2)Pd(14+x)B(5-y) compounds, with M =  La, Ce, Pr, Nd, Sm, Eu, Gd, Lu and Th.

PubMed

Royanian, E; Bauer, E; Kaldarar, H; Galatanu, A; Khan, R T; Hilscher, G; Michor, H; Reissner, M; Rogl, P; Sologub, O; Giester, G; Gonçalves, A P

2009-07-29

Novel ternary compounds, M(2)Pd(14+x)B(5-y) (M =  La, Ce, Pr, Nd, Sm, Eu, Gd, Lu, Th; x∼0.9, y∼0.1), have been synthesized by arc melting. The crystal structures of Nd(2)Pd(14+x)B(5-y) and Th(2)Pd(14+x)B(5-y) were determined from x-ray single-crystal data and both are closely related to the structure type of Sc(4)Ni(29)B(10). All compounds were characterized by Rietveld analyses and found to be isotypic with the Nd(2)Pd(14+x)B(5-y) type. Measurements of the temperature dependent susceptibility and specific heat as well as the temperature and field dependent resistivity were employed to derive basic information on bulk properties of these compounds. The electrical resistivity of M(2)Pd(14+x)B(5-y), in general, is characterized by small RRR (residual resistance ratio) values originating from defects inherent to the crystal structure. Whereas the compounds based on Ce, Nd, Sm and Gd exhibit magnetic order, those based on Pr and Eu seem to be non-magnetic, at least down to 400 mK. While the non-magnetic ground state of the Pr based compound is a consequence of crystalline electric field effects in the context of the non-Kramers ion Pr, the lack of magnetic order in the case of the Eu based compound results from an intermediate valence state of the Eu ion.

Synthesis, crystal structure and magnetic properties of a new B-site ordered double perovskite Sr{sub 2}CuIrO{sub 6}

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

Vasala, Sami; Yamauchi, Hisao; Karppinen, Maarit, E-mail: maarit.karppinen@aalto.fi

2014-12-15

Here we synthesize and characterize a new double-perovskite oxide Sr{sub 2}CuIrO{sub 6}. The synthesis requires the use of high oxygen pressure to stabilize the VI oxidation state of iridium. The compound has a tetragonally-distorted crystal structure due to the Jahn–Teller active Cu{sup II} ion, and a high degree of B-site cation order. Magnetic transition is apparent at 15 K, but the zero-field-cooled and field-cooled susceptibilities diverge below this temperature. The high degree of cation order would exclude the possibility of a typical spin-glass, indicating that the divergence is probably due to a frustration of the magnetic interactions between Cu andmore » Ir, with a high frustration factor of f≈25. - Graphical abstract: A new member of the A{sub 2}B′B″O{sub 6} double-perovskite family with JT-active Cu{sup II} at the B′ site and Ir{sup VI} at the B″ site is synthesized through high pressure synthesis and characterized for the structural and magnetic properties. - Highlights: • New member of the A{sub 2}CuB″O{sub 6} double-perovskite family is synthesized with B″=Ir. • Stabilization of Ir{sup VI} requires the use of high oxygen pressure synthesis. • Crystal structure is tetragonally distorted due to JT-active Cu{sup II}. • Divergence of ZFC and FC curves is seen below the T{sub N} of 15 K. • This is presumably due to a frustration effect.« less

A unified picture of the crystal structures of metals

NASA Astrophysics Data System (ADS)

Söderlind, Per; Eriksson, Olle; Johansson, Börje; Wills, J. M.; Boring, A. M.

1995-04-01

THE crystal structures of the light actinides have intrigued physicists and chemists for several decades1. Simple metals and transition metals have close-packed, high-symmetry structures, such as body-centred cubic, face-centred cubic and hexagonal close packing. In contrast, the structures of the light actinides are very loosely packed and of low symmetry-tetragonal, orthorhombic and monoclinic. To understand these differences, we have performed total-energy calculations, as a function of volume, for both high-and low-symmetry structures of a simple metal (aluminium), a non-magnetic transition metal (niobium), a ferromagnetic transition metal (iron) and a light actinide (uranium). We find that the crystal structure of all of these metals is determined by the balance between electrostatic (Madelung) interactions, which favour high symmetry, and a Peierls distortion of the crystal lattice, which favours low symmetry. We show that simple metals and transition metals can adopt low-symmetry structures on expansion of the lattice; and we predict that, conversely, the light actinides will undergo transitions to structures of higher symmetry on compression.

X-ray magnetic circular dichroism and hard X-ray photoelectron spectroscopy of tetragonal Mn72Ge28 epitaxial thin film

NASA Astrophysics Data System (ADS)

Kim, Jinhyeok; Mizuguchi, Masaki; Inami, Nobuhito; Ueno, Tetsuro; Ueda, Shigenori; Takanashi, Koki

2018-04-01

An epitaxially grown Mn72Ge28 film with a tetragonal crystal structure was fabricated. It was clarified that the film had a perpendicular magnetization and a high perpendicular magnetic anisotropy energy of 14.3 Merg/cm3. The electronic structure was investigated by X-ray magnetic circular dichroism and hard X-ray photoelectron spectroscopy. The obtained X-ray magnetic circular dichroism spectrum revealed that the Mn orbital magnetic moment governed the magnetocrystalline anisotropy of the Mn72Ge28 film. A doublet structure was observed for the Mn 2p3/2 peak of hard X-ray photoelectron spectrum, indicating the spin exchange interaction between the 2p core-hole and 3d valence electrons.

Structural investigation of chemically synthesized ferrite magnetic nanomaterials

NASA Astrophysics Data System (ADS)

Uyanga, E.; Sangaa, D.; Hirazawa, H.; Tsogbadrakh, N.; Jargalan, N.; Bobrikov, I. A.; Balagurov, A. M.

2018-05-01

In recent times, interest in ferrite magnetic nanomaterials has considerably grown, mainly due to their highly promising medical and biological applications. Spinel ferrite powder samples, with high heat generation abilities in AC magnetic fields, were studied for their application to the hyperthermia treatment of cancer tumors. These properties of ferrites strongly depend on their chemical composition, ion distribution between crystallographic positions, magnetic structure and method of preparation. In this study, crystal and magnetic structures of several magnetic spinels were investigated by neutron diffraction. The explanation of the mechanism triggering the heat generation ability in the magnetic materials, and the electronic and magnetic states of ferrite-spinel type structures, were theoretically defined by a first-principles method. Ferrites with the composition of CuxMg1-xFe2O4 have been investigated as a heat generating magnetic nanomaterial. Atomic fraction of copper in ferrite was varied between 0 and 100% (that is, x between 0 and 1.0 with 0.2 steps), with the copper dope limit corresponding to appear a tetragonal phase.

Ammonium–cobalt–nickel phosphates, NH{sub 4}[Co{sub 1−x}Ni{sub x}PO{sub 4}]·H{sub 2}O

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

Torre-Fernández, Laura; Trobajo, Camino; Pedro, Imanol de

The ammonium–cobalt–nickel phosphates, NH{sub 4}[Co{sub 1−x}Ni{sub x}PO{sub 4}]·H{sub 2}O (x=0.00, 0.34, 0.59, 0.70, 1.00), and the deuterated forms, ND{sub 4}[Co{sub 1−x}Ni{sub x}PO{sub 4}]·D{sub 2}O (x=0.00, 0.38, 0.48, 0.69, 0.85), have been synthesized under mild hydrothermal conditions and characterised using X-ray and neutron diffraction, chemical and thermal analysis, and magnetic measurements. Their crystal structures, including hydrogen positions, were determined by Rietveld refinement using single-crystal X-ray and neutron powder diffraction data. The space group of these orthorhombic crystals modifies as a function of their composition. The magnetic susceptibility and magnetization measurements of these ammonium–cobalt–nickel phosphates show antiferromagnetic behaviour, and the Neel temperaturemore » evolves from 5.5 K (x=0.00) up to 13.2 K (x=1.00). - Graphical abstract: We obtained single crystals for all the members of the family. In this series, although all crystals are orthorhombic, the space group changes as a function of the composition, showing how the single-crystal diffraction data is capable to manifest structural subtleties that had not been described before for this group of materials. All the investigated materials behave antiferromagnetically with ordering temperatures from 5.5 K up to 13.2 K. Display Omitted - Highlights: • The ammonium–cobalt–nickel phosphates, NH{sub 4}[Co{sub 1−x}Ni{sub x}PO{sub 4}]·H{sub 2}O (x=0.00, 0.34, 0.59, 0.70, 1.00) and the deuterated forms ND4[Co1-xNixPO4]·D{sub 2}O (x=0.00, 0.38, 0.49, 0.68, 0.85) have synthesized by hydrothermal synthesis. • The structural studies of these compounds are introduced as a function of the composition. • The magnetic studies show an antiferromagnetically behavior with ordering temperatures from 5.5 K to 13.2 K.« less

Magnetic and transport properties of Ga-Mn-Co full Heusler alloy

NASA Astrophysics Data System (ADS)

Samanta, Tamalika; Bhobe, P. A.

2018-04-01

We report structural, electrical and magnetic studies of the Ga rich Heusler compound Ga48Mn25Co27. The Ga-Co-Mn compounds have been predicted to be useful candidates for spintronic applications. We found that the Ga48Mn25Co27 compound crystallizes in cubic L21 structure. It shows a very low curie temperature of 88 K and a soft magnetic behavior. We observed an unusual, non-saturating magnetic hysteresis loop where the virgin curve stays out of the loop. The origin of such behavior might lie in the fact that there exist two competing magnetic sub-lattices with different exchange interactions.

New structures of Fe3S for rare-earth-free permanent magnets

NASA Astrophysics Data System (ADS)

Yu, Shu; Zhao, Xin; Wu, Shunqing; Nguyen, Manh Cuong; Zhu, Zi-zhong; Wang, Cai-Zhuang; Ho, Kai-Ming

2018-02-01

We applied an adaptive genetic algorithm (AGA) to search for low-energy crystal structures of Fe3S. A number of structures with energies lower than that of the experimentally reported Pnma and I-4 structures have been obtained from our AGA searches. These low-energy structures can be classified as layer-motif and column-motif structures. In the column-motif structures, Fe atoms self-assemble into rods with a bcc type of underlying lattice, which are separated by the holes terminated by S atoms. In the layer-motif structures, the bulk Fe is broken into slabs of several layers passivated by S atoms. Magnetic property calculations showed that the column-motif structures exhibit reasonably high uniaxial magnetic anisotropy. In addition, we examined the effect of Co doping to Fe3S and found that magnetic anisotropy can be enhanced through Co doping.

New structures of Fe3S for rare-earth-free permanent magnets

DOE PAGES

Yu, Shu; Zhao, Xin; Wu, Shunqing; ...

2018-02-25

We applied adaptive genetic algorithm (AGA) to search for low-energy crystal structures of Fe 3S. A number of structures with energies lower than that of the experimentally reported Pnma and I-4 structures have been obtained from our AGA searches. These low-energy structures can be classified as layer-motif and column-motif structures. In the column-motif structures, Fe atoms self-assemble into rods with bcc type of underlying lattice, which are separated by the holes terminated by S atoms. In the layer-motif structures, the bulk Fe is broken into slabs of several layers passivated by S atoms. Magnetic properties calculations showed that the column-motifmore » structures exhibit reasonably high uniaxial magnetic anisotropy. In addition, we examined the effect of Co doping to Fe 3S and found magnetic anisotropy can be enhanced through Co doping.« less

Lanthanides in molecular magnetism: old tools in a new field.

PubMed

Sorace, Lorenzo; Benelli, Cristiano; Gatteschi, Dante

2011-06-01

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure-property relationships in these systems.

Unexpected Magnetic Ordering on the Cr Substructure in UCr2Si2C and Structural Relationships in Quaternary U-Cr-Si-C Compounds.

PubMed

Lemoine, Pierric; Vernière, Anne; Pasturel, Mathieu; Venturini, Gérard; Malaman, Bernard

2018-03-05

Previous experimental and theoretical studies revealed that carbon insertion into the RCr 2 Si 2 compounds drastically affects the magnetic behavior, since chromium does not carry any magnetic moment in RCr 2 Si 2 C (R = Y, La-Sm, Gd-Er) compounds in contrast to RCr 2 Si 2 (R = Y, Sm, Gd-Lu, Th) compounds. In this study, we report on the unexpected magnetic ordering of chromium atoms in the isotype quaternary UCr 2 Si 2 C compound. While specific heat and magnetic measurements suggest a Pauli paramagnetic behavior, neutron powder diffraction reveals an antiferromagnetic ordering of the chromium substructure at high temperature ( T N > 300 K), while that of uranium remains nonmagnetically ordered down to 2 K. Its magnetic behavior, inverse in comparison to the RCr 2 Si 2 C carbides involving a magnetic lanthanide, is discussed in relation with the singularity of its crystal structure among the series. Moreover, the crystallographic structures and the structural stability of UCr 2 Si 2 C and of two other quaternary U-Cr-Si-C compounds (i.e., UCr 3 Si 2 C and U 2 Cr 3 Si 2 C 3 ), based on the full occupancy of interstitial sites by carbon atoms, are discussed and compared to those of the related ternary intermetallics. Finally, the low-temperature form of UCr 2 Si 2 , corresponding to a displacive transformation around 210 K of the ThCr 2 Si 2 -type structure, is reinvestigated by considering a higher symmetry monoclinic unit cell ( C2/ m) instead of the previously reported triclinic cell ( P1̅). The antiferromagnetic ordering at low temperature ( T N = 30(2) K) of the uranium substructure is confirmed, and its magnetic structure is reanalyzed and discussed considering the monoclinic crystal structure.

Snynthesis and magnetization of BaLn2O4 (Ln = lanthanide)

NASA Astrophysics Data System (ADS)

Lundberg, Matthew

The BaLn2O4 family has been synthesized successfully as single crystals by the flux-growth method. The phases crystallize in the CaV2O4 structure prototype in space group Pnma (# 62). The structure has been studied using single-crystal x-ray diffraction, and stoichiometry confirmed with EDS, and the unit cell parameters and atomic positions have been determined for the whole lanthanide series (with the exception of the Lu compound). The effects of the lanthanide ionic radius on the atomic positions in the unit cell has been studied in terms of fractional atomic coordinates, bond lengths and angles, and bond valence sums. Magnetic measurements have been performed on the series with the exception of the La, Eu, and Lu members in the form of susceptibility versus temperature. The crystals all show signs of geometric antiferromagnetic frustration with the Neel temperatures significantly below the temperature predicted by the Weiss constant. Additionally some members of the family, namely BaCe2O4, BaNd2O4, BaPr 2O4, BaSm2O4, BaTb2O 4, and BaYb2O4 show significant crystal field splitting, that causes deviation from Currie-Weiss behavior.

Magnetic ordering in TmGa.

PubMed

Cadogan, J M; Stewart, G A; Muñoz Pérez, S; Cobas, R; Hansen, B R; Avdeev, M; Hutchison, W D

2014-03-19

We have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and (169)Tm Mössbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an incommensurate antiferromagnetic structure described by the propagation vector k1 = [0 0.275(2) 0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) μB at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) μB. The (169)Tm hyperfine magnetic field at 5 K is 631(1) T.

Yb3+-doped cadmium molybdato-tungstate single crystal - Its structural, optical, magnetic and transport properties

NASA Astrophysics Data System (ADS)

Groń, T.; Tomaszewicz, E.; Berkowski, M.; Głowacki, M.; Oboz, M.; Kusz, J.; Sawicki, B.; Kukuła, Z.; Duda, H.

2018-06-01

Single crystal of new cadmium and ytterbium molybdato-tungstate (Cd0.9706⎕0.0098Yb0.0196(MoO4)0.9706(WO4)0.0294, where ⎕ denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray crystallographic analysis reveals that the as-grown single crystal belongs to a scheelite-type structure (a = b = 5.15539(12) and c = 11.1919(3) Å, space group I41/a), in which Yb3+ ions do not show long-range order and are randomly distributed in the unit cell, substituting the Cd2+ ones. The as-grown single crystal does not show anisotropy of optical properties, i.e. its direct band gap reaches Eg = 1.76 or 1.75 eV along (100) and (001) crystallographic directions, respectively. The single crystal exhibits paramagnetic state with short-range antiferromagnetic and long-range ferrimagnetic interactions, a magnetization with zero coercivity and, a remanence that is almost a universal function of H/T, characterizing superparamagnetic-like behaviour. Electrical studies of the new ytterbium-doped cadmium molybdato-tungstate single crystal show a relatively small dielectric constant (εr<12), large lossiness of Joule-Lenz type observed at low frequencies as well as nonlinear I-V characteristics of Schottky or Maxwell-Wagner type.

Microwave-Assisted Synthesis, Microstructure, and Magnetic Properties of Rare-Earth Cobaltites.

PubMed

Gutiérrez Seijas, Julia; Prado-Gonjal, Jesús; Ávila Brande, David; Terry, Ian; Morán, Emilio; Schmidt, Rainer

2017-01-03

The series of perovskite rare-earth (RE) doped cobaltites (RE)CoO 3 (RE = La-Dy) was prepared by microwave-assisted synthesis. The crystal structure undergoes a change of symmetry depending on the size of the RE cation. LaCoO 3 is rhombohedral, S.G. R3̅c (No. 167), while, for the rest of the RE series (Pr-Dy), the symmetry is orthorhombic, S.G. Pnma (No. 62). The crystal structure obtained by X-ray diffraction was confirmed by high-resolution transmission electron microscopy, which yielded a good match between experimental and simulated images. It is further shown that the well-known magnetism in LaCoO 3 , which involves a thermally induced Co 3+ (d 6 ) low spin to intermediate or high spin state transition, is strongly modified by the RE cation, and a rich variety of magnetic order has been detected across the series.

The random field Blume-Capel model revisited

NASA Astrophysics Data System (ADS)

Santos, P. V.; da Costa, F. A.; de Araújo, J. M.

2018-04-01

We have revisited the mean-field treatment for the Blume-Capel model under the presence of a discrete random magnetic field as introduced by Kaufman and Kanner (1990). The magnetic field (H) versus temperature (T) phase diagrams for given values of the crystal field D were recovered in accordance to Kaufman and Kanner original work. However, our main goal in the present work was to investigate the distinct structures of the crystal field versus temperature phase diagrams as the random magnetic field is varied because similar models have presented reentrant phenomenon due to randomness. Following previous works we have classified the distinct phase diagrams according to five different topologies. The topological structure of the phase diagrams is maintained for both H - T and D - T cases. Although the phase diagrams exhibit a richness of multicritical phenomena we did not found any reentrant effect as have been seen in similar models.

Synthesis and structural characterization of bulk Sb2Te3 single crystal

NASA Astrophysics Data System (ADS)

Sultana, Rabia; Gahtori, Bhasker; Meena, R. S.; Awana, V. P. S.

2018-05-01

We report the growth and characterization of bulk Sb2Te3 single crystal synthesized by the self flux method via solid state reaction route from high temperature melt (850˚C) and slow cooling (2˚C/hour) of constituent elements. The single crystal X-ray diffraction pattern showed the 00l alignment and the high crystalline nature of the resultant sample. The rietveld fitted room temperature powder XRD revealed the phase purity and rhombohedral structure of the synthesized crystal. The formation and analysis of unit cell structure further verified the rhombohedral structure composed of three quintuple layers stacked one over the other. The SEM image showed the layered directional growth of the synthesized crystal carried out using the ZEISS-EVOMA-10 scanning electron microscope The electrical resistivity measurement was carried out using the conventional four-probe method on a quantum design Physical Property Measurement System (PPMS). The temperature dependent electrical resistivity plot for studied Sb2Te3 single crystal depicts metallic behaviour in the absence of any applied magnetic field. The synthesis as well as the structural characterization of as grown Sb2Te3 single crystal is reported and discussed in the present letter.

Indirect estimation of the tectonic evolution of magnetic structures along the Indiavaí-Lucialva Shear Zone, Mato Grosso, Brazil

NASA Astrophysics Data System (ADS)

Louro, V. H.; Ribeiro, V. B.; Mantovani, M. S.; Geolit Team

2013-05-01

The Indiavaí-Lucialva Shear Zone (ILSZ) has a notorious cinematic standard, moving from SW to NE, juxtaposing the Santa Helena Granitic Batholith to the metavolcanosedimentary sets and orthogneisses from the Jauru Domain basement. Along the ILSZ, a sequence of magnetic anomalies of high interference, with each other, and varied polarities occurs, what suggests the presence of different lithologies or times of (re)crystallization of the ferromagnetic minerals from these magnetic structures. In its southernmost portion, the sequence of magnetic anomalies splits in two directions, SW and SE, with the first invading the limits of the Santa Helena batholith and, the latest, accompanying the ILSZ. This study aimed for the comprehension of complex tectonic setting of this region. It analyzed the set of anomalies estimating their lateral limits, depths and directions of total magnetization, with the Enhanced Horizontal Derivatives (EHD), its extrapolation for depth estimative (EHD-Depth), and through an iterative reduction to the magnetic pole, respectively. This procedure allowed the composition of initial models for further inversions of magnetic data which, results, indicate contrasts of magnetic susceptibility in sub-surface. Once known the approximated 3-D shape of the magnetic structures along the ILSZ, the total magnetization intensity of each anomaly was recovered, what consequently allowed, by vector subtraction, to estimate their individual remnant magnetization. The remnant magnetization's inclinations and declinations of the anomalies sources and their latitudes and longitudes permitted the calculus of their respective virtual magnetic paleopoles. When confronted with the South American paleopole wander path and the datings linked to this path, available in the literature, it was possible to have an indirect approximation of the age of (re)crystallization of each magnetic structure near the ILSZ. This procedure indicated an increasing of the ages of the structures from SE (1298 Ma) to NW (1439 Ma). The southwestern anomalies invading the Santa Helena batholith showed ages of approximately 1419 Ma, what allows to infer their allocation with the rest of the intrusion of the batholith.; Total magnetic field map of the region of the ILSZ, locating the studied anomalies, mineral occurences and tectonic limits.

