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Sample records for incommensurate magnetic structure

  1. Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2

    NASA Astrophysics Data System (ADS)

    Makino, Koya; Okuyama, Daisuke; Avdeev, Maxim; Sato, Taku J.

    2016-07-01

    Magnetic susceptibility and neutron powder diffraction experiments have been performed on the noncentrosymmetric ternary compound Pr5Ru3Al2. The previously reported ferromagnetic transition at 24 K was not detected in our improved-quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at T{c} ≃ 3.8 K. The neutron powder diffraction experiment further indicates that an incommensurate magnetic structure is established below Tc with the magnetic modulation vector {{q}} ≃ (0.066,0.066,0.066) (r.l.u.). A candidate for the magnetic structure is proposed using representation analysis.

  2. Incommensurate magnetic structure in the orthorhombic perovskite ErMnO3

    NASA Astrophysics Data System (ADS)

    Ye, F.; Lorenz, B.; Huang, Q.; Wang, Y. Q.; Sun, Y. Y.; Chu, C. W.; Fernandez-Baca, J. A.; Dai, Pengcheng; Mook, H. A.

    2007-08-01

    By combining dielectric, specific heat, and magnetization measurements and high-resolution neutron powder diffraction, we have investigated the thermodynamic and magnetic and structural properties of the metastable orthorhombic perovskite ErMnO3 prepared by high-pressure synthesis. The system becomes antiferromagnetically correlated below 42K and undergoes a lock-in transition at 28K with propagation wave vector (0,kb,0) , which remains incommensurate at low temperature. The intercorrelation between the magnetic structure and electric properties and the role of the rare earth moment are discussed.

  3. Incommensurate and commensurate magnetic structures of the ternary germanide CeNiGe3

    NASA Astrophysics Data System (ADS)

    Durivault, L.; Bourée, F.; Chevalier, B.; André, G.; Weill, F.; Etourneau, J.; Martinez-Samper, P.; Rodrigo, J. G.; Suderow, H.; Vieira, S.

    2003-01-01

    The structural properties of CeNiGe3 have been investigated via electron diffraction and neutron powder diffraction (NPD). This ternary germanide crystallizes in the orthorhombic SmNiGe3-type structure (Cmmm space group). Electrical resistivity, ac- and dc-magnetization measurements show that CeNiGe3 orders antiferromagnetically below TN = 5.5(2) K and exclude the occurrence at low temperatures of a spin-glass state for CeNiGe3 as previously reported. Specific heat measurements and NPD both reveal two magnetic transitions, observed at TN1 = 5.9(2) K and TN2 = 5.0(2) K. Between TN1 and TN2, the Ce magnetic moments in CeNiGe3 are ordered in a collinear antiferromagnetic structure associated with the k1 = (100) wavevector and showing a relationship with the magnetic structure of the Ce3Ni2Ge7 ternary germanide. Below TN2, this k1 = (100) commensurate magnetic structure coexists with an incommensurate helicoîdal magnetic structure associated with k2 = (00.409(1)1/2). This last magnetic structure is highly preponderant below TN2 (93(5)% in volume). At 1.5 K, the Ce atoms in CeNiGe3 carry a reduced ordered magnetic moment (0.8(2) muB). This value, smaller than that obtained in Ce3Ni2Ge7, results from an important hybridization of the 4f(Ce) orbitals with those of the Ni and Ge ligands.

  4. The incommensurate magnetic structure of Er3Cu4Ge4below 1 K

    NASA Astrophysics Data System (ADS)

    Cadogan, J. M.; Ryan, D. H.; Cranswick, L. M. D.

    2010-01-01

    The magnetic structure of Er3Cu4Ge4 was previously studied down to 1.5 K by Wawrzyńska et al. who found that the Er(2d) sublattice orders at 8 K in a commensurate, doubled structure (kd = [0 1/2 0]) with an Er moment close to the free-ion value of 9 μB. By contrast, the Er(4e) sublattice ordered at 3.5 K in an incommensurate structure (ke = [0 0.883(2) 0]) with a greatly reduced moment (about one-third of the free-ion value). We have extended this study by high-resolution neutron powder diffraction down to 0.34 K in an effort to establish if the Er(4e) sublattice eventually locks-in and attains its free-ion moment (in keeping with our 166Er Mössbauer work). We observed a change in the Er(4e) order, beginning at 1.4 K, leading to a magnetic structure at 0.34 K which has almost locked-in but with (ke = [0.1 2/3 0]) and a still-reduced Er moment.

  5. Incommensurate magnetic structure, Fe/Cu chemical disorder, and magnetic interactions in the high-temperature multiferroic YBaCuFeO 5

    NASA Astrophysics Data System (ADS)

    Morin, M.; Scaramucci, A.; Bartkowiak, M.; Pomjakushina, E.; Deng, G.; Sheptyakov, D.; Keller, L.; Rodriguez-Carvajal, J.; Spaldin, N. A.; Kenzelmann, M.; Conder, K.; Medarde, M.

    2015-02-01

    Motivated by the recent observations of incommensurate magnetic order and electric polarization in YBaCuFeO5 up to temperatures TN 2 as high as 230 K [B. Kundys et al., Appl. Phys. Lett. 94, 072506 (2009), 10.1063/1.3086309; Y. Kawamura et al., J. Phys. Soc. Jpn 79, 073705 (2010), 10.1143/JPSJ.79.073705], we report here for the first time a model for the incommensurate magnetic structure of this material, which we complement with ab initio calculations of the magnetic exchange parameters. Using neutron powder diffraction, we show that the appearance of polarization below TN 2 is accompanied by the replacement of the high-temperature collinear magnetic order by a circular inclined spiral with propagation vector ki=(1 /2 ,1 /2 ,1 /2 ±q ). Moreover, we find that the polarization approximately scales with the modulus of the magnetic modulation vector q down to the lowest temperature investigated (˜3 K). Further, we observe occupational Fe/Cu disorder in the FeO5-CuO5 bipyramids, although a preferential occupation of such units by Fe-Cu pairs is supported by the observed magnetic order and by density functional calculations. We calculate exchange coupling constants for different Fe/Cu distributions and show that, for those containing Fe-Cu dimers, the resulting magnetic order is compatible with the experimentally observed collinear magnetic structure [ kc=(1 /2 ,1 /2 ,1 /2 ) ,TN 2>T >TN 1=440 K]. Based on these results, we discuss possible origins for the incommensurate modulation and its coupling with ferroelectricity.

  6. From ferromagnetism to incommensurate magnetic structures: A neutron diffraction study of the chemical substitution effects in TbPt1-xCux

    NASA Astrophysics Data System (ADS)

    Señas, A.; Rodríguez Fernández, J.; Gómez Sal, J. C.; Campo, J.; Rodríguez-Carvajal, J.

    2004-11-01

    We report the magnetic structures of the TbPt1-xCux system obtained by means of neutron diffraction experiments. Symmetry analyses have been carried out for the R3+ magnetic site. The compounds with copper concentrations x<0.3 present the same magnetic structure than the extreme TbPt, which is of noncollinear ferromagnetic type, -CxFz ; on the contrary, for copper concentrations 0.3incommensurate amplitude-modulated structures in which the moment modulus varies sinusoidally with a propagation vector along the b -axis. For concentrations x>0.5 , the propagation vector lies in the ac -plane being the structure also amplitude-modulated. For the intermediate compound, TbPt0.7Cu0.3 , we observe an evolution from an amplitude-modulated incommensurate structure to a noncollinear commensurate one, -CxFz , that remains stable down to very low temperatures. The different kinds of magnetic ordering in the TbPt1-xCux series, along which the volume remains constant, are discussed in terms of the competition between RKKY interactions and magneto-crystalline anisotropy, and they are compared to those observed in TbNi1-xCux .

  7. Complex incommensurate helicoidal magnetic ordering of EuNiGe3

    NASA Astrophysics Data System (ADS)

    Ryan, D. H.; Cadogan, J. M.; Rejali, Rasa; Boyer, C. D.

    2016-07-01

    151Eu Mössbauer spectroscopy and neutron powder diffraction are combined to show that the tetragonal (I4mm #107) compound EuNiGe3 orders magnetically below {{T}\\text{N}}∼ 14 K and adopts a complex incommensurate helicoidal magnetic structure at 3.6 K, with a propagation vector \\mathbf{k}=≤ft[0.255(1),~0.054(14),~0\\right] and a Eu moment of 7.1(2) {μ\\text{B}} . On warming through 6 K an incommensurate sinusoidal modulation develops and dominates the magnetic order by 12 K.

  8. Detailed structure of the low-energy magnetic dispersion of the diagonal incommensurate phase in La1.975Sr0.025CuO4

    NASA Astrophysics Data System (ADS)

    Matsuda, M.; Fernandez-Baca, J. A.; Fujita, M.; Yamada, K.; Tranquada, J. M.

    2011-09-01

    Inelastic neutron scattering experiments have been performed on lightly doped La1.975Sr0.025CuO4, which contains a hole concentration slightly higher than the critical concentration for three-dimensional long-range antiferromagnetic order. We previously found that the magnetic excitation spectrum in the insulating phase with a diagonal incommensurate spin modulation has similarities to that in the superconducting regime, where the spin modulation is bond parallel. In this study, we investigate the excitations in detail around Ecross, at which the excitations become most nearly commensurate. It is found that both the magnitude and the anisotropy of the momentum width of the excitations change abruptly at Ecross. Our experimental results suggest that the magnetic excitations rising from the pair of (diagonally) incommensurate wave vectors merge at Ecross into isotropic excitations.

  9. NMR determination of an incommensurate helical antiferromagnetic structure in EuCo2As2

    DOE PAGES

    Ding, Q. -P.; Higa, N.; Sangeetha, N. S.; ...

    2017-05-05

    In this paper, we report 153Eu, 75As, and 59Co nuclear magnetic resonance (NMR) results on EuCo2As2 single crystal. Observations of 153Eu and 75As NMR spectra in zero magnetic field at 4.3 K below an antiferromagnetic (AFM) ordering temperature TN = 45 K and its external magnetic field dependence clearly evidence an incommensurate helical AFM structure in EuCo2As2. Furthermore, based on 59Co NMR data in both the paramagnetic and the incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73 ± 0.07)2π/c, where c is the c lattice parameter. Finally, the incommensurate helical AFMmore » state was characterized by only NMR data with model-independent analyses, showing NMR to be a unique tool for determination of the spin structure in incommensurate helical AFMs.« less

  10. Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model.

    PubMed

    Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter

    2016-03-04

    We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Néel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.

  11. Synthesis, Crystal Structure, and Magnetic Properties of Sr1.31Co0.63Mn0.37O3: A Derivative of the Incommensurate Composite Hexagonal Perovskite Structure

    SciTech Connect

    Mandal,T.; Abakumov, A.; Hadermann, J.; Van Tendeloo, G.; Croft, M.; Greenblatt, M.

    2007-01-01

    We report the synthesis, structural investigation, and magnetic property studies of Sr1.31Co0.63Mn0.37O3 that adopts an incommensurate composite hexagonal perovskite-related structure. The crystal structure has been solved using a (3 + 1)-dimensional superspace approach from powder X-ray and neutron diffraction data (SSG Rm(00 )0s, a = 9.5548(1) Angstroms, c = 2.5599(1) Angstroms, q = 0.65581(4)c*, RB = 0.041, RP = 0.059). The structure consists of face-sharing chains of octahedra and trigonal prisms, wherein the trigonal prismatic sites are preferentially occupied by Co with some cation disorder. A combination of electron diffraction and high-resolution electron microscopic analysis has demonstrated that the compound possesses a complicated microstructure related to the formation of domains with slightly different lengths of the modulation vector. X-ray absorption near-edge spectroscopic (XAS) studies clearly indicate the presence of Mn in the 4+ and Co in the 3+ oxidation state. While the magnetic susceptibility data indicates the presence of antiferromagnetic correlations in the system, the calculation of effective paramagnetic moment ({mu}cal = 3.561 {mu}B), assuming the metal oxidation states as obtained from XAS and the cation distribution as obtained from neutron refinement, is in agreement with the value obtained experimentally ({mu}exp = 3.676 {mu}B).

  12. Direct observation of incommensurate structure in Mo3Si.

    PubMed

    Gulec, Ahmet; Yu, Xiaoxiang; Taylor, Matthew; Perepezko, John H; Marks, Laurence

    2016-11-01

    Z-contrast imaging, electron diffraction, atom-probe tomography (APT) and density functional theory calculations were used to study the crystal structure of the Mo3Si phase which was previously reported to have an A15 crystal structure. The results showed that Mo3Si has an incommensurate crystal structure with a non-cubic unit cell. The small off-stoichiometry in composition of the sample which was revealed by APT and atomic resolution Z-contrast imaging suggested that site substitution caused the development of split atomic positions, disorder and vacancies.

  13. New type of incommensurate magnetic ordering in Mn{sub 3}TeO{sub 6}

    SciTech Connect

    Ivanov, S.A.; Nordblad, P.; Mathieu, R.; Tellgren, R.; Ritter, C.; Golubko, N.V.; Politova, E.D.; Weil, M.

    2011-11-15

    Highlights: {yields} Mn{sub 3}TeO{sub 6} has a corundum related structure and orders magnetically below 23 K. {yields} The magnetic structure consists of several types of Mn-chains. {yields} The unique Mn site is split into two magnetically different orbits. {yields} One orbit forms a perfect helix with the spiral axis along the c-axis. {yields} The other orbit has a sine wave character along the c-axis. -- Abstract: The complex metal oxide Mn{sub 3}TeO{sub 6} exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R3{sup -bar} with a = 8.8679(1) A, c = 10.6727(2) A. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis.

  14. Incommensurate-commensurate magnetic phase transition in SmRu2Al10

    NASA Astrophysics Data System (ADS)

    Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi

    2015-11-01

    Magnetic properties of single crystalline SmRu2Al10 have been investigated by electrical resistivity, magnetic susceptibility, and specific heat. We have confirmed the successive magnetic phase transitions at TN=12.3 K and TM=5.6 K. Resonant x-ray diffraction has also been performed to study the magnetic structures. Below TN, the Sm3 + moments order in an incommensurate structure with q1=(0 ,0.759 ,0 ) . The magnetic moments are oriented along the orthorhombic b axis, which coincides with the magnetization easy axis in the paramagnetic phase. A very weak third harmonic peak is also observed at q3=(0 ,0.278 ,0 ) . The transition at TM is a lock-in transition to the commensurate structure described by q1=(0 ,0.75 ,0 ) . A well-developed third harmonic peak is observed at q3=(0 ,0.25 ,0 ) . From the discussion of the magnetic structure, we propose that the long-range RKKY interaction plays an important role, in addition to the strong nearest-neighbor antiferromagnetic interaction.

  15. Complex magnetic incommensurability and electronic charge transfer through the ferroelectric transition in multiferroic Co3TeO6.

    PubMed

    Lee, Chi-Hung; Wang, Chin-Wei; Zhao, Yang; Li, Wen-Hsien; Lynn, Jeffrey W; Harris, A Brooks; Rule, Kirrily; Yang, Hung-Duen; Berger, Helmuth

    2017-07-25

    Polarized and unpolarized neutron diffractions have been carried out to investigate the nature of the magnetic structures and transitions in monoclinic Co3TeO6. As the temperature is lowered below 26 K long range order develops, which is fully incommensurate (ICM) in all three crystallographic directions. Below 19.5 K additional commensurate magnetic peaks develop, consistent with the Γ4 irreducible representation, along with a splitting of the ICM peaks along the h direction which indicates that there are two separate sets of magnetic modulation vectors. Below 18 K, this small additional magnetic incommensurability disappears, ferroelectricity develops, an additional commensurate magnetic structure consistent with Γ3 irreducible representation appears, and the k component of the ICM wave vector disappears. Synchrotron x-ray diffraction measurements demonstrate that there is a significant shift of the electronic charge distribution from the Te ions at the crystallographic 8 f sites to the neighboring Co and O ions. These results, together with the unusually small electric polarization, its strong magnetic field dependence, and the negative thermal expansion in all three lattice parameters, suggest this material is an antiferroelectric. Below15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin.

  16. Topological incommensurate magnetization plateaus in quasi-periodic quantum spin chains.

    PubMed

    Hu, Hai-Ping; Cheng, Chen; Luo, Hong-Gang; Chen, Shu

    2015-02-13

    Uncovering topologically nontrivial states in nature is an intriguing and important issue in recent years. While most studies are based on the topological band insulators, the topological state in strongly correlated low-dimensional systems has not been extensively explored due to the failure of direct explanation from the topological band insulator theory on such systems and the origin of the topological property is unclear. Here we report the theoretical discovery of strongly correlated topological states in quasi-periodic Heisenberg spin chain systems corresponding to a series of incommensurate magnetization plateaus under the presence of the magnetic field, which are uniquely determined by the quasi-periodic structure of exchange couplings. The topological features of plateau states are demonstrated by the existence of non-trivial spin-flip edge excitations, which can be well characterized by nonzero topological invariants defined in a two-dimensional parameter space. Furthermore, we demonstrate that the topological invariant of the plateau state can be read out from a generalized Streda formula and the spin-flip excitation spectrum exhibits a similar structure of the Hofstadter's butterfly spectrum for the two-dimensional quantum Hall system on a lattice.

  17. Topological incommensurate magnetization plateaus in quasi-periodic quantum spin chains

    PubMed Central

    Hu, Hai-Ping; Cheng, Chen; Luo, Hong-Gang; Chen, Shu

    2015-01-01

    Uncovering topologically nontrivial states in nature is an intriguing and important issue in recent years. While most studies are based on the topological band insulators, the topological state in strongly correlated low-dimensional systems has not been extensively explored due to the failure of direct explanation from the topological band insulator theory on such systems and the origin of the topological property is unclear. Here we report the theoretical discovery of strongly correlated topological states in quasi-periodic Heisenberg spin chain systems corresponding to a series of incommensurate magnetization plateaus under the presence of the magnetic field, which are uniquely determined by the quasi-periodic structure of exchange couplings. The topological features of plateau states are demonstrated by the existence of non-trivial spin-flip edge excitations, which can be well characterized by nonzero topological invariants defined in a two-dimensional parameter space. Furthermore, we demonstrate that the topological invariant of the plateau state can be read out from a generalized Streda formula and the spin-flip excitation spectrum exhibits a similar structure of the Hofstadter's butterfly spectrum for the two-dimensional quantum Hall system on a lattice. PMID:25678145

  18. Localized electrons on a lattice with incommensurate magnetic flux

    NASA Astrophysics Data System (ADS)

    Fishman, Shmuel; Shapir, Yonathan; Wang, Xiang-Rong

    1992-11-01

    The magnetic-field effects on lattice wave functions of Hofstadter electrons strongly localized at boundaries are studied analytically and numerically. The exponential decay of the wave function is modulated by a field-dependent amplitude J(t)=tprodt-1r=02 cos(παr), where α is the magnetic flux per plaquette (in units of a flux quantum) and t is the distance from the boundary (in units of the lattice spacing). The behavior of ||J(t)|| is found to depend sensitively on the value of α. While for rational values α=p/q the envelope of J(t) increases as 2t/q, the behavior for α irrational (q-->∞) is erratic with an aperiodic structure which drastically changes with α. For algebraic α it is found that J(t) increases as a power law tβ(α) while it grows faster (presumably as tβ(α)lnt) for transcendental α. This is very different from the growth rate J(t)~e√t that is typical for cosines with random phases. The theoretical analysis is extended to products of the type Jν(t)=tprodt-1r=02 cos(παrν) with ν>0. Different behavior of Jν(t) is found in various regimes of ν. It changes from periodic for small ν to randomlike for large ν.

  19. Incommensurate magnetism in non-superconducting PrBa{sub 2}Cu{sub 3}O{sub 6.92}

    SciTech Connect

    Boothroyd, A.T.; Hill, J.P.; McMorrow, D.F.; Andersen, N.H.; Stunault, A.; Vettier, C.; Wolf, T.