Syntheses, structure and magnetic properties of two vanadate garnets Ca{sub 5}M{sub 4}V{sub 6}O{sub 24} (M=Co, Ni)

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

Wang, Nannan; College of Materials Science and Engineering, Fuzhou University, Fuzhou, Fujian 350108; He, Zhangzhen, E-mail: hcz1988@hotmail.com

2015-08-15

Two vanadate compounds Ca{sub 5}M{sub 4}V{sub 6}O{sub 24} (M=Co, Ni) have been synthesized by a high-temperature solid-state reaction. The compounds are found to crystallize in the cubic system with a space group Ia-3d, which exhibit a typical garnet structural framework. Magnetic measurements show that Ca{sub 5}M{sub 4}V{sub 6}O{sub 24} (M=Co, Ni) exhibit similar magnetic behaviors, in which Ca{sub 5}Co{sub 4}V{sub 6}O{sub 24} possesses an antiferromagnetic ordering at T{sub N}=~6 K while Ca{sub 5}Ni{sub 4}V{sub 6}O{sub 24} shows an antiferromagnetic ordering at T{sub N}=~7 K. - Graphical abstract: Garnet vanadate compounds Ca{sub 5}M{sub 4}V{sub 6}O{sub 24} (M=Co, Ni) have been synthesizedmore » by a high-temperature solid-state reaction. Structural features and magnetic behaviors are also investigated. - Highlights: • New type of garnet vanadates Ca{sub 5}M{sub 4}V{sub 6}O{sub 24} (M=Co, Ni) are synthesized by a high-temperature solid-state reaction. • Structural features are confirmed by single crystal samples. • Magnetic behaviors are firstly investigated in the systems.« 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.

Transport properties of RCo_2B_2C with R = Dy, Ho, and Pr single

NASA Astrophysics Data System (ADS)

Duran, Alejandro; Escudero, Roberto

2002-03-01

Single crystals of (Dy, Ho, Pr)Co_2B_2C have been grown by a cold copper crucible method. Metallurgical and structural studies indicate that this borocarbide family melts incongruently and crystallizes as a derivative structure of the ThCr_2Si_2. The family accepts rare earth atoms depending on the type of transition metals used to form the compound. For instance with Ni atoms, all lanthanides ranging from the large lanthanum to lutetium ions are reported to form RNi_2B_2C single crystals, so far no single crystals have been obtained when changing Ni by Cobalt. A comparison of the structural parameters of the RCo_2B_2C with the RNiHo, Pr) compounds indicate that the atomic distance between transition metal atoms contracts with the insertion of the Co ion, resulting in an increasing of the c parameter and decreasing volume. Several recent reports published in the current literature related on the physical properties of RCo_2B_2C (R = rare earth metals and Y) have been only performed on polycrystalline samples, they commonly contain small amounts of second phases. High quality single crystals are necessaries in order to better understand the physical properties, such as anisotropy in the transport and in the magnetic properties. In this report we show magnetic susceptibility and resistivity measurements performed in single crystals in the ab-plane and c direction for 2 - 320 K temperature range for the three single crystals of (Dy, Ho, Pr)Co_2B_2C.

RESEARCH ACTIVITIES IN THE FIELD OF MATERIALS SCIENCE.

DTIC Science & Technology

MAGNETIC RESONANCE, COMPLEX COMPOUNDS, CRYSTAL STRUCTURE, ELECTROCHEMISTRY, CHEMILUMINESCENCE, PHOTOCHEMICAL REACTIONS, PHOSPHORUS HETEROCYCLIC COMPOUNDS...RADIATION CHEMISTRY, POLYMERS, ROCK, SUPERCONDUCTORS, POSITRONS , DAMAGE, RADIATION EFFECTS, HALIDES

On the nature of the phase transition in uranium dioxide

NASA Astrophysics Data System (ADS)

Gofryk, K.; Mast, D.; Antonio, D.; Shrestha, K.; Andersson, D.; Stanek, C.; Jaime, M.

Uranium dioxide (UO2) is by far the most studied actinide material as it is a primary fuel used in light water nuclear reactors. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. UO2 crystalizes in the face-centered-cubic fluorite structure and is a Mott-Hubbard insulator with well-localized uranium 5 f-electrons. In addition, below 30 K, a long range antiferromagnetic ordering of the electric-quadrupole of the uranium moments is observed, forming complex non-collinear 3-k magnetic structure. This transition is accompanied by Jahn-Teller distortion of oxygen atoms. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion. Here we present results of our extensive thermodynamic investigations on well-characterized and oriented single crystals of UO2+x (x = 0, 0.033, 0.04, and 0.11). By focusing on the transition region under applied magnetic field we are able to study the interplay between different competing interactions (structural, magnetic, and electrical), its dynamics, and relationship to the oxygen content. We will discuss implications of these results. Work supported by the Department of Energy, Office of Basic Energy Sciences, Materials Sciences, and Engineering Division.

Assessment of off-stoichiometric Zr33-xFe52+xSi15 C14 Laves phase compounds as permanent magnet materials

NASA Astrophysics Data System (ADS)

Gabay, A. M.; Hadjipanayis, G. C.

2018-05-01

Recently, Fe-based rare-earth-free compounds with non-cubic crystal structures were proposed as a base for permanent magnets which would not rely on critical elements. In this work, two series of alloys, Zr27Fe73-wSiw (0 ≤ w ≤ 15) and Zr33-xFe52+xSi15 (0 ≤ x ≤ 11), were prepared and characterized after annealing at 1538 K in order to determine the fundamental magnetic properties of the C36 and C14 hexagonal Laves phase compounds. A mixture of the cubic C15 and Zr6Fe23 structures was observed instead of the expected C36 structure. The hexagonal C14 was found in all Zr33-xFe52+xSi15 alloys with its lattice parameters linearly decreasing as the Fe(Si) atoms occupy the Zr sites in the Laves phase crystal structure. The solubility limit of Fe in the C14 structure at 1538 K corresponds to x = 9.5. The Curie temperature of the C14 compounds increases with deviation from the Laves phase stoichiometry from 290 K to 530 K. The room-temperature spontaneous magnetization also increases reaching, after correcting for the non-magnetic impurities, a value of 6.7 kG. The magnetocrystalline anisotropy of the off-stoichiometric C14 Laves phase was found to be uniaxial with the easy magnetization direction parallel to the hexagonal axis. Unfortunately, the anisotropy field, which does not exceed 10 kOe, is not sufficiently high to make the compounds interesting as permanent magnet materials.

A spin-frustrated trinuclear copper complex based on triaminoguanidine with an energetically well-separated degenerate ground state.

PubMed

Spielberg, Eike T; Gilb, Aksana; Plaul, Daniel; Geibig, Daniel; Hornig, David; Schuch, Dirk; Buchholz, Axel; Ardavan, Arzhang; Plass, Winfried

2015-04-06

We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.

Ferromagnetic Switching of Knotted Vector Fields in Liquid Crystal Colloids.

PubMed

Zhang, Qiaoxuan; Ackerman, Paul J; Liu, Qingkun; Smalyukh, Ivan I

2015-08-28

We experimentally realize polydomain and monodomain chiral ferromagnetic liquid crystal colloids that exhibit solitonic and knotted vector field configurations. Formed by dispersions of ferromagnetic nanoplatelets in chiral nematic liquid crystals, these colloidal ferromagnets exhibit spontaneous long-range alignment of magnetic dipole moments of individual platelets, giving rise to a continuum of the magnetization field M(r). Competing effects of surface confinement and chirality prompt spontaneous formation and enable the optical generation of localized twisted solitonic structures with double-twist tubes and torus knots of M(r), which exhibit a strong sensitivity to the direction of weak magnetic fields ∼1  mT. Numerical modeling, implemented through free energy minimization to arrive at a field-dependent three-dimensional M(r), shows a good agreement with experiments and provides insights into the torus knot topology of observed field configurations and the corresponding physical underpinnings.

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–xK x)Fe 2As 2 single crystal with x = 0.24

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

Liu, Yong; Tanatar, Makariy A.; Timmons, Erik

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–xK x)Fe 2As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–xK x)Fe 2As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~more » 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–xK x)Fe 2As 2 single crystal with x = 0.24

DOE PAGES

Liu, Yong; Tanatar, Makariy A.; Timmons, Erik; ...

2016-11-09

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–xK x)Fe 2As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–xK x)Fe 2As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~more » 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

Fe-Cluster Compounds of Chalcogenides: Candidates for Rare-Earth-Free Permanent Magnet and Magnetic Nodal-Line Topological Material

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

Zhao, Xin; Wang, Cai-Zhuang; Kim, Minsung

Here, Fe-cluster-based crystal structures are predicted for chalcogenides Fe 3X 4 (X = S, Se, Te) using an adaptive genetic algorithm. Topologically different from the well-studied layered structures of iron chalcogenides, the newly predicted structures consist of Fe clusters that are either separated by the chalcogen atoms or connected via sharing of the vertex Fe atoms. Additionally, using first-principles calculations, we demonstrate that these structures have competitive or even lower formation energies than the experimentally synthesized Fe 3X 4 compounds and exhibit interesting magnetic and electronic properties. In particular, we show that Fe 3X 4 can be a good candidatemore » as a rare-earth-free permanent magnet and Fe 3X 4 can be a magnetic nodal-line topological material.« less

Fe-Cluster Compounds of Chalcogenides: Candidates for Rare-Earth-Free Permanent Magnet and Magnetic Nodal-Line Topological Material

DOE PAGES

Zhao, Xin; Wang, Cai-Zhuang; Kim, Minsung; ...

2017-11-13

Here, Fe-cluster-based crystal structures are predicted for chalcogenides Fe 3X 4 (X = S, Se, Te) using an adaptive genetic algorithm. Topologically different from the well-studied layered structures of iron chalcogenides, the newly predicted structures consist of Fe clusters that are either separated by the chalcogen atoms or connected via sharing of the vertex Fe atoms. Additionally, using first-principles calculations, we demonstrate that these structures have competitive or even lower formation energies than the experimentally synthesized Fe 3X 4 compounds and exhibit interesting magnetic and electronic properties. In particular, we show that Fe 3X 4 can be a good candidatemore » as a rare-earth-free permanent magnet and Fe 3X 4 can be a magnetic nodal-line topological material.« less

Antiferromagnetic defect structure in LaNi O 3 – δ single crystals

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

Wang, Bi -Xia; Rosenkranz, Stephan; Rui, X.

Here, the origins of the metal-insulator and magnetic transitions exhibited by perovskite rare-earth nickelates, RNiO 3 (where R is a rare-earth element), remain open issues, with charge disproportionation, magnetic interactions, and lattice response across multiple length scales being among the many possible origins. Recently, growth of single crystals of LaNiO 3, which is the only member of these compounds that remains metallic in its ground state, has been reported, opening a new chapter in the investigation of the perovskite nickelates. Here, using a combination of magnetometry, heat capacity, and neutron scattering on as-grown and purposely reduced LaNiO 3–δ crystals, wemore » show that both antiferromagnetic and ferromagnetic phases with a Néel temperature of ~152 K and a Curie temperature of ~225 K can be induced by reduction of the oxygen content. Transmission electron microscopy shows that these phases are characterized by ordered oxygen vacancy defect structures that exist as dilute secondary phases in as-grown crystals despite growth in partial oxygen pressures up to at least 130 bar. The demonstration of antiferromagnetism resulting from oxygen vacancy ordered structures implies that stoichiometry must be explicitly considered when interpreting the bulk properties of LaNiO 3–δ single crystals; accordingly, the implications of our results for putative oxygen-stoichiometric LaNiO 3 are discussed.« less

Antiferromagnetic defect structure in LaNi O3 -δ single crystals

NASA Astrophysics Data System (ADS)

Wang, Bi-Xia; Rosenkranz, S.; Rui, X.; Zhang, Junjie; Ye, F.; Zheng, H.; Klie, R. F.; Mitchell, J. F.; Phelan, D.

2018-06-01

The origins of the metal-insulator and magnetic transitions exhibited by perovskite rare-earth nickelates, RNiO3 (where R is a rare-earth element), remain open issues, with charge disproportionation, magnetic interactions, and lattice response across multiple length scales being among the many possible origins. Recently, growth of single crystals of LaNiO3, which is the only member of these compounds that remains metallic in its ground state, has been reported, opening a new chapter in the investigation of the perovskite nickelates. Here, using a combination of magnetometry, heat capacity, and neutron scattering on as-grown and purposely reduced LaNi O3 -δ crystals, we show that both antiferromagnetic and ferromagnetic phases with a Néel temperature of ˜152 K and a Curie temperature of ˜225 K can be induced by reduction of the oxygen content. Transmission electron microscopy shows that these phases are characterized by ordered oxygen vacancy defect structures that exist as dilute secondary phases in as-grown crystals despite growth in partial oxygen pressures up to at least 130 bar. The demonstration of antiferromagnetism resulting from oxygen vacancy ordered structures implies that stoichiometry must be explicitly considered when interpreting the bulk properties of LaNi O3 -δ single crystals; accordingly, the implications of our results for putative oxygen-stoichiometric LaNiO3 are discussed.

Crystal growth of incommensurate members of 2H-hexagonal perovskite related oxides: Ba{sub 4}M{sub z}Pt{sub 3−z}O{sub 9} (M=Co, Ni, Cu, Zn, Mg, Pt)

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

Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho

2016-04-15

Millimeter sized crystals of six oxides of approximate composition Ba{sub 4}M{sub z}Pt{sub 3-z}O{sub 9} (M=Co, Ni, Cu, Zn, Mg, Pt) were grown from molten K{sub 2}CO{sub 3} fluxes and found to crystallize in a 2H hexagonal perovskite-related structure type. The compositions of these incommensurate structures, which belong to the A{sub 3n+3m}A′{sub n}B{sub 3m+n}O{sub 9m+6n} family of 2H hexagonal perovskite related oxides, were characterized by X-ray diffraction, energy dispersive spectroscopy, and magnetic susceptibility measurements. The specific synthetic considerations, crystal growth conditions, and magnetic susceptibility measurements are discussed. - Graphical abstract: SEM image and average commensurate unit cell of Ba{sub 4}Pt{sub 3}O{submore » 9.} - Highlights: • Single crystals of the series Ba{sub 4}A′{sub z}Pt{sub 3-z}O{sub 9} were grown via a molten carbonate flux. • Ba{sub 4}Pt{sub 3}O{sub 9} and all substitutional variants are incommensurate, composite structures. • All compounds have an approximate stoichiometry of Ba{sub 4}A′Pt{sub 2}O{sub 9.}.« less

Antiferromagnetic defect structure in LaNi O 3 – δ single crystals

DOE PAGES

Wang, Bi -Xia; Rosenkranz, Stephan; Rui, X.; ...

2018-06-12

Here, the origins of the metal-insulator and magnetic transitions exhibited by perovskite rare-earth nickelates, RNiO 3 (where R is a rare-earth element), remain open issues, with charge disproportionation, magnetic interactions, and lattice response across multiple length scales being among the many possible origins. Recently, growth of single crystals of LaNiO 3, which is the only member of these compounds that remains metallic in its ground state, has been reported, opening a new chapter in the investigation of the perovskite nickelates. Here, using a combination of magnetometry, heat capacity, and neutron scattering on as-grown and purposely reduced LaNiO 3–δ crystals, wemore » show that both antiferromagnetic and ferromagnetic phases with a Néel temperature of ~152 K and a Curie temperature of ~225 K can be induced by reduction of the oxygen content. Transmission electron microscopy shows that these phases are characterized by ordered oxygen vacancy defect structures that exist as dilute secondary phases in as-grown crystals despite growth in partial oxygen pressures up to at least 130 bar. The demonstration of antiferromagnetism resulting from oxygen vacancy ordered structures implies that stoichiometry must be explicitly considered when interpreting the bulk properties of LaNiO 3–δ single crystals; accordingly, the implications of our results for putative oxygen-stoichiometric LaNiO 3 are discussed.« less

Space-Time Crystal and Space-Time Group

NASA Astrophysics Data System (ADS)

Xu, Shenglong; Wu, Congjun

2018-03-01

Crystal structures and the Bloch theorem play a fundamental role in condensed matter physics. We extend the static crystal to the dynamic "space-time" crystal characterized by the general intertwined space-time periodicities in D +1 dimensions, which include both the static crystal and the Floquet crystal as special cases. A new group structure dubbed a "space-time" group is constructed to describe the discrete symmetries of a space-time crystal. Compared to space and magnetic groups, the space-time group is augmented by "time-screw" rotations and "time-glide" reflections involving fractional translations along the time direction. A complete classification of the 13 space-time groups in one-plus-one dimensions (1 +1 D ) is performed. The Kramers-type degeneracy can arise from the glide time-reversal symmetry without the half-integer spinor structure, which constrains the winding number patterns of spectral dispersions. In 2 +1 D , nonsymmorphic space-time symmetries enforce spectral degeneracies, leading to protected Floquet semimetal states. We provide a general framework for further studying topological properties of the (D +1 )-dimensional space-time crystal.

Space-Time Crystal and Space-Time Group.

PubMed

Xu, Shenglong; Wu, Congjun

2018-03-02

Crystal structures and the Bloch theorem play a fundamental role in condensed matter physics. We extend the static crystal to the dynamic "space-time" crystal characterized by the general intertwined space-time periodicities in D+1 dimensions, which include both the static crystal and the Floquet crystal as special cases. A new group structure dubbed a "space-time" group is constructed to describe the discrete symmetries of a space-time crystal. Compared to space and magnetic groups, the space-time group is augmented by "time-screw" rotations and "time-glide" reflections involving fractional translations along the time direction. A complete classification of the 13 space-time groups in one-plus-one dimensions (1+1D) is performed. The Kramers-type degeneracy can arise from the glide time-reversal symmetry without the half-integer spinor structure, which constrains the winding number patterns of spectral dispersions. In 2+1D, nonsymmorphic space-time symmetries enforce spectral degeneracies, leading to protected Floquet semimetal states. We provide a general framework for further studying topological properties of the (D+1)-dimensional space-time crystal.

Concentration and structure inhomogeneities in GaSb(Si) single crystals grown at different heat and mass transfer conditions

NASA Astrophysics Data System (ADS)

Serebryakov, Yu. A.; Prokhorov, I. A.; Vlasov, V. N.; Korobeynikova, E. N.; Zakharov, B. G.; Shul'pina, I. L.; Marchenko, M. P.; Fryazinov, I. V.

2007-06-01

Results of ground-based experiments on crystallization of gallium antimonide on the POLIZON facility carried out within the framework of space experiment preparation aboard FOTON satellite are submitted. Technical and technological opportunities of suppression of disturbing factors for improvement of quality of grown crystals in space are substantiated. Features of formation of concentration and structure inhomogeneities in GaSb:Si crystals grown under non-stationary and stationary convection conditions are investigated. Experimental data about structure and dopant distribution inhomogeneities are discussed taking into account results of numerical researches of GaSb:Si crystallization. Also earlier received results of modeling of GaSb:Te crystallization under close temperature conditions are used. Correlation between computational and experimental data is shown. The data on intensity of flows close to crystallization front are received at which non-stationary or stationary conditions of crystallization are realized. The forecast for space conditions is made. The influence of a rotating magnetic field on convection in melt for application in space experiment projected is investigated.

Synthesis and magnetic properties of the high-pressure scheelite-type GdCrO{sub 4} polymorph

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

Dos santos-Garcia, A.J., E-mail: adossant@quim.ucm.es; Climent-Pascual, E.; Gallardo-Amores, J.M.

The scheelite-type polymorph of GdCrO{sub 4} has been obtained from the corresponding zircon-type compound under high pressure and temperature conditions, namely 4 GPa and 803 K. The crystal structure has been determined by X-ray powder diffraction. This GdCrO{sub 4} scheelite crystallizes in a tetragonal symmetry with space group I4{sub 1}/a (No. 88, Z=4), a=5.0501(1) A, c=11.4533(2) A and V=292.099(7) A{sup 3}. The thermal decomposition leads to the formation of the zircon-polymorph as intermediate phase at 773 K to end in the corresponding GdCrO{sub 3} distorted perovskite-structure at higher temperatures. Magnetic susceptibility and magnetization measurements suggest the existence of long-range antiferromagneticmore » interactions which have been also confirmed from specific heat measurements. Neutron powder diffraction data reveal the simultaneous antiferromagnetic Gd{sup 3+} and Cr{sup 5+} ordering in the scheelite-type GdCrO{sub 4} with a T{sub N}{approx}20 K. The magnetic propagation vector was found to be k=(0 0 0). Combined with group theory analysis, the best neutron powder diffraction fit was obtained with a collinear antiferromagnetic coupling in which the m{sub Cr{sup 5}{sup +}} and m{sub Gd{sup 3}{sup +}} magnetic moments are confined in the tetragonal basal plane according to the mixed representation {Gamma}{sub 6} Circled-Plus {Gamma}{sub 8}. Thermal decomposition of the GdCrO{sub 4} high pressure polymorph, from the scheelite-type through the zircon-type structure as intermediate to end in the GdCrO{sub 3} perovskite. Highlights: Black-Right-Pointing-Pointer New high pressure GdCrO{sub 4} polymorph crystallizing in the scheelite type structure. Black-Right-Pointing-Pointer It is an antiferromagnet with a metamagnetic transition at low magnetic fields. Black-Right-Pointing-Pointer We have determined its magnetic structure from powder neutron diffraction data. Black-Right-Pointing-Pointer Otherwise, the room pressure zircon-polymorph is a ferromagnet. Black-Right-Pointing-Pointer The paper will be a great contribution in the study of 3d-4f magnetic interactions.« less

Magnetic anisotropy on the single crystal UNi4B probed by 11B NMR

NASA Astrophysics Data System (ADS)

Kishimoto, Yasuki; Matsuno, Haruki; Kotegawa, Hisashi; Tou, Hideki; Saito, Hiraku; Amitsuka, Hiroshi; Homma, Yoshiya; Nakamura, Ai; Li, Dexin; Honda, Fuminori; Aoki, Dai

2018-05-01

We have performed a susceptibility M / H and 11B NMR measurements to investigate the static magnetic anisotropy of a single crystal UNi4B. The Knight shift 11K and the hyperfine coupling constant Ahf evaluated by 11K- M / H plot show anisotropic behavior between H ∥ [ 11 2 bar 0 ] and H ∥ [ 0001 ] , reflecting the bulk susceptibility. The evaluated transferred term Atr of Ahf for H ∥ [ 11 2 bar 0 ] is much larger than the one for H ∥ [ 0001 ] . The strong hybridization in the [0001]-plane due to a itinerant 5f-electron is strongly associated with the unique magnetic structure in this compound.