    1998-12-31

    The authors report the discovery of incommensurate magnetic order in non-superconducting single crystals PrBa{sub 2}Cu{sub 3}O{sub 6.92}. Resonant x-ray magnetic scattering at the Pr L{sub II} and L{sub III} edges and high resolution neutron diffraction were used to characterize the magnetic order on the different magnetic sublattices. The data reveal that the Pr sublattice orders at a temperature of 19 K in an incommensurate structure with ordering wavevector (0.5 {+-} {delta}, 0.5, 0) or (0.5, 0.5 {+-} {delta}, p), {delta} {approx} 0.006--0.008. A spin reorientation in the Pr sublattice to a commensurate antiferromagnetic structures with ordering wavevector (0.5, 0.5, 0.5) takes place at a temperature close to 9 K.

  20. Incommensurate magnetism in PrBa{sub 2}Cu{sub 3}O{sub 6.92}

    SciTech Connect

    Hill, J.P.; Boothroyd, A.T.; Andersen, N.H.; Wolf, T.

    1998-11-01

    We report resonant x-ray magnetic scattering and high-resolution neutron-diffraction studies of the Pr site magnetism in high quality single crystals of PrBa{sub 2}Cu{sub 3}O{sub 6.92}. These studies reveal that the Pr sublattice orders at 19thinspK in a well correlated, long period incommensurate structure with probable wave vector (0.5{plus_minus}{delta},0.5,0) or (0.5,0.5{plus_minus}{delta},0) with {delta}=0.006 r.l.u. The observed x-ray scattering results from dipole transitions, demonstrating the existence of an ordered 5d Pr moment and implying a large 4f moment at the Pr site. A spin reorientation transition to a commensurate antiferromagnetic structure of wave vector (0.5,0.5,0.5) is observed at lower temperatures. {copyright} {ital 1998} {ital The American Physical Society}

  1. Low temperature incommensurately modulated and noncollinear spin structure in FeCr2S4.

    PubMed

    Kalvius, G M; Krimmel, A; Hartmann, O; Wäppling, R; Wagner, F E; Litterst, F J; Tsurkan, V; Loidl, A

    2010-02-10

    FeCr(2)S(4) orders magnetically at T(N)≈ 170 K. According to neutron diffraction, the ordered state down to 4.2 K is a simple collinear ferrimagnet maintaining the cubic spinel structure. Later studies, however, claimed trigonal distortions below ∼ 60 K coupled to the formation of a spin glass type ground state. To obtain further insight, muon spin rotation/relaxation (μSR) spectroscopy was carried out between 5 and 200 K together with new (57)Fe Mössbauer measurements. Below ∼ 50 K, our data point to the formation of an incommensurately modulated noncollinear spin arrangement like a helical spin structure. Above 50 K, the spectra are compatible with collinear ferrimagnetism, albeit with a substantial spin disorder on the scale of a few lattice constants. These spin lattice distortions become very large at 150 K and the magnetic state is now better characterized as consisting of rapidly fluctuating short-range ordered spins. The Néel transition is of second order, but ill defined, extending over a range of ∼ 10 K. The Mössbauer data around 10 K confirm the onset of orbital freezing and are also compatible with the noncollinear order of iron. The absence of a major change in the quadrupole interaction around 50 K renders the distortion of crystal symmetry to be small.

  2. Incommensurate magnetic order in Ag2NiO2 studied with muon-spin-rotation and relaxation spectroscopy

    NASA Astrophysics Data System (ADS)

    Sugiyama, J.; Ikedo, Y.; Mukai, K.; Brewer, J. H.; Ansaldo, E. J.; Morris, G. D.; Chow, K. H.; Yoshida, H.; Hiroi, Z.

    2006-06-01

    The nature of the magnetic transition of the half-filled triangular antiferromagnet Ag2NiO2 with TN=56K was studied with positive muon-spin-rotation and relaxation (μ+SR) spectroscopy. Zero field μ+SR measurements indicate the existence of a static internal magnetic field at temperatures below TN . Two components with slightly different precession frequencies and wide internal-field distributions suggest the formation of an incommensurate antiferromagnetic order below 56K . This implies that the antiferromagnetic interaction is predominant in the NiO2 plane in contrast to the case of the related compound NaNiO2 . An additional transition was found at ˜22K by both μ+SR and susceptibility measurements. It was also clarified that the transition at ˜260K observed in the susceptibility of Ag2NiO2 is induced by a purely structural transition.

  3. Incommensurate spin-density wave and magnetic lock-in transition in CaFe{sub 4}As{sub 3}.

    SciTech Connect

    Manuel, P.; Chapon, L. C.; Todorov, I. S.; Chung, D. Y.; Castellan, J.-P.; Rosenkranz, S.; Osborn, R.; Toledano, P.; Kanatzidis, M. G.; Materials Science Division; Rutherford Appleton Lab.; Univ. of Picardie; Northwestern Univ.

    2010-05-01

    The magnetic structure for the recently synthesized iron-arsenide compound CaFe4As3 has been studied by neutron-powder diffraction. Long-range magnetic order is detected below 85 K, with an incommensurate modulation described by the propagation vector k=(0,?,0), ??0.39. Below ?25 K, our measurements detect a first-order phase transition where ? locks into the commensurate value 3/8. A model of the magnetic structure is proposed for both temperature regimes, based on Rietveld refinements of the powder data and symmetry considerations. The structures correspond to longitudinal spin-density waves with magnetic moments directed along the b axis. A Landau analysis captures the change in thermodynamic quantities observed at the two magnetic transitions, in particular, the drop in resistivity at the lock-in transition.

  4. Incommensurate host-guest structures in compressed elements: Hume—Rothery effects as origin

    NASA Astrophysics Data System (ADS)

    Degtyareva, V. F.

    2015-11-01

    Discovery of the incommensurate structure in the element Ba under pressure 15 years ago was followed by findings of a series of similar structures in other compressed elements. Incommensurately modulated structures of the host-guest type consist of a tetragonal host structure and a guest structure. The guest structure forms chains of atoms embedded in the channels of host atoms so that the axial ratio of these subcells along the c axis is not rational. Two types of the host-guest structures have been found so far: with the host cells containing 8 atoms and 16 atoms; in these both types the guest cells contain 2 atoms. These crystal structures contain a non-integer number of atoms in their unit cell: tI11* in Bi, Sb, As, Ba, Sr, Sc and tI19* in Na, K, Rb. We consider here a close structural relationship of these host-guest structures with the binary alloy phase Au3Cd5-tI32. This phase is related to the family of the Hume-Rothery phases that is stabilized by the Fermi sphere-Brillouin zone interaction. From similar considerations for alkali and alkaline-earth elements a necessary condition for structural stability emerges in which the valence electrons band overlaps with the upper core electrons and the valence electron count increases under compression.

  5. Incommensurate modulated structure study of a Cu-Zn-Al-Zr phase

    SciTech Connect

    Chung, C.Y.; Zou, W.H.; Han, X.D.; Lam, C.W.H.; Lai, J.K.L.; Gao, M.; Duan, X.F.

    1998-09-18

    Zr was added to Cu-Zn-Al shape memory alloy as a grain refinement element. There are two new phases, Cu{sub 50.2}Zr{sub 24.6}Al{sub 17.3}Zn{sub 7.9} (at%) (Z{sub 1} phase) and Cu{sub 57.4}Zr{sub 20.4}Zn{sub 10.3}Al{sub 11.9} (at%) (Z{sub 2}) phase is studied in detail in the present paper. The results of electron diffraction and high-resolution electron microscopy (HREM) investigations indicated a one-dimensional incommensurate modulated structure in the Z{sub 2} phase. The average structure of the phase is base-centered orthorhombic. The systematic reflection conditions associated with the main and satellite reflections demonstrate that the Bravais class of the Z{sub 2} phases is P{sub 11{bar 1}}{sup Cmmm} type in a (3 + 1) dimensional space for the incommensurate modulated structure. The substitution modulation effects of the Al and Zr elements are revealed by energy-filtered transmission electron microscopy (EFTEM), {l_brace}1{bar 3}{bar 2}{r_brace} compound-type twins are observed in the Z{sub 2} phase. The relationship between the Z{sub 1} and Z{sub 2} phases in the alloy is discussed.

  6. Incommensurability and Multiple Models: Representations of the Structure of Matter in Undergraduate Chemistry Students

    ERIC Educational Resources Information Center

    Flores-Camacho, Fernando; Gallegos-Cazares, Leticia; Garritz, Andoni; Garcia-Franco, Alejandra

    2007-01-01

    The notion of incommensurability has provided a rationality criterion for the development of scientific theories, as well as some insight into theories developed by students while learning science. However, the relationship between the multiple models held by students and incommensurability requires further discussion. We present the results of…

  7. Interlayer coupling in commensurate and incommensurate bilayer structures of transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Wang, Zhan; Yao, Wang; Liu, Gui-Bin; Yu, Hongyi

    2017-03-01

    The interlayer couplings in commensurate and incommensurate bilayer structures of transition-metal dichalcogenides are investigated with perturbative treatment. The interlayer coupling in ±K valleys can be decomposed into a series of hopping terms with distinct phase factors. In H-type and R-type commensurate bilayers, the interference between the three main hopping terms leads to a sensitive dependence of the interlayer coupling strength on the translation that can explain the position dependent local band gap modulation in a heterobilayer moiré superlattice. The interlayer couplings in the Γ valley of valence band and Q valley of conduction band are also studied, where the strong coupling strengths of several hundred meV can play important roles in mediating the ultrafast interlayer charge transfer in heterobilayers of transition-metal dichalcogenides.

  8. Magnetic dispersion of the diagonal incommensurate phase in lightly doped La2-xSrxCuO4.

    PubMed

    Matsuda, M; Fujita, M; Wakimoto, S; Fernandez-Baca, J A; Tranquada, J M; Yamada, K

    2008-11-07

    We present inelastic neutron scattering experiments on a single-domain crystal of lightly doped La1.96Sr0.04CuO4. We find that the magnetic excitation spectrum in this insulating phase with a diagonal incommensurate spin modulation is remarkably similar to that in the superconducting regime, where the spin modulation is bond parallel. In particular, we find that the dispersion slope at low energy is essentially independent of doping and temperature over a significant range. The energy at which the excitations cross the commensurate antiferromagnetic wave vector increases roughly linearly with doping through the underdoped regime.

  9. Pseudogap and Incommensurate Magnetic Fluctuations in YBa{sub 2}Cu{sub 3}O{sub 6.6}

    SciTech Connect

    Dai, P., Mook, H.A., , Dogan, F.

    1997-07-24

    Unpolarized inelastic neutron scattering is used to study the temperature and wave vector dependence of the dynamical magnetic susceptibility, {xi}`` (q,{omega}), of a well characterized single crystal YBa{sub 2}Cu{sub 3}O{sub 6.6} (T{sub c} = 62.7 K). We find that a pseudogap opens in the spin fluctuation spectrum at temperatures well above T{sub c}. We speculate that the appearance of the low frequency incommensurate fluctuations is associated with the opening of the pseudogap. To within the error of the measurements, a gap in the spin fluctuation spectrum is found in the superconducting state.

  10. Domain structure in biphenyl incommensurate phase II observed by electron paramagnetic resonance

    NASA Astrophysics Data System (ADS)

    Véron, A.; Emery, J.; Spiesser, M.

    1994-11-01

    The domain structure in incommensurate phase II of single biphenyl crystal has been observed by investigations of the optically excited states of the Electronic Paramagnetic Resonance (E.P.R.) deuterated naphthalene molecular probes which substitute biphenyl molecules. Our results confirm that this phase is a 1q bi-domain one. The analysis of the spectra obtained in X band (9.5 GHz) experiments, in relation with the spin Hamiltonian parameter properties permits us to show that the E.P.R. probe rotates around a direction perpendicular to its long axis while the biphenyl molecule undergoes a twist movement around this axis. They also account for a regime which is like a “ multi-soliton " regime while the modulation is a plane wave one in the pure single crystal. The two molecules of the high temperature cell do not exactly experience the saure displacement field in the incommensurate phase and consequently the two domains can be distinguished. The spin Hamiltonian parameters which characterize the E.P.R. probes have been determined in the incommensurate phase II of biphenyl. La structure en domaines de la phase II du biphényle est mise en évidence par les investigations dans les états photo-excités des molécules de naphtalène deutéré, utilisées comme sondes de Résonance Paramagnétique Electronique, se substituant de manière diluée dans le mono-cristal de biphényle. Ceci confirme que cette phase est 1q bi-domaine. L'analyse des spectres obtenus dans des expériences en bande X (9.5 GHz) en relation avec les propriétés de l'hamiltonien de spin permet de montrer que la sonde moléculaire tourne autour d'une direction perpendiculaire à son grand axe alors que la molécule de biphényle subit un mouvement de twist autour de cet axe. Les résultats montrent que ces sondes rendent compte d'un régime qui est comme un régime “ multi-solitons " alors que la modulation est plane dans le cristal pur. Les deux molécules sondes de la cellule

  11. Commensurate states on incommensurate lattices. [for superconducting arrays in magnetic fields

    NASA Technical Reports Server (NTRS)

    Grest, Gary S.; Chaikin, Paul M.; Levine, Dov

    1988-01-01

    A simple one-dimensional model related to flux quantization on superconducting networks or charged particles on a substrate is proposed to investigate whether commensurate states can exist on incommensurate lattices. For both periodic and quasi-crystalline patterns, a set of low-energy states is found which is related to decimation symmetry and periodicity. It is suggested that the present quasi-periodic arrays which possess a decimation operation can be generalized to more-dimensional quasi-crystalline systems.

  12. Commensurate states on incommensurate lattices. [for superconducting arrays in magnetic fields

    NASA Technical Reports Server (NTRS)

    Grest, Gary S.; Chaikin, Paul M.; Levine, Dov

    1988-01-01

    A simple one-dimensional model related to flux quantization on superconducting networks or charged particles on a substrate is proposed to investigate whether commensurate states can exist on incommensurate lattices. For both periodic and quasi-crystalline patterns, a set of low-energy states is found which is related to decimation symmetry and periodicity. It is suggested that the present quasi-periodic arrays which possess a decimation operation can be generalized to more-dimensional quasi-crystalline systems.

  13. The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds

    NASA Astrophysics Data System (ADS)

    Couzi, Michel; Guillaume, François; Harris, Kenneth D. M.; Palmer, Benjamin A.; Christensen, Kirsten; Collins, Stephen P.

    2016-12-01

    The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3 + 1)-dimensional superspace groups.

  14. Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase.

    PubMed

    Fredrickson, Rie T; Fredrickson, Daniel C

    2016-10-01

    Despite being one of the most common minerals in the earth's crust the crystal structure of intermediate e-plagioclase remains only partially understood, due in a large part to its complex diffraction patterns including satellite reflections. In this article we present a detailed analysis of the structure of e-plagioclase (An44) using single-crystal X-ray diffraction measured at ambient and low temperature (T = 100 K), in which the full modulated structure is successfully refined. As in earlier studies, the diffraction pattern exhibits strong main a-reflections and weak e-satellite reflections. The average structure could be solved in terms of an albite-like basic cell with the triclinic centrosymmetric and non-centrosymmetric space groups P \\bar 1 and P1 (treated in its C \\bar 1 and C1 setting, respectively, to follow conventions in the literature), while the incommensurately modulated structure was modeled in (3 + 1)D superspace, employing both the centro- and non-centrosymmetric superspace groups X \\bar 1(αβγ)0 and X1(αβγ)0, where X refers to a special (3 + 1)D lattice centering with centering vectors (0 0 ½ ½), (½ ½ 0 ½), and (½ ½ ½ 0). Individual positional and occupational modulations for Ca/Na were refined with deeper insights being revealed in the non-centrosymmetric structure model. Through the structural details emerging from this model, the origin of the modulation can be traced to the communication between Ca/Na site positions through their bridging aluminosilicate (Si/Al)O4 tetrahedra.

  15. Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures.

    PubMed

    Thomas, Sarah A; Uhoya, Walter O; Tsoi, Georgiy M; Wenger, Lowell E; Vohra, Yogesh K; Chesnut, Gary N; Weir, Samuel T; Tulk, Christopher A; dos Santos, Antonio M

    2012-05-30

    Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Néel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

  16. Neutron diffraction and electrical transport studies on the incommensurate magnetic phase transition in holmium at high pressures

    SciTech Connect

    Thomas, Sarah; Uhoya, Walter; Tsoi, Georgiy; Wenger, Lowell E; Vohra, Yogesh; Chesnut, Gary Neal; Weir, S. T.; Tulk, Christopher A; Moreira Dos Santos, Antonio F

    2012-01-01

    Neutron diffraction and electrical transport measurements have been made on the heavy rare earth metal holmium at high pressures and low temperatures in order to elucidate its transition from a paramagnetic (PM) to a helical antiferromagnetic (AFM) ordered phase as a function of pressure. The electrical resistance measurements show a change in the resistance slope as the temperature is lowered through the antiferromagnetic Neel temperature. The temperature of this antiferromagnetic transition decreases from approximately 122 K at ambient pressure at a rate of -4.9 K GPa(-1) up to a pressure of 9 GPa, whereupon the PM-to-AFM transition vanishes for higher pressures. Neutron diffraction measurements as a function of pressure at 89 and 110 K confirm the incommensurate nature of the phase transition associated with the antiferromagnetic ordering of the magnetic moments in a helical arrangement and that the ordering occurs at similar pressures as determined from the resistance results for these temperatures.

  17. Anomalous fast dynamics of adsorbate overlayers near an incommensurate structural transition.

    PubMed

    Granato, Enzo; Ying, S C; Elder, K R; Ala-Nissila, T

    2013-09-20

    We investigate the dynamics of a compressively strained adsorbed layer on a periodic substrate via a simple two-dimensional model that admits striped and hexagonal incommensurate phases. We show that the mass transport is superfast near the striped-hexagonal phase boundary and in the hexagonal phase. For an initial step profile separating a bare substrate region (or "hole") from the rest of a striped incommensurate phase, the superfast domain wall dynamics leads to a bifurcation of the initial step profile into two interfaces or profiles propagating in opposite directions with a hexagonal phase in between. This yields a theoretical understanding of the recent experiments for the Pb/Si(111) system.

  18. Comment on ``Incommensurate composite structure of the superconductor Bi2Sr2CaCu2O8+δ''

    NASA Astrophysics Data System (ADS)

    Grebille, D.; Leligny, H.; Pérez, O.

    2001-09-01

    J. Etrillard, P. Bourges, and C.T. Lin [Phys. Rev. B 62, 150 (2000)] compared the structural description of the aperiodic structure of the so-called high-TC superconductor Bi-2212 in the incommensurate modulated structure model and in the composite model. According to neutron diffraction data, they disqualified the first one. Another calculation proves that this conclusion is not justified. The structural equivalence between both descriptions is demonstrated, using previous structural results, and using the 4D formalism for aperiodic crystals.

  19. Incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)2.

    PubMed

    Bolotina, Nadezhda B; Gavryushkin, Pavel N; Korsakov, Andrey V; Rashchenko, Sergey V; Seryotkin, Yurii V; Golovin, Alexander V; Moine, Bertrand N; Zaitsev, Anatoly N; Litasov, Konstantin D

    2017-04-01

    The incommensurately modulated twin structure of nyerereite Na1.64K0.36Ca(CO3)2 has been first determined in the (3 + 1)-dimensional symmetry group Cmcm(α00)00s with modulation vector q = 0.383a*. Unit-cell values are a = 5.062 (1), b = 8.790 (1), c = 12.744 (1) Å. Three orthorhombic components are related by threefold rotation about [001]. Discontinuous crenel functions are used to describe the occupation modulation of Ca and some CO3 groups. The strong displacive modulation of the O atoms in vertexes of such CO3 groups is described using x-harmonics in crenel intervals. The Na, K atoms occupy mixed sites whose occupation modulation is described in two ways using either complementary harmonic functions or crenels. The nyerereite structure has been compared both with the commensurately modulated structure of K-free Na2Ca(CO3)2 and with the widely known incommensurately modulated structure of γ-Na2CO3.

  20. Structure of an incommensurate 90° Si grain boundary resolved with the help of a Cs-corrector for illumination

    NASA Astrophysics Data System (ADS)

    Rouviere, J. L.; Lançon, F.; Rousseau, K.; Caliste, D.; Jouneau, P. H.; Fournel, F.

    2010-02-01

    The atomic structure of an incommensurate (001)/(110) Si grain boundary (GB) or 90° Si GB has been studied by transmission electron microscopy (TEM) and refined by atomistic simulations (Stillinger-Weber potential). Samples were made by bonding one (001) Si wafer with one (110) Si wafer and carefully orienting the 2 wafers in order that they have a common [1bar 10] direction. In the interfacial direction perpendicular to [1bar 10], the [110]I direction of grain I is parallel to the [001]II direction of grain II and, as the ratio of these 2 vectors is sqrt2, it is impossible to find 2 integers n and m such that n[110]I=m[001]II. The structure is incommensurate in this direction. Z-contrast images obtained in an FEI-Titan microscope equipped with a probe Cs-corrector easily resolve the Si dumb-bells in the two grains and allow us to determine the complex atomic structures of the interface. On the other hand, near on-axis high resolution TEM images obtained in a JEOL 4000EX microscope are very efficient to analyse the long range order of the interface.

  1. Incommensurate and commensurate modulations of Ba5RTi3Nb7O30 (R = La, Nd) tungsten bronzes and the ferroelectric domain structures

    NASA Astrophysics Data System (ADS)

    Mao, Min Min; Li, Kun; Zhu, Xiao Li; Chen, Xiang Ming

    2015-04-01

    Incommensurate and commensurate structural modulations of Ba5RTi3Nb7O30 (R = La, Nd) tungsten bronze ceramics were investigated by using a cooling holder equipped transmission electron microscopy in the temperature range from 100 K to 363 K. The incommensurate modulation was observed in both Ba5LaTi3Nb7O30 and Ba5NdTi3Nb7O30 at room temperature, while there was a transition from incommensurate tilted structure to commensurate superstructure for Ba5NdTi3Nb7O30 with decreasing temperature. The incommensurate and commensurate modulations were determined by the A-site occupancy of Ba and R cations. The A-site disorder resulted in larger incommensurability parameter δ and the diffusion of the satellite reflection spots. The effect of A-site disorder on the coupling between long-range dipolar order and the commensurate modulation was also discussed. The obvious ferroelectric 180° domains with spike-like shape parallel to c axis were observed for Ba5NdTi3Nb7O30, while no macro ferroelectric domain was determined for Ba5LaTi3Nb7O30.

  2. Short-range Incommensurate Magnetic Order Near the Superconducting Phase Boundary in Fe1+δTe1−xSex

    SciTech Connect

    Wen, J.; Xu, G.; Xu, Z.; Lin, Z.W.; Li, Q.; Ratcliff, W.; Gu, G.; Tranquada, J.M.

    2009-09-10

    We performed elastic neutron-scattering and magnetization measurements on Fe{sub 1.07}Te{sub 0.75}Se{sub 0.25} and FeTe{sub 0.7}Se{sub 0.3}. Short-range incommensurate magnetic order is observed in both samples. In the former sample with higher Fe content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature, while in FeTe{sub 0.7}Se{sub 0.3}, the broad magnetic peak is found to be closer to the antiferromagnetic (AFM) wave vector (0.5,0,0.5). The incommensurate peaks are only observed on one side of the AFM wave vector for both samples, which can be modeled in terms of an imbalance of ferromagnetic/antiferromagnetic correlations between nearest-neighbor spins. We also find that with higher Se (and lower Fe) concentration, the magnetic order becomes weaker while the superconducting temperature and volume increase.

  3. Incommensurately Modulated Cadmium Apatites

    NASA Astrophysics Data System (ADS)

    Henning, Peter Alberius; Moustiakimov, Marat; Lidin, Sven

    2000-02-01

    Two cadmium apatites, Cd5(PO4)3Br and Cd5(VO4)3I, earlier reported to be halogenide deficient, were prime suspects of being modulated. In this study, incommensurate ordering was found in satellites occurring in planes perpendicular to c*. The structure of Cd5(PO4)3Br was refined from single-crystal X-ray diffraction data in the four-dimensional super space group R=Poverline3:(00γ): a=16.932(2) Å, c=6.451(1) Å, Z=6, R=0.043. The modulation of the structure is due to a misfit between the large halogenide ions and the surrounding rigid Ca-PO4 substructure. From the refined model of the Cd5(PO4)3Br structure a "chain-packing" model was confirmed with a Br-Br distance of 3.466 Å.

  4. Incommensurate structure of GdBaCo{sub 2}O{sub 5+{delta}}({delta}{approx}0.38)

    SciTech Connect

    Ishizawa, N.; Asaka, T.; Kudo, T.; Fukuda, K.; Abe, N.; Arima, T.

    2013-02-15

    The incommensurate structure of the GdBaCo{sub 2}O{sub 5+{delta}} ({delta}{approx}0.38) paramagnetic phase was studied using the single-crystal X-ray diffraction. The basic structure of the compound is a double-layered perovskite with an alternating layer sequence of [GdO{sub {delta}}]-[CoO{sub 2}]-[BaO]-[CoO{sub 2}] along the c axis. The crystal belongs to the five-dimensional superspace group P4/mmm({alpha}00)0000(0{alpha}0)0000, {alpha}=0.3368(1), with a 1 Multiplication-Sign 1 Multiplication-Sign 2-type tetragonal fundamental unit cell of a=3.8934(1) A and c=7.5267(1) A. The structure was refined to R=0.028 for all the observed 2216 reflections with I>3{sigma}(I), including 331 main reflections (R=0.017), 1039 observed first-order satellites (R=0.033), and 846 observed second-order satellites (R=0.045). The crystal has oxygen deficiency that occurs only in the [GdO{sub {delta}}] layer; however, it causes many positional modulations of the constituent atoms throughout the crystal in association with a valence fluctuation of Co between the divalent and trivalent states. Because the value of {alpha} was very close to 1/3, the structure was also investigated using both the commensurately modulated approach and the conventional three-dimensional approach assuming a 3 Multiplication-Sign 3 Multiplication-Sign 2 supercell of P4/mmm symmetry. These approaches successfully reproduced a prime structure of the compound that consists of intersecting CoO{sub 5} pyramidal arrays parallel to a or b axes. The bond valence sum and the charge neutrality principle suggested that the divalent and trivalent cobalt cations are distributed in an ordered way. The incommensurate approach also indicated the possible presence of a local disorder having a structural similarity with that of a high-temperature modification. - Graphical abstract: Changes in the Co-O3 bond length and bond valence sum of Co on the t-u section in the five-dimensional superspace and the local distortion of Co

  5. Incommensurate phases of a bosonic two-leg ladder under a flux

    NASA Astrophysics Data System (ADS)

    Orignac, E.; Citro, R.; Di Dio, M.; De Palo, S.; Chiofalo, M.-L.

    2016-05-01

    A boson two-leg ladder in the presence of a synthetic magnetic flux is investigated by means of bosonization techniques and density matrix renormalization group (DMRG). We follow the quantum phase transition from the commensurate Meissner to the incommensurate vortex phase with increasing flux at different fillings. When the applied flux is ρπ and close to it, where ρ is the filling per rung, we find a second incommensuration in the vortex state that affects physical observables such as the momentum distribution, the rung-rung correlation function and the spin-spin and charge-charge static structure factors.

  6. Structural reorganization of parallel actin bundles by crosslinking proteins: Incommensurate states of twist

    NASA Astrophysics Data System (ADS)

    Shin, Homin; Grason, Gregory M.

    2010-11-01

    We construct a coarse-grained model of parallel actin bundles crosslinked by compact globular bundling proteins, such as fascin and espin, necessary components of filopodial and mechanosensory bundles. Consistent with structural observations of bundles, we find that the optimal geometry for crosslinking is overtwisted, requiring a coherent structural change of the helical geometry of the filaments. We study the linker-dependent thermodynamic transition of bundled actin filaments from their native state to the overtwisted state and map out the “twist-state” phase diagram in terms of the availability as well as the flexibility of crosslinker proteins. We predict that the transition from the uncrosslinked to fully crosslinked state is highly sensitive to linker flexibility: flexible crosslinking smoothly distorts the twist state of bundled filaments, while rigidly crosslinked bundles undergo a phase transition, rapidly overtwisting filaments over a narrow range of free crosslinker concentrations. Additionally, we predict a rich spectrum of intermediate structures, composed of alternating domains of sparsely bound (untwisted) and strongly bound (overtwisted) filaments. This model reveals that subtle differences in crosslinking agents themselves modify not only the detailed structure of parallel actin bundles, but also the thermodynamic pathway by which they form.

  7. The incommensurately modulated crystal structure of beta-Pb2BiVO6: interpretation of the phase transition alpha --> beta --> delta and conduction properties of related materials.

    PubMed

    Roussel, Pascal; Labidi, Olfa; Huve, Marielle; Drache, Michel; Wignacourt, Jean Pierre; Petricek, Vaclav

    2009-08-01

    A new polymorph of Pb(2)BiVO(6) was prepared under ambient conditions and its crystal structure was determined by single-crystal X-ray diffraction. The phase transitions alpha --> beta and beta --> delta were identified in the mother phase; the high-temperature form delta-Pb(2)BiVO(6) eventually decomposes at 753 K to a mixture of Pb(4)BiVO(8) and the high-temperature form of PbBiVO(5) before showing recombination at 923 K. beta-Pb(2)BiVO(6) has an incommensurate monoclinic modulated structure. This crystal structure is twinned and complementary structural investigations of a powder sample of beta-Pb(2)BiVO(6) by TEM diffraction studies confirmed the lattice and incommensurate modulation character. Log sigma = f(T(-1)) dependences for Pb(2)BiVO(6)-related materials (6% M-for-V-substituted compositions; M = Cr, Mn, P) are reported, which allow the characterization (E(a) and isothermal sigma values) of the beta- as well as the delta- and alpha-Pb(2)BiVO(6) varieties.

  8. Incommensurate and commensurate modulations of Ba{sub 5}RTi{sub 3}Nb{sub 7}O{sub 30} (R = La, Nd) tungsten bronzes and the ferroelectric domain structures

    SciTech Connect

    Mao, Min Min; Li, Kun; Zhu, Xiao Li; Chen, Xiang Ming

    2015-04-07

    Incommensurate and commensurate structural modulations of Ba{sub 5}RTi{sub 3}Nb{sub 7}O{sub 30} (R = La, Nd) tungsten bronze ceramics were investigated by using a cooling holder equipped transmission electron microscopy in the temperature range from 100 K to 363 K. The incommensurate modulation was observed in both Ba{sub 5}LaTi{sub 3}Nb{sub 7}O{sub 30} and Ba{sub 5}NdTi{sub 3}Nb{sub 7}O{sub 30} at room temperature, while there was a transition from incommensurate tilted structure to commensurate superstructure for Ba{sub 5}NdTi{sub 3}Nb{sub 7}O{sub 30} with decreasing temperature. The incommensurate and commensurate modulations were determined by the A-site occupancy of Ba and R cations. The A-site disorder resulted in larger incommensurability parameter δ and the diffusion of the satellite reflection spots. The effect of A-site disorder on the coupling between long-range dipolar order and the commensurate modulation was also discussed. The obvious ferroelectric 180° domains with spike-like shape parallel to c axis were observed for Ba{sub 5}NdTi{sub 3}Nb{sub 7}O{sub 30}, while no macro ferroelectric domain was determined for Ba{sub 5}LaTi{sub 3}Nb{sub 7}O{sub 30}.

  9. The modulated structure of Co3Al4Si2: incommensurability and Co-Co interactions in search of filled octadecets.

    PubMed

    Fredrickson, Rie T; Fredrickson, Daniel C

    2013-03-18

    Incommensurate modulations are increasingly being recognized as a common phenomenon in solid-state compounds ranging from inorganic materials to molecular crystals. The origins of such modulations are often mysterious, but appear to be as diverse as the compounds in which they arise. In this Article, we describe the crystal structure and bonding of Co3Al4Si2, the δ phase of the Co-Si-Al system, whose modulated structure can be traced to a central concept of inorganic chemistry: the 18 electron rule. The structure is monoclinic, conforming to the 3 + 1D superspace group C/2m(0β0)s0. The basis of the crystal structure is a rod packing of columns of the fluorite (CaF2) type, a theme that is shared by the recently determined structure of Fe8Al(17.4)Si(7.6). The columns are arranged into sheets, within which the fluorite structure's primitive cubic network of Si/Al atoms continues uninterrupted from column to column. Between the sheets, layers of interstitial Si/Al atoms occur, some of which are arranged with a periodicity incommensurate with that of the fluorite-type columns. Strong modulations in the interstitial layers result. Electronic structure calculations, using a DFT-calibrated Hückel model on a commensurate approximate structure, reveal that the complex pattern of atoms within these interstitial layers serves to distribute Si/Al atoms around the Co atoms in order to reach 18 electron counts (filled octadecets). Central to this bonding scheme is the covalent sharing of electron pairs between Co atoms. The shared electron pairs occupy orbitals that are isolobal to classical Co-Co σ and π bonds, but whose stability is tied to multicenter character involving bridging Si/Al atoms. Through these features, Co3Al4Si2 expands the structural and electronic manifestations of the 18 electron rule in solid-state inorganic compounds.

  10. Two-dimensional incommensurately modulated structure of (Sr0.13Ca0. 87)2CoSi2O7 crystals.

    PubMed

    Bagautdinov, B; Hagiya, K; Kusaka, K; Ohmasa, M; Iishi, K

    2000-10-01

    The incommensurate structure of (Sr(0.13)Ca(0.87))(2)CoSi(2)O(7) at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) A with the space group P4;2(1)m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q(1) = 0.286 (3)(a* + b*) and q(2) = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group P(p4mg)(P4;2(1)(m)), the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO(4) and SiO(4) tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca(2)CoSi(2)O(7) clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations.

  11. Magnetic multilayer structure

    DOEpatents

    Herget, Philipp; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2017-03-21

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  12. Magnetic multilayer structure

    SciTech Connect

    Herget, Philipp; O'Sullivan, Eugene J.; Romankiw, Lubomyr T.; Wang, Naigang; Webb, Bucknell C.

    2016-07-05

    A mechanism is provided for an integrated laminated magnetic device. A substrate and a multilayer stack structure form the device. The multilayer stack structure includes alternating magnetic layers and diode structures formed on the substrate. Each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by a diode structure.

  13. Incommensurate spin correlations in highly oxidized cobaltates La2−xSrxCoO4

    PubMed Central

    Li, Z. W.; Drees, Y.; Kuo, C. Y.; Guo, H.; Ricci, A.; Lamago, D.; Sobolev, O.; Rütt, U.; Gutowski, O.; Pi, T. W.; Piovano, A.; Schmidt, W.; Mogare, K.; Hu, Z.; Tjeng, L. H.; Komarek, A. C.

    2016-01-01

    We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2−xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2−xSrxCoO4. PMID:27117928

  14. NMR studies of the incommensurate helical antiferromagnet EuCo2P2 : Determination of antiferromagnetic propagation vector

    NASA Astrophysics Data System (ADS)

    Higa, Nonoka; Ding, Qing-Ping; Yogi, Mamoru; Sangeetha, N. S.; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika; Johnston, D. C.; Furukawa, Yuji

    2017-07-01

    Recently, Q.-P. Ding et al. [Phys. Rev. B 95, 184404 (2017), 10.1103/PhysRevB.95.184404] reported that their nuclear magnetic resonance (NMR) study on EuCo2As2 successfully characterized the antiferromagnetic (AFM) propagation vector of the incommensurate helix AFM state, showing that NMR is a unique tool for determination of the spin structures in incommensurate helical AFMs. Motivated by this work, we have carried out 153Eu, 31P, and 59Co NMR measurements on the helical antiferromagnet EuCo2P2 with an AFM ordering temperature TN=66.5 K. An incommensurate helical AFM structure was clearly confirmed by 153Eu and 31P NMR spectra on single-crystalline EuCo2P2 in zero magnetic field at 1.6 K and its external magnetic field dependence. Furthermore, based on 59Co NMR data in both the paramagnetic and incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k =(0 ,0 ,0.73 ±0.09 )2 π /c , where c is the c -axis lattice parameter. The temperature dependence of k is also discussed.

  15. NMR studies of the incommensurate helical antiferromagnet EuCo2P2: Determination of antiferromagnetic propagation vector

    DOE PAGES

    Higa, Nonoka; Ding, Qing -Ping; Yogi, Mamoru; ...

    2017-07-06

    Recently, Q.-P. Ding et al. reported that their nuclear magnetic resonance (NMR) study on EuCo2As2 successfully characterized the antiferromagnetic (AFM) propagation vector of the incommensurate helix AFM state, showing that NMR is a unique tool for determination of the spin structures in incommensurate helical AFMs. Motivated by this work, we have carried out 153Eu, 31P, and 59Co NMR measurements on the helical antiferromagnet EuCo2P2 with an AFM ordering temperature TN = 66.5 K. An incommensurate helical AFM structure was clearly confirmed by 153Eu and 31P NMR spectra on single-crystalline EuCo2P2 in zero magnetic field at 1.6 K and its externalmore » magnetic field dependence. Furthermore, based on 59Co NMR data in both the paramagnetic and incommensurate AFM states, we have determined the model-independent value of the AFM propagation vector k = (0,0,0.73±0.09)2π/c, where c is the c-axis lattice parameter. As a result, the temperature dependence of k is also discussed.« less

  16. Inelastic neutron scattering studies on the incommensurate-to-commensurate transformation of low energy magnetic excitations in Fe1 + δ - y(Ni / Cu) y Te1 - x Sex

    NASA Astrophysics Data System (ADS)

    Xu, Zhijun; Wen, Jinsheng; Schneeloch, John; Zhao, Yang; Matsuda, Masaaki; Ku, Wei; Liu, Xuerong; Gu, Genda; Lee, D.-H.; Birgeneau, R. J.; Tranquada, J. M.; Xu, Guangyong

    2013-03-01

    We have performed a series of neutron scattering and magnetization measurements on Fe1 + δ - y(Ni / Cu) y Te1 - x Sex system to study the interplay between magnetism and superconductivity. Both non-superconducting and superconducting samples with Tc 8 ~15K are studied. The low energy magnetic excitations of all samples at T > >Tc consist of two incommensurate vertical columns. They change to a distinctly different U-shaped dispersion at T >Tc for the superconducting samples and the transition temperature depend on the composition. On the other hand, for all non-superconducting samples, there is no clear temperature dependence, and the low energy magnetic excitations remain two columns for temperatures down to 1.5 K. Work is supported by the Office of Basic Energy Sciences, DOE.

  17. Magnetic structure of rare-earth dodecaborides

    SciTech Connect

    Siemensmeyer, K. . E-mail: siemensmeyer@hmi.de; Flachbart, K.; Gabani, S.; Matas, S.; Paderno, Y.; Shitsevalova, N.

    2006-09-15

    We have investigated the magnetic structure of HoB{sub 12}, ErB{sub 12} and TmB{sub 12} by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5T reveal modulated incommensurate magnetic structures in these compounds. The basic reflections can be indexed with q=(1/2+/-{delta}, 1/2+/-{delta}, 1/2+/-{delta}), where {delta}=0.035 both for HoB{sub 12} and TmB{sub 12} and with q=(3/2+/-{delta}, 1/2+/-{delta}, 1/2+/-{delta}), where {delta}=0.035, for ErB{sub 12}. In an applied magnetic field, new phases are observed. The complex magnetic structure of these materials seems to result from the interplay between the RKKY and dipole-dipole interaction. The role of frustration due to the fcc symmetry of dodecaborides and the crystalline electric field effect is also considered.

  18. Capabilities and limitations of a (3 + d)-dimensional incommensurately modulated structure as a model for the derivation of an extended family of compounds: example of the scheelite-like structures.