Method and apparatus for forming ceramic oxide superconductors with ordered structure

DOEpatents

Nellis, W.J.; Maple, M.B.

1987-12-23

Disclosed are products and processes for making improved magnetic and superconducting articles from anisotropic starting materials by initially reducing the starting materials into a powdered form composed of particles of uniform directional crystal structures, forming a directionally uniform aggregate of particles by exposing the aggregate to a magnetic field of desired magnitude and direction, and then compacting the aggregate into an integral solid body. 2 Figs.

Magnetic behaviour of synthetic Co(2)SiO(4).

PubMed

Sazonov, Andrew; Meven, Martin; Hutanu, Vladimir; Heger, Gernot; Hansen, Thomas; Gukasov, Arsen

2009-12-01

Synthetic Co(2)SiO(4) crystallizes in the olivine structure (space group Pnma) with two crystallographically non-equivalent Co positions and shows antiferromagnetic ordering below 50 K. We have investigated the temperature variation of the Co(2)SiO(4) magnetic structure by means of non-polarized and polarized neutron diffraction for single crystals. Measurements with non-polarized neutrons were made at 2.5 K (below T(N)), whereas polarized neutron diffraction experiments were carried out at 70 and 150 K (above T(N)) in an external magnetic field of 7 T parallel to the b axis. Additional accurate non-polarized powder diffraction studies were performed in a broad temperature range from 5 to 500 K with small temperature increments. Detailed symmetry analysis of the Co(2)SiO(4) magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (G(x), C(y), A(z)) for the 4a site with inversion symmetry 1 (Co1 position) and (0,C(y),0) for the 4c site with mirror symmetry m (Co2 position). The temperature dependence of the Co1 and Co2 magnetic moments obtained from neutron diffraction experiments was fitted in a modified molecular-field model. The polarized neutron study of the magnetization induced by an applied field shows a non-negligible amount of magnetic moment on the oxygen positions, indicating a delocalization of the magnetic moment from Co towards neighbouring O owing to superexchange coupling. The relative strength of the exchange interactions is discussed based on the non-polarized and polarized neutron data.

Skyrmion robustness in noncentrosymmetric magnets with axial symmetry: The role of anisotropy and tilted magnetic fields

NASA Astrophysics Data System (ADS)

Leonov, A. O.; Kézsmárki, I.

2017-12-01

We investigate the stability of Néel skyrmions against tilted magnetic fields in polar magnets with uniaxial anisotropy ranging from easy-plane to easy-axis type. We construct the corresponding phase diagrams and investigate the internal structure of skewed skyrmions with displaced cores. We find that moderate easy-plane anisotropy increases the stability range of Néel skyrmions for fields along the symmetry axis, while moderate easy-axis anisotropy enhances their robustness against tilted magnetic fields. We stress that the direction along which the skyrmion cores are shifted depends on the symmetry of the underlying crystal lattice. The cores of Néel skyrmions, realized in polar magnets with Cn v symmetry, are displaced either along or opposite to the off-axis (in-plane) component of the magnetic field depending on the rotation sense of the magnetization, dictated by the sign of the Dzyaloshinskii constant. The core shift of antiskyrmions, present in noncentrosymmetric magnets with D2 d symmetry, depends on the in-plane orientation of the magnetic field and can be parallel, antiparallel, or perpendicular to it. We argue that the role of anisotropy in magnets with axially symmetric crystal structure is different from that in cubic helimagnets. Our results can be applied to address recent experiments on polar magnets with C3 v symmetry, GaV4S8 and GaV4Se8 , and Mn1.4Pt0.9Pd0.1Sn with D2 d symmetry.

Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (Sr,Ca)FeO 2 . 5 + δ

NASA Astrophysics Data System (ADS)

Carlo, J. P.; Evans, M. E.; Anczarski, J. A.; Ock, J.; Boyd, K.; Pollichemi, J. R.; Leahy, I. A.; Vogel, W.; Viescas, A. J.; Papaefthymiou, G. C.

A variety of compounds crystallize into perovskite and similar structures, making them versatile laboratories for many phenomena and applications, including multiferroicity, superconductivity, and photovoltaics. Oxygen-deficient perovskites ABOx have attracted interest for use in fuel cells and related applications due to high oxygen mobility and the possibility of charge disproportionation. Vast chemical flexibility is obtained through reductions in lattice symmetry and rotation/distortion of the BO6 octahedra, as well as ordering of oxygen vacancies. We have synthesized and studied the structural and magnetic properties of oxygen-deficient perovskites (Sr,Ca)FeO2 . 5 + δ using x-ray diffraction and Mossbauer spectroscopy. While the ideal perovskite has δ = 0.5, this requires Fe4+, and hence strongly oxidizing environments. When grown in air, Fe3+ is favored, yielding δ ~ 0. SrFeO2 . 5 + δ exhibits cubic symmetry and paramagnetism at 300K, but CaFeO2 . 5 + δ crystallizes into the orthorhombic brownmillerite structure, and is magnetically ordered at 300K. In the doped intermediaries we find coexistence of cubic/paramagnetic and orthorhombic/magnetic phases over a wide range of Ca content. Financial support from the Villanova Undergraduate Research Fellowship program and the Research Corporation for Science Advancement.

Structural, magnetic and luminescent characteristics of Pr3+-doped ZrO2 powders synthesized by a sol-gel method

NASA Astrophysics Data System (ADS)

Isasi-Marín, J.; Pérez-Estébanez, M.; Díaz-Guerra, C.; Castillo, J. F.; Correcher, V.; Cuervo-Rodríguez, M. R.

2009-04-01

The structural, magnetic and luminescence properties of praseodymium-doped zirconia powders of compositions Pr0.03Zr0.97O2 and Pr0.05Zr0.95O2 synthesized by a sol-gel process have been investigated. X-ray diffraction patterns indicate that these materials crystallize in a tetragonal fluorite-type structure. Scanning electron microscopy shows that the powders exhibit an agglomerated microcrystalline structure and the grain size may be in the order of 5-20 µm. The study of the magnetic properties of these doped metal oxides indicates a Curie-Weiss behaviour in the temperature range (100-300) K that allow us to estimate an effective magnetic moment of 3.51 μB, which indicates the presence of Pr3+ in the grown samples. Cathodoluminescence spectra recorded at temperatures between 85 and 295 K show emission peaks that can be attributed to transitions between different states within the 4f2 configuration of Pr3+ ions incorporated in the zirconia crystal lattice. Thermoluminescence measured at temperatures ranging from 373 to 773 K and at 550 nm wavelength show an intense and broad peak around 653 K for the Pr-doped zirconia which is not observed in the undoped material.

Structure, magnetic properties, polarized neutron diffraction, and theoretical study of a copper(II) cubane.

PubMed

Aronica, Christophe; Chumakov, Yurii; Jeanneau, Erwann; Luneau, Dominique; Neugebauer, Petr; Barra, Anne-Laure; Gillon, Béatrice; Goujon, Antoine; Cousson, Alain; Tercero, Javier; Ruiz, Eliseo

2008-01-01

The paper reports the synthesis, X-ray and neutron diffraction crystal structures, magnetic properties, high field-high frequency EPR (HF-EPR), spin density and theoretical description of the tetranuclear CuII complex [Cu4L4] with cubane-like structure (LH2=1,1,1-trifluoro-7-hydroxy-4-methyl-5-aza-hept-3-en-2-one). The simulation of the magnetic behavior gives a predominant ferromagnetic interaction J1 (+30.5 cm(-1)) and a weak antiferromagnetic interaction J2 (-5.5 cm(-1)), which correspond to short and long Cu-Cu distances, respectively, as evidence from the crystal structure [see formulate in text]. It is in agreement with DFT calculations and with the saturation magnetization value of an S=2 ground spin state. HF-EPR measurements at low temperatures (5 to 30 K) provide evidence for a negative axial zero-field splitting parameter D (-0.25+/-0.01 cm(-1)) plus a small rhombic term E (0.025+/-0.001 cm(-1), E/D = 0.1). The experimental spin distribution from polarized neutron diffraction is mainly located in the basal plane of the CuII ion with a distortion of yz-type for one CuII ion. Delocalization on the ligand (L) is observed but to a smaller extent than expected from DFT calculations.

Crystal structure and phase stability in Fe{sub 1{minus}x}Co{sub x} from AB initio theory

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

Soederlind, P.; Abrikosov, I.A.; James, P.

1996-06-01

For alloys between Fe and Co, their magnetic properties determine their structure. From the occupation of d states, a phase diagram is expected which depend largely on the spin polarization. A method more elaborate than canonical band models is used to calculate the spin moment and crystal structure energies. This method was the multisublattice generalization of the coherent potential approximation in conjunction with the Linear-Muffin-Tin-Orbital method in the atomic sphere approximation. To treat itinerant magnetism, the Vosko-Wilk-Nusair parameterization was used for the local spin density approximation. The fcc, bcc, and hcp phases were studied as completely random alloys, while themore » {alpha}{prime} phase for off-stoichiometries were considered as partially ordered. Results are compared with experiment and canonical band model.« less

Influences of alkaline earth metal substitution on the crystal structure and physical properties of magnetic RuSr1.9A0.1GdCu2O8 (A = Ca, Sr, and Ba) superconductors.

PubMed

Hur, Su Gil; Park, Dae Hoon; Hwang, Seong-Ju; Kim, Seung Joo; Lee, J H; Lee, Sang Young

2005-11-24

We have investigated the effect of alkaline earth metal substitution on the crystal structure and physical properties of magnetic superconductors RuSr(1.9)A(0.1)GdCu(2)O(8) (A = Ca, Sr, and Ba) in order to probe an interaction between the magnetic coupling of the RuO(2) layer and the superconductivity of the CuO(2) layer. X-ray diffraction and X-ray absorption spectroscopic analyses demonstrate that the isovalent substitution of Sr ions with Ca or Ba ions makes it possible to tune the interlayer distance between the CuO(2) and the RuO(2) layers. From the measurements of electrical resistance and magnetic susceptibility, it was found that, in contrast to negligible change of magnetization, both of the alkaline earth metal substitutions lead to a notable depression of zero-resistance temperature T(c) (DeltaT(c) approximately 17-19 K). On the basis of the absence of a systematic correlation between the T(c) and the interlayer distance/magnetization, we have concluded that the internal magnetic field of the RuO(2) layer has insignificant influence on the superconducting property of the CuO(2) layer in the ruthenocuprate.

Flux growth of Yb(6.6)Ir(6)Sn(16) having mixed-valent ytterbium.

PubMed

Peter, Sebastian C; Subbarao, Udumula; Rayaprol, Sudhindra; Martin, Joshua B; Balasubramanian, Mahalingam; Malliakas, Christos D; Kanatzidis, Mercouri G

2014-07-07

The compound Yb6.6Ir6Sn16 was obtained as single crystals in high yield from the reaction of Yb with Ir and Sn run in excess indium. Single-crystal X-ray diffraction analysis shows that Yb6.6Ir6Sn16 crystallizes in the tetragonal space group P42/nmc with a = b = 9.7105(7) Å and c = 13.7183(11) Å. The crystal structure is composed of a [Ir6Sn16] polyanionic network with cages in which the Yb atoms are embedded. The Yb sublattice features extensive vacancies on one crystallographic site. Magnetic susceptibility measurements on single crystals indicate Curie-Weiss law behavior <100 K with no magnetic ordering down to 2 K. The magnetic moment within the linear region (<100 K) is 3.21 μB/Yb, which is ∼70% of the expected value for a free Yb(3+) ion suggesting the presence of mixed-valent ytterbium atoms. X-ray absorption near edge spectroscopy confirms that Yb6.6Ir6Sn16 exhibits mixed valence. Resistivity and heat capacity measurements for Yb6.6Ir6Sn16 indicate non-Fermi liquid metallic behavior.

Influence of Fe/Co ratio on structural and magnetic properties of (Fe100-xCox)84.5Nb5B8.5P2 alloy

NASA Astrophysics Data System (ADS)

Gehlot, K.; Kane, S. N.; Sinha, A. K.; Ghodke, N.; Varga, L. K.

2018-05-01

Structural and magnetic properties of a series of (Fe100-xCox)84.5Nb5B8.5P2 (x = 20, 40, 60) have been investigated respectively by using synchrotron x-ray diffraction and magnetic measurements. Results show that Fe/Co ratio: i) affects stability of the alloy against crystallization, ii) shows evidence for ordering, which has considerable effect on magnetic properties, iii) influences the grain diameter and volume fraction of the formed nano-grains range between 4.8 - 9.5 nm and 1.5 - 9 %, affects magnetic properties considerably. An empirical relation is obtained, which shows linear relationship between interatomic distances for 1st, 2nd co-ordination shell, suggests strong correlation between structural, magnetic properties.

Anisotropic Properties of Single-Crystalline CeNiGe2

NASA Astrophysics Data System (ADS)

Jung, M. H.; Harrison, N.; Lacerda, A. H.; Pagliuso, P. G.; Sarrao, J. L.; Thompson, J. D.

2002-07-01

The anisotropic properties of CeNiGe2 with a layered crystal structure have been studied by measurements of electrical resistivity, magnetic susceptibility and magnetization. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at TNI = 4 K and TNII = 3 K as reported earlier on polycrystalline samples. CeNiGe2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H//b)/M(H⊥b) is estimated to be about 15 at 5 T. The in-plane resistivity ρ⊥b(T) shows double maxima typical of that expected when an interplay of crystal-field and Kondo effects plays a role. The low-T maximum at 4 K in ρ⊥b(T) is strongly suppressed with increasing magnetic field. This negative magnetoresistance is a result of the strong reduction of magnetic scattering by the ferromagnetic alignment of Ce magnetic moments.

Two Keggin-type heteropolytungstates with transition metal as a central atom: Crystal structure and magnetic study with 2D-IR correlation spectroscopy

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

Chai, Feng; Chen, YiPing, E-mail: ypchen007@sina.com; State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002

2013-06-01

Two Keggin-type heteropolytungstates, [Co(phen)₃]₃[CoW₁₂O₄₀]·9H₂O 1 (phen=1,10-phenanthroline) and [Fe(phen)₃]₂[FeW₁₂O₄₀]·H₃O·H₂O 2, have been synthesized via the hydrothermal technique and characterized by single crystal X-ray diffraction analyses, IR, XPS, TG analysis, UV–DRS, XRD, thermal-dependent and magnetic-dependent 2D-COS IR (two-dimensional infrared correlation spectroscopy). Crystal structure analysis reveals that the polyanions in compound 1 are linked into 3D supramolecule through hydrogen bonding interactions between lattice water molecules and terminal oxygen atoms of polyanion units, and [Co(phen)₃]²⁺ cations distributed in the polyanion framework with many hydrogen bonding interactions. The XPS spectra indicate that all the Co atoms in 1 are +2 oxidation state, the Fe atomsmore » in 2 existing with +2 and +3 mixed oxidation states. - Graphical abstract: The magnetic-dependent synchronous 2D correlation IR spectra of 1 (a), 2 (b) over 0–50 mT in the range of 600–1000 cm⁻¹, the obvious response indicate two Keggin polyanions skeleton susceptible to applied magnetic field. Highlights: • Two Keggin-type heteropolytungstates with transition metal as a central atom has been obtained. • Compound 1 forms into 3D supramolecular architecture through hydrogen bonding between water molecules and polyanions. • Magnetic-dependent 2D-IR correlation spectroscopy was introduced to discuss the magnetism of polyoxometalate.« less

Effect of crystallographical and geometrical changes of a ferrite head on magnetic signals during the sliding process with magnetic tape

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.; Tanaka, K.

1986-01-01

This paper reviews changes in the crystalline structure and geometry of lapped Mn-Zn ferrite heads in sliding contact with magnetic tape and the effects of these changes on magnetic signals. A highly textured, polycrystalline structure was produced on the surface of a single-crystal Mn-Zn ferrite head when it was finished with an aluminum oxide lapping tape. Sliding this lapped surface against a magnetic tape produced a nearly amorphous structure. The sliding process led to a degradation in readback signal of 1 to 2 dB (short-wavelength recording). Furthermore, wear of the magnetic head caused geometrical changes in the head surface. The signal read back with the worn magnetic head was sensitive to operating parameters such as head displacement and tape tension. A change in operating parameters created head-to-tape spacings and, consequently, excessive gains or losses in the readback signal.

Debye temperatures and magnetic structures of UFe xAl 12- x (3.6⩽ x⩽5) intermetallic alloys

NASA Astrophysics Data System (ADS)

Rećko, K.; Dobrzyński, L.; Szymański, K.; Hoser, A.

2000-03-01

Uranium ternary compounds UFe xAl 12- x crystallize in a body-centred tetragonal structure ThMn 12 (I 4/mmm No.139). The neutron powder diffraction, magnetization measurements as well as Mössbauer investigations clearly indicate the magnetic ordering within the iron sites. The rearrangement of iron magnetic moments from uncompensated antiferromagnetic system in UFe xAl 12- x with x<4, through coexistence of antiferro- and ferromagnetic iron components (4⩽ x<5) to pure ferromagnetic ordering for alloy with x=5 is observed. The neutron diffraction studies of magnetic structures of the aforementioned powder samples show a very rich world of possible uranium-iron magnetic interactions. For all these alloys the magnetic neutron scattering is generally weak in comparison to the nuclear one. Because of identical chemical and magnetic unit cells there are no pure magnetic reflections. Therefore, in order to extract magnetic part of the scattering one should be particularly careful in taking proper account of the thermal vibration effects.

Eu 3Ir 2In 15: A mixed-valent and vacancy-filled variant of the Sc 5Co 4Si 10 structure type with anomalous magnetic properties

DOE PAGES

Sarkar, Sumanta; Jana, Rajkumar; Siva, Ramesh; ...

2015-10-27

Here, a new compound, Eu 3Ir 2In 15 has been synthesized using indium as an active metal flux. The compound crystallizes in tetragonal P4/mbm space group with lattice parameters, a = 14.8580(4) Å, b = 14.8580(4) Å, c = 4.3901(2) Å. It was further characterized by SEM-EDX studies. The temperature dependent magnetic susceptibility suggests that Eu in this compound is exclusively in divalent state. The effective magnetic moment (μ eff) of this compound is 7.35 μ B/Eu ion with paramagnetic Curie temperature (θ p) of -28 K suggesting antiferromagnetic interaction. The mixed valent nature of Eu observed in magnetic measurementsmore » was confirmed by XANES measurements. The compound undergoes demagnetization at a low magnetic field (10 Oe), which is quite unusual for Eu based intermetallic compounds. Temperature dependent resistivity studies reveal that the compound is metallic in nature. A comparative study was made between Eu 3Ir 2In 15 and hypothetical vacancy variant Eu 5Ir 4In 10 which also crystallizes in the same crystal structure However our computational studies along with control experiments suggest that the latter is thermodynamically less feasible compared to the former and hence we proposed that it is highly unlikely that a RE 5T 4X 10 would exist with X as a group 13 elements.« less

Magnetic and neutron diffraction study on quaternary oxides MTeMoO6 (M = Mn and Zn)

NASA Astrophysics Data System (ADS)

Doi, Yoshihiro; Suzuki, Ryo; Hinatsu, Yukio; Ohoyama, Kenji

2009-01-01

Crystal structures and magnetic properties of quaternary oxides MTeMoO6 (M = Mn and Zn) were investigated. From the Rietveld analyses for the powder x-ray and neutron diffraction measurements, their detailed structures have been determined. Both compounds have orthorhombic structure with space group P 21212 and a charge configuration of M2+Te4+Mo6+O6. ZnTeMoO6 shows diamagnetic behavior. In this structure, M ions are arranged in a square-planar manner. The temperature dependence of the magnetic susceptibility for MnTeMoO6 shows a broad peak at ~33 K, which is due to a two-dimensional characteristic of the magnetic interaction. In addition, this compound shows an antiferromagnetic transition at 20 K. The magnetic structure was determined by the powder neutron diffraction measurement at 3.3 K. The magnetic moments of Mn2+ ions (4.45 μB) order in a collinear antiferromagnetic arrangement along the b axis.

Crystal growth and magnetic characterization of a tetragonal polymorph of NiNb2O6

NASA Astrophysics Data System (ADS)

Munsie, T. J. S.; Millington, A.; Dube, P. A.; Dabkowska, H. A.; Britten, J.; Luke, G. M.; Greedan, J. E.