    PubMed

    Arakcheeva, Alla; Chapuis, Gervais

    2008-02-01

    The previously reported incommensurately modulated scheelite-like structure KNd(MoO(4))(2) has been exploited as a natural (3 + 1)-dimensional superspace model to generate the scheelite-like three-dimensional structure family. Although each member differs in its space-group symmetry, unit-cell parameters and compositions, in (3 + 1)-dimensional space, they share a common superspace group, a common number of building units in the basic unit cell occupying Wyckoff sites with specific coordinates (x, y, z) and specific basic unit-cell axial ratios (c/a, a/b, b/c) and angles. Variations of the modulation vector q, occupation functions and t(0) are exploited for the derivation. Eight topologically and compositionally different known structures are compared with their models derived from the KNd(MoO(4))(2) structure in order to evaluate the capabilities and limitations of the incommensurately modulated structure to act as a superspace generating model. Applications of the KNd(MoO(4))(2) structure as a starting model for the refinement and prediction of some other modulated members of the family is also illustrated. The (3 + 1)-dimensional presentation of the scheelite-like structures reveals new structural relations, which remain hidden if only conventional three-dimensional structure descriptions are applied.

  19. Magnetic structures and related properties of some rare-earth intermetallic compounds, RCu 2

    NASA Astrophysics Data System (ADS)

    Lebech, B.; Smetana, Z.; S̆íma, V.

    1987-12-01

    The magnetic structures and some relevant bulk magnetic properties of R(Cu, Ni) 2 (R = Tb, Tb zY 1- z, Dy, Ho, Er and Tm) are summarized. Basically, the magnetic structures are antiferromagnetically modulated with propagation vector {1}/{3}a∗. For R = Tb, Dy, Ho the a-axis anisotropy dominates and the structures are longitudinally modulated. For R = Tm, Er (probably) the b-axis anisotropy dominates and this results in transversely modulated structures. For R = Tb, Dy the structures are collinear, For R = Ho, Er, Tm (probably) an incommensurate modulation coexists with the commensurate a∗-axis modulation at the lowest temperature.

  20. Strain-induced incommensurate phases in hexagonal manganites

    NASA Astrophysics Data System (ADS)

    Xue, Fei; Wang, Xueyun; Shi, Yin; Cheong, Sang-Wook; Chen, Long-Qing

    2017-09-01

    An incommensurate phase refers to a solid state in which the period of a superstructure is incommensurable with its primitive unit cell. It was recently shown that an incommensurate phase, which displays a single chiral modulation of six domain variants, could be induced by applying an in-plane strain to a hexagonal manganite. Here we combine Landau theory description of thermodynamics and the phase-field method to investigate and understand the formation of the incommensurate phase in hexagonal manganites. It is shown that the equilibrium wavelength of the incommensurate phase is determined by both the temperature and the magnitude of the applied strain, and a temperature-strain phase diagram is constructed for graphically displaying the temperature and strain conditions for the stability of the incommensurate phase. Temporal evolution of domain structures reveals that the applied strain not only produces the force pulling the vortices and antivortices in opposite directions, but also results in the creation and annihilation of vortex-antivortex pairs.

  1. Elastic lattice in an incommensurate background

    SciTech Connect

    Dickman, R.; Chudnovsky, E.M. )

    1995-01-01

    We study a harmonic triangular lattice, which relaxes in the presence of an incommensurate short-wavelength potential. Monte Carlo simulations reveal that the elastic lattice exhibits only short-ranged translational correlations, despite the absence of defects in either lattice. Extended orientational order, however, persists in the presence of the background. Translational correlation lengths exhibit approximate power-law dependence upon cooling rate and background strength. Our results may be relevant to Wigner crystals, atomic monolayers on crystals surfaces, and flux-line and magnetic bubble lattices.

  2. Multidataset Refinement Resonant Diffraction, and Magnetic Structures

    PubMed Central

    Attfield, J. Paul

    2004-01-01

    The scope of Rietveld and other powder diffraction refinements continues to expand, driven by improvements in instrumentation, methodology and software. This will be illustrated by examples from our research in recent years. Multidataset refinement is now commonplace; the datasets may be from different detectors, e.g., in a time-of-flight experiment, or from separate experiments, such as at several x-ray energies giving resonant information. The complementary use of x rays and neutrons is exemplified by a recent combined refinement of the monoclinic superstructure of magnetite, Fe3O4, below the 122 K Verwey transition, which reveals evidence for Fe2+/Fe3+ charge ordering. Powder neutron diffraction data continue to be used for the solution and Rietveld refinement of magnetic structures. Time-of-flight instruments on cold neutron sources can produce data that have a high intensity and good resolution at high d-spacings. Such profiles have been used to study incommensurate magnetic structures such as FeAsO4 and β–CrPO4. A multiphase, multidataset refinement of the phase-separated perovskite (Pr0.35Y0.07Th0.04Ca0.04Sr0.5)MnO3 has been used to fit three components with different crystal and magnetic structures at low temperatures. PMID:27366599

  3. Spherical neutron polarimetry of the magnetic structure in HoNi{sub 2}B{sub 2}C: Interplay between magnetic phases and superconductivity

    SciTech Connect

    Schneider, M.; Zaharko, O.; Gasser, U.; Kreyssig, A.; Brown, P. J.; Canfield, P. C.

    2006-09-01

    Spherical neutron polarimetry has been used to answer open questions about different magnetic phases in HoNi{sub 2}B{sub 2}C, which are important in their interplay with superconductivity. We established that the incommensurate a{sup *} structure of k{sub 3}=(0.585 0 0) at 5.4 K in a zero magnetic field is a transverse-amplitude modulated wave with the magnetic moment along the b direction of the tetragonal structure. The depolarization of a neutron beam scattered from the k{sub 2}=(0 0 0.915) reflections reveals a multidomain state but does not allow an unambiguous determination of the spin configuration. Based on present knowledge of borocarbides and other rare-earth systems we give preference to a long-range incommensurate helical structure as the origin of the k{sub 2}=(0 0 0.915) reflections.

  4. Magnetic and charge structures in itinerant-electron magnets: Coexistence of multiple spin-density and charge-density waves

    NASA Astrophysics Data System (ADS)

    Ohkawa, Fusayoshi J.

    2002-06-01

    A theory of Kondo lattices is applied to studying possible magnetic and charge structures of itinerant-electron antiferromagnets. Even helical spin structures can be stabilized when the nesting of the Fermi surface is not sharp and the superexchange interaction, which arises from the virtual exchange of pair excitations across the Mott-Hubbard gap, is mainly responsible for magnetic instability. Sinusoidal spin structures or spin-density waves (SDW's) are only stabilized when the nesting of the Fermi surface is sharp enough or when an exchange interaction arising from that of pair excitations of quasiparticles is mainly responsible for magnetic instability. In particular, multiple SDW's are stabilized when their incommensurate ordering wave numbers +/-Q are multiple; magnetizations of different +/-Q components are orthogonal to each other in double and triple SDW's when magnetic anisotropy is weak enough. Unless +/-2Q are commensurate, charge-density waves (CDW's) with +/-2Q coexist with SDW's with +/-Q. Because the quenching of magnetic moments by the Kondo effect or local quantum spin fluctuations depends on local numbers of electrons, the phase of CDW's or electron densities is such that magnetic moments are large where the quenching is weak. It is proposed that the so-called stripe order must be the coexisting state of double incommensurate SDW's and CDW's in tetragonal cuprate-oxide high temperature superconductors, in particular, those with the square CuO2 lattices.

  5. Determination of the magnetic structure of CePt2In7 by means of neutron diffraction

    NASA Astrophysics Data System (ADS)

    Raba, M.; Ressouche, E.; Qureshi, N.; Colin, C. V.; Nassif, V.; Ota, S.; Hirose, Y.; Settai, R.; Rodière, P.; Sheikin, I.

    2017-04-01

    The magnetic structure of the heavy fermion antiferromagnet CePt2In7 is determined using neutron diffraction. We find a magnetic wave vector qM=(1 /2 ,1 /2 ,1 /2 ) , which is temperature independent up to TN=5.5 K. A staggered moment of 0.45 (1 ) μB at 2 K resides on the Ce ion. The nearest-neighbor moments in the tetragonal basal plane are aligned antiferromagnetically. The moments rotate by 90∘ from one CeIn3 plane to another along the c axis. A much weaker satellite peak with an incommensurate magnetic wave vector qM=(1 /2 ,1 /2 ,0.47 ) seems to develop at low temperature. However, the experimental data available so far are not sufficient to draw a definitive conclusion about the possible coexistence of commensurate and incommensurate magnetic structures in this material.

  6. Commensurate magnetic structure of CeRhIn4.85 Hg0.15

    SciTech Connect

    Bao, Wei C; Ronning, Filip; Bauer, Eric D; Thompson, Joe D; Gasparovic, Y; Lynn, J; Fisk, Z

    2008-01-01

    We show using neutron diffraction that the magnetic structure of CrRhIn{sub 4.85}Hg{sub 0.15} is characterized by a commensurate propagation vector (1,2,1/2,1/2). This is different from the magnetic structure in the parent compound CeRhIn{sub 5}, which orders with an incommensurate propagation vector (1/2,1/2,0.297). The special relation between the commensurate magnetic mode and unconventional superconductivity has been shown previously for this class of heavy fermion superconductors. This work provides further evidence for the ubiquity of this antiferromagnetic mode.

  7. Influence of temperature on the magnetic structure of HoCu 2

    NASA Astrophysics Data System (ADS)

    Smetana, Z.; S̆ima, V.; Lebech, B.; Gratz, E.

    1985-05-01

    neutron powder diffraction measurements of orthorhombic HoCu 2 are reported. The results confirm that the two cusps observed at ∼ 7 K and 10 K in the magnetization data reflect a change of the magnetic structure and the Néel temperature. In the temperature range 7 K < T < 10 K the magnetic structure is commensurable with the unit cell with a wave vector q1 = {1}/{3}a∗ and the magnetic moments aligned along the a-axis. Below 7 K two groups of magnetic reflections are observed. The first group is identical to the reflections observed between 7 and 10 K; the second group may be interpreted in terms of an incommensurably modulated component along c∗ with the magnetic moment aligned along the b-axis. Hence, the low temperature magnetic structure of HoCu 2 is incommensurably modulated and non-collinear, characterized by wave vectors q1 = {1}/{3}a∗, q2 = qcc∗ and 2 q2. Descriptions of both magnetic structures are proposed.

  8. Incommensurate Graphene Foam as a High Capacity Lithium Intercalation Anode

    PubMed Central

    Paronyan, Tereza M.; Thapa, Arjun Kumar; Sherehiy, Andriy; Jasinski, Jacek B.; Jangam, John Samuel Dilip

    2017-01-01

    Graphite’s capacity of intercalating lithium in rechargeable batteries is limited (theoretically, 372 mAh g−1) due to low diffusion within commensurately-stacked graphene layers. Graphene foam with highly enriched incommensurately-stacked layers was grown and applied as an active electrode in rechargeable batteries. A 93% incommensurate graphene foam demonstrated a reversible specific capacity of 1,540 mAh g−1 with a 75% coulombic efficiency, and an 86% incommensurate sample achieves above 99% coulombic efficiency exhibiting 930 mAh g−1 specific capacity. The structural and binding analysis of graphene show that lithium atoms highly intercalate within weakly interacting incommensurately-stacked graphene network, followed by a further flexible rearrangement of layers for a long-term stable cycling. We consider lithium intercalation model for multilayer graphene where capacity varies with N number of layers resulting LiN+1C2N stoichiometry. The effective capacity of commonly used carbon-based rechargeable batteries can be significantly improved using incommensurate graphene as an anode material. PMID:28059110

  9. Incommensurate Graphene Foam as a High Capacity Lithium Intercalation Anode

    NASA Astrophysics Data System (ADS)

    Paronyan, Tereza M.; Thapa, Arjun Kumar; Sherehiy, Andriy; Jasinski, Jacek B.; Jangam, John Samuel Dilip

    2017-01-01

    Graphite’s capacity of intercalating lithium in rechargeable batteries is limited (theoretically, 372 mAh g‑1) due to low diffusion within commensurately-stacked graphene layers. Graphene foam with highly enriched incommensurately-stacked layers was grown and applied as an active electrode in rechargeable batteries. A 93% incommensurate graphene foam demonstrated a reversible specific capacity of 1,540 mAh g‑1 with a 75% coulombic efficiency, and an 86% incommensurate sample achieves above 99% coulombic efficiency exhibiting 930 mAh g‑1 specific capacity. The structural and binding analysis of graphene show that lithium atoms highly intercalate within weakly interacting incommensurately-stacked graphene network, followed by a further flexible rearrangement of layers for a long-term stable cycling. We consider lithium intercalation model for multilayer graphene where capacity varies with N number of layers resulting LiN+1C2N stoichiometry. The effective capacity of commonly used carbon-based rechargeable batteries can be significantly improved using incommensurate graphene as an anode material.

  10. Modulated spin helicity stabilized by incommensurate orbital density waves in a quadruple perovskite manganite

    NASA Astrophysics Data System (ADS)

    Johnson, R. D.; Khalyavin, D. D.; Manuel, P.; Bombardi, A.; Martin, C.; Chapon, L. C.; Radaelli, P. G.

    2016-05-01

    Through a combination of neutron diffraction and Landau theory we describe the spin ordering in the ground state of the quadruple perovskite manganite CaMn7O12 —a magnetic multiferroic supporting an incommensurate orbital density wave that onsets above the magnetic ordering temperature, TN 1=90 K. The multi-k magnetic structure in the ground state was found to be a nearly-constant-moment helix with modulated spin helicity, which oscillates in phase with the orbital occupancies on the Mn3 + sites via trilinear magneto-orbital coupling. Our phenomenological model also shows that, above TN 2=48 K, the primary magnetic order parameter is locked into the orbital wave by an admixture of helical and collinear spin density wave structures. Furthermore, our model naturally explains the lack of a sharp dielectric anomaly at TN 1 and the unusual temperature dependence of the electrical polarization.

  11. Commensurate and Incommensurate Phases in the System A4A'Ir 2O 9( A=Sr, Ba; A'=Cu, Zn)

    NASA Astrophysics Data System (ADS)

    Battle, Peter D.; Blake, Graeme R.; Sloan, Jeremy; Vente, Jaap F.

    1998-02-01

    The crystal structure of Sr 4CuIr 2O 9is very sensitive to the conditions of synthesis. Prolonged heating of a commensurate trigonal sample prepared at 1120°C leads to the adoption of an incommensurate structure which can be regarded as a composite of two substructures having common unit cell parameters aand bbut different parameters c1and c2. No detectable change in chemical composition accompanies the structural transition, nor do the magnetic properties of the sample change significantly. The structure of the commensurate form has been determined from neutron powder diffraction data collected at 4.5 K (space group P321, a=9.68540(3) Å, c=8.04726(6) Å). Ir 2O 9octahedral dimers and CuO 6trigonal prisms alternate in chains parallel to z, with the Sr cations located between the chains; the Cu 2+cations are disordered within the prisms. The incommensurate form has been studied by X-ray diffraction and electron microscopy ( a=9.7020(6) Å, c1=4.0069(5) Å, c2=2.6993(4) Å). The relationship between the commensurate and incommensurate unit cells is discussed ( c˜2 c1˜3 c2). No commensurate Ba 4A'Ir 2O 9phases could be prepared, but incommensurate samples having A'=Cu, Zn showed behavior similar to that of Sr 4CuIr 2O 9.

  12. Flexoelectricity, incommensurate phases and the Lifshitz point

    NASA Astrophysics Data System (ADS)

    Pöttker, Henning; Salje, Ekhard K. H.

    2016-02-01

    The solutions for the minimizers of the energy density f (q, p)  =  A q 2 + B q 4 + p 2 + g A,B + β ≤ft({{q}\\prime}p-{{p}\\prime}q\\right) + |{{q}\\prime}{{|}2} + κ |{{p}\\prime}{{|}2} describe the flexoelectric effect with a flexoelectric coupling coefficient β. The order parameters q and p can be visualized as strain and polarisation, respectively. The parameter κ denotes the ratio of intrinsic length scales for q and p. We show that the structural ground-states include 3 phases, namely the paraelastic state q  =  p  =  0, the ferroelastic state where polarization exists inside and near twin boundaries, and the incommensurate (modulated) phases with a very rich array of structural modulations ranging from nearly pure sine waves to kink arrays and ripple states. The phases coincide in the multicritical Lifshitz point. Linear flexoelectricity p∼ {{q}\\prime} is encountered only approximately inside the ferroelastic phase and near the phase boundary between the paraelastic phase and the incommensurate phase. The relationship between the polarisation and the strain gradient is highly non-linear in all other states. The spatial profiles and energy distributions are discussed in detail.

  13. Flexoelectricity, incommensurate phases and the Lifshitz point.

    PubMed

    Pöttker, Henning; Salje, Ekhard K H

    2016-02-24

    The solutions for the minimizers of the energy density f (q, p)  =  Aq² + Bq⁴ + p² + gA,B + β(q'p - p'q)+ |q'|² +κ|p'|²] describe the flexoelectric effect with a flexoelectric coupling coefficient β. The order parameters q and p can be visualized as strain and polarisation, respectively. The parameter κ denotes the ratio of intrinsic length scales for q and p. We show that the structural ground-states include 3 phases, namely the paraelastic state q  =  p  =  0, the ferroelastic state where polarization exists inside and near twin boundaries, and the incommensurate (modulated) phases with a very rich array of structural modulations ranging from nearly pure sine waves to kink arrays and ripple states. The phases coincide in the multicritical Lifshitz point. Linear flexoelectricity p~q' is encountered only approximately inside the ferroelastic phase and near the phase boundary between the paraelastic phase and the incommensurate phase. The relationship between the polarisation and the strain gradient is highly non-linear in all other states. The spatial profiles and energy distributions are discussed in detail.

  14. Structural characterization of the hollandite host lattice for the confinement of radioactive cesium: Quantification of the amorphous phase taking into account the incommensurate modulated character of the crystallized part

    SciTech Connect

    Leinekugel-le-Cocq-Errien, A.Y.; Deniard, P. Jobic, S.; Gautier, E.; Evain, M.; Aubin, V.; Bart, F.

    2007-01-15

    X-ray patterns of the Ba{sub 1}Cs{sub 0.28}Fe{sub 0.82}Al{sub 1.46}Ti{sub 5.72}O{sub 16} compound evidence two wide peaks at low angle in addition to the well defined peaks of the I4/m hollandite structure type. Two hypotheses have been explored to account for these features: the coexistence of the hollandite phase with an amorphous phase and the appearance of a commensurate or incommensurate modulated structure associated with a cationic ordering, as proposed in the literature. Actually, even if the amorphous phase quantification by the Rietveld method reveals about 15 wt% of non-crystalline phase in some of the powdered sample, the origin of the two wide peaks was found to stem from the incommensurate modulated character of the hollandite structure type (super space group I4/m(0 0 {gamma})0 0) with a distribution of the modulation wavevectors presumably related to slight chemical composition changes. - Graphical abstract: Amorphous phase localization.

  15. Entropic Commensurate-Incommensurate Transition

    NASA Astrophysics Data System (ADS)

    Nikola, Nikolai; Hexner, Daniel; Levine, Dov

    2013-03-01

    The equilibrium properties of a minimal tiling model are investigated. The model has extensive ground state entropy, with each ground state having a quasiperiodic sequence of rows. It is found that the transition from the ground state to the high temperature disordered phase proceeds through a sequence of periodic arrangements of rows, in analogy with the commensurate-incommensurate transition. We show that the effective free energy of the model resembles the Frenkel-Kontorova Hamiltonian, but with temperature playing the role of the strength of the substrate potential, and with the competing lengths not explicitly present in the basic interactions.

  16. Entropic commensurate-incommensurate transition.

    PubMed

    Nikola, Nikolai; Hexner, Daniel; Levine, Dov

    2013-03-22

    The equilibrium properties of a minimal tiling model are investigated. The model has extensive ground state entropy, with each ground state having a quasiperiodic sequence of rows. It is found that the transition from the ground state to the high temperature disordered phase proceeds through a sequence of periodic arrangements of rows, in analogy with the commensurate-incommensurate transition. We show that the effective free energy of the model resembles the Frenkel-Kontorova Hamiltonian, but with temperature playing the role of the strength of the substrate potential, and with the competing lengths not explicitly present in the basic interactions.