2016-04-01

A previously unidentified polymorph of nickel niobate, NiNb2O6, was grown and stabilized in single crystalline form using an optical floating zone furnace. Key parameters of the growth procedure involved use of a slight excess of NiO (1.2% by mol), an O2 atmosphere and a growth rate of 25 mm/h. The resulting boule consisted of a polycrystalline exterior shell of the columbite structure - columbite is the thermodynamically stable form of NiNb2O6 under ambient conditions - and a core region consisting of transparent yellow-green single crystals up to 5 mm×2 mm×1 mm in dimension of the previously unidentified phase. The crystal structure, solved from single crystal x-ray diffraction data, is described in the P42/n space group. Interestingly, this is not a subgroup of P42/mnm, the rutile space group. The Ni2+ ions form layers which are displaced such that interlayer magnetic frustration is anticipated. Magnetic susceptibility data shows a broad maximum at approximately 22 K and evidence for long range antiferromagnetic order at approximately 14 K, obtained by Fisher heat capacity analysis as well as heat capacity measurements. The susceptibility data for T > 25 K are well fit by a square lattice S = 1 model, consistent with the Ni sublattice topology.

"Building" 3D visualization skills in mineralogy

NASA Astrophysics Data System (ADS)

Gaudio, S. J.; Ajoku, C. N.; McCarthy, B. S.; Lambart, S.

2016-12-01

Studying mineralogy is fundamental for understanding the composition and physical behavior of natural materials in terrestrial and extraterrestrial environments. However, some students struggle and ultimately get discouraged with mineralogy course material because they lack well-developed spatial visualization skills that are needed to deal with three-dimensional (3D) objects, such as crystal forms or atomic-scale structures, typically represented in two-dimensional (2D) space. Fortunately, spatial visualization can improve with practice. Our presentation demonstrates a set of experiential learning activities designed to support the development and improvement of spatial visualization skills in mineralogy using commercially available magnetic building tiles, rods, and spheres. These instructional support activities guide students in the creation of 3D models that replicate macroscopic crystal forms and atomic-scale structures in a low-pressure learning environment and at low cost. Students physically manipulate square and triangularly shaped magnetic tiles to build 3D open and closed crystal forms (platonic solids, prisms, pyramids and pinacoids). Prismatic shapes with different closing forms are used to demonstrate the relationship between crystal faces and Miller Indices. Silica tetrahedra and octahedra are constructed out of magnetic rods (bonds) and spheres (oxygen atoms) to illustrate polymerization, connectivity, and the consequences for mineral formulae. In another activity, students practice the identification of symmetry elements and plane lattice types by laying magnetic rods and spheres over wallpaper patterns. The spatial visualization skills developed and improved through our experiential learning activities are critical to the study of mineralogy and many other geology sub-disciplines. We will also present pre- and post- activity assessments that are aligned with explicit learning outcomes.

Magnetic response of hybrid ferromagnetic and antiferromagnetic core-shell nanostructures

NASA Astrophysics Data System (ADS)

Khan, U.; Li, W. J.; Adeela, N.; Irfan, M.; Javed, K.; Wan, C. H.; Riaz, S.; Han, X. F.

2016-03-01

The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3&cmb.macr;. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ~25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required.The synthesis of FeTiO3-Ni(Ni80Fe20) core-shell nanostructures by a two-step method (sol-gel and DC electrodeposition) has been demonstrated. XRD analysis confirms the rhombohedral crystal structure of FeTiO3(FTO) with space group R3&cmb.macr;. Transmission electron microscopy clearly depicts better morphology of nanostructures with shell thicknesses of ~25 nm. Room temperature magnetic measurements showed significant enhancement of magnetic anisotropy for the permalloy (Ni80Fe20)-FTO over Ni-FTO core-shell nanostructures. Low temperature magnetic measurements of permalloy-FeTiO3 core-shell structure indicated a strong exchange bias mechanism with magnetic coercivity below the antiferromagnetic Neel temperature (TN = 59 K). The exchange bias is attributed to the alignment of magnetic moments in the antiferromagnetic material at low temperature. Our scheme opens a path towards optimum automotive systems and wireless communications wherein broader bandwidths and smaller sizes are required. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr07946b

Effect of Fe-substitution on the structure and magnetism of single crystals Mn2-xFexBO4

NASA Astrophysics Data System (ADS)

Platunov, M. S.; Kazak, N. V.; Knyazev, Yu. V.; Bezmaternykh, L. N.; Moshkina, E. M.; Trigub, A. L.; Veligzhanin, A. A.; Zubavichus, Y. V.; Solovyov, L. A.; Velikanov, D. A.; Ovchinnikov, S. G.

2017-10-01

Single crystalline Mn2-xFexBO4 with x = 0.3, 0.5, 0.7 grown by the flux method have been studied by means of X-ray diffraction and X-ray absorption spectroscopy at both Mn and Fe K edges. The compounds were found to crystallize in an orthorhombic warwickite structure (sp. gr. Pnam). The lattice parameters change linearly with x thus obeying the Vegard's law. The Fe3+ substitution for Mn3+ has been deduced from the X-ray absorption near-edge structure (XANES) spectra. Two energy positions of the absorption edges have been observed in Mn K-edge XANES spectra indicating the presence of manganese in two different oxidation states. Extended X-ray absorption fine structure (EXAFS) analysis has shown the reduction of local structural distortions upon Fe substitution. The magnetization data have revealed a spin-glass transition at TSG = 11, 14 and 18 K for x = 0.3, 0.5 and 0.7, respectively.

Single crystal growth, magnetic and thermal properties of perovskite YFe0.6Mn0.4O3 single crystal

NASA Astrophysics Data System (ADS)

Xie, Tao; Shen, Hui; Zhao, Xiangyang; Man, Peiwen; Wu, Anhua; Su, Liangbi; Xu, Jiayue

2016-11-01

High quality YFe0.6Mn0.4O3 single crystal was grown by floating zone technique using a four-mirror-image-furnace under flowing air. Powder X-ray diffraction gives well evidence that the specimen has an orthorhombic structure, with space group Pbnm. Temperature dependence of the magnetizations of YFe0.6Mn0.4O3 single crystal were studied under ZFC and FC modes in the temperature range from 5 K to 400 K. A clear spin reorientation transition behavior (Γ4→Γ1) is observed in the temperature range of 322-316 K, due to the substitution of Mn at the Fe site of YFeO3. Its Néel temperature is around 385 K. Moreover, the spin reorientation is verified by the change of magnetic hysteresis loops of the sample along [001] axis in the temperature range of 50-385 K. The thermal properties of the sample were measured by the differential scanning calorimeter (DSC) from 300 K to 500 K, which also clearly appear anomaly in the spin reorientation region.

High-quality single-crystal thulium iron garnet films with perpendicular magnetic anisotropy by off-axis sputtering

NASA Astrophysics Data System (ADS)

Wu, C. N.; Tseng, C. C.; Lin, K. Y.; Cheng, C. K.; Yeh, S. L.; Fanchiang, Y. T.; Hong, M.; Kwo, J.

2018-05-01

High-quality single-crystal thulium iron garnet (TmIG) films of 10-30 nm thick were grown by off-axis sputtering at room temperature (RT) followed by post-annealing. X-ray photoelectron spectroscopy (XPS) was employed to determine the TmIG film composition to optimize the growth conditions, along with the aid of x-ray diffraction (XRD) structural analysis and atomic force microscope (AFM) for surface morphology. The optimized films exhibited perpendicular magnetic anisotropy (PMA) and the saturation magnetization at RT was ˜99 emu/cm3, close to the RT bulk value ˜110 emu/cm3 with a very low coercive field of ˜2.4 Oe. We extracted the H⊥ of 1734 Oe and the peak-to-peak linewidth ΔH of ferromagnetic resonance are only about 99 Oe, significantly lower than that of PLD grown TmIG film and bulk single crystals. The high-quality sputtered single-crystal TmIG films show great potential to be integrated with topological insulators or heavy metals with strong spin-orbit coupling for spintronic applications.

Complex magnetic phase diagram with multistep spin-flop transitions in L a0.25P r0.75C o2P2

NASA Astrophysics Data System (ADS)

Tan, Xiaoyan; Garlea, V. Ovidiu; Kovnir, Kirill; Thompson, Corey M.; Xu, Tongshuai; Cao, Huibo; Chai, Ping; Tener, Zachary P.; Yan, Shishen; Xiong, Peng; Shatruk, Michael

2017-01-01

L a0.25P r0.75C o2P2 crystallizes in the tetragonal ThC r2S i2 structure type and shows multiple magnetic phase transitions driven by changes in temperature and magnetic field. The nature of these transitions was investigated by a combination of magnetic and magnetoresistance measurements and both single crystal and powder neutron diffraction. The Co magnetic moments order ferromagnetically (FM) parallel to the c axis at 282 K, followed by antiferromagnetic (AFM) ordering at 225 K. In the AFM structure, the Co magnetic moments align along the c axis with FM [C o2P2] layers arranged in an alternating sequence, ↑↑↓↓ , which leads to the doubling of the c axis in the magnetic unit cell. Another AFM transition is observed at 27 K, due to the ordering of a half of Pr moments in the a b plane. The other half of Pr moments undergoes AFM ordering along the c axis at 11 K, causing simultaneous reorientation of the previously ordered Pr moments into an AFM structure with the moments being canted with respect to the c axis. This AFM transition causes an abrupt decrease in electrical resistivity at 11 K. Under applied magnetic field, two metamagnetic transitions are observed in the Pr sublattice at 0.8 and 5.4 T. They correlate with two anomalies in magnetoresistance measurements at the same critical fields. A comparison of the temperature- and field-dependent magnetic properties of L a0.25P r0.75C o2P2 to the magnetic behavior of PrC o2P2 is provided.

A non-magnetic spacer layer effect on spin layers (7/2,3) in a bi-layer ferromagnetic dendrimer structure: Monte Carlo study

NASA Astrophysics Data System (ADS)

Jabar, A.; Tahiri, N.; Bahmad, L.; Benyoussef, A.

2016-11-01

A bi-layer system consisting of layers of spins (7/2, 3) in a ferromagnetic dendrimer structure, separated by a non-magnetic spacer, is studied by Monte Carlo simulations. The effect of the RKKY interactions is investigated and discussed for such system. It is shown that the magnetic properties in the two magnetic layers depend strongly on the thickness of the magnetic and non-magnetic layers. The total magnetizations and susceptibilities are studied as a function of the reduced temperature. The effect of the reduced exchange interactions as well as the reduced crystal field is outlined. On other hand, the critical temperature is discussed as a function of the magnetic layer values. To complete this study we presented and discussed the magnetic hysteresis cycles.

Bi-directional evolutionary optimization for photonic band gap structures

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

Meng, Fei; School of Civil Engineering, Central South University, Changsha 410075; Huang, Xiaodong, E-mail: huang.xiaodong@rmit.edu.au

2015-12-01

Toward an efficient and easy-implement optimization for photonic band gap structures, this paper extends the bi-directional evolutionary structural optimization (BESO) method for maximizing photonic band gaps. Photonic crystals are assumed to be periodically composed of two dielectric materials with the different permittivity. Based on the finite element analysis and sensitivity analysis, BESO starts from a simple initial design without any band gap and gradually re-distributes dielectric materials within the unit cell so that the resulting photonic crystal possesses a maximum band gap between two specified adjacent bands. Numerical examples demonstrated the proposed optimization algorithm can successfully obtain the band gapsmore » from the first to the tenth band for both transverse magnetic and electric polarizations. Some optimized photonic crystals exhibit novel patterns markedly different from traditional designs of photonic crystals.« less

Structural control of ultra-fine CoPt nanodot arrays via electrodeposition process

NASA Astrophysics Data System (ADS)

Wodarz, Siggi; Hasegawa, Takashi; Ishio, Shunji; Homma, Takayuki

2017-05-01

CoPt nanodot arrays were fabricated by combining electrodeposition and electron beam lithography (EBL) for the use of bit-patterned media (BPM). To achieve precise control of deposition uniformity and coercivity of the CoPt nanodot arrays, their crystal structure and magnetic properties were controlled by controlling the diffusion state of metal ions from the initial deposition stage with the application of bath agitation. Following bath agitation, the composition gradient of the CoPt alloy with thickness was mitigated to have a near-ideal alloy composition of Co:Pt =80:20, which induces epitaxial-like growth from Ru substrate, thus resulting in the improvement of the crystal orientation of the hcp (002) structure from its initial deposition stages. Furthermore, the cross-sectional transmission electron microscope (TEM) analysis of the nanodots deposited with bath agitation showed CoPt growth along its c-axis oriented in the perpendicular direction, having uniform lattice fringes on the hcp (002) plane from the Ru underlayer interface, which is a significant factor to induce perpendicular magnetic anisotropy. Magnetic characterization of the CoPt nanodot arrays showed increase in the perpendicular coercivity and squareness of the hysteresis loops from 2.0 kOe and 0.64 (without agitation) to 4.0 kOe and 0.87 with bath agitation. Based on the detailed characterization of nanodot arrays, the precise crystal structure control of the nanodot arrays with ultra-high recording density by electrochemical process was successfully demonstrated.

Effects of neutron and electron irradiation on superconducting HgBa 2CuO 4+ δ single crystals

NASA Astrophysics Data System (ADS)

Zehetmayer, M.; Eisterer, M.; Kazakov, S. M.; Karpinski, J.; Wisniewski, A.; Puzniak, R.; Daignere, A.; Weber, H. W.

2004-08-01

We report on measurements of the magnetic moment in superconducting HgBa 2CuO 4+ δ single crystals by SQUID magnetometry. Neutron and electron irradiation are employed to modify the defect structure. Both types of radiation affect the irreversible properties, but characteristic qualitative differences occur, which will be discussed.

Change of magnetic domain structure by mechanically induced twin boundary motion in Ni-Mn-Ga single crystal

NASA Astrophysics Data System (ADS)

Kopecký, Vít; Heczko, Oleg

2017-10-01

The single variant state exhibits usual labyrinth and band magnetic domains depending on orientation of easy magnetization axis. By the passage of single twin boundary induced by mechanical stress the rake and granular domain patterns are formed. These domain patterns are further modified by repeated passage of the twin boundary resulting in similar domain patterns in the sample even though the orientation of the magnetization is different.

FAST TRACK COMMUNICATION: Pyroxenes: a new class of multiferroics

NASA Astrophysics Data System (ADS)

Jodlauk, S.; Becker, P.; Mydosh, J. A.; Khomskii, D. I.; Lorenz, T.; Streltsov, S. V.; Hezel, D. C.; Bohatý, L.

2007-10-01

Pyroxenes with the general formula AMSi2O6 (A = mono- or divalent metal, M = di- or trivalent metal) are shown to be a new class of multiferroic materials. In particular, we have found so far that NaFeSi2O6 becomes ferroelectric in a magnetically ordered state below ~6 K. Similarly, magnetically driven ferroelectricity is also detected in the Li homologues, LiFeSi2O6 (TC~18 K) and LiCrSi2O6 (TC~11 K). In all these monoclinic systems the electric polarization can be strongly modified by magnetic fields. Measurements of magnetic susceptibility, pyroelectric current and dielectric constants (and their dependence on magnetic field) are performed using a natural crystal of aegirine (NaFeSi2O6) and synthetic crystals of LiFeSi2O6 and LiCrSi2O6 grown from melt solution. For NaFeSi2O6 a temperature versus magnetic field phase diagram is proposed. Exchange constants are computed on the basis of ab initio band structure calculations. The possibility of a spiral magnetic structure caused by frustration to be the reason for the origin of the multiferroic behaviour is discussed. We propose that other pyroxenes may also be multiferroic, and that the versatility of this family offers an exceptional opportunity to study general conditions for and mechanisms of magnetically driven ferroelectricity.

Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO 4

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

Cevallos, F. Alex; Stolze, Karoline; Kong, Tai

Here, the crystal growth, structure, and basic magnetic properties of TmMgGaO 4 are reported. The Tm ions are located in a planar triangular lattice consisting of distorted TmO6 octahedra, while the Mg and Ga atoms randomly occupy intermediary bilayers of M-O triangular bipyramids. The Tm ions are positionally disordered. The material displays an antiferromagnetic Curie Weiss theta of ~ -20 -25 K, with no clear ordering visible in the magnetic susceptibility down to 1.8 K; the structure and magnetic properties suggest that ordering of the magnetic moments is frustrated by both structural disorder and the triangular magnetic motif. Single crystalmore » magnetization measurements indicate that the magnetic properties are highly anisotropic, with large moments measured perpendicular to the triangular planes. At 2 K, a broad step-like feature is seen in the field-dependent magnetization perpendicular to the plane on applied field near 2 Tesla.« less

Surprises in low dimensional spin 1/2 magnets - from crystal chemistry to microscopic magnetic models of complex oxides

NASA Astrophysics Data System (ADS)

Rosner, Helge

2011-03-01

A microscopic understanding of the structure-properties relation in crystalline materials is a main goal of modern solid state chemistry and physics. Due to their peculiar magnetism, low dimensional spin 1/2 systems are often highly sensitive to structural details. Seemingly unimportant structural details can be crucial for the magnetic ground state of a compound, especially in the case of competing interactions, frustration and near-degeneracy. Here, we present for selected, complex Cu 2+ systems that a first principles based approach can reliably provide the correct magnetic model, especially in cases where the interpretation of experimental data meets serious difficulties or fails. We demonstrate that the magnetism of low dimensional insulators crucially depends on the magnetically active orbitals which are determined by details of the ligand field of the magnetic cation. Our theoretical results are in very good agreement with thermodynamic and spectroscopic data and provide deep microscopic insight into topical low dimensional magnets.

Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO 4

DOE PAGES

Cevallos, F. Alex; Stolze, Karoline; Kong, Tai; ...

2018-04-30

Here, the crystal growth, structure, and basic magnetic properties of TmMgGaO 4 are reported. The Tm ions are located in a planar triangular lattice consisting of distorted TmO6 octahedra, while the Mg and Ga atoms randomly occupy intermediary bilayers of M-O triangular bipyramids. The Tm ions are positionally disordered. The material displays an antiferromagnetic Curie Weiss theta of ~ -20 -25 K, with no clear ordering visible in the magnetic susceptibility down to 1.8 K; the structure and magnetic properties suggest that ordering of the magnetic moments is frustrated by both structural disorder and the triangular magnetic motif. Single crystalmore » magnetization measurements indicate that the magnetic properties are highly anisotropic, with large moments measured perpendicular to the triangular planes. At 2 K, a broad step-like feature is seen in the field-dependent magnetization perpendicular to the plane on applied field near 2 Tesla.« less

Magnetic structure and local lattice distortion in giant negative thermal expansion material Mn3Cu1-xGexN

NASA Astrophysics Data System (ADS)

Iikubo, S.; Kodama, K.; Takenaka, K.; Takagi, H.; Shamoto, S.

2010-11-01

Magnetic and local structures in an antiperovskite system, Mn3Cu1-xGexN, with a giant negative thermal expansion have been studied by neutron powder diffraction measurement. We discuss (1) an importance of an averaged cubic crystal structure and a ΓG5g antiferromagnetic spin structure for the large magneto-volume effect (MVE) in this itinerant electron system, (2) an unique role of a local lattice distortion well described by the low temperature tetragonal structure of Mn3GeN for the broadening of MVE.

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.

At last! The single-crystal X-ray structure of a naturally occurring sample of the ilmenite-type oxide FeCrO3.

PubMed

Pérez-Cruz, María Ana; Elizalde-González, María de la Paz; Escudero, Roberto; Bernès, Sylvain; Silva-González, Rutilo; Reyes-Ortega, Yasmi

2015-10-01

A natural single crystal of the ferrimagnetic oxide FeCrO3, which was found in an opencast mine situated in the San Luis Potosí State in Mexico, has been characterized in order to elucidate some outstanding issues about the actual structure of this material. The single-crystal X-ray analysis unambiguously shows that transition metal cations are segregated in alternating layers normal to the threefold crystallographic axis, affording a structure isomorphous to that of ilmenite (FeTiO3), in the space group R3̅. The possible occurrence of cation antisite and vacancy defects is below the limit of detection available from X-ray data. Structural and magnetic results are in agreement with the coherent slow intergrowth of magnetic phases provided by the two antiferromagnetic corundum-type parent oxides Fe2O3 (hematite) and Cr2O3 (eskolaite). Our results are consistent with the most recent density functional theory (DFT) studies carried out on digital FeCrO3 [Sadat Nabi & Pentcheva (2011). Phys. Rev. B, 83, 214424], and suggest that synthetic samples of FeCrO3 might present a cation distribution different to that of the ilmenite structural type.

Hydrothermal synthesis, crystal structure, and magnetic properties of a new inorganic vanadium(III) phosphate with a chain structure.

PubMed

Ferdov, Stanislav; Reis, Mario S; Lin, Zhi; Ferreira, Rute A Sá

2008-11-03

A new vanadium(III) phosphate, Na3V(OH)(HPO4)(PO4), has been synthesized by using mild hydrothermal conditions under autogeneous pressure. This material represents a very rare example of sodium vanadium(III) phosphate with a chain structure. The crystal structure has been determined by refinement of powder X-ray diffraction data, starting from the atomic coordinates of an isotypic compound, Na3Al(OH)(HPO4)(PO4), which was obtained under high temperature and high pressure. The phase crystallizes in monoclinic space group C2/m (No. 12) with lattice parameters a = 15.423(9) A, b = 7.280(0) A, c = 7.070(9) A, beta = 96.79(7) degrees, V = 788.3(9) A(3), and Z = 4. The structure consists of one-dimensional chains composed of corner-sharing VO5(OH) octahedra running along the b direction. They are decorated by isolated PO4 and HPO4 tetrahedra sharing two of their corners with the ones of the vanadium octahedra. The interconnection between the chains is assured by three crystallographically distinct Na(+) cations. Magnetic investigation confirms the 3+ oxidation state of the vanadium ions and reveals an antiferromagnetic arrangement between those ions through the chain.

Finite element method analysis of band gap and transmission of two-dimensional metallic photonic crystals at terahertz frequencies.