  17. Thermally induced structural changes in incommensurate calcium barium niobate Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN28)

    SciTech Connect

    Graetsch, H.A.; Schreuer, J.; Burianek, M.; Muehlberg, M.

    2012-12-15

    The incommensurately modulated crystal structure of relaxor ferroelectric CBN28 was refined at elevated temperatures up to 330 Degree-Sign C in the 3+2 dimensional superspace group P4bm({alpha}{alpha}1/2,-{alpha}{alpha}1/2). The structural modulations mainly consisting of cooperative tilting of NbO{sub 6} octahedra and an occupational modulation of the large cation site Me2 persist beyond the diffuse ferroelectric transition with slightly reduced amplitudes. A change of symmetry was not observed. Both symmetrically non-equivalent NbO{sub 6} octahedra are distorted by off center shifts of the Nb atoms in the same direction along the tetragonal c-axis. The displacements of the Nb atoms are gradually reduced with increasing temperatures until one of the Nb atoms crosses the center of its coordination polyhedron near the transition temperature T{sub M} adopting an uncompensated anti-ferroelectric configuration. This change is accompanied by enhanced thermal motions of the Nb atoms along the c-axis. Structural distortions and electric polarization do not completely vanish at T{sub M} but may persist in fluctuating polar nanodomains. - Graphical abstract: Cross-over of the off-center shifts of both symmetrically non-equivalent niobium atoms from parallel to anti-parallel configuration in the incommensurately modulated crystal structure of relaxor ferroelectric Ca{sub 0.28}Ba{sub 0.72}Nb{sub 2}O{sub 6} (CBN28) at elevated temperatures (left side). The arrows point to columns of octahedra containing Nb1. The remaining octahedra are occupied by Nb2 atoms. Highlights: Black-Right-Pointing-Pointer The incommensurate structure of relaxor ferroelectric CBN28 was refined at high temperatures. Black-Right-Pointing-Pointer The modulations consist of a wave-like occupation of cation sites and displacements of the O atoms. Black-Right-Pointing-Pointer The modulations survive the ferroelectric phase transition and no change of symmetry was found. Black-Right-Pointing-Pointer Atomic

  18. Modeling solar magnetic structures

    NASA Technical Reports Server (NTRS)

    Low, B. C.

    1985-01-01

    Some ideas in the theoretical study of force-free magnetic fields and magnetostatic fields, which are relevant to the effort of using magnetograph data as inputs to model the quasi-static, large-scale magnetic structures in the solar atmosphere are discussed. Basic physical principles will be emphasized. An attempt will be made to assess what we may learn, physically, from the models based on these ideas. There is prospect for learning useful physics and this ought to be an incentive for intensifying the efforts to improve vector magnetograph technology and to solve the basic radiative-transfer problems encountered in the interpretation of magnetograph raw data.

  19. CeCoAl4: An incommensurate antiferromagnet

    NASA Astrophysics Data System (ADS)

    Dhar, S. K.; Rama, B.; Ramakrishnan, S.

    1995-08-01

    The orthorhombic compound CeCoAl4 orders antiferromagnetically at a relatively high Néel temperature TN of 13 K. The resistivity of CeCoAl4 shows a sharp increase near the magnetic transition before decreasing with temperature below 12 K. We believe that such behavior is due to the energy gaps induced by the incommensurate antiferromagnetic order. We have also studied the solid solutions LaxCe1-xCoAl4 for x=0.1 and 0.2 and CeCo1-yTyAl4 for T=Ni, Cu, and Pd. The crystal structure changes to YNiAl4-type even at low values of y (y~=0.1 and T=Ni and Pd). We find that TN decreases when La or Cu is substituted for Ce and Co, respectively. The sharp increase in the resistivity near TN in CeCoAl4 is almost smeared out in these pseudoternaries.

  20. Transformation between spin-Peierls and incommensurate fluctuating phases of Sc-doped TiOCl

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Wölfel, Alexander; Bykov, Maxim; Schönleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.; Williamson, Hailey L.

    2014-07-01

    Single crystals of ScxTi1-xOCl(x=0.005) have been grown by the vapor phase transport technique. Specific heat measurements prove the absence of phase transitions for 4-200 K. Instead, an excess entropy is observed over a range of temperatures that encompasses the incommensurate phase transition at 90 K and the spin-Peierls transition at 67 K of pure TiOCl. Temperature-dependent x-ray diffraction on ScxTi1-xOCl gives broadened diffraction maxima at incommensurate positions between Tc1=61.5(3) and ˜90 K, and at commensurate positions below 61.5 K. These results are interpreted as due to the presence of an incommensurate phase without long-range order at intermediate temperatures, and of a highly disturbed commensurate phase without long-range order at low temperatures. The commensurate phase is attributed to a fluctuating spin-Peierls state on an orthorhombic lattice. The monoclinic symmetry and local structure of the fluctuations are equal to the symmetry and structure of the ordered spin-Peierls state of TiOCl. A novel feature of ScxTi1-xOCl(x =0.005) is a transformation from one fluctuating phase (the incommensurate phase at intermediate temperatures) to another fluctuating phase (the spin-Peierls-like phase). This transformation is not a phase transition occurring at a critical temperature, but it proceeds gradually over a temperature range of ˜10 K wide. The destruction of long-range order requires much lower levels of doping in TiOCl than in other low-dimensional electronic crystals, like the canonical spin-Peierls compound CuGeO3. An explanation for the higher sensitivity to doping has not been found, but it is noticed that it may be the result of an increased two-dimensional character of the doped magnetic system. The observed fluctuating states with long correlation lengths are reminiscent of Kosterlitz-Thouless-type phases in two-dimensional systems.

  1. Kinetic control of structural and magnetic states in LuBaCo4O7.

    SciTech Connect

    Avci, S.; Chmaissem, O.; Zheng, H.; Huq, A.; Khalyavin, D.; Stephens, P.; Suchomel, M.; Manuel, P.; Mitchell, J.

    2012-01-01

    The RBaCo{sub 4}O{sub 7} (R = Ca, Y, Tb, Ho, Tm, Yb, Lu) compounds provide a novel topology for studying the competition between triangular geometry and magnetic order. Here, we report the structural and magnetic behavior of the Lu member of this series via neutron and synchrotron x-ray diffraction, magnetization, and resistivity measurements. We determined sequential phase transitions and a strong competition between a stable and a metastable low-temperature state that critically depends on controlled cooling rates and the associated heat removal kinetics. No evidence for long-range ordered magnetism was detected by neutron diffraction at any temperature. However, very slow spin dynamics are evidenced by time-dependent neutron diffraction measurements and can be explained by several competing magnetic phases with incommensurate short-range correlations coexisting in this material.

  2. Investigation of the commensurate magnetic structure in the heavy-fermion compound CePt2In7 using magnetic resonant x-ray diffraction

    NASA Astrophysics Data System (ADS)

    Gauthier, Nicolas; Wermeille, Didier; Casati, Nicola; Sakai, Hironori; Baumbach, Ryan E.; Bauer, Eric D.; White, Jonathan S.

    2017-08-01

    We investigated the magnetic structure of the heavy-fermion compound CePt2In7 below TN=5.34 (2 ) K using magnetic resonant x-ray diffraction at ambient pressure. The magnetic order is characterized by a commensurate propagation vector k1 /2=(1/2 ,1/2 ,1/2 ) with spins lying in the basal plane. Our measurements did not reveal the presence of an incommensurate order propagating along the high-symmetry directions in reciprocal space but cannot exclude other incommensurate modulations or weak scattering intensities. The observed commensurate order can be described equivalently by either a single-k structure or by a multi-k structure. Furthermore we explain how a commensurate-only ordering may explain the broad distribution of internal fields observed in nuclear quadrupolar resonance experiments [Sakai et al., Phys. Rev. B 83, 140408 (2011), 10.1103/PhysRevB.83.140408] that was previously attributed to an incommensurate order. We also report powder x-ray diffraction showing that the crystallographic structure of CePt2In7 changes monotonically with pressure up to P =7.3 GPa at room temperature. The determined bulk modulus B0=81.1 (3 ) GPa is similar to those of the Ce-115 family. Broad diffraction peaks confirm the presence of pronounced strain in polycrystalline samples of CePt2In7 . We discuss how strain effects can lead to different electronic and magnetic properties between polycrystalline and single crystal samples.

  3. Neutron diffraction study of the magnetic structure of HoCu 2

    NASA Astrophysics Data System (ADS)

    Smetana, Z.; Šíma, V.; Lebech, B.

    1986-05-01

    Neutron diffraction measurements show that in the temperature range from 7.4 to TN=10.4 K the magnetic structure of HoCu 2 is a commensurably modulated a-axis collinear structure with a wave vector q1=1/3 a∗. Below 7.4 K an additional structure component develops and the low temperature magnetic structure of HoCu 2 is found to be an incommensurably modulated non-collinear structure characterized by wave vectors q 1=/13; a∗, q2= qcc∗ and 2 q2, where a∗ and c∗ are reciprocal lattice vectors of the orthorhombic structure and qc=0.300±0.005. The corresponding moment components μ- q1, μq2 and μ2q2 lie along the a, b and b directions of the orthorhombic crystal lattice, respectively.

  4. Incommensurate lattice modulations in Potassium Vanadate

    NASA Astrophysics Data System (ADS)

    Chakoumakos, Bryan; Banerjee, Arnab; Mark, Lumsden; Cao, Huibo; Kim, Jong-Woo; Hoffman, Christina; Wang, Xiaoping

    Potassium Vanadate (K2V3O8) is an S = 1/2 2D square lattice antiferromagnet that shows spin reorientation indicating a strong coupling between the magnetism and its dielectric properties with a promise of rich physics that promises multiferroicity. These tangible physical properties are strongly tied through a spin-lattice coupling to the underlying lattice and superlattice behavior. It has a superlattice (SL) onsetting below Tc = 115 K with an approximate [3 x 3 x 2] modulation. Here we present our recent experiments at TOPAZ beamline at SNS which for the first time proves conclusively that the lattice modulations are incommensurate, with an in-plane Q of 0.315. We will also show our attempts to refine the data using JANA which requires a redefinition of the lattice, as well as the temperature and Q dependence of the superlattice modulation measured using neutrons at HFIR and synchrotron x-rays at APS. Our results are not only relevant for the ongoing search of multifunctional behavior in K2V3O8 but also generally for the superlattice modulations observed in a large family of fresnoites. Work performed at ORNL and ANL is supported by U.S. Dept. of Energy, Office of Basic Energy Sciences and Office of User Facilities Division.

  5. Determination of the zero-field magnetic structure of the helimagnet MnSi at low temperature

    NASA Astrophysics Data System (ADS)

    Dalmas de Réotier, P.; Maisuradze, A.; Yaouanc, A.; Roessli, B.; Amato, A.; Andreica, D.; Lapertot, G.

    2016-04-01

    Below a temperature of approximately 29 K the manganese magnetic moments of the cubic binary compound MnSi order to a long-range incommensurate helical magnetic structure. Here we quantitatively analyze a high-statistic zero-field muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi by exploiting the result of representation theory as applied to the determination of magnetic structures. Instead of a gradual rotation of the magnetic moments when moving along a <111 > axis, we find that the angle of rotation between the moments of certain subsequent planes is essentially quenched. It is the magnetization of pairs of planes which rotates when moving along a <111 > axis, thus preserving the overall helical structure.

  6. CME Magnetic Structure and Magnetic Cloud Signature

    NASA Astrophysics Data System (ADS)

    Li, Yan; Luhmann, J.

    2006-06-01

    An interplanetary coronal mass ejection (ICME) is the counterpart of a coronal mass ejection by definition. However, the relationship between the magnetic structures of the CMEs and that of the situ observations of ICMEs is still quite far from clear, due to observational gaps and the state of our understanding of CMEs. Some studies suggested that the magnetic cloud (MC, a group of ICMEs with fluxrope signatures) magnetic polarity follows the solar large scale magnetic field, and others suggested it follows the local magnetic field of the CME source region. Recent studies found that the relationship is more complex. While solar cycle dependence of the magnetic signature of MCs is clearly evident, the polarity of the MCs does not reverse at the same time when the solar large scale field reverses around solar maximum, but begins to have mixed polarities, and the new polarity may only prevail at the midst of the declining phase. Interestingly, in an independent study of the magnetic topology at the CME source regions, we found a similar solar cycle dependence of the bipolar and quadrupolar topologie. In this work, the link between CMEs and ICMEs is made and the results will shed light on our understanding about the relationship between CME and ICME magnetic structures and how these structures are related to solar local and large scale magnetic fields.Acknowledgement: ATM/NSF-0451438, SRT/NASA-NNG06GE51G and CISM/NSF.

  7. Continual approach at T=0 in the mean field theory of incommensurate magnetic states in the frustrated Heisenberg ferromagnet with an easy axis anisotropy

    NASA Astrophysics Data System (ADS)

    Martynov, S. N.; Tugarinov, V. I.; Martynov, A. S.

    2017-10-01

    The algorithm of approximate solution was developed for the differential equation describing the anharmonical change of the spin orientation angle in the model of ferromagnet with the exchange competition between nearest and next nearest magnetic neighbors and the easy axis exchange anisotropy. The equation was obtained from the collinearity constraint on the discrete lattice. In the low anharmonicity approximation the equation is resulted to an autonomous form and is integrated in quadratures. The obvious dependence of the angle velocity and second derivative of angle from angle and initial condition was derived by expanding the first integral of the equation in the Taylor series in vicinity of initial condition. The ground state of the soliton solutions was calculated by a numerical minimization of the energy integral. The evaluation of the used approximation was made for a triple point of the phase diagram.

  8. Magnetic structures in RNi{sub 2}B{sub 2}C (R = Ho, Er) superconductors

    SciTech Connect

    Stassis, C.; Goldman, A.I.; Dervenagas, P.; Zarestky, J.; Canfield, P.C.; Cho, B.K.; Johnston, D.C.; Sternlieb, B.; Sternlieb, B.

    1994-12-31

    Single crystal neutron diffraction techniques have been employed to study the evolution of magnetic structures in RNi{sub 2}B{sub 2}C compounds in an attempt to understand the relationship between magnetic ordering and superconductivity in several members of this series. For HoNi{sub 2}B{sub 2}C, below the superconducting transition (T{sub c} = 8 K), an incommensurate magnetic structure characterized by two wave vectors (0.585 a* and 0.915 c*) is found in a narrow temperature range between 4.7 K and 6 K. This is the same temperature range where bulk measurements find a deep minimum in the upper critical field, H{sub c2}. Below 4.7 K, HoNi{sub 2}B{sub 2}C is a simple collinear antiferromagnet. ErNi{sub 2}B{sub 2}C ({Tc} = 11 K) orders in an incommensurate modulated antiferromagnetic state characterized by an ordering wave vector 0.553 a* below 7 K, which coexists with superconductivity.

  9. Helical magnetism and structural anomalies in triangular lattice α-SrCr2O4.

    PubMed

    Dutton, S E; Climent-Pascual, E; Stephens, P W; Hodges, J P; Huq, A; Broholm, C L; Cava, R J

    2011-06-22

    α-SrCr(2)O(4) has a triangular planar lattice of d(3) Cr(3+) made from edge sharing CrO(6) octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of - 596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi-two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0, 0.3217(8), 0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-plane spacing on cooling below 100 K and an inflection in the cell parameters at the magnetic ordering temperature. These anomalies indicate the presence of a moderate degree of magnetostructural coupling.

  10. Artificially structured magnetic materials

    SciTech Connect

    Falco, C.M.

    1990-09-28

    This document reports the progress made during the first six months of the current three-year DOE grant on Artificially Structured Magnetic Materials.'' However, because some of the results of our previous three-year DOE grant on Artificially Structured Superconductors'' continue to emerge, both topics are addressed in this Progress Report. This report describes progress with DOE funding during the current calendar year; description of the research to be conducted during the remaining six months of the current grant year; a description of the status of the graduate students working on this research; lists of the invited talks, seminars and colloquia, of other recognition of our research, and of the publications crediting DOE sponsorship; and a summary of current and pending federal support. Since the research proposed to be conducted during the next 2 1/2 years is described in detail in our DOE proposal, it is only briefly reviewed here.

  11. Anisotropically structured magnetic aerogel monoliths

    NASA Astrophysics Data System (ADS)

    Heiligtag, Florian J.; Airaghi Leccardi, Marta J. I.; Erdem, Derya; Süess, Martin J.; Niederberger, Markus

    2014-10-01

    Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. Electronic supplementary information (ESI) available: Digital photographs of dispersions and gels with different water-to-ethanol ratios; magnetic measurements of an anatase aerogel containing 0.25 mol% Fe3O4 nanoparticles; XRD patterns of the iron oxide and

  12. Generalized Kubo formulas for the transport properties of incommensurate 2D atomic heterostructures

    NASA Astrophysics Data System (ADS)

    Cancès, Eric; Cazeaux, Paul; Luskin, Mitchell

    2017-06-01

    We give an exact formulation for the transport coefficients of incommensurate two-dimensional atomic multilayer systems in the tight-binding approximation. This formulation is based upon the C* algebra framework introduced by Bellissard and collaborators [Coherent and Dissipative Transport in Aperiodic Solids, Lecture Notes in Physics (Springer, 2003), Vol. 597, pp. 413-486 and J. Math. Phys. 35(10), 5373-5451 (1994)] to study aperiodic solids (disordered crystals, quasicrystals, and amorphous materials), notably in the presence of magnetic fields (quantum Hall effect). We also present numerical approximations and test our methods on a one-dimensional incommensurate bilayer system.

  13. Incommensurateness in nanotwinning models of modulated martensites

    NASA Astrophysics Data System (ADS)

    Benešová, Barbora; Frost, Miroslav; Kampschulte, Malte; Melcher, Christof; Sedlák, Petr; Seiner, Hanuš

    2015-11-01

    We study the formation of modulated martensites in ferromagnetic shape memory alloys by a mathematical model originating from the nanotwinning concept. The results show that the incommensurateness, systematically observed in experiments for the modulated phases, may be understood as a precursor effect of the intermartensitic transitions, and its appearance does not contradict the nanotwinning concept itself. The model sufficiently explains the different levels of incommensurateness reported from different experimental observations for the 14-layered and 10-layered martensites of the Ni-Mn-Ga alloy and outlines the mechanism of formation of faults in the stacking sequences of these materials.

  14. Non-collinear magnetic structure of manganese quadruple perovskite CdMn7O12

    PubMed Central

    Guo, H.; Fernández-Daz, M. T.; Zhou, L.; Yin, Y.; Long, Y.; Komarek, A. C.

    2017-01-01

    We report on the magnetic structure of CdMn7O12 determined by powder neutron diffraction. We were able to measure the magnetic structure of this Cd containing and highly neutron absorbing material by optimizing the sample geometry and by blending the CdMn7O12 with Aluminum powder. Below its Néel temperature TN1 all magnetic reflections can be indexed by a single commensurate propagation vector k = (0, 0, 1). This is different to the case of CaMn7O12 where the propagation vector is incommensurate and where an in-plane helical magnetic structure has been found. We observe a commensurate non-collinear magnetic structure in CdMn7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12. However, the commensurate propagation vector prevents the appearance of a helical magnetic structure in CdMn7O12. Finally, we also observe a third structural phase transition below ~60 K that can be attributed to phase separation. PMID:28378833

  15. Incommensurate Spin Density Wave state in metamagnetic Fe3Ga4

    NASA Astrophysics Data System (ADS)

    Wu, Yan; Cao, Huibo; Dos Santos, António; McCandless, Greg; Chan, Julia; Karki, Amar; Jin, Rongying; Ditusa, John

    Fe3Ga4 displays a rich competition between magnetic states without structural transitions: a ferromagnetic(FM) ground state transitions to an antiferromagnetic(AFM) intermediate state above 68 K followed by a reemergence of the FM state above room temprature(T). The reentrance of the FM state hints of a coupling of the magnetic degrees of freedom to other modes. To explore the nature of the magnetic states, we have performed extensive single crystal neutron diffraction measurements over a wide range of T and pressure. These measurements revealed two very different magnetic states with the low T FM state having magnetic moments along the c-axis while we discovered that the AFM state is in an incommensurate spin density wave(SDW) order with moments mostly along the a-axis. However, there is still considerable non-collinear and non-coplanar contributions along the b- and c-axial directions. This non-coplanar moment is likely to be the origin of the very large anomalous Hall effect(HE) including a substantial topological HE that we discovered in Fe3Ga4. Study of the effect of hydrostatic pressure indicates a reduction of the Tc and a destabilization of the SDW phase.