PubMed

Degirmenci, Elif; Landais, Pascal

2013-10-20

Photonic band gap and transmission characteristics of 2D metallic photonic crystals at THz frequencies have been investigated using finite element method (FEM). Photonic crystals composed of metallic rods in air, in square and triangular lattice arrangements, are considered for transverse electric and transverse magnetic polarizations. The modes and band gap characteristics of metallic photonic crystal structure are investigated by solving the eigenvalue problem over a unit cell of the lattice using periodic boundary conditions. A photonic band gap diagram of dielectric photonic crystal in square lattice array is also considered and compared with well-known plane wave expansion results verifying our FEM approach. The photonic band gap designs for both dielectric and metallic photonic crystals are consistent with previous studies obtained by different methods. Perfect match is obtained between photonic band gap diagrams and transmission spectra of corresponding lattice structure.

New mixed valence defect dicubane cobalt(II)/cobalt(III) complex: Synthesis, crystal structure, photoluminescence and magnetic properties

NASA Astrophysics Data System (ADS)

Coban, Mustafa Burak; Gungor, Elif; Kara, Hulya; Baisch, Ulrich; Acar, Yasemin

2018-02-01

A new defect dicubane cobalt(II)/cobalt(III), [(CoII2CoIII2L42(H2O)(CH3COO)(CH3COOH]. 4H2O complex (1) where H2L = [1-(3-hydroxypropyliminomethyl)naphthalene-2-ol], has been synthesized and characterized by element analysis, FT-IR, solid UV-Vis spectroscopy and single crystal X-ray diffraction. The crystal structure determination shows a cationic tetrameric arrangement consisting of a defect dicubane core with two missing vertexes. Each cobalt ion has a distorted octahedral geometry with six coordinate ordered CoII and CoIII ions. The solid state photoluminescence properties of complex (1) and its ligand H2L have been investigated under UV light at 349 nm in the visible region. H2L exhibits blue emission while complex (1) shows red emission at room temperature. Variable-temperature magnetic susceptibility measurements on the complex (1) in the range 2-300 K indicate an antiferromagnetic interaction.

SEMICONDUCTOR MATERIALS: Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

NASA Astrophysics Data System (ADS)

Xiaofeng, Chen; Nuofu, Chen; Jinliang, Wu; Xiulan, Zhang; Chunlin, Chai; Yude, Yu

2009-08-01

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

Magnetocaloric behavior in ternary europium indides EuT 5In: Probing the design capability of first-principles-based methods on the multifaceted magnetic materials

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

Bigun, Inna; Steinberg, Simon; Smetana, Volodymyr

The most favorable structures and the types of magnetic ordering predicted from first-principles-based methods in a family of closely related transition-metal-rich indides EuT 5In (T = Cu, Ag, Au) are gauged against relevant experiments. The EuT5In compounds adopt a different structure for each different coinage metal—EuCu 5In ( hR42; Rmore » $$\\overline{3}$$m, a = 5.0933(7), c = 30.557(6) Å), EuAg 5In ( oP28; Pnma, a = 9.121(2), b = 5.645(1), c = 11.437(3) Å), and EuAu 5In ( tI14; I4/ mmm, a = 7.1740(3), c = 5.4425(3) Å)—and crystallize with the Sr 5Al 9, CeCu 6, and YbMo 2Al 4 structure types, respectively. EuCu 5In and EuAg 5In order antiferromagnetically at T N = 12 and 6 K, respectively, whereas EuAu 5In is ferromagnetic below T C = 13 K. EuCu 5In exhibits complex magnetism: after the initial drop at T N, the magnetization rises again below 8 K, and a weak metamagnetic-like transition occurs at 2 K in μ 0H = 1.8 T. The electronic heat capacity of EuCu 5In, γ = ~400 mJ/(mol K 2), points to strong electronic correlations. Spin-polarized densities of states suggest that the magnetic interactions in the three materials studied are supported via mixing 4 f and 5 d states of Eu. As a result, a chemical bonding analysis based on the Crystal Orbital Hamilton populations reveals the tendency to maximize overall bonding as a driving force to adopt a particular type of crystal structure.« less

Magnetocaloric behavior in ternary europium indides EuT 5In: Probing the design capability of first-principles-based methods on the multifaceted magnetic materials

DOE PAGES

Bigun, Inna; Steinberg, Simon; Smetana, Volodymyr; ...

2017-01-27

The most favorable structures and the types of magnetic ordering predicted from first-principles-based methods in a family of closely related transition-metal-rich indides EuT 5In (T = Cu, Ag, Au) are gauged against relevant experiments. The EuT5In compounds adopt a different structure for each different coinage metal—EuCu 5In ( hR42; Rmore » $$\\overline{3}$$m, a = 5.0933(7), c = 30.557(6) Å), EuAg 5In ( oP28; Pnma, a = 9.121(2), b = 5.645(1), c = 11.437(3) Å), and EuAu 5In ( tI14; I4/ mmm, a = 7.1740(3), c = 5.4425(3) Å)—and crystallize with the Sr 5Al 9, CeCu 6, and YbMo 2Al 4 structure types, respectively. EuCu 5In and EuAg 5In order antiferromagnetically at T N = 12 and 6 K, respectively, whereas EuAu 5In is ferromagnetic below T C = 13 K. EuCu 5In exhibits complex magnetism: after the initial drop at T N, the magnetization rises again below 8 K, and a weak metamagnetic-like transition occurs at 2 K in μ 0H = 1.8 T. The electronic heat capacity of EuCu 5In, γ = ~400 mJ/(mol K 2), points to strong electronic correlations. Spin-polarized densities of states suggest that the magnetic interactions in the three materials studied are supported via mixing 4 f and 5 d states of Eu. As a result, a chemical bonding analysis based on the Crystal Orbital Hamilton populations reveals the tendency to maximize overall bonding as a driving force to adopt a particular type of crystal structure.« less

Synthesis aspects, structural, spectroscopic, antimicrobial and room temperature ferromagnetism of zinc iodide complex with Schiff based ligand

NASA Astrophysics Data System (ADS)

Shakila, K.; Kalainathan, S.

2015-01-01

In this paper, we report the successful growth of complex compound of zinc iodide with thiocarbamide by slow evaporation method. The single crystal XRD study reveals that the crystal belongs to monoclinic system with centrosymmetric space group and powder XRD analysis shows that the perfect crystalline nature of the crystal. The presence of functional group and element were confirmed from FT-IR and EDAX analysis. Optical absorbance of the grown crystal was studied by UV-Vis spectrophotometer. The optical constants were calculated from the optical absorbance data such as refractive index (n), extinction coefficient (K) and reflectance (R). The optical band gap (Eg) of thiocarbamide zinc iodide crystal is 4.22 eV. The magnetic properties of grown crystal have been determined by Vibrating Sample Magnetometry (VSM). Room temperature magnetization revealed a ferromagnetic behaviour for the grown crystal. The antibacterial and antifungal activities of the title compound were performed by well diffusion method and MIC method against the standard bacteria like Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia and against fungus like Aspergillus niger, Rhizopus sps and Penicillium sps. Thermal behaviour of the crystal has been investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA).

Nanoscale-driven crystal growth of hexaferrite heterostructures for magnetoelectric tuning of microwave semiconductor integrated devices.

PubMed

Hu, Bolin; Chen, Zhaohui; Su, Zhijuan; Wang, Xian; Daigle, Andrew; Andalib, Parisa; Wolf, Jason; McHenry, Michael E; Chen, Yajie; Harris, Vincent G

2014-11-25

A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25-40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals was found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ∼150 K for Co2Y ferrite, compared to 5-10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on a wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.

Crystal field effects in the intermetallic R Ni3Ga9 (R =Tb , Dy, Ho, and Er) compounds

NASA Astrophysics Data System (ADS)

Silva, L. S.; Mercena, S. G.; Garcia, D. J.; Bittar, E. M.; Jesus, C. B. R.; Pagliuso, P. G.; Lora-Serrano, R.; Meneses, C. T.; Duque, J. G. S.

2017-04-01

In this paper, we report temperature-dependent magnetic susceptibility, electrical resistivity, and heat-capacity experiments in the family of intermetallic compounds R Ni3Ga9 (R = Tb, Dy, Ho, and Er). Single-crystalline samples were grown using Ga self-flux method. These materials crystallize in a trigonal ErNi3Al9 -type structure with space group R 32 . They all order antiferromagnetically with TN<20 K . The anisotropic magnetic susceptibility presents large values of the ratio χeasy/χhard indicating strong crystalline electric-field (CEF) effects. The evolution of the crystal-field scheme for each R was analyzed in detail by using a spin model including anisotropic nearest-neighbor Ruderman-Kittel-Kasuya-Yosida interaction and the trigonal CEF Hamiltonian. Our analysis allows one to understand the distinct direction of the ordered moments along the series—the Tb-, Dy-, and Ho-based compounds have the ordered magnetic moments in the easy ab plane and the Er sample magnetization easy axis is along the c ̂ direction.

Magnetic properties of single crystal alpha-benzoin oxime: An EPR study

NASA Astrophysics Data System (ADS)

Sayin, Ulku; Dereli, Ömer; Türkkan, Ercan; Ozmen, Ayhan

2012-02-01

The electron paramagnetic resonance (EPR) spectra of gamma irradiated single crystals of alpha-benzoinoxime (ABO) have been examined between 120 and 440 K. Considering the dependence on temperature and the orientation of the spectra of single crystals in the magnetic field, we identified two different radicals formed in irradiated ABO single crystals. To theoretically determine the types of radicals, the most stable structure of ABO was obtained by molecular mechanic and B3LYP/6-31G(d,p) calculations. Four possible radicals were modeled and EPR parameters were calculated for the modeled radicals using the B3LYP method and the TZVP basis set. Calculated values of two modeled radicals were in strong agreement with experimental EPR parameters determined from the spectra. Additional simulated spectra of the modeled radicals, where calculated hyperfine coupling constants were used as starting points for simulations, were well matched with experimental spectra.

Synthesis, crystal structure and magnetic properties of superconducting single crystals of HgBa2CuO4+δ

NASA Astrophysics Data System (ADS)

Bertinotti, A.; Viallet, V.; Colson, D.; Marucco, J.-F.; Hammann, J.; Forget, A.; Le Bras, G.

1996-02-01

Single crystals of HgBa2CuO4+δ of submillimetric sizes were grown with the same one step, low pressure, gold amalgamation technique used to obtain single crystals of HgBa2Ca2Cu3O8+δ. Remarkable superconducting properties are displayed by the samples which are optimally doped as grown. The sharpness of the transition profiles of the magnetic susceptibility, its anisotropy dependence and the volume fraction exhibiting the Meissner effect exceed the values obtained with the best crystal samples of Hg-1223. X-rays show that no substitutional defects have been found in the mercury plane, in particular no mixed occupancy of copper at the mercury site. The interstitial oxygen content at (1/2, 1/2, 0) δ = 0.066+/-0.008 is about one third that observed in optimally doped Hg-1223, resulting in an identical doping level per CuO2 plane in both compounds.

Recrystallization inhibition in ice due to ice binding protein activity detected by nuclear magnetic resonance.

PubMed

Brown, Jennifer R; Seymour, Joseph D; Brox, Timothy I; Skidmore, Mark L; Wang, Chen; Christner, Brent C; Luo, Bing-Hao; Codd, Sarah L

2014-09-01

Liquid water present in polycrystalline ice at the interstices between ice crystals results in a network of liquid-filled veins and nodes within a solid ice matrix, making ice a low porosity porous media. Here we used nuclear magnetic resonance (NMR) relaxation and time dependent self-diffusion measurements developed for porous media applications to monitor three dimensional changes to the vein network in ices with and without a bacterial ice binding protein (IBP). Shorter effective diffusion distances were detected as a function of increased irreversible ice binding activity, indicating inhibition of ice recrystallization and persistent small crystal structure. The modification of ice structure by the IBP demonstrates a potential mechanism for the microorganism to enhance survivability in ice. These results highlight the potential of NMR techniques in evaluation of the impact of IBPs on vein network structure and recrystallization processes; information useful for continued development of ice-interacting proteins for biotechnology applications.

Tungsten-encapsulated gadolinium nanoislands with enhanced magnetocaloric response

DOE PAGES

Logan, Jonathan M.; Rosenmann, Daniel; Sangpo, Tenzin; ...

2017-07-03

Here, we report a method for growing chemically pure, oxide-free, air-stable Gd nanoislands with enhanced magnetic properties. These nanoislands are grown by solid-state dewetting and are fully encapsulated in tungsten such that they remain stable in ambient environments. They display good crystalline properties with hexagonally close-packed crystal structure and strong preferential orientation. We show that the choice of substrate strongly affects their shape, crystal orientation, and magnetic properties. The temperature-dependent magnetic coercivity and remanence of the Gd islands can vary by as much as a factor of three depending on the substrate used. The magneto- caloric properties of Gd islandsmore » grown on a sapphire substrate exceed those of high-quality Gd thin films.« less

Giant photonic Hall effect in magnetophotonic crystals.

PubMed

Merzlikin, A M; Vinogradov, A P; Inoue, M; Granovsky, A B

2005-10-01

We have considered a simple, square, two-dimensional (2D) PC built of a magneto-optic matrix with square holes. It is shown that using such a magnetophotonic crystal it is possible to deflect a light beam at very large angles by applying a nonzero external magnetic field. The effect is called the giant photonic Hall effect (GPHE) or the magnetic superprism effect. The GPHE is based on magneto-optical properties, as is the photonic Hall effect [B. A. van Tiggelen and G. L. J. A. Rikken, in, edited by V. M. Shalaev (Springer-Verlag, Berlin, 2002), p. 275]; however GPHE is not caused by asymmetrical light scattering but rather by the influence of an external magnetic field on the photonic band structure.

Element-resolved magnetism across the temperature- and pressure-induced spin reorientation in MnBi

DOE PAGES

Choi, Yongseong; Jiang, Xiujuan; Bi, Wenli; ...

2016-11-01

Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong magnetic anisotropy above its 90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) shows induced magnetism in Bi 5d band, which is strongly coupled to the magnetism of Mn. A clear increase in Bi orbital-to-spin moment ratio is observed above the SRT. Hydrostatic pressure mimics the e*ect of temperature on the SRT, and the pressure effect also leads to anisotropic lattice contraction, which is known to be induced by cooling. These results reveal that temperature and pressure can similarly induce the coupled structural and magnetic responses, suggesting themore » importance of the anisotropic lattice change and Mn-Bi hybridization to the magnetic anisotropy change across the SRT.« less

High second-harmonic generation of antiferromagnetic/ionic-crystal composite medium with negative refraction

NASA Astrophysics Data System (ADS)

Song, Yu-Ling; Ta, Jin-Xing; Wang, Xuan-Zhang

2012-03-01

Second harmonic generation (SHG) from a short-period structure composed of alternating antiferromagnetic (AF) and ionic-crystal layers is investigated, where the generated harmonic waves are situated in the far-infrared range and attributed to the magnetically nonlinear interaction in AF layers. The presence of a kind of appropriate ionic-crystal layers in the structure can support negative refraction for the pumping wave and positive refraction for the SH wave, so the SHG is greatly amplified in the vicinity of each AF resonant frequency. For the composite structure FeF2/TlBr, we found that the SH output is about 8 times higher than that of the FeF2 bulk in the same frequency range.

Crystal structure and physical properties of a novel Kondo antiferromagnet: U3Ru4Al12

NASA Astrophysics Data System (ADS)

Pasturel, M; Tougait, O; Potel, M; Roisnel, T; Wochowski, K; Noël, H; Troć, R

2009-03-01

A novel ternary compound U3Ru4Al12 has been identified in the U-Ru-Al ternary diagram. Single-crystal x-ray diffraction indicates a hexagonal Gd3Ru4Al12-type structure for this uranium-based intermetallic. While this structure type usually induces geometrically a spin-glass behaviour, an antiferromagnetic ordering is observed at TN = 8.4 K in the present case. The reduced effective magnetic moment of U atoms (μeff = 2.6 µB) can be explained by Kondo-like interactions and crystal field effects that have been identified by a logarithmic temperature dependence of the electrical resistivity, negative values of the magnetoresistivity and particular shape of the Seebeck coefficient.

Effect of Eu magnetism on the electronic properties of the candidate Dirac material EuMnBi2

NASA Astrophysics Data System (ADS)

May, Andrew F.; McGuire, Michael A.; Sales, Brian C.

2014-08-01

The crystal structure and physical properties of the layered material EuMnBi2 have been characterized by measurements on single crystals. EuMnBi2 is isostructural with the Dirac material SrMnBi2 based on single-crystal x-ray diffraction, crystallizing in the I4/mmm space group (No. 139). Magnetic susceptibility measurements suggest antiferromagnetic (AFM) ordering of moments on divalent Eu ions near TN=22 K. For low fields, the ordered Eu moments are aligned along the c axis, and a spin flop is observed near 5.4 T at 5 K. The moment is not saturated in an applied field of 13 T at 5 K, which is uncommon for compounds containing Eu2+. The magnetic behavior suggests an anisotropy enhancement via interaction between Eu and the Mn moments that appear to be ordered antiferromagnetically below ≈310 K. A large increase in the magnetoresistance is observed across the spin flop, with absolute magnetoresistance reaching ≈650% at 5 K and 12 T. Hall effect measurements reveal a decrease in the carrier density below TN, which implies a manipulation of the Fermi surface by magnetism on the sites surrounding the Bi square nets that lead to Dirac cones in this family of materials.

EuCo 2P 2: A Model Molecular-Field Helical Heisenberg Antiferromagnet

DOE PAGES

Sangeetha, N. S.; Cuervo-Reyes, Eduardo; Pandey, Abhishek; ...

2016-07-19

The metallic compound EuCo 2P 2 with the body-centered tetragonal ThCr 2Si 2 structure containing Eu spins-7/2 was previously shown from single-crystal neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM) structure below T N=66.5 K with the helix axis along the c axis and with the ordered moments aligned within the ab plane. Here we report crystallography, electrical resistivity, heat capacity, magnetization, and magnetic susceptibility measurements on single crystals of this compound. We demonstrate that EuCo 2P 2 is a model molecular-field helical Heisenberg antiferromagnet from comparisons of the anisotropic magnetic susceptibility χ, high-field magnetization, and magnetic heat capacitymore » of EuCo 2P 2 single crystals at temperature T≤TN with the predictions of our recent formulation of molecular-field theory. Values of the Heisenberg exchange interactions between the Eu spins are derived from the data. The low-T magnetic heat capacity ~T 3 arising from spin-wave excitations with no anisotropy gap is calculated and found to be comparable to the lattice heat capacity. The density of states at the Fermi energy of EuCo 2P 2 and the related compound BaCo 2P 2 are found from the heat capacity data to be large, 10 and 16 states/eV per formula unit for EuCo 2P 2 and BaCo 2P 2, respectively. These values are enhanced by a factor of ~2.5 above those found from DFT electronic structure calculations for the two compounds. Additionally, the calculations also find ferromagnetic Eu–Eu exchange interactions within the ab plane and AFM interactions between Eu spins in nearest- and next-nearest planes, in agreement with the MFT analysis of χ ab(T≤TN).« less

EuCo 2P 2: A Model Molecular-Field Helical Heisenberg Antiferromagnet

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

Sangeetha, N. S.; Cuervo-Reyes, Eduardo; Pandey, Abhishek

The metallic compound EuCo 2P 2 with the body-centered tetragonal ThCr 2Si 2 structure containing Eu spins-7/2 was previously shown from single-crystal neutron diffraction measurements to exhibit a helical antiferromagnetic (AFM) structure below T N=66.5 K with the helix axis along the c axis and with the ordered moments aligned within the ab plane. Here we report crystallography, electrical resistivity, heat capacity, magnetization, and magnetic susceptibility measurements on single crystals of this compound. We demonstrate that EuCo 2P 2 is a model molecular-field helical Heisenberg antiferromagnet from comparisons of the anisotropic magnetic susceptibility χ, high-field magnetization, and magnetic heat capacitymore » of EuCo 2P 2 single crystals at temperature T≤TN with the predictions of our recent formulation of molecular-field theory. Values of the Heisenberg exchange interactions between the Eu spins are derived from the data. The low-T magnetic heat capacity ~T 3 arising from spin-wave excitations with no anisotropy gap is calculated and found to be comparable to the lattice heat capacity. The density of states at the Fermi energy of EuCo 2P 2 and the related compound BaCo 2P 2 are found from the heat capacity data to be large, 10 and 16 states/eV per formula unit for EuCo 2P 2 and BaCo 2P 2, respectively. These values are enhanced by a factor of ~2.5 above those found from DFT electronic structure calculations for the two compounds. Additionally, the calculations also find ferromagnetic Eu–Eu exchange interactions within the ab plane and AFM interactions between Eu spins in nearest- and next-nearest planes, in agreement with the MFT analysis of χ ab(T≤TN).« less

Boric acid flux synthesis, structure and magnetic property of MB₁₂O₁₄(OH)₁₀ (M=Mn, Fe, Zn)

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

Yang, Dingfeng; Cong, Rihong; Gao, Wenliang, E-mail: gaowl@cqu.edu.cn

2013-05-01

Three new borates MB₁₂O₁₄(OH)₁₀ (M=Mn, Fe, Zn) have been synthesized by boric acid flux methods, which are isotypic to NiB₁₂O₁₄(OH)₁₀. Single-crystal XRD was performed to determine the crystal structures in detail. They all crystallize in the monoclinic space group P2₁/c. The size of MO{sub 6} (M=Mg, Mn, Fe, Co, Ni, Zn) octahedron shows a good agreement with the Shannon effective ionic radii of M²⁺. Magnetic measurements indicate MnB₁₂O₁₄(OH)₁₀ is antiferromagnetic without a long-range ordering down to 2 K. The values of its magnetic superexchange constants were evaluated by DFT calculations, which explain the observed magnetic behavior. The UV–vis diffuse reflectancemore » spectrum of ZnB₁₂O₁₄(OH)₁₀ suggests a band gap ~4.6 eV. DFT calculations indicate it has a direct band gap 4.9 eV. The optical band gap is contributed by charge transfers from the occupied O 2p to the unoccupied Zn 4s states. - Graphical abstract: Experimental and theoretical studies indicate MnB₁₂O₁₄(OH)₁₀ is antiferromagnetic without a long-range ordering. DFT calculations show ZnB₁₂O₁₄(OH)₁₀ has a direct band gap of 4.9 eV. Highlights: • MB₁₂O₁₄(OH)₁₀ (M=Mn, Fe, Zn) are synthesized by two-step boric acid flux method. • Single-crystal XRD was performed to determine the crystal structures in detail. • Size of MO₆ (M=Mg, Mn, Fe, Co, Ni, Zn) agrees with the effective ionic radii. • MnB₁₂O₁₄(OH)₁₀ is antiferromagnetic without a long-range ordering down to 2 K. • DFT calculations indicate ZnB₁₂O₁₄(OH)₁₀ has a direct band gap 4.9 eV.« less

Crystal growth of hexaferrite architecture for magnetoelectrically tunable microwave semiconductor integrated devices

NASA Astrophysics Data System (ADS)

Hu, Bolin

Hexaferrites (i.e., hexagonal ferrites), discovered in 1950s, exist as any one of six crystallographic structural variants (i.e., M-, X-, Y-, W-, U-, and Z-type). Over the past six decades, the hexaferrites have received much attention owing to their important properties that lend use as permanent magnets, magnetic data storage materials, as well as components in electrical devices, particularly those operating at RF frequencies. Moreover, there has been increasing interest in hexaferrites for new fundamental and emerging applications. Among those, electronic components for mobile and wireless communications especially incorporated with semiconductor integrated circuits at microwave frequencies, electromagnetic wave absorbers for electromagnetic compatibility, random-access memory (RAM) and low observable technology, and as composite materials having low dimensions. However, of particular interest is the magnetoelectric (ME) effect discovered recently in the hexaferrites such as SrScxFe12-xO19 (SrScM), Ba2--xSrxZn 2Fe12O22 (Zn2Y), Sr4Co2Fe 36O60 (Co2U) and Sr3Co2Fe 24O41 (Co2Z), demonstrating ferroelectricity induced by the complex internal alignment of magnetic moments. Further, both Co 2Z and Co2U have revealed observable magnetoelectric effects at room temperature, representing a step toward practical applications using the ME effect. These materials hold great potential for applications, since strong magnetoelectric coupling allows switching of the FE polarization with a magnetic field (H) and vice versa. These features could lead to a new type of storage devices, such as an electric field-controlled magnetic memory. A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25--40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals were a found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ~150 K for Co 2Y ferrite, compared to 5--10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.