  16. Incommensurate short-range multipolar order parameter of phase II in Ce3Pd20Si6

    NASA Astrophysics Data System (ADS)

    Portnichenko, P. Y.; Paschen, S.; Prokofiev, A.; Vojta, M.; Cameron, A. S.; Mignot, J.-M.; Ivanov, A.; Inosov, D. S.

    2016-12-01

    The clathrate compound Ce3Pd20Si6 is a heavy-fermion metal that exhibits magnetically hidden order at low temperatures. Reputedly, this exotic type of magnetic ground state, known as "phase II", could be associated with the ordering of Ce 4 f quadrupolar moments. In contrast to conventional (dipolar) order, it has vanishing Bragg intensity in zero magnetic field and, as a result, has escaped direct observation by neutron scattering until now. Here we report the observation of diffuse magnetic neutron scattering induced by an application of magnetic field along either the [1 1 ¯0 ] or the [001 ] direction within phase II. The broad elastic magnetic signal that surrounds the (111) structural Bragg peak can be attributed to a short-range G -type antiferromagnetic arrangement of field-induced dipoles modulated by the underlying multipolar order on the simple-cubic sublattice of Ce ions occupying the 8 c Wyckoff site. In addition, for magnetic fields applied along the [001 ] direction, the diffuse magnetic peaks in Ce3Pd20Si6 become incommensurate, suggesting a more complex modulated structure of the underlying multipolar order that can be continuously tuned by a magnetic field.

  17. Van der Waals-coupled electronic states in incommensurate double-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Liu, Kaihui; Jin, Chenhao; Hong, Xiaoping; Kim, Jihoon; Zettl, Alex; Wang, Enge; Wang, Feng

    2014-10-01

    Non-commensurate two-dimensional materials such as a twisted graphene bilayer or graphene on boron nitride, consisting of components that have no finite common unit cell, exhibit emerging moiré physics such as novel Van Hove singularities, Fermi velocity renormalization, mini Dirac points and Hofstadter butterflies. Here we use double-walled carbon nanotubes as a model system for probing moiré physics in incommensurate one-dimensional systems, by combining structural and optical characterizations. We show that electron wavefunctions between incommensurate inner- and outer-wall nanotubes can hybridize strongly, contrary to the conventional wisdom of negligible electron hybridization due to destructive interference. The chirality-dependent inter-tube electronic coupling is described by one-dimensional zone folding of the electronic structure of twisted-and-stretched graphene bilayers. Our results demonstrate that incommensurate van der Waals interactions can be important for engineering the electronic structure and optical properties of one-dimensional materials.

  18. Extending the range of low energy electron diffraction (LEED) surface structure determination: Co-adsorbed molecules, incommensurate overlayers and alloy surface order studied by new video and electron counting LEED techniques

    SciTech Connect

    Ogletree, D.F.

    1986-11-01

    LEED multiple scattering theory is briefly summarized, and aspects of electron scattering with particular significance to experimental measurements such as electron beam coherence, instrument response and phonon scattering are analyzed. Diffuse LEED experiments are discussed. New techniques that enhance the power of LEED are described, including a real-time video image digitizer applied to LEED intensity measurements, along with computer programs to generate I-V curves. The first electron counting LEED detector using a ''wedge and strip'' position sensitive anode and digital electronics is described. This instrument uses picoampere incident beam currents, and its sensitivity is limited only by statistics and counting times. Structural results on new classes of surface systems are presented. The structure of the c(4 x 2) phase of carbon monoxide adsorbed on Pt(111) has been determined, showing that carbon monoxide molecules adsorb in both top and bridge sites, 1.85 +- 0.10 A and 1.55 +- 0.10 A above the metal surface, respectively. The structure of an incommensurate graphite overlayer on Pt(111) is analyzed. The graphite layer is 3.70 +- 0.05 A above the metal surface, with intercalated carbon atoms located 1.25 +- 0.10 A above hollow sites supporting it. The (2..sqrt..3 x 4)-rectangular phase of benzene and carbon monoxide coadsorbed on Pt(111) is analyzed. Benzene molecules adsorb in bridge sites parallel to and 2.10 +- 0.10 A above the surface. The carbon ring is expanded, with an average C-C bond length of 1.72 +- 0.15 A. The carbon monoxide molecules also adsorb in bridge sites. The structure of the (..sqrt..3 x ..sqrt..3) reconstruction on the (111) face of the ..cap alpha..-CuAl alloy has been determined.

  19. The Hypothesis of Incommensurability and Multicultural Education

    ERIC Educational Resources Information Center

    McDonough, Tim

    2009-01-01

    This article describes the logical and rhetorical grounds for a multicultural pedagogy that teaches students the knowledge and skills needed to interact creatively in the public realm betwixt and between cultures. I begin by discussing the notion of incommensurability. I contend that this hypothesis was intended to perform a particular rhetorical…

  20. Quantum incommensurate skyrmion crystals and commensurate to in-commensurate transitions in cold atoms and materials with spin-orbit couplings in a Zeeman field

    NASA Astrophysics Data System (ADS)

    Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming

    2017-08-01

    In this work, we study strongly interacting spinor atoms in a lattice subject to a two dimensional (2d) anisotropic Rashba type of spin orbital coupling (SOC) and an Zeeman field. We find the interplay between the Zeeman field and the SOC provides a new platform to host rich and novel classes of quantum commensurate and in-commensurate phases, excitations and phase transitions. These commensurate phases include two collinear states at low and high Zeeman field, two co-planar canted states at mirror reflected SOC parameters respectively. Most importantly, there are non-coplanar incommensurate Skyrmion (IC-SkX) crystal phases surrounded by the four commensurate phases. New excitation spectra above all the five phases, especially on the IC-SKX phase are computed. Three different classes of quantum commensurate to in-commensurate transitions from the IC-SKX to its four neighboring commensurate phases are identified. Finite temperature behaviors and transitions are discussed. The critical temperatures of all the phases can be raised above that reachable by current cold atom cooling techniques simply by tuning the number of atoms N per site. In view of recent impressive experimental advances in generating 2d SOC for cold atoms in optical lattices, these new many-body phenomena can be explored in the current and near future cold atom experiments. Applications to various materials such as MnSi, {{Fe}}0.5 {{Co}}0.5Si, especially the complex incommensurate magnetic ordering in Li2IrO3 are given.

  1. Magnetic cellulose-derivative structures

    DOEpatents

    Walsh, M.A.; Morris, R.S.

    1986-09-16

    Structures to serve as selective magnetic sorbents are formed by dissolving a cellulose derivative such as cellulose triacetate in a solvent containing magnetic particles. The resulting solution is sprayed as a fine mist into a chamber containing a liquid coagulant such as n-hexane in which the cellulose derivative is insoluble but in which the coagulant is soluble or miscible. On contact with the coagulant, the mist forms free-flowing porous magnetic microspheric structures. These structures act as containers for the ion-selective or organic-selective sorption agent of choice. Some sorption agents can be incorporated during the manufacture of the structure. 3 figs.

  2. Magnetic cellulose-derivative structures

    DOEpatents

    Walsh, Myles A.; Morris, Robert S.

    1986-09-16

    Structures to serve as selective magnetic sorbents are formed by dissolving a cellulose derivative such as cellulose triacetate in a solvent containing magnetic particles. The resulting solution is sprayed as a fine mist into a chamber containing a liquid coagulant such as n-hexane in which the cellulose derivative is insoluble but in which the coagulant is soluble or miscible. On contact with the coagulant, the mist forms free-flowing porous magnetic microspheric structures. These structures act as containers for the ion-selective or organic-selective sorption agent of choice. Some sorbtion agents can be incorporated during the manufacture of the structure.

  3. Low temperature magnetic structure of CeRhIn5 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 CeRhIn5 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

  4. Commensurate-incommensurate transition and domain wall dynamics of adsorbed overlayers on a honeycomb substrate

    NASA Astrophysics Data System (ADS)

    Elder, K. R.; Achim, C. V.; Granato, E.; Ying, S. C.; Ala-Nissila, T.

    2016-12-01

    We introduce an effective one-mode phase-field crystal model for studying the commensurate-incommensurate transition and domain wall dynamics of the (\\sqrt{3}×\\sqrt{3})R30\\circ phase found in systems such as Xe/Pt(111), or Xe and Kr on graphite. The model allows us to study large systems where the domain walls can be separated over large macroscopic distances and at the same time incorporate the microscopic details of the domain wall structures. The resulting phase diagram shows that an intermediate stripe incommensurate phase always separates the commensurate phase from the honeycomb incommensurate phases. The energy of the domain wall crossing is investigated. We also find that near a step edge, the domain walls tend to align perpendicularly to the step edge, in agreement with recent experimental observations.

  5. Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure

    NASA Astrophysics Data System (ADS)

    Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.

    2017-01-01

    Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system.

  6. Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure

    PubMed Central

    Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.

    2017-01-01

    Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system. PMID:28134296

  7. Magnetic structure of the crust

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1985-01-01

    The bibuniqueness aspect of geophysical interpretation must be constrained by geological insight to limit the range of theoretically possible models. An additional step in depth understanding of the relationship between rock magnetization and geological circumstances on a grand scale is required. Views about crustal structure and the distribution of lithologies suggests a complex situation with lateral and vertical variability at all levels in the crust. Volcanic, plutonic, and metamorphic processes together with each of the observed anomalies. Important questions are addressed: (1) the location of the magnetic bottom; (2) whether the source is a discrete one or are certain parts of the crust cumulatively contributing to the overall magnetization; (3) if the anomaly to some recognizable surface expression is localized, how to arrive at a geologically realistic model incorporating magnetization contrasts which are realistic; (3) in the way the primary mineralogies are altered by metamorphism and the resulting magnetic contracts; (4) the effects of temperature and pressure on magnetization.

  8. Are Allopathic and Holistic Medicine Incommensurable?

    PubMed

    Evangelatos, Nikolaos; Eliadi, Irini

    2016-01-01

    The shift from the Aristotelian to the Newtonian scientific paradigm gave birth to progresses in the natural, hard sciences and contributed to the emergence of modernity. Allopathic medicine gradually implemented those progresses, transforming itself into contemporary biomedicine. In the early 20th century, replacement of Newtonian physics by quantum mechanics and Einstein's theory of relativity resulted in a new paradigm shift in the natural, hard sciences. This shift gave birth to post-modern perceptions, which attempt to put those changes in context. Within this new context, holistic therapeutic approaches are considered more compatible with the new paradigm. Different paradigms in the natural, hard sciences are considered to be incommensurable (in the Kuhnian sense). This incommensurability is also transferred to the different societal contexts, the different «Weltanschauungen» that rely on different scientific paradigms. However, drawing on arguments that range from historical and philosophical to practical and sociological ones, we argue that, although based on different scientific paradigms, allopathic and holistic medicine are not incommensurable, but rather complementary. This may be related to the inherent attributes of medicine, a fact that reinforces the debate on its epistemological status. © 2016 S. Karger GmbH, Freiburg.

  9. Plated lamination structures for integrated magnetic devices

    SciTech Connect

    Webb, Bucknell C.

    2014-06-17

    Semiconductor integrated magnetic devices such as inductors, transformers, etc., having laminated magnetic-insulator stack structures are provided, wherein the laminated magnetic-insulator stack structures are formed using electroplating techniques. For example, an integrated laminated magnetic device includes a multilayer stack structure having alternating magnetic and insulating layers formed on a substrate, wherein each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by an insulating layer, and a local shorting structure to electrically connect each magnetic layer in the multilayer stack structure to an underlying magnetic layer in the multilayer stack structure to facilitate electroplating of the magnetic layers using an underlying conductive layer (magnetic or seed layer) in the stack as an electrical cathode/anode for each electroplated magnetic layer in the stack structure.

  10. Homochiral magnetic structures at surfaces

    NASA Astrophysics Data System (ADS)

    Blugel, Stefan

    2008-03-01

    Electrons propagating in the vicinity of inversion asymmetric environments such as surfaces, interfaces, ultrathin films or nanostructures can give rise to an important antisymmetric exchange interaction, known as Dzyaloshinskii-Moriya (DM) interaction. Although this interaction, favoring spatially rotating spin structures, is in principle known for about 50 years, its consequences for the magnetic structure in low-dimensional magnets remained nearly unexplored and has been basically overlooked the past 20 years. Theoretical models considering isotropic exchange, magnetic anisotropy and the DM interaction display a rich phase diagram of complex magnetic phases on different length scales depending on the strength of the different contributions. Today, it is unknown how large is the strength of the DM interaction. Is this just a small perturbation to the collinear uniaxial ferro- or antiferromagnetic state, determined by exchange and magnetic anisotropy or is it strong enough to create new phases which had been overlooked? Surprisingly little first-principles calculations deal with the DM interaction. There might be several reasons for this: The investigation requires the treatment of non-collinear magnetism together with spin-orbit interactions of large magnetic structures in low-symmetry situations. We developed a perturbative strategy implemented into the FLAPW code FLEUR which can cope with this challenge. We show by first- principles calculations based on the vector-spin density formulation of the density- functional theory (DFT) that that there are circumstances whre the DM interaction is indeed sufficiently strong to compete with the interactions that favor collinear spin alignment causing magnetic phases of unique handedness e.g.homochiral magnetic phases such as a left rotation cycloidal spiral in Mn on W(110) [M. Bode et al., Nature 447, 190 (2007)] or favoring magnetic domain-walls with unique turning sense.

  11. Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6 oxide.

    PubMed

    Dos santos-García, Antonio J; Solana-Madruga, Elena; Ritter, Clemens; Ávila-Brande, David; Fabelo, Oscar; Sáez-Puche, Regino

    2015-06-21

    The perovskite polymorph of Mn(2)CrSbO(6) compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P21/n space group with cell parameters a = 5.2180 (2) Å, b = 5.3710(2) Å, c = 7.5874(1) Å and β = 90.36(1)°. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn(2+) and Cr(3+) sublattices below TN = 55 K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector κ = [1/2 0 1/2]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R3[combining macron] space group with cell parameters a = 5.2084 (4) Å and c = 14.4000 (11) Å. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with κ = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to κ = [00 0.54] at about 10 K.

  12. Variable defect structures cause the magnetic low-temperature transition in natural monoclinic pyrrhotite

    NASA Astrophysics Data System (ADS)

    Koulialias, D.; Kind, J.; Charilaou, M.; Weidler, P. G.; Löffler, J. F.; Gehring, A. U.

    2016-02-01

    Non-stoichiometric monoclinic 4C pyrrhotite (Fe7S8) is a major magnetic remanence carrier in the Earth's crust and in extraterrestrial materials. Because of its low-temperature magnetic transition around 30 K also known as Besnus transition, which is considered to be an intrinsic property, this mineral phase is easily detectable in natural samples. Although the physical properties of pyrrhotite have intensively been studied, the mechanism behind the pronounced change in magnetization at the low-temperature transition is still debated. Here we report magnetization experiments on a pyrrhotite crystal (Fe6.6S8) that consists of a 4C and an incommensurate 5C* superstructure that are different in their defect structure. The occurrence of two superstructures is magnetically confirmed by symmetric inflection points in hysteresis measurements above the transition at about 30 K. The disappearance of the inflection points and the associated change of the hysteresis parameters indicate that the two superstructures become strongly coupled to form a unitary magnetic anisotropy system at the transition. From this it follows that the Besnus transition in monoclinic pyrrhotite is an extrinsic magnetic phenomenon with respect to the 4C superstructure and therefore the physics behind it is in fact different from that of the well-known Verwey transition.

  13. Microwave sol-gel synthesis and upconversion photoluminescence properties of CaGd2(WO4)4:Er3+/Yb3+ phosphors with incommensurately modulated structure

    NASA Astrophysics Data System (ADS)

    Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor

    2015-08-01

    CaGd2-x(WO4)4:Er3+/Yb3+ phosphors with the doping concentrations of Er3+ and Yb3+ (x=Er3++Yb3+, Er3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) have been successfully synthesized by the microwave sol-gel method. The crystal structure of CaGd2-x(WO4)4:Er3+/Yb3+ tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 °C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd2(WO4)4:Er3+/Yb3+ particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd2(WO4)4 revealed about 12 narrow lines. The strongest band observed at 903 cm-1 was assigned to the ν1 symmetric stretching vibration of WO4 tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er3+ luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at 2H11/2→4I15/2 transition is weak in the range of erbium doping level xEr=0.05-0.2, while, for transition 4S3/2→4I15/2, the signs of concentration quenching become pronounced at xEr=0.2.

  14. Magnetic structure and domain conversion of the quasi-2D frustrated antiferromagnet CuCrO{sub 2} probed by NMR

    SciTech Connect

    Sakhratov, Yu. A.; Svistov, L. E.; Kuhns, P. L.; Zhou, H. D.; Reyes, A. P.

    2014-11-15

    We have carried out {sup 63,65}Cu NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO{sub 2}. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.

  15. Magnetic and electronic structure of Mn nanostructures on Ag(111) and Au(111)

    NASA Astrophysics Data System (ADS)

    Cardias, R.; Bezerra-Neto, M. M.; Ribeiro, M. S.; Bergman, A.; Szilva, A.; Eriksson, O.; Klautau, A. B.

    2016-01-01

    We present results of the electronic and magnetic structure of Mn nanowires adsorbed on Ag(111) and Au(111) surfaces. For finite Mn nanowires on Ag(111) and Au(111) surfaces, our ab initio results show that the large difference between the spin-orbit splitting of these two surfaces leads to completely different magnetic configurations. The magnetic ordering for Mn nanowires adsorbed on Ag(111) is governed by the strong exchange interaction between Mn adatoms. For Mn nano-chains on Au(111), the competition between Heisenberg and Dzyaloshinskii-Moriya interactions leads to a complex magnetic structure of the clusters considered here. Among the more conspicuous results we note a spin-spiral helical type for the nanowire with seven atoms, and a complex magnetic configuration incommensurate with the substrate lattice for a double-sized Mn wire. The effect of the structural relaxation is also investigated, showing sensitivity of the exchange interactions to the bond distance to the substrate. We also demonstrate that small changes in the band filling of these Mn chains results in drastically different changes of the interatomic exchange. Finally, we show that dispersion of the electronic energy spectrum is possible even in nanostructures with bounded spatial extension.

  16. Chemical Pressure-Driven Incommensurability in CaPd5: Clues to High-Pressure Chemistry Offered by Complex Intermetallics.

    PubMed

    Kilduff, Brandon J; Fredrickson, Daniel C

    2016-07-05

    While composition and pressure are generally considered orthogonal parameters in the synthesis and optimization of solid state materials, their distinctness is blurred by the concept of chemical pressure (CP): microscopic pressure arising from lattice constraints rather than an externally applied force. In this article, we describe the first cycle of an iterative theoretical/experimental investigation into this connection. We begin by theoretically probing the ability of physical pressure to promote structural transitions in CaCu5-type phases that are driven by CP in other systems. Our results point to the instability of the reported CaCu5-type CaPd5 phase to such a transition even at ambient pressure, suggesting that new structural chemistry should arise at only modest pressures. We thus attempted to synthesize CaPd5 as a starting material for high-pressure experiments. However, rather than obtaining the expected CaCu5-type phase, we encountered crystals of an incommensurately modulated variant CaPd5+q/2, whose composition is related to its satellite spacing, q = qbbasic* with q ≈ 0.44. Its structure was solved and refined in the (3 + 1)D superspace group Cmcm(0β0)s00, revealing CaCu5-type slabs separated by distorted Pd hexagonal nets with an incommensurate periodicity. DFT-CP analysis on a commensurate model for CaPd5+q/2 indicates that the new Pd nets serve to relieve intense negative CPs that the Ca atoms would experience in a CaCu5-type CaPd5 phase but suffer from a desire to contract relative to the rest of the structure. In this way, both the Pd layer substitution and incommensurability in CaPd5+q/2 are anticipated by the CP schemes of simpler model systems, with CP quadrupoles tracing the paths of the favorable atomic motions. This picture offers predictions for how elemental substitution and physical pressure should affect these structural motifs, which could be applicable to the magnetic phase Zr2Co11 whose previously proposed structures show close

  17. Incommensurate antiferromagnetism in a pure spin system via cooperative organization of local and itinerant moments

    PubMed Central

    Feng, Yejun; Wang, Jiyang; Silevitch, D. M.; Mihaila, B.; Kim, J. W.; Yan, J.-Q.; Schulze, R. K.; Woo, Nayoon; Palmer, A.; Ren, Y.; van Wezel, Jasper; Littlewood, P. B.; Rosenbaum, T. F.

    2013-01-01

    Materials with strong correlations are prone to spin and charge instabilities, driven by Coulomb, magnetic, and lattice interactions. In materials that have significant localized and itinerant spins, it is not obvious which will induce order. We combine electrical transport, X-ray magnetic diffraction, and photoemission studies with band structure calculations to characterize successive antiferromagnetic transitions in GdSi. GdSi has both sizable local moments and a partially nested Fermi surface, without confounding contributions from orbital effects. We identify a route to incommensurate order where neither type of moment dominates, but is rooted in cooperative feedback between them. The nested Fermi surface of the itinerant electrons induces strong interactions between local moments at the nesting vector, whereas the ordered local moments in turn provide the necessary coupling for a spin-density wave to form among the itinerant electrons. This mechanism echoes the cooperative interactions between electrons and ions in charge-density–wave materials, and should be germane across a spectrum of transition-metal and rare-earth intermetallic compounds. PMID:23401555

  18. Stability of an icosahedral incommensurate phase formed in an immiscible alloy system

    NASA Astrophysics Data System (ADS)

    Huang, L. J.; Liu, B. X.; Li, H.-D.

    1990-05-01

    A stability study of the icosahedral incommensurate Fe60Cu40 phase formed directly by ion mixing at room temperature indicates that this metastable phase is unstable against thermal annealing to 300+/-25 °C, but annealing to the higher temperature (800+/-25 °C) reestablished the icosahedral order. The changes of the magnetic properties associated with the icosahedral phase formation are also presented.

  19. Boundary conditions for equilibrating incommensurate periodic patterns.

    PubMed

    Ogawa, Hiroto; Uchida, Nariya

    2005-11-01

    Simulation of periodic patterns often suffer from artifacts due to incommensurability of the intrinsic length scale and the system size. We introduce a simple numerical scheme to avoid this problem in finding equilibrium domain morphologies from a Ginzburg-Landau-type free energy. In this scheme, the boundary values are determined only by the local equilibrium condition at the adjacent bulk sites. The scheme is especially advantageous in equilibrating patterns that have two or more characteristic lengths. We demonstrate it using a model of lamellar-lamellar coexistence in block copolymer blends.

  20. Are humanistic and positive psychology really incommensurate?

    PubMed

    Friedman, Harris

    2014-01-01

    Comments on the article "The humanistic psychology-positive psychology divide: Contrasts in philosophical foundations" by Waterman (see record 2013-12501-001). Waterman has provided some broad-brush generalizations about differences between humanistic psychology and positive psychology, many of which do not hold in all cases, and he has pointed out some difficulties that would be involved in reconciling them. However, he has not presented any convincing argument that the two are irreconcilable. Essentially, Waterman has confounded difficulties with impossibilities by concluding these are incommensurate. PsycINFO Database Record (c) 2014 APA, all rights reserved.

  1. Incommensurate magnetic ordering in Cu{sub 2}Te{sub 2}O{sub 5}X{sub 2} (X=Cl,Br) studied by single crystal neutron diffraction

    SciTech Connect

    Zaharko, O.; Roennow, H.; Mesot, J.; Crowe, S. J.; Paul, D. McK.; Brown, P. J.; Daoud-Aladine, A.; Meents, A.; Wagner, A.; Prester, M.; Berger, H.

    2006-02-01

    Polarized and unpolarized neutron-diffraction studies have been carried out on single crystals of the coupled spin tetrahedra systems Cu{sub 2}Te{sub 2}O{sub 5}X{sub 2} (X=Cl,Br). A model of the magnetic structure associated with the propagation vectors k{sup '}{sub Cl}{approx_equal}(-0.150,0.422,(1/2)) and k{sup '}{sub Br}{approx_equal}(-0.172,0.356,(1/2)) and stable below T{sub N}=18 K for X=Cl and T{sub N}=11 K for X=Br is proposed. A feature of the model, common to both the bromide and chloride, is a canted coplanar motif for the four Cu{sup 2+} spins on each tetrahedron which rotates on a helix from cell to cell following the propagation vector. The Cu{sup 2+} magnetic moment determined for X=Br,0.395(5){mu}{sub B}, is significantly less than for X=Cl,0.88(1){mu}{sub B} at 2 K. The magnetic structure of the chloride associated with the wave vector k{sup '} differs from that determined previously for the wave vector k{approx_equal}(0.150,0.422,(1/2)) [O. Zaharko et al., Phys. Rev. Lett. 93, 217206(E) (2004)].

  2. Phase diagram and incommensurate antiferroelectric structure in (Pb{sub 1−1.5x}La{sub x})(Zr{sub 0.42}Sn{sub 0.40}Ti{sub 0.18})O{sub 3} ceramics discovered by band-to-band optical transitions

    SciTech Connect

    Ding, X. J.; Xu, L. P.; Hu, Z. G. Chu, J. H.; Chen, X. F.; Wang, G. S.; Dong, X. L.

    2014-09-29

    Optical properties and phase transitions of (Pb{sub 1−1.5x}La{sub x})(Zr{sub 0.42}Sn{sub 0.40}Ti{sub 0.18})O{sub 3} (PLZST 100x/42/40/18) ceramics with different compositions have been investigated by temperature dependent spectroscopic ellipsometry. Two interband critical points (E{sub cp1} and E{sub cp2}) located at about 3.9 and 5.1 eV can be obtained by fitting standard line shapes to the second derivatives of the complex dielectric functions. Based on the band-to-band transitions, the phase diagram of PLZST ceramics can be well presented. Moreover, a peculiar incommensurate antiferroelectric state has been found to exist above the temperature of the normal commensurate antiferroelectric tetragonal structure. It can be stable below Curie temperature, evolving slowly with decreasing temperature towards the commensurate structure, which is due to strong pinning of incommensurate domain walls. The phenomena can result from a competition between ferroelectric ordering and antiferroelectric ordering caused by the lanthanum modification.

  3. Field-induced incommensurate-to-commensurate phase transition in the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22

    NASA Astrophysics Data System (ADS)

    Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Chai, Yi Sheng; Kim, Kee Hoon; Reehuis, M.; Prokeš, K.; Mat'Aš, S.

    2011-04-01

    Using neutron diffraction, we investigated the spin structures of magnetoelectric hexaferrite, Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 (x=0.08) under a magnetic field (H⊥c). When the crystal was cooled in a zero field, longitudinal spin cones were observed at low temperatures. These incommensurate phases, however, were replaced by the commensurate phase [k1=(0,0,(3)/(2))] when the ferroelectricity was induced by an external field perpendicular to the c axis. Magnetic structure refinement confirms that this commensurate order is compatible with the spin-current polarization. We argue that planar magnetic anisotropy plays an important role in determining the magnetic structure that is responsible for its magnetoelectricity.

  4. Pressure-induced normal-incommensurate and incommensurate-commensurate phase transitions in CrOCl

    PubMed Central

    Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander

    2015-01-01

    The high-pressure behavior of layered CrOCl is shown to be governed by non-bonded interactions between chlorine atoms in relation to a rigid framework composed of Cr and O atoms. The competition between optimizing intra- and interlayer Cl–Cl distances and the general trend towards denser packing defines a novel mechanism for high-pressure phase transitions of inorganic materials. CrOCl possesses an incommensurate phase for 16–51 GPa. Single-crystal x-ray diffraction in a diamond anvil cell provides an accurate description of the evolution of the incommensurate wave with pressure. It thus demonstrates a continuous increase of the amplitude up to 30 GPa, followed by a decrease of the wavelength until a lock-in transition occurs at 51 GPa. PMID:25999303

  5. The incommensurability of psychoanalysis and history.

    PubMed

    Scott, Joan W

    2012-01-01

    This article argues that, although psychoanalysis and history have different conceptions of time and causality, there can be a productive relationship between them. Psychoanalysis can force historians to question their certainty about facts, narrative, and cause; it introduces disturbing notions about unconscious motivation and the effects of fantasy on the making of history. This was not the case with the movement for psychohistory that began in the 1970s. Then the influence of American ego-psychology on history-writing promoted the idea of compatibility between the two disciplines in ways that undercut the critical possibilities of their interaction. The work of the French historian Michel de Certeau provides theoretical insight into the uses of incommensurability, while that of Lyndal Roper demonstrates both its limits and its value for enriching historical understanding.

  6. Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.

    2016-10-01

    The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multi-domain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature.

  7. Friction Boosted by Equilibrium Misalignment of Incommensurate Two-Dimensional Colloid Monolayers

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2015-03-01

    Colloidal two-dimensional monolayers sliding in an optical lattice are of recent importance as a frictional system. In the general case when the monolayer and optical lattices are incommensurate, we predict two important novelties, one in the static equilibrium structure, the other in the frictional behavior under sliding. Structurally, realistic simulations show that the colloid layer should possess in full equilibrium a small misalignment rotation angle relative to the optical lattice, an effect so far unnoticed but visible in some published experimental moiré patterns. Under sliding, this misalignment has the effect of boosting the colloid monolayer friction by a considerable factor over the hypothetical aligned case discussed so far. A frictional increase of similar origin must generally affect other incommensurate adsorbed monolayers and contacts, to be sought out case by case.

  8. Domain structure and magnetic resonance studies of ferroelastic BiVO4 revisited

    NASA Astrophysics Data System (ADS)

    Choh, Sung Ho; Jang, Min Su

    2016-04-01

    Bismuth vanadate (BiVO4) is a ferroelastic material undergoing a reversible second order phase transition at 528 K(T c) between the tetragonal and monoclinic structure. There have been experimental studies on the incommensurate domain wall (W‧) which reported different orientation angles. In order to clarify this we have tried to calculate it numerically in terms of lattice constants above and below T c by employing the theory of Sapriel, and obtained it to be either 35.9° or 54.1°. It also turns out that the shear strain (S 21) in the ferroelastic phase depends on the crystal growing condition. The remaining internal stress appears to be responsible for the formation of W‧ wall. The host atom nuclear magnetic resonance and the S-state impurity electron magnetic resonance are also reviewed. The nuclear electric quadrupole interaction of 51V and 209Bi in BiVO4 was evaluated in terms of the point charge model based on the crystal structure. The result of electric field gradient tensor turns out to be reasonable with experimental values. The zero-field splitting tensor of Mn2+, Fe3+ and Gd3+ are also compared, and the deduced local environment of these ions in the host are confirmed. Finally the second-order phase transition according to the Landau’s framework is found in this crystal from the temperature dependence of magnetic resonance parameters. Supported by The National Academy of Sciences, Republic of Korea (2014) through SHC.

  9. Magnetic structures and physical properties of Tm3Cu4Ge4 and Tm3Cu4Sn4.

    PubMed

    Baran, S; Kaczorowski, D; Szytuła, A; Gil, A; Hoser, A

    2013-02-13

    Tm(3)Cu(4)Ge(4) crystallizes in the orthorhombic Gd(3)Cu(4)Ge(4)-type crystal structure (space group Immm) whereas Tm(3)Cu(4)Sn(4) crystallizes in a distorted variant of this structure (monoclinic space group C2/m). The compounds were studied by means of neutron diffraction, specific heat, electrical resistivity and magnetic measurements. Analysis of experimental data revealed the presence of an antiferromagnetic order below 2.8 K in both compounds. In Tm(3)Cu(4)Ge(4) the magnetic unit cell is doubled in respect to the crystal unit cell and the magnetic structure can be described by a propagation vector k = [0, 1/2, 0]. A larger magnetic unit cell was found in Tm(3)Cu(4)Sn(4), given by a propagation vector k = [1/2, 1/2, 0] (for simplicity the orthorhombic description is used for both the germanide and the stannide). Close to 2 K, in each compound an incommensurate antiferromagnetic order develops. This low-temperature magnetic phase is characterized by a propagation vector k = [1/4, 0, k(z)], where k(z) is close to 0.49 and 0.47 in Tm(3)Cu(4)Ge(4) and Tm(3)Cu(4)Sn(4), respectively. The antiferromagnetic phase transitions are clearly seen in the bulk magnetic and specific heat data of both compounds.

  10. Discrete-to-continuum modeling of weakly interacting incommensurate chains

    NASA Astrophysics Data System (ADS)

    Español, Malena I.; Golovaty, Dmitry; Wilber, J. Patrick

    2017-09-01

    In this paper we use a formal discrete-to-continuum procedure to derive a continuum variational model for two chains of atoms with slightly incommensurate lattices. The chains represent a cross section of a three-dimensional system consisting of a graphene sheet suspended over a substrate. The continuum model recovers both qualitatively and quantitatively the behavior observed in the corresponding discrete model. The numerical solutions for both models demonstrate the presence of large commensurate regions separated by localized incommensurate domain walls.

  11. Distribution of cations at two tetrahedral sites in Ca2MgSi2O7-Ca2Fe3+AlSiO7 series synthetic melilite and its relation to incommensurate structure

    NASA Astrophysics Data System (ADS)

    Hamada, Maki; Akasaka, Masahide

    2013-03-01

    Synthetic melilites on the join Ca2MgSi2O7 (åkermanite: Ak)-Ca2Fe3+AlSiO7 (ferrialuminium gehlenite: FAGeh) were studied using X-ray powder diffraction and 57Fe Mössbauer spectroscopic methods to determine the distribution of Fe3+ between two different tetrahedral sites (T1 and T2), and the relationship between ionic substitution and incommensurate (IC) structure. Melilites were synthesized from starting materials with compositions of Ak100, Ak80FAGeh20, Ak70FAGeh30 and Ak50FAGeh50 by sintering at 1,170-1,350 °C and 1 atm. The average chemical compositions and end-member components, Ak, FAGeh and Geh (Ca2Al2SiO7), of the synthetic melilites were Ca2.015Mg1.023Si1.981O7 (Ak100), Ca2.017Mg0.788Fe{0.187/3+}Al0.221Si1.791O7 (Ak78FAGeh19Geh3), Ca1.995Mg0.695Fe{0.258/3+}Al0.318Si1.723O7 (Ak69FAGeh25Geh6) and Ca1.982Mg0.495Fe{0.449/3+}Al0.519Si1.535O7 (Ak49FAGeh44Geh7), respectively. Rietveld refinements using X-ray powder diffraction data measured using Cu K α -radiation at room temperature converged successfully with goodness-of-fits of 1.15-1.26. The refined Fe occupancies at the T1 and T2 sites and the Mg and Si contents determined by electron microprobe analysis gave the site populations of [0.788Mg + 0.082Fe3+ + 0.130Al]T1[0.104Fe3+ + 0.104Al + 1.792Si]T2 for Ak78FAGeh19Geh3, [0.695Mg + 0.127Fe3+ + 0.178Al]T1[0.132Fe3+ + 0.144Al + 1.724Si]T2 for Ak69FAGeh25Geh6 and [0.495Mg + 0.202Fe3+ + 0.303Al]T1[0.248Fe3+ + 0.216Al + 1.536Si]T2 for Ak49FAGeh44Geh7 (apfu: atoms per formula unit), respectively. The results indicate that Fe3+ is distributed at both the T1 and the T2 sites. The mean T1-O distance decreases with the substitution of Fe3+ + Al3+ for Mg2+ at the T1 site, whereas the mean T2-O distance increases with substitution of Fe3+ + Al3+ for Si4+ at the T2 site, causing decrease in the a dimension and increase in the c dimension. However, in spite of the successful Rietveld refinements for the X-ray powder diffraction data measured using Cu K α-radiation at

  12. Structural and magnetic states in layered manganites: An expanding view of the phase diagram

    SciTech Connect

    Mitchell, J. F.; Millburn, J. E.; Ling, C.; Argyriou, D. N.; Bordallo, H. N.

    2000-01-05

    Colossal magnetoresistive (CMR) manganites display a spectacular range of structural, magnetic, and electronic phases as a function of hole concentration, temperature, magnetic field, etc. A1though the bulk of research has concentrated on the 3-D perovskite manganites, the ability to study anisotropic magnetic and electronic interactions made available in reduced dimensions has accelerated interest in the layered Ruddlesden-Popper (R-P) phases of the manganite class. The quest for understanding the coupling among lattice, spin, and electronic degrees of freedom (and dimensionality) is driven by the availability of high quality materials. In this talk, the authors will present recent results on synthesis and magnetic properties of layered manganites from the La{sub 2{minus}2x}Sr{sub 1+2x}Mn{sub 2}O{sub 7} series in the Mn{sup 4+}-rich regime x >0.5. This region of the composition diagram is populated by antiferromagnetic structures that evolve from the A-type layered order to G-type ''rocksalt'' order as x increases. Between these two regimes is a wide region (0.7 < x < 0.9) where an incommensurate magnetic structure is observed. The IC structure joins spin canting and phase separation as a mode for mixed-valent manganites to accommodate FM/AF competition. Transport in these materials is dominated by highly insulating behavior, although a region close to x = 0.5 exhibits metal-nonmetal transitions and an extreme sensitivity to oxygen content. They suggest two possible explanations for this transport behavior at doping just above x = O.5: localization by oxygen defects or charge ordering of Mn{sup 3+}/Mn{sup 4+}sites.

  13. Quantum Domain Walls Induce Incommensurate Supersolid Phase on the Anisotropic Triangular Lattice

    NASA Astrophysics Data System (ADS)

    Zhang, Xue-Feng; Hu, Shijie; Pelster, Axel; Eggert, Sebastian

    2016-11-01

    We investigate the extended hard-core Bose-Hubbard model on the triangular lattice as a function of spatial anisotropy with respect to both hopping and nearest-neighbor interaction strength. At half-filling the system can be tuned from decoupled one-dimensional chains to a two-dimensional solid phase with alternating density order by adjusting the anisotropic coupling. At intermediate anisotropy, however, frustration effects dominate and an incommensurate supersolid phase emerges, which is characterized by incommensurate density order as well as an anisotropic superfluid density. We demonstrate that this intermediate phase results from the proliferation of topological defects in the form of quantum bosonic domain walls. Accordingly, the structure factor has peaks at wave vectors, which are linearly related to the number of domain walls in a finite system in agreement with extensive quantum Monte Carlo simulations. We discuss possible connections with the supersolid behavior in the high-temperature superconducting striped phase.

  14. 87Rb spin-lattice relaxation times in ferroelectric-paraelectric-incommensurate phases of Rb2CoBr4 using static NMR and MAS NMR

    NASA Astrophysics Data System (ADS)

    Lim, Ae Ran

    2017-04-01

    To better elucidate the structural properties of Rb2CoBr4 in paraelectric, incommensurate, and ferroelectric phases, we studied the 87Rb nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times in laboratory frame T1 and in rotating frame T1ρ. The resonance frequency and the chemical shift do not change abruptly near the phase transition temperature of Ti = 333 K and TC = 192 K, whereas T1 and T1ρ display discontinuous changes near Ti and TC. The abrupt changes in the relaxation times near these temperatures seem to be a result of the structural phase transitions. The results are distinctly different from those reported for Rb2CoCl4.