Magnetocaloric effect in cubic spinel Co(Cr0.95Fe0.05)2O4

NASA Astrophysics Data System (ADS)

Kumar, Ram; Rayaprol, S.; Xiao, Y.; Ji, W.; Siruguri, V.; Pal, D.

2018-04-01

The crystal structure, magnetic properties and magnetocaloric effect (MCE) of Co(Cr0.95Fe0.05)2O4 have been studied. Co(Cr0.95Fe0.05)2O4 synthesized by solid-state reaction method, crystallizes in normal cubic spinel structure with Fd-3m space group. Neutron powder diffraction (NPD) and magnetic measurements when compared to the undoped CoCr2O4, show that the compound is ferrimagnetic (FIM) and transition temperature (TC) is enhanced due to Fe substitution. Analysis of structural and magnetic properties shows the existence of two different sites of magnetic clusters due to Fe/Cr cation disorder. The competition between the moments of the two different sub-lattices gives rise to the temperature induced magnetization reversal at compensation tempearature (Tcomp) = 44 K. The magnetocaloric effect (simply the change in magnetic entropy i.e, -ΔSM) has been observed in Co(Cr0.95Fe0.05)2O4 with different applied magnetic fields (max. H = 90 kOe). We found maximum change of magnetic entropy ˜1.2 J/kg K, for a field change of 90 kOe at FIM transition temperature (TC˜110 K) with relative cooling power (RCP) of ˜13 J/kg. Moreover, the sign change of -ΔSM across the compensation temperature (Tcomp˜ 44 K) shows another phase transition across Tcomp in Co(Cr0.95Fe0.05)2O4. The values of MCE and RCP are also appreciable so as to consider Co(Cr0.95Fe0.05)2O4 as a magnetic refrigerant above liquid nitrogen temperature.

The properties of the extraordinary mode and surface plasmon modes in the three-dimensional magnetized plasma photonic crystals based on the magneto-optical Voigt effects

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

Zhang, Hai-Feng, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn; Nanjing Artillery Academy, Nanjing 211132; Liu, Shao-Bin, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn

2014-06-15

In this paper, the properties of the extraordinary mode and surface plasmon modes in the three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) with face-centered-cubic lattices that are composed of the core tellurium (Te) spheres with surrounded by the homogeneous magnetized plasma shells inserted in the air, are theoretically investigated in detail by the plane wave expansion method, as the magneto-optical Voigt effects of magnetized plasma are considered (the incidence electromagnetic wave vector is perpendicular to the external magnetic field at any time). The optical switching or wavelength division multiplexer can be realized by the proposed 3D MPPCs. Our analyses demonstratemore » that the complete photonic band gaps (PBGs) and two flatbands regions for the extraordinary mode can be observed obviously. PBGs can be tuned by the radius of core Te sphere, the plasma density and the external magnetic field. The flatbands regions are determined by the existence of surface plasmon modes. Numerical simulations also show that if the thickness of magnetized plasma shell is larger than a threshold value, the band structures of the extraordinary mode will be similar to those obtained from the same structure containing the pure magnetized plasma spheres. In this case, the band structures also will not be affected by the inserted core spheres. It is also provided that the upper edges of two flatbands regions will not depend on the topology of lattice. However, the frequencies of lower edges of two flatbands regions will be convergent to the different constants for different lattices, as the thickness of magnetized plasma shell is close to zero.« less

Magnetic characteristics of polymorphic single crystal compounds DyIr2Si2

NASA Astrophysics Data System (ADS)

Uchima, Kiyoharu; Shigeoka, Toru; Uwatoko, Yoshiya

2018-05-01

We have confirmed that the tetragonal ternary compound DyIr2Si2 shows polymorphism; the ThCr2Si2-type structure as a low temperature phase (I-phase) and the CaBe2Ge2-type one as a high temperature phase (P-phase) exist. A comparative study on magnetic characteristics of the morphs was performed on the I- and P-phase single crystals in order to elucidate how magnetic properties are influenced by crystallographic symmetry. The magnetic behavior changes drastically depending on the structure. The DyIr2Si2(I) shows an antiferromagnetic ordering below TN = 30 K, additional magnetic transitions of T1 = 17 K and T2 = 10 K, and a strong uniaxial magnetic anisotropy with the easy [001] direction. The [001] magnetization shows four metamagnetic transitions at low temperatures. On the other hand, the DyIr2Si2(P) has comparatively low ordering temperature of TN1 = 9.4 K and an additional transition temperature of TN2 = 3.0 K, and exhibits an easy-plane magnetic anisotropy with the easy [110] direction. Two metamagnetic transitions appear in the basal plane magnetization processes. In both the morphs, the χ-T behavior suggests the existence of component-separated magnetic transitions. The ab-component of magnetic moments orders at the higher transition temperature TN1 for the P-phase compound, which is contrast to the I-phase behavior; the c-component orders firstly at TN. The crystalline electric field (CEF) analysis was made, and the difference in magnetic behaviors between both the morphs is explained by the CEF effects.

Cesium vacancy ordering in phase-separated C s x F e 2 - y S e 2

DOE PAGES

Taddei, Keith M.; Sturza, M.; Chung, Duck -Yung; ...

2015-09-14

By simultaneously displaying magnetism and superconductivity in a single phase, the iron-based superconductors provide a model system for the study of magnetism's role in superconductivity. The class of intercalated iron selenide superconductors is unique among these in having the additional property of phase separation and coexistence of two distinct phases—one majority phase with iron vacancy ordering and strong antiferromagnetism, and the other a poorly understood minority microscopic phase with a contested structure. Adding to the intrigue, the majority phase has never been found to show superconductivity on its own while the minority phase has never been successfully synthesized separate frommore » the majority phase. In order to better understand this minority phase, a series of high-quality Cs xFe 2–ySe 2 single crystals with (0.8 ≤ x ≤ 1;0 ≤ y ≤ 0.3) were grown and studied. Neutron and x-ray powder diffraction performed on ground crystals show that the average I4/mmm structure of the minority phase is distinctly different from the high-temperature I4/mmm parent structure. Moreover, single-crystal diffraction reveals the presence of discrete superlattice reflections that remove the degeneracy of the Cs sites in both the majority and minority phases and reduce their structural symmetries from body centered to primitive. Group theoretical analysis in conjunction with structural modeling shows that the observed superlattice reflections originate from three-dimensional Cs vacancy ordering. This model predicts a 25% vacancy of the Cs site in the minority phase which is consistent with the site's refined occupancy. Magnetization measurements performed in tandem with neutron single-crystal diffraction provide evidence that the minority phase is the host of superconductivity. Lastly, our results also reveal a superconducting dome in which the superconducting transition temperature varies as a function of the nominal valence of iron.« less

Mosaic anisotropy model for magnetic interactions in mesostructured crystals

NASA Astrophysics Data System (ADS)

Goldman, Abby R.; Asenath-Smith, Emily; Estroff, Lara A.

2017-10-01

We propose a new model for interpreting the magnetic interactions in crystals with mosaic texture called the mosaic anisotropy (MA) model. We test the MA model using hematite as a model system, comparing mosaic crystals to polycrystals, single crystal nanoparticles, and bulk single crystals. Vibrating sample magnetometry confirms the hypothesis of the MA model that mosaic crystals have larger remanence (Mr/Ms) and coercivity (Hc) compared to polycrystalline or bulk single crystals. By exploring the magnetic properties of mesostructured crystalline materials, we may be able to develop new routes to engineering harder magnets.

The Effects of a Magnetic Field on the Crystallization of a Fluorozirconate Glass

NASA Technical Reports Server (NTRS)

Tucker, Dennis S.; Lapointe, Michael R.; Jia, Zhiyong

2006-01-01

An axial magnetic field of 0.1T was applied to ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fibers during heating to the glass crystallization temperature. Scanning electron microscopy and x-ray diffraction were used to identify crystal phases. It was shown that fibers exposed to the magnetic field did not crystallize while fibers not exposed to the field did crystallize. A hypothesis based on magnetic work was proposed to explain the results and tested by measuring the magnetic susceptibilities of the glass and crystal.

Crystal structure and low-energy Einstein mode in ErV{sub 2}Al{sub 20} intermetallic cage compound

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

Winiarski, Michał J., E-mail: mwiniarski@mif.pg.gda.pl; Klimczuk, Tomasz

Single crystals of a new ternary aluminide ErV{sub 2}Al{sub 20} were grown using a self-flux method. The crystal structure was determined by powder X-ray diffraction measurements and Rietveld refinement, and physical properties were studied by means of electrical resistivity, magnetic susceptibility and specific heat measurements. These measurements reveal that ErV{sub 2}Al{sub 20} is a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment μ{sub eff} =9.27(1) μ{sub B} and Curie-Weiss temperature Θ{sub CW} =−0.55(4) K. The heat capacity measurements show a broad anomaly at low temperatures that is attributed to the presence of a low-energy Einstein mode withmore » characteristic temperature Θ{sub E} =44 K, approximately twice as high as in the isostructural ‘Einstein solid’ VAl{sub 10.1}. - Graphical abstract: A low-energy Einstein mode is observed in a novel intermetallic cage compound ErV{sub 2}Al{sub 20} by specific heat and resistivity measurements. - Highlights: • Single crystals of a new compound ErV{sub 2}Al{sub 20} were grown by self-flux method. • Crystal structure is reported, based on powder x-ray diffraction. • ErV{sub 2}Al{sub 20} is a Curie-Weiss paramagnet. • Low-energy ‘rattling’ phonon mode (Θ{sub E}=44 K) is found in specific heat measurements.« less

Structural, magnetic and magnetocaloric properties of Co-doped nanocrystalline La0.7Te0.3Mn0.7Co0.3O3

NASA Astrophysics Data System (ADS)

Meenakshi; Kumar, Amit; Mahato, Rabindra Nath

2018-02-01

Structural, magnetic and magnetocaloric properties of the nanocrystalline La0.7Te0.3Mn0.7Co0.3O3 perovskite manganite were investigated. X-ray diffraction pattern indicated that the nanocrystalline sample crystallized in orthorhombic crystal structure with Pbnm space group. The average particle size was calculated using scanning electron microscope and it was found to be ∼150 nm. Temperature dependence magnetization measurements revealed ferromagnetic-paramagnetic phase transition and the Curie temperature (TC) was found to be ∼201 K. Field dependence magnetization showed the hysteresis at low temperature with a coercive field of ∼0.34 T and linear dependence at high temperature corresponds to paramagnetic region. Based on the magnetic field dependence magnetization data, the maximum entropy change and relative cooling power (RCP) were estimated and the values were 1.002 J kg-1 K-1 and 90 J kg-1 for a field change of 5 T respectively. Temperature dependent resistivity ρ(T) data exhibited semiconducting-like behavior at high temperature and the electrical transport was well explained by Mott's variable-range hopping (VRH) conduction mechanism in the temperature range of 250 K-300 K. Using the VRH fit, the calculated hoping distance (Rh) at 300 K was 54.4 Å and density of states N(EF) at room temperature was 7.04 × 1018 eV-1 cm-3. These values were comparable to other semiconducting oxides.

Two-dimensional 3d-4f heterometallic coordination polymers: syntheses, crystal structures, and magnetic properties of six new Co(II)-Ln(III) compounds.

PubMed

Díaz-Gallifa, Pau; Fabelo, Oscar; Pasán, Jorge; Cañadillas-Delgado, Laura; Lloret, Francesc; Julve, Miguel; Ruiz-Pérez, Catalina

2014-06-16

Six new heterometallic cobalt(II)-lanthanide(III) complexes of formulas [Ln(bta)(H2O)2]2[Co(H2O)6]·10H2O [Ln = Nd(III) (1) and Eu(III) (2)] and [Ln2Co(bta)2(H2O)8]n·6nH2O [Ln = Eu(III) (3), Sm(III) (4), Gd(III) (5), and Tb(III) (6)] (H4bta = 1,2,4,5-benzenetretracaboxylic acid) have been synthesized and characterized via single-crystal X-ray diffraction. 1 and 2 are isostructural compounds with a structure composed of anionic layers of [Ln(bta)(H2O)2]n(n-) sandwiching mononuclear [Co(H2O)6](2+) cations plus crystallization water molecules, which are interlinked by electrostatic forces and hydrogen bonds, leading to a supramolecular three-dimensional network. 3-6 are also isostructural compounds, and their structure consists of neutral layers of formula [Ln2Co(bta)2(H2O)8]n and crystallization water molecules, which are connected through hydrogen bonds to afford a supramolecular three-dimensional network. Heterometallic chains formed by the regular alternation of two nine-coordinate lanthanide(III) polyhedra [Ln(III)O9] and one compressed cobalt(II) octahedron [Co(II)O6] along the crystallographic c-axis are cross-linked by bta ligands within each layer of 3-6. Magnetic susceptibility measurements on polycrystalline samples for 3-6 have been carried out in the temperature range of 2.0-300 K. The magnetic behavior of these types of Ln(III)-Co(II) complexes, which have been modeled by using matrix dagonalization techniques, reveals the lack of magnetic coupling for 3 and 4, and the occurrence of weak antiferromagnetic interactions within the Gd(III)-Gd(III) (5) and Tb(III)-Tb(III) (6) dinuclear units through the exchange pathway provided by the double oxo(carboxylate) and double syn-syn carboxylate bridges.

First-principles investigation of the interlayer coupling in chromium-trichloride-a layered magnetic insulator

NASA Astrophysics Data System (ADS)

Kc, Santosh; McGuire, Michael A.; Cooper, Valentino R.

The crystallographic, electronic and magnetic properties of layered CrCl3were investigated using density functional theory. We use the newly developed spin van der Waals density functional (svdW-DF) in order to explore the atomic, electronic and magnetic structure. Our results indicate that treatment of the long-range interlayer forces with the svdW-DF improves the accuracy of crystal structure predictions. The cleavage energy was estimated to be 0.29 J/m2 suggesting that CrCl3 should be cleavable using standard mechanical exfoliation techniques. The inclusion of spin in the non-local vdW-DF allows us to directly probe the coupling between the magnetic structure and lattice degrees of freedom. An understanding of the link between electronic, magnetic and structural properties can be useful for novel device applications such as magnetoelectric devices, spin transistors, and 2D magnet. Research was sponsored by the US DOE, Office of Science, BES, MSED and Early Career Research Programs and used resources at NERSC.

Monte Carlo Study of Magnetic Properties of Mixed Spins in a Fullerene X 30 Y 30-Like Structure

NASA Astrophysics Data System (ADS)

Mhirech, A.; Aouini, S.; Alaoui-Ismaili, A.; Bahmad, L.

2018-03-01

In this work, inspiring form of the fullerene-C60 structures, we study the mixed X_{30} Y_{30} fullerene-like structure and investigate its magnetic properties. In a such a structure, the carbons are assumed to be replaced by magnetic atoms having spin moments σ = 1/2 and S = 1. Firstly, we elaborate the ground-state phase diagrams in different physical parameter planes. In a second stage, we investigate the exchange coupling interaction effects in the absence or presence of both external magnetic and crystal fields. Using the Monte Carlo method, we carried out a study of the system magnetic properties and the thermal behavior of such a system for the ferromagnetic case. It is found that the critical temperature increases when increasing the coupling exchange interactions. On the other hand, the coercive magnetic field increases also when increasing the coupling exchange interactions. However, this physical parameter decreases when increasing the reduced temperature.

Interaction between Convection and Heat Transfer in Crystal Growth

NASA Technical Reports Server (NTRS)

1998-01-01

Crystals are integral components in some of our most sophisticated and rapidly developing industries. Single crystals are solids with the most uniform structures that can be obtained on an atomic scale. Because of their structural uniformity, crystals can transmit acoustic and electromagnetic waves and charged particles with essentially no scattering or interferences. This transparency, which can be selectively modified by controlled additions of impurities known as dopants, is the foundation of modern electronic industry. It has brought about widespread application of crystals in transistors, lasers, microwave devices, infrared detectors, magnetic memory devices, and many other magnets and electro-optic components. The performance of a crystal depends strongly on its compositional homogeneity. For instance, in modern microcircuitry, compositional variations of a few percent (down to a submicron length scale) can seriously jeopardize predicted yields. Since crystals are grown by carefully controlled phase transformations, the compositional adjustment in the solid is often made during growth from the nutrient. Hence, a detailed understanding of mass transfer in the nutrient is essential. Moreover, since mass transfer is often the slowest process during growth, it is usually the rate limiting mechanism. Crystal growth processes are usually classified according to the nature of the parent phase. Nevertheless, whether the growth occurs by solidification from a melt (melt growth), nucleation from a solution (solution growth), condensation from a vapor (physical vapor transport) or chemical reaction of gases (chemical vapor deposition), the parent phase is a fluid. As is with most non-equilibrium processes involving fluids, liquid or vapor, fluid motion plays an important role, affecting both the concentration and temperature gradients at the soli-liquid interface.

On the synthesis, characterization and magnetic properties of two new phases discovered in the PbO–Fe{sub 2}O{sub 3}–P{sub 2}O{sub 5} system

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

El Hafid, Hassan; Velázquez, Matias, E-mail: matias.velazquez@icmcb-bordeaux.cnrs.fr; Pérez, Olivier

2013-06-15

The PbFe{sub 3}O(PO{sub 4}){sub 3} powder compound was studied by means of X-ray diffraction (XRD) from 300 to 6 K, electron-probe microanalysis (EPMA) coupled with wavelength dispersion spectroscopy (WDS), calorimetric (DSC and specific heat) and magnetic properties measurements. Magnetization, magnetic susceptibility and specific heat measurements carried out on PbFe{sub 3}O(PO{sub 4}){sub 3} powders firmly establish a series of three ferromagnetic (FM)-like second order phase transitions spanned over the 32–8 K temperature range. Discrepancies between magnetization and specific heat data obtained in PbFe{sub 3}O(PO{sub 4}){sub 3} powders and single crystals are highlighted. A first extraction of the critical exponents (β,γ,δ) wasmore » performed by ac magnetic susceptibility in both PbFe{sub 3}O(PO{sub 4}){sub 3} powders and single crystals and the values were found to be consistent with mean-field theory. Further exploration of the PbO–Fe{sub 2}O{sub 3}–P{sub 2}O{sub 5} system led to the discovery of a new langbeinite phase, Pb{sub 1.5}Fe{sub 2}(PO{sub 4}){sub 3}, the crystal structure of which was solved by room temperature single crystal XRD (P2{sub 1}3, Z=4, a=9.7831(2) Å). This phase does not undergo any structural phase transition down to 6 K nor any kind of long range ordering down to 2 K. - Graphical abstract: Three ferromagnetic-like phase transitions discovered in the new compound PbFe{sub 3}O(PO{sub 4}){sub 3} by specific heat and ZFC/FC magnetization measurements. - Highlights: • Three FM-like second order phase transitions in PbFe{sub 3}O(PO{sub 4}){sub 3} powders. • Critical exponents (β,γ,δ) in PbFe{sub 3}O(PO{sub 4}){sub 3} consistent with mean-field behavior. • Discovery of a new langbeinite phase, Pb{sub 1.5}Fe{sub 2}(PO{sub 4}){sub 3}.« less

Pb 2MnTeO 6 Double Perovskite: An Antipolar Anti-ferromagnet

DOE PAGES

Retuerto, Maria; Skiadopoulou, Stella; Li, Man-Rong; ...

2016-04-08

Pb 2MnTeO 6, a new double perovskite, has been synthesized. Its crystal structure was determined by synchrotron X-ray and powder neutron diffraction.Pb 2MnTeO 6 is monoclinic (I2/m) at room temperature with a regular arrangement of all the cations in their polyhedra. However, when the temperature is lowered to ~120 K it undergoes a phase transition from I2/m to C2/c structure. This transition is accompanied by a displacement of the Pb atoms from the center of their polyhedra due to the 6s 2 lone-pair electrons, together with a surprising off-centering of Mn 2+ (d 5) magnetic cations. This strong first-order phasemore » transition is also evidenced by specific heat, dielectric, Raman, and infrared spectroscopy measurements. The magnetic characterizations indicate an anti-ferromagnetic (AFM) order below T N ≈ 20 K; analysis of powder neutron diffraction data confirms the magnetic structure with propagation vector k = (0 1 0) and collinear AFM spins. The observed jump in dielectric permittivity near ~150 K implies possible anti-ferroelectric behavior; however, the absence of switching suggests that Pb 2MnTeO 6 can only be antipolar. First-principle calculations confirmed that the crystal and magnetic structures determined are locally stable and that anti-ferroelectric switching is unlikely to be observed in Pb 2MnTeO 6.« less

Comparative study of heterogeneous magnetic state above TC in La0.82Sr0.18CoO3 cobaltite and La0.83Sr0.17MnO3 manganite

NASA Astrophysics Data System (ADS)

Ryzhov, V. A.; Lazuta, A. V.; Molkanov, P. L.; Khavronin, V. P.; Kurbakov, A. I.; Runov, V. V.; Mukovskii, Ya. M.; Pestun, A. E.; Privezentsev, R. V.

2012-10-01

The magnetic, transport and structural properties are studied for La0.83Sr0.17MnO3 and La0.82Sr0.18CoO3 single crystals with nearly the same doping and the metallic ground state. Their comparisons have shown that ferromagnetic clusters originate in the paramagnetic matrix below Т*>TC in both samples and exhibit similar properties. This suggests the possible universality of such phenomena in doped mixed-valence oxides of transition metals with the perovskite-type structure. The cluster density increases on cooling and plays an important role on the physical properties of these systems. The differences in cluster evolutions and scenarios of their insulator-metal transitions are related to different magnetic behaviors of the matrixes in these crystals that is mainly due to distinct spin states of the Mn3+ and Co3+ ions.

Noncollinear antiferromagnetic Mn3Sn films

NASA Astrophysics Data System (ADS)

Markou, A.; Taylor, J. M.; Kalache, A.; Werner, P.; Parkin, S. S. P.; Felser, C.

2018-05-01

Noncollinear hexagonal antiferromagnets with almost zero net magnetization were recently shown to demonstrate giant anomalous Hall effect. Here, we present the structural and magnetic properties of noncollinear antiferromagnetic Mn3Sn thin films heteroepitaxially grown on Y:ZrO2 (111) substrates with a Ru underlayer. The Mn3Sn films were crystallized in the hexagonal D 019 structure with c -axis preferred (0001) crystal orientation. The Mn3Sn films are discontinuous, forming large islands of approximately 400 nm in width, but are chemical homogeneous and characterized by near perfect heteroepitaxy. Furthermore, the thin films show weak ferromagnetism with an in-plane uncompensated magnetization of M =34 kA/m and coercivity of μ0Hc=4.0 mT at room temperature. Additionally, the exchange bias effect was studied in Mn3Sn /Py bilayers. Exchange bias fields up to μ0HEB=12.6 mT can be achieved at 5 K. These results show Mn3Sn films to be an attractive material for applications in antiferromagnetic spintronics.

Synthesis, structure, optical, photoluminescence and magnetic properties of K2[Co(C2O4)2(H2O)2]·4H2O

NASA Astrophysics Data System (ADS)

Narsimhulu, M.; Hussain, K. A.

2018-06-01

The synthesis, crystal structure, optical, photoluminescence and magnetic behaviour of potassium bis(oxalato)cobaltate(II)tertrahydrate{K2[Co(C2O4)2(H2O)2]·4H2O} are described. The compound was grown at room temperature from mixture of aqueous solutions by slow evaporation method. The X-ray crystallographic data showed that the compound belongs to the monoclinic crystal system with P21/n space group and Z = 4. The UV-visible diffuse absorbance spectra exhibited bands at 253, 285 and 541 nm in the visible and ultraviolet regions. The optical band gap of the compound was estimated as 3.4 eV. At room temperature, an intense photoluminescence was observed from this material around 392 nm when it excited at 254 nm. The variable temperature dc magnetic susceptibility measurements exposed paramagnetic behaviour at high temperatures and antiferromagnetic ordering at low temperatures.

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

Zhou, Sixuan; Latturner, Susan E., E-mail: latturner@chem.fsu.edu

The intermetallic compounds RE{sub 6}Co{sub 5}Ge{sub 1+x}Al{sub 3−x} (RE=Pr{sub ,} Nd) were synthesized from the reaction of germanium and aluminum in RE/Co eutectic flux. These phases crystallize with the Nd{sub 6}Co{sub 5}Ge{sub 2.2} structure type in hexagonal space group P-6m2 (a=9.203(2)Å, c=4.202(1) Å, R{sub 1}=0.0109 for Pr{sub 6}Co{sub 5}Ge{sub 1.80}Al{sub 2.20}; and a=9.170(3) Å, c=4.195(1) Å, R{sub 1}=0.0129 for Nd{sub 6}Co{sub 5}Ge{sub 1.74}Al{sub 2.26}). The structure features chains of face-sharing Ge@RE{sub 9} clusters intersecting hexagonal cobalt nets linked by aluminum atoms. Magnetic susceptibility measurements indicate that both phases exhibit ferromagnetic ordering of the cobalt layers with T{sub C} in themore » range of 130–140 K. The magnetic moments of the rare earth ions order at lower temperature (30–40 K). Magnetic measurements on oriented crystals of Nd{sub 6}Co{sub 5}Ge{sub 1.74}Al{sub 2.26} show a strong preference of the moments to order along the c-axis. - Graphical abstract: RE{sub 6}Co{sub 5}Ge{sub 1+x}Al{sub 3−x} (RE=Pr{sub ,} Nd) were grown as large crystals from reactions of Ge and Al in RE/Co eutectic melts. Magnetic measurements indicate ordering of the 2-D cobalt nets at 130–140 K, and ordering of the rare earth moments at 30–40 K. Display Omitted - Highlights: • RE{sub 6}Co{sub 5}Ge{sub 1+x}Al{sub 3−x} (RE=Pr{sub ,} Nd) grown as large crystals from RE/Co eutectic flux. • RE{sub 6}Co{sub 5}Ge{sub 1+x}Al{sub 3−x} structure features hexagonal cobalt nets stacked along c-axis. • Cobalt layers order ferromagnetically with T{sub c}=130–140 K. • Rare earth magnetic moments order at low temperature (30–40 K).« less

Crystallographic Data Centre Services and Publications.

ERIC Educational Resources Information Center

Cambridge Univ. (England). Chemical Lab.

The Cambridge Crystallographic Data Centre is concerned with the retrieval, evaluation, synthesis, and dissemination of structural data based on diffraction methods. The source of input is almost entirely primary journals. Bibliographic information and numeric data on crystal and molecular structures are on magnetic tapes. The bibliographic file…

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

Effect of Molybdenum Incorporation on the Structure and Magnetic Properties of Cobalt Ferrite

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

Orozco, C.; Melendez, A.; Manadhar, S.

Here, we report on the effect of molybdenum (Mo) incorporation on the crystal structure, surface morphology, Mo chemical valence state, and magnetic properties of cobalt ferrite (CoFe 2O 4, referred to CFO). Molybdenum incorporated cobalt ferrite (CoFe 2–xMo xO 4, referred to CFMO) ceramics were prepared by the conventional solid-state reaction method by varying the Mo concentration in the range of x = 0.0–0.3. X-ray diffraction studies indicate that the CFMO materials crystallize in inverse spinel cubic phase. Molybdenum incorporation induced lattice parameter increase from 8.322 to 8.343 Å coupled with a significant increase in density from 5.4 to 5.7more » g/cm 3 was evident in structural analyses. Scanning electron microscopy imaging analyses indicate that the Mo incorporation induces agglomeration of particles leading to larger particle size with increasing x(Mo) values. Detailed X-ray photoelectron spectroscopic (XPS) analyses indicate the increasing Mo content with increasing x from 0.0 to 0.3. XPS confirms that the chemistry of Mo is complex in these CFMO compounds; Mo ions exist in the lower oxidation state (Mo 4+) for higher x while in a mixed chemical valence state (Mo 4+, Mo 5+, Mo 6+) for lower x values. From the temperature-dependent magnetization, the samples show ferrimagnetic behavior including the pristine CFO. From the isothermal magnetization measurements, we find almost 2-fold decrease in coercive field ( H c) from 2143 to 1145 Oe with the increase in Mo doping up to 30%. This doping-dependent H c is consistently observed at all the temperatures measured (4, 100, 200, and 300 K). Furthermore, the saturation magnetization estimated at 4 K and at 1.5 T (from M–H loops) goes through a peak at 92 emu/g (at 15% Mo doping) from 81 emu/g (pristine CFO), and starts decreasing to 79 emu/g (at 30% Mo doping). The results demonstrate that the crystal structure, microstructure, and magnetic properties can be tuned by controlling the Mo-content in the CFMO materials.« less

Effect of Molybdenum Incorporation on the Structure and Magnetic Properties of Cobalt Ferrite

DOE PAGES

Orozco, C.; Melendez, A.; Manadhar, S.; ...

2017-09-26

Here, we report on the effect of molybdenum (Mo) incorporation on the crystal structure, surface morphology, Mo chemical valence state, and magnetic properties of cobalt ferrite (CoFe 2O 4, referred to CFO). Molybdenum incorporated cobalt ferrite (CoFe 2–xMo xO 4, referred to CFMO) ceramics were prepared by the conventional solid-state reaction method by varying the Mo concentration in the range of x = 0.0–0.3. X-ray diffraction studies indicate that the CFMO materials crystallize in inverse spinel cubic phase. Molybdenum incorporation induced lattice parameter increase from 8.322 to 8.343 Å coupled with a significant increase in density from 5.4 to 5.7more » g/cm 3 was evident in structural analyses. Scanning electron microscopy imaging analyses indicate that the Mo incorporation induces agglomeration of particles leading to larger particle size with increasing x(Mo) values. Detailed X-ray photoelectron spectroscopic (XPS) analyses indicate the increasing Mo content with increasing x from 0.0 to 0.3. XPS confirms that the chemistry of Mo is complex in these CFMO compounds; Mo ions exist in the lower oxidation state (Mo 4+) for higher x while in a mixed chemical valence state (Mo 4+, Mo 5+, Mo 6+) for lower x values. From the temperature-dependent magnetization, the samples show ferrimagnetic behavior including the pristine CFO. From the isothermal magnetization measurements, we find almost 2-fold decrease in coercive field ( H c) from 2143 to 1145 Oe with the increase in Mo doping up to 30%. This doping-dependent H c is consistently observed at all the temperatures measured (4, 100, 200, and 300 K). Furthermore, the saturation magnetization estimated at 4 K and at 1.5 T (from M–H loops) goes through a peak at 92 emu/g (at 15% Mo doping) from 81 emu/g (pristine CFO), and starts decreasing to 79 emu/g (at 30% Mo doping). The results demonstrate that the crystal structure, microstructure, and magnetic properties can be tuned by controlling the Mo-content in the CFMO materials.« less

Suppression of Magnetic Order before the Superconducting Dome in MnP

NASA Astrophysics Data System (ADS)

Yano, Shin-ichiro; Lançon, Diane; Rønnow, Henrik M.; Hansen, Thomas C.; Ressouche, Eric; Qureshi, Navid; Ouladdiaf, Bachir; Gardner, Jason S.

2018-02-01

We have performed neutron diffraction experiments on the manganese superconductor, MnP, under applied pressure. Higher harmonics of the previously reported double helix (2δ and 3δ) at ambient pressure were observed and a new magnetic phases was discovered as hydrostatic pressure was applied to a polycrystalline sample below the pressure required to induce superconductivity. The double helix magnetic structure is suppressed by 0.7 GPa. A new incommensurate magnetic structure with propagation vector ˜ (0.25,0.25,0.125) was found at 1.5 GPa. The application of higher pressures results in the quenching of the incommensurate phase and broad, diffuse magnetic scattering develops before the superconducting phase. Single crystal studies complement the polycrystalline data confirming the magnetic propagation vector in the low pressure phase.

Giant magneto-optical Kerr rotation, quality factor and figure of merit in cobalt-ferrite magnetic nanoparticles doped in silica matrix as the only defect layer embedded in magnetophotonic crystals

NASA Astrophysics Data System (ADS)

Zamani, Mehdi; Hocini, Abdesselam

2018-03-01

In this work, we report on the theoretical study of one-dimensional magnetophotonic crystals (MPC) comprising of periodic dielectric structure Si/SiO and of silica matrix doped with cobalt-ferrite (CoFe2O4) magnetic nanoparticles as the only magnetic defect layer. Such structure can be prepared by sol-gel dip coating method that controls the thickness of each layer with nanometer level, hence, can overcome the problem of integration of the magneto-optical (MO) devices. We have studied the influence of the volume fraction (concentration of magnetic nanoparticles VF%) on the optical (reflectance, transmittance and absorption) and MO (Kerr rotation) responses in reflection-type one-dimensional MPCs. During investigation of the influence of magnetic nanoparticle's concentration, we found that giant Kerr rotations (even ≈135° for VF = 39%) can be obtained accompanied by large reflectance and low amounts for transmittance and absorption. We report on the demonstration of large MO quality factor and figure of merit in cobalt-ferrite magnetic nanoparticles in the infrared regime. Given the large Kerr rotation, high reflectance accompanied by low absorption and nearly zero transmittance of the 1D MPC containing cobalt-ferrite magnetic nanoparticles, large MO Q factor and figure of merit are obtained.

Atomic level structural modulation during the structural relaxation and its effect on magnetic properties of Fe81Si4B10P4Cu1 nanocrystalline alloy

NASA Astrophysics Data System (ADS)

Cao, C. C.; Zhu, L.; Meng, Y.; Zhai, X. B.; Wang, Y. G.

2018-06-01

The evolution of local structure and defects in the Fe81Si4B10P4Cu1 amorphous alloy during the structural relaxation has been investigated by Mössbauer spectroscopy, positron annihilation lifetime spectroscopy and transmission electron microscopy to explore their effects on magnetic properties of the nanocrystalline. The atomic rearrangements at the early stage of the structural relaxation cause the density increase of the amorphous matrix, but the subsequent atomic rearrangements contribute to the transformation of Fe3B-like atomic arrangements to FeB-like ones with the temperature increasing. As the structural relaxation processes, the released Fe atoms both from Fe3B- and Fe3P-like atomic arrangements result in the formation of new Fe clusters and the increase of Fe-Fe coordination number in the existing Fe clusters and the nucleation sites for α-Fe gradually increase, both of which promote the crystallization. However, the homogeneity of amorphous matrix will be finally destroyed under excessive relaxation temperature, which coarsens nanograins during the crystallization instead. Therefore, soft magnetic properties of the Fe81Si4B10P4Cu1 nanocrystalline alloy can be improved by pre-annealing the amorphous precursor at an appropriate temperature due to the atomic level structural optimization.

Structural and electronic evolution of Cr[subscript 2]O[subscript 3] on compression to 55 GPa

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

Dera, Przemyslaw; Lavina, Barbara; Meng, Yue

2016-08-15

Synchrotron single-crystal x-ray diffraction experiments have been performed on corundum-type Cr{sub 2}O{sub 3} up to a pressure of 55 GPa in Ne and He pressure transmitting media. Diffraction experiments were complemented by measurements of optical absorption spectra with single crystal samples up to 60 GPa. Results of the diffraction data analysis rule out the earlier reported monoclinic distortion at 15-30 GPa, but indicate evidence of two discontinuous transitions of electronic or magnetic nature, most likely associated with a change in magnetic ordering and charge transfer. The compression mechanism established from single crystal refinements indicates much smaller distortion of the Cr{supmore » 3+} coordination environment than was previously assumed.« less

Local Structure and Anisotropy in the Amorphous Precursor= to Ba-Hexaferrite Thin Films

NASA Astrophysics Data System (ADS)

Snyder, J. E.; Harris, V. G.; Koon, N. C.; Sui, X.; Kryder, M. H.

1996-03-01

Ba-hexaferrite thin-films for recording media applications are commonly fabricated by a two-step process: sputter-deposition of an amorphous precursor, followed by annealing to crystallize the BaFe_12O_19 phase. The magnetic anisotropy of the crystalline films can be either in-plane or perpendicular, depending on the sputtering process used in the first step. However, conventional characterization techniques (x-ray diffraction and TEM) have been unable to observe any structure in the amorphous precursor films. In this study, such films are investigated by PD-EXAFS (polarization-dependent extended x-ray absorption fine structure). An anisotropic local ordered structure is observed around both Fe and Ba atoms in the "amorphous" films. This anisotropic local structure appears to determine the orientation of the fast-growing basal plane directions during crystallization, and thus the directions of the c-axes and the magnetic anisotropy. Results suggest that the structure of the amorphous films consists of networks made up of units of Fe atoms surrounded by their O nearest neighbors, that are connected together. Ba atoms appear to fit into in-between spaces as network-modifiers.

Evolution of magnetism in single-crystal C a 2 R u 1 - x I r x O 4 ( 0 ≤ x ≤ 0.65 )

DOE PAGES

Yuan, S. J.; Terzic, J.; Wang, J. C.; ...

2015-07-24

In this paper, we report structural, magnetic, transport, and thermal properties of single-crystal Ca 2Ru 1-xIr xO 4(0≤x≤0.65). Ca 2RuO 4 is a structurally driven Mott insulator with a metal-insulator transition at T MI=357K, which is well separated from antiferromagnetic order at T N=110K. Substitution of a 5d element, Ir, for Ru enhances spin-orbit coupling and locking between the structural distortions and magnetic moment canting. Ir doping intensifies the distortion or rotation of Ru/IrO 6 octahedra and induces weak ferromagnetic behavior along the c axis. In particular, Ir doping suppresses T N but concurrently causes an additional magnetic ordering Tmore » N2 at a higher temperature up to 210 K for x=0.65. The effect of Ir doping sharply contrasts with that of 3d-element doping such as Cr, Mn, and Fe, which suppresses T N and induces unusual negative volume thermal expansion. Finally, the stark difference between 3d- and 5d-element doping underlines a strong magnetoelastic coupling inherent in the Ir-rich oxides.« less

Magnetic phase transitions and ferromagnetic short-range correlations in single-crystal Tb5Si2.2Ge1.8

NASA Astrophysics Data System (ADS)

Zou, M.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Schlagel, D. L.; Lograsso, T. A.

2008-07-01

Magnetic phase transitions in a Tb5Si2.2Ge1.8 single crystal have been studied as a function of temperature and magnetic field. Magnetic-field dependencies of the critical temperatures are highly anisotropic for both the main magnetic ordering process occurring around 120 K and a spin reorientation transition at ˜70K . Magnetic-field-induced phase transitions occur with the magnetic field applied isothermally along the a and b axes (but not along the c axis) between 1.8 and 70 K in fields below 70 kOe. Strong anisotropic thermal irreversibility is observed in the Griffiths phase regime between 120 and 200 K with applied fields ranging from 10 to 1000 Oe. Our data (1) show that the magnetic and structural phase transitions around 120 K are narrowly decoupled; (2) uncover the anisotropy of ferromagnetic short-range order in the Griffiths phase; and (3) reveal some unusual magnetic domain effects in the long-range ordered state of the Tb5Si2.2Ge1.8 compound. The temperature-magnetic field phase diagrams with field applied along the three major crystallographic directions have been constructed.

The cluster compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} containing Mo{sub 14} clusters and the new mono- and bi-capped trioctahedral Mo{sub 15} and Mo{sub 16} clusters: Synthesis, crystal structure, and electrical and magnetic properties

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

Gall, Philippe; Guizouarn, Thierry; Gougeon, Patrick, E-mail: Patrick.Gougeon@univ-rennes1.fr

2015-07-15

Single crystals of the new quaternary compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} were obtained by solid state reaction. The crystal structure was determined by single-crystal X-ray diffraction. In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} crystallizes in the orthorhombic space group Pbca with unit-cell parameters a=9.4432(14) Å, b=11.4828(12) Å, c=20.299(4) Å and Z=4. Full-matrix least-squares refinement on F{sup 2} using 3807 independent reflections for 219 refinable parameters resulted in R{sub 1}=0.0259 and wR{sub 2}=0.0591. The crystal structure contains in addition to Mo{sub 14} clusters the first examples of mono- and bi-capped trioctahedral Mo{sub 14} i.e. Mo{sub 15} and Mo{sub 16} clusters.more » The oxygen framework derives from a stacking along the a direction of close-packed layers with sequence (…ABAC…). The Mo–Mo distances range between 2.6938(5) and 2.8420(6) Å and the Mo–O distances between 1.879(5) and 2.250(3) Å, as usually observed in molybdenum oxide clusters. The indium atoms form In{sub 4}{sup 6+} bent chains with In–In distances of 2.6682(5) and 2.6622(8) Å and the Ti atoms are in highly distorted octahedral sites of oxygen atoms with Ti–O distances ranging between 1.865(4) and 2.161(4) Å. Magnetic susceptibility measurements confirm the presence of Ti{sup 4+} cations and the absence of localized moments on the Mo network. Electrical resistivity measurements on a single crystal of In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} show a semimetallic behavior. - Graphical abstract: We present here the synthesis, the crystal structure, and the electrical and magnetic properties of the new compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} in which Mo{sub 14} clusters coexist statistically with mono- and bi-capped trioctahedral Mo{sub 14} that is Mo{sub 15} and Mo{sub 16} clusters. - Highlights: • Single crystals of In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} were obtained by solid state reaction. • The crystal structure contains Mo{sub 14}, Mo{sub 15} and Mo{sub 16} clusters. • The indium atoms form In{sub 4}{sup 6+} bent chains. • Poorly metallic behavior. • Absence of localized moments on the Mo network as well as on the Ti atoms.« less

Neutron diffraction and μ SR studies of two polymorphs of nickel niobate NiNb 2 O 6

DOE PAGES

Munsie, T. J. S.; Wilson, M. N.; Millington, A.; ...

2017-10-13

Neutron diffraction and muon spin relaxation (μSR) studies are presented in this paper for the newly characterized polymorph of NiNb 2O 6 (β-NiNb 2O 6) with space group P4 2/n and μSR data only for the previously known columbite structure polymorph with space group Pbcn. The magnetic structure of the P4 2/n form was determined from neutron diffraction using both powder and single-crystal data. Powder neutron diffraction determined an ordering wave vector →k=( 1/ 2, 1/ 2, 1/ 2). Single-crystal data confirmed the same →k vector and showed that the correct magnetic structure consists of antiferromagnetically coupled chains running alongmore » the a or b axis in adjacent Ni 2+ layers perpendicular to the c axis, which is consistent with the expected exchange interaction hierarchy in this system. The refined magnetic structure is compared with the known magnetic structures of the closely related trirutile phases, NiSb 2O 6 and NiTa 2O 6. μSR data finds a transition temperature of T N~15K for this system, while the columbite polymorph exhibits a lower T N=5.7(3) K. Our μSR measurements also allowed us to estimate the critical exponent of the order parameter β for each polymorph. We found β =0.25(3) and 0.16(2) for the β and columbite polymorphs, respectively. The single-crystal neutron scattering data give a value for the critical exponent β =0.28(3) for β-NiNb 2O 6, in agreement with the μSR value. While both systems have β values less than 0.3, which is indicative of reduced dimensionality, this effect appears to be much stronger for the columbite system. Finally, in other words, although both systems appear to be well described by S=1 spin chains, the interchain interactions in the β polymorph are likely much larger.« less

Neutron diffraction and μ SR studies of two polymorphs of nickel niobate NiNb2O6

NASA Astrophysics Data System (ADS)

Munsie, T. J. S.; Wilson, M. N.; Millington, A.; Thompson, C. M.; Flacau, R.; Ding, C.; Guo, S.; Gong, Z.; Aczel, A. A.; Cao, H. B.; Williams, T. J.; Dabkowska, H. A.; Ning, F.; Greedan, J. E.; Luke, G. M.

2017-10-01

Neutron diffraction and muon spin relaxation (μ SR ) studies are presented for the newly characterized polymorph of NiNb2O6 (β -NiNb2O6) with space group P4 2/n and μ SR data only for the previously known columbite structure polymorph with space group P b c n . The magnetic structure of the P4 2/n form was determined from neutron diffraction using both powder and single-crystal data. Powder neutron diffraction determined an ordering wave vector k ⃗=(1/2 ,1/2 ,1/2 ) . Single-crystal data confirmed the same k ⃗ vector and showed that the correct magnetic structure consists of antiferromagnetically coupled chains running along the a or b axis in adjacent Ni2 + layers perpendicular to the c axis, which is consistent with the expected exchange interaction hierarchy in this system. The refined magnetic structure is compared with the known magnetic structures of the closely related trirutile phases, NiSb2O6 and NiTa2O6 . μ SR data finds a transition temperature of TN˜15 K for this system, while the columbite polymorph exhibits a lower TN=5.7 (3 ) K. Our μ SR measurements also allowed us to estimate the critical exponent of the order parameter β for each polymorph. We found β =0.25 (3 ) and 0.16(2) for the β and columbite polymorphs, respectively. The single-crystal neutron scattering data give a value for the critical exponent β =0.28 (3 ) for β -NiNb2O6 , in agreement with the μ SR value. While both systems have β values less than 0.3, which is indicative of reduced dimensionality, this effect appears to be much stronger for the columbite system. In other words, although both systems appear to be well described by S =1 spin chains, the interchain interactions in the β polymorph are likely much larger.

Neutron diffraction and μ SR studies of two polymorphs of nickel niobate NiNb 2 O 6

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

Munsie, T. J. S.; Wilson, M. N.; Millington, A.

Neutron diffraction and muon spin relaxation (μSR) studies are presented in this paper for the newly characterized polymorph of NiNb 2O 6 (β-NiNb 2O 6) with space group P4 2/n and μSR data only for the previously known columbite structure polymorph with space group Pbcn. The magnetic structure of the P4 2/n form was determined from neutron diffraction using both powder and single-crystal data. Powder neutron diffraction determined an ordering wave vector →k=( 1/ 2, 1/ 2, 1/ 2). Single-crystal data confirmed the same →k vector and showed that the correct magnetic structure consists of antiferromagnetically coupled chains running alongmore » the a or b axis in adjacent Ni 2+ layers perpendicular to the c axis, which is consistent with the expected exchange interaction hierarchy in this system. The refined magnetic structure is compared with the known magnetic structures of the closely related trirutile phases, NiSb 2O 6 and NiTa 2O 6. μSR data finds a transition temperature of T N~15K for this system, while the columbite polymorph exhibits a lower T N=5.7(3) K. Our μSR measurements also allowed us to estimate the critical exponent of the order parameter β for each polymorph. We found β =0.25(3) and 0.16(2) for the β and columbite polymorphs, respectively. The single-crystal neutron scattering data give a value for the critical exponent β =0.28(3) for β-NiNb 2O 6, in agreement with the μSR value. While both systems have β values less than 0.3, which is indicative of reduced dimensionality, this effect appears to be much stronger for the columbite system. Finally, in other words, although both systems appear to be well described by S=1 spin chains, the interchain interactions in the β polymorph are likely much larger.« less

Syntheses, crystal structures, and characterization of two new Tl+-Cu2+-Te6+ oxides: Tl4CuTeO6 and Tl6CuTe2O10

NASA Astrophysics Data System (ADS)

Yeon, Jeongho; Kim, Sang-Hwan; Green, Mark A.; Bhatti, Kanwal Preet; Leighton, C.; Shiv Halasyamani, P.

2012-12-01

Crystals and polycrystalline powders of two new oxide materials, Tl4CuTeO6 and Tl6CuTe2O10, have been synthesized by hydrothermal and solid-state methods. The materials were structurally characterized by single-crystal X-ray diffraction. Tl4CuTeO6 and Tl6CuTe2O10 exhibit one dimensional anionic slabs of [CuTeO6]4- and [CuTe2O10]6-, respectively. Common to both slabs is the occurrence of Cu2+O4 distorted squares and Te6+O6 octahedra. The slabs are separated by Tl+ cations. For Tl4CuTeO6, magnetic measurements indicate a maximum at ∼8 K in the temperature dependence of the susceptibility. Low temperature neutron diffraction data confirm no long-range magnetic ordering occurs and the susceptibility was adequately accounted for by fits to a Heisenberg alternating chain model. For Tl6CuTe2O10 on the other hand, magnetic measurements revealed paramagnetism with no evidence of long-range magnetic ordering. Infrared, UV-vis spectra, thermogravimetric, and differential thermal analyses are also reported. Crystal data: Tl4CuTeO6, Triclinic, space group P-1 (No. 2), a=5.8629(8) Å, b=8.7848(11) Å, c=9.2572(12) Å, α=66.0460(10), β=74.2010(10), γ=79.254(2), V=417.70(9) Å3, and Z=2; Tl6CuTe2O10, orthorhombic, space group Pnma (No. 62), a=10.8628(6) Å, b=11.4962(7) Å, c=10.7238(6) Å, V=1339.20(13) Å3, and Z=4.

Magnetic Control of the Light Reflection Anisotropy in a Biogenic Guanine Microcrystal Platelet.

PubMed

Iwasaka, Masakazu; Mizukawa, Yuri; Roberts, Nicholas W

2016-01-12

Bioinspired but static optical devices such as lenses, retarders, and reflectors have had a significant impact on the designs of many man-made optical technologies. However, while numerous adaptive and flexible optical mechanisms are found throughout the animal kingdom, highly desirable biomimetic copies of these remarkable smart systems remain, in many cases, a distant dream. Many aquatic animals have evolved highly efficient reflectors based on multilayer stacks of the crystallized nucleic acid base guanine. With exceptional levels of spectral and intensity control, these reflectors represent an interesting design pathway towards controllable micromirror structures. Here we show that individual guanine crystals, with dimensions of 5 μm × 20 μm × 70 nm, can be magnetically controlled to act as individual micromirrors. By applying magnetic fields of 500 mT, the reflectivity of these crystals can be switched off and on for the change in reflectivity. Overall, the use of guanine represents a novel design scheme for a highly efficient and controllable synthetic organic micromirror array.

Temperature and field induced strain measurements in single crystal Gd 5Si 2Ge 2

DOE PAGES

McCall, S. K.; Nersessian, N.; Carman, G. P.; ...

2016-03-29

The first-order magneto-structural transformation that occurs in Gd 5Si 2Ge 2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd 5Si 2.05Ge 1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of –8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of –8500 ppm, +900 ppm and +2300 ppm were measured along the a,more » b and c axes, respectively. Furthermore, using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.« less

Magneto-transport properties of Co3O4 nanoparticles added (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting phase

NASA Astrophysics Data System (ADS)

Mumtaz, M.; Baig, Mirza Hassan; Waqee-ur-Rehman, M.; Nasir Khan, M.

2018-05-01

Solid-state reaction method was used to synthesize Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase and sol-gel method was used to prepare cobalt oxide (Co3O4) magnetic nanoparticles. These Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223; x = 0-2.00 wt.% nanoparticles-superconductor composites. The effects of Co3O4 nanoparticles on crystal structure, phase formation, phase purity and infield superconducting transport properties of CuTl-1223 phase were investigated at different operating temperatures and external applied magnetic fields. The crystal structure and phase formation of Co3O4 nanoparticles and CuTl-1223 superconductor were determined by X-ray diffraction (XRD) technique. XRD peaks of Co3O4 nanoparticles were well indexed according to FCC crystal structure and the average particle size of 70 nm was calculated by using Debye-Scherer's formula. The unaltered crystal structure of host CuTl-1223 superconducting phase (i.e. Tetragonal) with the addition of Co3O4 nanoparticles indicated the dispersion of nanoparticles at inter-granular sites. Temperature dependent magneto-transport superconducting properties of (Co3O4)x/CuTl-1223 composites were investigated by zero field cooled (ZFC) and field cooled (FC) magnetic moment versus temperature (M-T) measurements. The onset transition temperatures {TcOnset (K)} was decreased along with the suppression of diamagnetic amplitude of CuTl-1223 superconducting phase with the addition of magnetic Co3O4 nanoparticles. Temperature dependent magnetic hysteresis (M-H loops) measurements of (Co3O4)x/CuTl-1223 composites were carried out at different operating temperatures from 5 K to 150 K. Critical current density (Jc) was calculated from M-H loops measurements by using Bean's model. Like the suppression of TcOnset (K) values, Jc was also decreased with the inclusion of Co3O4 nanoparticles. It was also observed that variation of Jc with H followed the power law Jc = βH-α at low operating temperatures 5 K and 20 K only.

Theoretical Prediction of Magnetism in C-doped TlBr

NASA Astrophysics Data System (ADS)

Zhou, Yuzhi; Haller, E. E.; Chrzan, D. C.

2014-05-01

We predict that C, N, and O dopants in TlBr can display large, localized magnetic moments. Density functional theory based electronic structure calculations show that the moments arise from partial filling of the crystal-field-split localized p states of the dopant atoms. A simple model is introduced to explain the magnitude of the moments.

Magnetic and magnetocaloric properties of spin-glass material DyNi 0.67Si 1.34

DOE PAGES

Chen, X.; Mudryk, Y.; Pathak, A. K.; ...

2017-04-18

Structural, magnetic, and magnetocaloric properties of DyNi 0.67Si 1.34 were investigated using X-ray powder diffraction, magnetic susceptibility, and magnetization measurements. X-ray powder diffraction pattern shows that DyNi 0.67Si 1.34 crystallizes in the AlB 2-type hexagonal structure (space group: P6/ mmm, No. 191, a = b = 3.9873(9) Å, and c = 3.9733(1) Å). The compound is a spin-glass with the freezing temperature TG = 6.2 K. The ac magnetic susceptibility measurements confirm magnetic frustration in DyNi 0.67Si 1.34. Furthermore, the maximum value of the magnetic entropy change determined from M(H) data is –16.1 J/kg K at 10.5 K for amore » field change of 70 kOe.« less

Comparative study of synthesis, structural and magnetic properties of Cu2+ substituted Co-Ni, Co-Zn and Co-Mg nano ferrites

NASA Astrophysics Data System (ADS)

Ramakrishna, A.; Murali, N.; Margarette, S. J.; Samatha, K.; Veeraiah, V.

2018-02-01

Mixed ferrites of the form Co0.5M0.1Cu0.4Fe2O4 (M = Ni, Zn and Mg) have been synthesized using the sol-gel auto combustion technique. Structural analyses are carried out using powder X-ray diffraction to idntify pure ferrite phases. SEM analysis revealed clear crystal morphology with relatively uniform grain sizes with polygonal structures. The FT-IR studies also confirm the bond formation and cation vibrations at low (365-392 cm-1) and high (579-587 cm-1) bands that correspond to the tetrahedral and octahedral sites, respectively. The magnetic properties studied through vibrating sample magnetometer showed that the Ni substituted sample has more magnetic character by exhibiting the highest saturation magnetization.

Structural, magnetic and magnetocaloric properties of EuMnO3 perovskite manganite: A comprehensive MCE study

NASA Astrophysics Data System (ADS)

Phebe Kokila, I.; Kanagaraj, M.; Sathish Kumar, P.; Peter, Sebastian C.; Sekar, C.; Annal Therese, Helen

2018-02-01

Pervoskite manganite EuMnO3 synthesized by solid-state route was studied for their structural and magnetocaloric properties. EuMnO3 formed a single phase compound in orthorhombic crystal structure with a space group of Pbnm. The zero field cooling and field cooling magnetic responses exhibit an optimal Neel temperature (TN) of 57 K. A stronger magnetic coupling between the EuMnO3 particles are observed by a delay in reaching TN. The magnetocaloric effect analyzed extensively from the negative entropy (-ΔSm) change of 15.23 JKg-1K-1 for EuMnO3, exhibited a Relative Cooling Power (RCP) of ˜211 JKg-1 at 1.2 T proposing EuMnO3 as a potential magnetic refrigerant.

Synthesis, growth, structural characterization, Hirshfeld analysis and nonlinear optical studies of a methyl substituted chalcone

NASA Astrophysics Data System (ADS)

Prabhu, Shobha R.; Jayarama, A.; Chandrasekharan, K.; Upadhyaya, V.; Ng, Seik Weng

2017-05-01

A new chalcone compound (2E)-3-(3-methylphenyl)-1-(4-nitrophenyl)prop-2-en-1-one (3MPNP) with molecular formula C16H13NO3 has been synthesized and crystallized by slow solvent evaporation technique. The Fourier transform infrared, Fourier transform Raman and nuclear magnetic resonance techniques were used for structural characterization. UV-visible absorption studies were carried out to study the transparency of the crystal in the visible region. Differential scanning calorimetry study shows thermal stability of crystals up to temperature 122 °C. Single crystal X-ray diffraction and powder X-ray diffraction techniques were used to study crystal structure and cell parameters. The Hirshfeld surface and 2-D fingerprint analysis were performed to study the nature of interactions and their quantitative contributions towards the crystal packing. The third order non-linear optical properties have been studied using single beam Z-scan technique and the results show that the material is a potential candidate for optical device applications such as optical limiters and optical switches.

Single crystal growth of spin-ladder compound La8Cu7O19 by the travelling-solvent floating zone method

NASA Astrophysics Data System (ADS)

Mohan, A.; Singh, S.; Partzsch, S.; Zwiebler, M.; Geck, J.; Wurmehl, S.; Büchner, B.; Hess, C.

2016-08-01

Large single crystals of La8Cu7O19 have been grown using the travelling-solvent floating zone method. A rather high oxygen pressure of 9 bar in the growth chamber and a slow growth speed of 0.5 mm/h were among the most important parameters in stabilizing the growth of this incongruently melting compound. Interestingly, a novel growth scenario has been witnessed. The crystal structure of the grown La8Cu7O19 crystal has been analyzed using single crystal diffractometry to extract important structural parameters of this compound. We find that La8Cu7O19 crystallizes in a monoclinic structure with space group C 2 / c and has the lattice parameters a ≈ 13.83 Å, b ≈ 3.75 Å, c ≈ 34.59 Å, and β ≈ 99.33 °, in good agreement with the data obtained on polycrystalline samples in the literature. The magnetization shows a highly anisotropic behavior, and an anomaly at T ≈103 K.

The annealing temperature dependences of microstructures and magnetic properties in electro-chemical deposited CoNiFe thin films

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

Suharyadi, Edi, E-mail: esuharyadi@ugm.ac.id; Riyanto, Agus; Abraha, Kamsul

2016-04-19

CoNiFe thin films with various compositions had been successfully fabricated using electro-chemical deposition method. The crystal structure of Co{sub 65}Ni{sub 15}Fe{sub 20}, Co{sub 62}Ni{sub 15}Fe{sub 23}, and Co{sub 55}Ni{sub 15}Fe{sub 30} thin films was fcc, bcc-fcc mix, and bcc, respectively. The difference crystal structure results the difference in magnetic properties. The saturation magnetic flux density (Bs) of Co{sub 65}Ni{sub 15}Fe{sub 20}, Co{sub 62}Ni{sub 15}Fe{sub 23}, and Co{sub 55}Ni{sub 15}Fe{sub 30} thin films was 1.89 T, 1.93 T, and 2.05 T, respectively. An optimal annealing temperature was determined for controlling the microstructure and magnetic properties of CoNiFe thin films. Depending onmore » annealing temperature, the ratio of bcc and fcc structure varied without changing the film composition. By annealing at temperature of T ≥ 350°C, the intensity ratio of X-ray diffraction peaks for bcc(110) to fcc(111) increased. The increase of phase ratio of bcc(110) to fcc(111) caused the increase of Bs, from 1.89 T to 1.95 T. Coercivity (Hc) also increased after annealing, from 2.6 Oe to 18.6 Oe for fcc phase thin films, from 2.0 Oe to 12.0 Oe for fcc-bcc mix phase thin films, and 7.8 Oe to 8 Oe for bcc phase thin films. The changing crystal structures during annealing process indicated that the thermal treatment at high temperature cause the changing crystallinity and atomic displacement. The TEM bright-field images with corresponding selected-area electron diffraction (SAED) patterns showed that there are strongly effects of thermal annealing on the size of fcc and bcc phase crystalline grain as described by size of individual spot and discontinuous rings. The size of crystalline grains increased by thermal annealing. The evolution of bcc and fcc structures of CoNiFe during annealing is though to be responsible for the change of magnetic properties.« less

Giant crystal-electric-field effect and complex magnetic behavior in single-crystalline CeRh3Si2

NASA Astrophysics Data System (ADS)

Pikul, A. P.; Kaczorowski, D.; Gajek, Z.; Stȩpień-Damm, J.; Ślebarski, A.; Werwiński, M.; Szajek, A.

2010-05-01

Single-crystalline CeRh3Si2 was investigated by means of x-ray diffraction, magnetic susceptibility, magnetization, electrical resistivity, and specific-heat measurements carried out in wide temperature and magnetic field ranges. Moreover, the electronic structure of the compound was studied at room temperature by cerium core-level x-ray photoemission spectroscopy (XPS). The physical properties were analyzed in terms of crystalline electric field and compared with results of ab initio band-structure calculations performed within the density-functional theory approach. The compound was found to crystallize in the orthorhombic unit cell of the ErRh3Si2 type (space group Imma No.74, Pearson symbol: oI24 ) with the lattice parameters a=7.1330(14)Å , b=9.7340(19)Å , and c=5.6040(11)Å . Analysis of the magnetic and XPS data revealed the presence of well-localized magnetic moments of trivalent cerium ions. All the physical properties were found to be highly anisotropic over the whole temperature range studied and influenced by exceptionally strong crystalline electric field with the overall splitting of the 4f1 ground multiplet exceeding 5700 K. Antiferromagnetic order of the cerium magnetic moments at TN=4.70(1)K and their subsequent spin rearrangement at Tt=4.48(1)K manifest themselves as distinct anomalies in the temperature characteristic of all the physical properties investigated and exhibit complex evolution in an external magnetic field. A tentative magnetic B-T phase diagram, constructed for B parallel to the b axis being the easy magnetization direction, shows very complex magnetic behavior of CeRh3Si2 , similar to that recently reported for an isostructural compound CeIr3Si2 . The electronic band-structure calculations corroborated the antiferromagnetic ordering of the cerium magnetic moments and well-reproduced the experimental XPS valence-band spectrum.