  15. Stochastic self-assembly of incommensurate clusters.

    PubMed

    D'Orsogna, M R; Lakatos, G; Chou, T

    2012-02-28

    Nucleation and molecular aggregation are important processes in numerous physical and biological systems. In many applications, these processes often take place in confined spaces, involving a finite number of particles. Analogous to treatments of stochastic chemical reactions, we examine the classic problem of homogeneous nucleation and self-assembly by deriving and analyzing a fully discrete stochastic master equation. We enumerate the highest probability steady states, and derive exact analytical formulae for quenched and equilibrium mean cluster size distributions. Upon comparison with results obtained from the associated mass-action Becker-Döring equations, we find striking differences between the two corresponding equilibrium mean cluster concentrations. These differences depend primarily on the divisibility of the total available mass by the maximum allowed cluster size, and the remainder. When such mass "incommensurability" arises, a single remainder particle can "emulsify" the system by significantly broadening the equilibrium mean cluster size distribution. This discreteness-induced broadening effect is periodic in the total mass of the system but arises even when the system size is asymptotically large, provided the ratio of the total mass to the maximum cluster size is finite. Ironically, classic mass-action equations are fairly accurate in the coarsening regime, before equilibrium is reached, despite the presence of large stochastic fluctuations found via kinetic Monte-Carlo simulations. Our findings define a new scaling regime in which results from classic mass-action theories are qualitatively inaccurate, even in the limit of large total system size.

  16. Stochastic self-assembly of incommensurate clusters

    NASA Astrophysics Data System (ADS)

    DÓ Rsogna, Maria; Lakatos, Greg; Chou, Tom

    2013-03-01

    We examine the classic problem of homogeneous nucleation and self-assembly by deriving and analyzing a fully discrete stochastic master equation. We enumerate the highest probability steady-states, and derive exact analytical formulae for quenched and equilibrium mean cluster size distributions. Upon comparison with results obtained from the associated the mass-action Becker-Döring (BD) equations, we find striking differences between the two corresponding equilibrium mean cluster concentrations. These differences depend primarily on the divisibility of the total available mass by the maximum allowed cluster size, and the remainder. When such mass ``incommensurability'' arises, a single remainder particle can ``emulsify'' the system by significantly broadening the equilibrium mean cluster size distribution. This discreteness-induced broadening effect is periodic in the total mass of the system but arises even when the system size is asymptotically large, provided the ratio of the total mass to the maximum cluster size is finite. Our findings define a new scaling regime in which results from classic mass-action theories are qualitatively inaccurate, even in the limit of large total system size. This work supported by NSF DMS-1021818 and DMS-1021850

  17. Stochastic self-assembly of incommensurate clusters

    NASA Astrophysics Data System (ADS)

    D'Orsogna, M. R.; Lakatos, G.; Chou, T.

    2012-02-01

    Nucleation and molecular aggregation are important processes in numerous physical and biological systems. In many applications, these processes often take place in confined spaces, involving a finite number of particles. Analogous to treatments of stochastic chemical reactions, we examine the classic problem of homogeneous nucleation and self-assembly by deriving and analyzing a fully discrete stochastic master equation. We enumerate the highest probability steady states, and derive exact analytical formulae for quenched and equilibrium mean cluster size distributions. Upon comparison with results obtained from the associated mass-action Becker-Döring equations, we find striking differences between the two corresponding equilibrium mean cluster concentrations. These differences depend primarily on the divisibility of the total available mass by the maximum allowed cluster size, and the remainder. When such mass "incommensurability" arises, a single remainder particle can "emulsify" the system by significantly broadening the equilibrium mean cluster size distribution. This discreteness-induced broadening effect is periodic in the total mass of the system but arises even when the system size is asymptotically large, provided the ratio of the total mass to the maximum cluster size is finite. Ironically, classic mass-action equations are fairly accurate in the coarsening regime, before equilibrium is reached, despite the presence of large stochastic fluctuations found via kinetic Monte-Carlo simulations. Our findings define a new scaling regime in which results from classic mass-action theories are qualitatively inaccurate, even in the limit of large total system size.

  18. Field-induced magnetic states in holmium tetraboride

    NASA Astrophysics Data System (ADS)

    Brunt, D.; Balakrishnan, G.; Wildes, A. R.; Ouladdiaf, B.; Qureshi, N.; Petrenko, O. A.

    2017-01-01

    A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at TN 1=7.1 K to an incommensurate state with a propagation vector (δ ,δ ,δ') , where δ =0.02 and δ'=0.43 and at TN 2=5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3 ) -type reflections between 18 and 24 kOe. This field range is marked by the previously reported M /Msat=1/3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M /Msat≈3/5 . Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H -T phase diagram of HoB4 for the H ∥c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.

  19. Temperature-dependent multi-k magnetic structure in multiferroic Co{sub 3}TeO{sub 6}

    SciTech Connect

    Ivanov, S.A.; Tellgren, R.; Ritter, C.; Nordblad, P.; Mathieu, R.; Andre, G.; Golubko, N.V.; Politova, E.D.; Weil, M.

    2012-01-15

    Highlights: Black-Right-Pointing-Pointer Co{sub 3}TeO{sub 6} with corundum-related structure orders antiferromagnetically below 26 K. Black-Right-Pointing-Pointer A field-driven electrical polarization was observed in the antiferromagnetic state. Black-Right-Pointing-Pointer NPD data was collected and refined for ceramics and crushed single crystals. Black-Right-Pointing-Pointer Successive magnetic phase transformations are observed as a function of temperature. Black-Right-Pointing-Pointer The complex magnetic structure reflects the competing interactions in Co{sub 3}TeO{sub 6}. -- Abstract: A complex magnetic order of the multiferroic compound Co{sub 3}TeO{sub 6} has been revealed by neutron powder diffraction studies on ceramics and crushed single crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied temperature range 2-300 K but exhibits successive antiferromagnetic transitions at low temperature. Incommensurate antiferromagnetic order with the propagation vector k{sub 1} = (0, 0.485, 0.055) sets in at 26 K. A transition to a second antiferromagnetic structure with k{sub 2} = (0, 0, 0) takes place at 21.1 K. Moreover, a transition to a commensurate antiferromagnetic structure with k{sub 3} = (0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined by neutron powder diffraction using group theory analysis as a preliminary tool. Different coordinations of the Co{sup 2+} ions involved in the low-symmetry C2/c structure of Co{sub 3}TeO{sub 6} render the exchange-interaction network very complex by itself. The observed magnetic phase transformations are interpreted as an evidence of competing magnetic interactions. The temperature dependent changes in the magnetic structure, derived from refinements of high-resolution neutron data, are discussed and possible mechanisms connected with the spin reorientations are described.

  20. Mn substitution-driven structural and magnetic phase evolution in Bi1-xSmxFeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Khomchenko, V. A.; Troyanchuk, I. O.; Kovetskaya, M. I.; Paixão, J. A.

    2012-01-01

    X-ray diffraction and magnetization measurements of the Bi0.9Sm0.1Fe1-yMnyO3 and Bi0.86Sm0.14 Fe1-zMnzO3 (y ≤ 0.4, z ≤ 0.3) series were carried out in order to follow the effect of Mn doping on the room temperature crystal structure and magnetic properties of Sm-substituted BiFeO3. Initially polar rhombohedral Bi0.9Sm0.1FeO3 compound (space group R3c) was shown to undergo the Mn-substitution driven structural transformation into the orthorhombic Pnam phase at y ˜ 0.2. Further increasing of the Mn content stabilizes the modified structural phase demonstrating the features of incommensurability. In the Bi0.86Sm0.14Fe1-zMnzO3 series, the initially dominant antipolar orthorhombic Pnam phase transforms toward the nonpolar Pnma structure (z ˜ 0.3). Changes of the main magnetic state (from mixed antiferromagnetic/weak ferromagnetic to weak ferromagnetic) were found to correlate with the rhombohedral-to-orthorhombic transition; however, within the compositional range of the orthorhombically distorted compounds, the room temperature spontaneous magnetization rapidly decreases with increasing Mn content.

  1. 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)

    SciTech Connect

    Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho; Loye, Hans-Conrad zur

    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{sub 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.}.

  2. Quantum time crystal by decoherence: Proposal with an incommensurate charge density wave ring

    NASA Astrophysics Data System (ADS)

    Nakatsugawa, K.; Fujii, T.; Tanda, S.

    2017-09-01

    We show that time translation symmetry of a ring system with a macroscopic quantum ground state is broken by decoherence. In particular, we consider a ring-shaped incommensurate charge density wave (ICDW ring) threaded by a fluctuating magnetic flux: the Caldeira-Leggett model is used to model the fluctuating flux as a bath of harmonic oscillators. We show that the charge density expectation value of a quantized ICDW ring coupled to its environment oscillates periodically. The Hamiltonians considered in this model are time independent unlike "Floquet time crystals" considered recently. Our model forms a metastable quantum time crystal with a finite length in space and in time.

  3. Magnetic structure and dispersion relation of the S =1/2 quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8 in a transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Matsuda, M.; Onishi, H.; Okutani, A.; Ma, J.; Agrawal, H.; Hong, T.; Pajerowski, D. M.; Copley, J. R. D.; Okunishi, K.; Mori, M.; Kimura, S.; Hagiwara, M.

    2017-07-01

    BaCo2V2O8 consists of Co chains in which a Co2 + ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo2V2O8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis. We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 X X Z antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.

  4. Magnetic structure and dispersion relation of the S=12 quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8 in a transverse magnetic field

    DOE PAGES

    Matsuda, M.; Onishi, H.; Okutani, A.; ...

    2017-07-25

    Here, BaCo2V2O8 consists of Co chains in which a Co2+ ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo2V2O8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis. We also studied magnetic excitations as amore » function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 XXZ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.« less

  5. Guest Chain ``Melting'' in Incommensurate Host-Guest Potassium

    NASA Astrophysics Data System (ADS)

    McBride, Emma; Munro, Keith; McMahon, Malcolm

    2013-06-01

    Upon increasing pressure the group-I elements transform from close-packed structures (bcc and fcc) to a series of low-symmetry complex structures. Residing in the middle of the group, potassium (K) has numerous structures in common with its neighbours, and, in fact, is remarkably structurally similar to sodium (Na) and rubidium (Rb). For example, the post-fcc transition in K is to a composite incommensurate host-guest structure (tI19), and the host structure of this phase is isostructural with that found in Na and Rb. Previously we have reported that below 16.7GPa, the Bragg peaks from the guest component of tI19-Rb broaden considerably, signalling a loss of the inter-chain correlation, or a ``melting'' of the chains. Furthermore, in tI19-Na above 125 GPa, the Bragg peaks from the guest component are also broadened, suggesting that the guest chains are also nearly ``melted.'' During studies of the melting curve of K, we observed that the guest peaks from tI19-K broaden dramatically on heating. Here we report single-crystal, quasi-single-crystal, and powder synchrotron x-ray diffraction measurements of tI19-K to 50 GPa and 800 K, which allowed a detailed study of this chain ``melting'' transition. The order-disorder transition is clearly visible over a 30 GPa pressure range, and there are significant changes in the gradient of the phase boundary, which may be influenced by the nature of the guest structure. Furthermore, data extending the melting curve will also be presented.

  6. Structure and magnetism in the bond-frustrated spinel ZnC r2S e4

    NASA Astrophysics Data System (ADS)

    Zajdel, P.; Li, W.-Y.; van Beek, W.; Lappas, A.; Ziolkowska, A.; Jaskiewicz, S.; Stock, C.; Green, M. A.

    2017-04-01

    The crystal and magnetic structures of stoichiometric ZnC r2S e4 have been investigated using synchrotron x-ray and neutron powder diffraction, muon spin relaxation (μ SR ), and inelastic neutron scattering. Synchrotron x-ray diffraction shows a spin-lattice distortion from the cubic F d 3 ¯m spinel to a tetragonal I 41/a m d lattice below TN=21 K , where powder neutron diffraction confirms the formation of a helical magnetic structure with magnetic moment of 3.04 (3 ) μB at 1.5 K, close to that expected for high-spin C r3 + . μ SR measurements show prominent local spin correlations that are established at temperatures considerably higher (<100 K ) than the onset of long-range magnetic order. The stretched exponential nature of the relaxation in the local spin-correlation regime suggests a wide distribution of depolarizing fields. Below TN, unusually fast (>100 μ s-1) muon relaxation rates are suggestive of rapid site hopping of the muons in static field. Inelastic neutron scattering measurements show a gapless mode at an incommensurate propagation vector of k =[0 0 0.4648 (2 )] in the low-temperature magnetic ordered phase that extends to 0.8 meV. The dispersion is modeled by a two-parameter Hamiltonian, containing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions with a Jn n n/Jn n=-0.337 .

  7. Engineered Magnetic Core-Shell Structures.

    PubMed

    Alavi Nikje, Mir Mohammad; Vakili, Maryam

    2015-01-01

    In recent years, engineered magnetic core-shell structures are playing an important role in the wide range of various applications. These magnetic core-shell structures have attracted considerable attention because of their unique properties and various applications. Also, the synthesis of engineered magnetic core-shell structures has attracted practical interest because of potential applications in areas such as ferrofluids, medical imaging, drug targeting and delivery, cancer therapy, separations, and catalysis. So far a large number of engineered magnetic core-shell structures have been successfully synthesized. This review article focuses on the recent progress in synthesis and characterization of engineered magnetic core-shell structures. Also, this review gives a brief description of the various application of these structures. It is hoped that this review will play some small part in helping future developments in important field.

  8. Incommensurate phase of a triangular frustrated Heisenberg model studied via Schwinger-boson mean-field theory

    NASA Astrophysics Data System (ADS)

    Li, Peng; Su, Haibin; Dong, Hui-Ning; Shen, Shun-Qing

    2009-08-01

    We study a triangular frustrated antiferromagnetic Heisenberg model with nearest-neighbor interactions J1 and third-nearest-neighbor interactions J3 by means of Schwinger-boson mean-field theory. By setting an antiferromagnetic J3 and varying J1 from positive to negative values, we disclose the low-temperature features of its interesting incommensurate phase. The gapless dispersion of quasiparticles leads to the intrinsic T2 law of specific heat. The magnetic susceptibility is linear in temperature. The local magnetization is significantly reduced by quantum fluctuations. We address possible relevance of these results to the low-temperature properties of NiGa2S4. From a careful analysis of the incommensurate spin wavevector, the interaction parameters are estimated as J1≈-3.8755 K and J3≈14.0628 K, in order to account for the experimental data.

  9. Controlling magnetic dipole transition with magnetic plasmonic structures.

    PubMed

    Feng, Tianhua; Zhou, Ying; Liu, Dahe; Li, Jensen

    2011-06-15

    A plasmonic structure with double gold patches is proposed for enhancing the spontaneous emission of a magnetic dipole transition through a magnetic hot area. A Purcell factor of nearly 2000 can be obtained at optical frequencies together with a low sensitivity in spatial and spectral mismatches between the light emitter and the resonance mode. The associated resonance can be tuned from the visible to the IR frequencies, enabling efficient control of forbidden transitions using plasmonic structures.

  10. Depinning transition and 2D superlubricity in incommensurate colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    2014-03-01

    Colloidal monolayers sliding over periodic corrugated potential are highly tunable systems allowing to visualize the dynamics between crystalline surfaces. Based on molecular dynamics, Vanossi and coworkers reproduced the main experimental results and explored the potential impact of colloid sliding in nanotribology. The degree of interface commensurability was found to play a major role in determining the frictional properties, the static friction force Fs becoming vanishingly small in incommensurate geometries for weak corrugation U0.Lead by this result,here we systematically investigate the possibility to observe a 2D Aubry-like transition from a superlubric state to a pinned state for increasing U0. By using a reliable protocol, we generate annealed configurations at different values of U0 for an underdense monolayer. We find Fs to be vanishingly small up to a critical corrugation Uc coinciding with an abrupt structural transition in the ground state configuration. Similarly to what is observed in the Frenkel Kontorova model,this transition is characterized by a significant decrease in the number of particles sampling regions near the maxima of the substrate potential. Research partly sponsored by Sinergia Project CRSII2 136287-1 and ERC 2012ADG320796 MODPHYSFRICT.

  11. Magnetic order tuned by Cu substitution in Fe1.1-zCuzTe

    NASA Astrophysics Data System (ADS)

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, M. D.; Valdivia, P. N.; Bourret-Courchesne, E.; Gu, Genda; Lee, Dung-Hai; Tranquada, J. M.; Birgeneau, R. J.

    2012-07-01

    We study the effects of Cu substitution in Fe1.1Te, the nonsuperconducting parent compound of the iron-based superconductor, Fe1+yTe1-xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at ˜60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate ordering wave vector of (0.5-δ, 0, 0.5) with δ being the incommensurability of 0.02, and correlation length of 12 Å along the a axis and 9 Å along the c axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60 K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first-order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has a large effect on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.

  12. Magnetic order tuned by Cu substitution in Fe1.1–zCuzTe

    DOE PAGES

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; ...

    2012-07-02

    We study the effects of Cu substitution in Fe₁.₁Te, the nonsuperconducting parent compound of the iron-based superconductor, Fe₁₊yTe₁₋xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at ~60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate ordering wave vector of (0.5–δ, 0, 0.5) with δ being the incommensurability of 0.02, and correlation length of 12 Å along the a axis and 9 Å along the cmore » axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60 K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first-order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has a large effect on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.« less

  13. Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41

    DOE PAGES

    Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; ...

    2016-10-21

    Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7–1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gappedmore » and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. Furthermore, these findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.« less

  14. Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound S r14C u24O41

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Abernathy, Douglas L.; Aczel, Adam A.; Zhou, Jianshi; Delaire, Olivier; Shi, Li

    2016-10-01

    Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in S r14C u24O41 , which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7-1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in S r14C u24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. These findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.

  15. Incommensurate correlations in a S=1/2 4-leg quantum spin tube

    NASA Astrophysics Data System (ADS)

    Zheludev, Andrey; Garlea, Ovidiu; Regnault, Louis-Pierre; Habicht, Klaus

    2008-03-01

    Inelastic neutron scattering is used to investigate magnetic excitations in the quasi-one- dimensional quantum spin-liquid system Cu2Cl4-D8C4SO2. Contrary to previously conjectured models, the appropriate Heisenberg Hamiltonian is equivalent to that of a S=1/2 4-leg spin-tube with almost perfect one dimensionality and no bond alternation [1]. A partial geometric frustration of rung interactions induces a small incommensurability of short-range spin correlations. In high magnetic fields, a Bose-Einstein condensation of magnons induces a quantum phase transition to a incommensurate helimagnetic ordered state. Research at ORNL was funded by the United States Department of Energy, Office of Basic Energy Sciences- Materials Science, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. [1] V. O. Garlea , A. Zheludev, L.-P. Regnault, J.-H. Chung, Y. Qiu, M. Boehm, K. Habicht and M. Meissner, Phys. Rev. Lett., in press (2007); arXiv:0710.0891.

  16. High-field permanent-magnet structures

    SciTech Connect

    Leupoid, H.A.

    1989-08-29

    This patent describes a permanent magnet structure. It comprises an azimuthally circumscribed section of a hollow hemispherical magnetic flux source, the magnetic orientation in the section with respect to the polar axis being substantially equal to twice the polar angle, a superconducting planar sheet abutting one flat face of the section along a longitudinal meridian, and at least one other planar sheet of selected material abutting another flat face of the section and perpendicular to the first-mentioned sheet.

  17. The sun's magnetic sector structure

    NASA Technical Reports Server (NTRS)

    Svalgaard, L.; Wilcox, J. M.; Scherrer, P. H.; Howard, R.

    1975-01-01

    The synoptic appearance of solar magnetic sectors is studied using 454 sector boundaries observed at earth during 1959-1973. The sectors are clearly visible in the photospheric magnetic field. Sector boundaries can be clearly identified as north-south running demarcation lines between regions of persistent magnetic polarity imbalances. These regions extend up to about 35 deg of latitude on both sides of the equator. They generally do not extend into the polar caps. The polar cap boundary can be identified as an east-west demarcation line marking the poleward limit of the sectors. The typical flux imbalance for a magnetic sector is about 4 x 10 to the 21st power Maxwells.

  18. Disconnection of open coronal magnetic structures

    SciTech Connect

    McComas, D.J.; Phillips, J.L.; Hundhausen, A.J.; Burkepile, J.T.

    1991-01-01

    We have examined the Solar Maximum Mission coronagraph/polarimeter observations for evidence of magnetic disconnection of previously open magnetic structures and a number of likely examples have been found. Probable coronal disconnections typically appear as pinching off of helmet streamers followed by the release and outward acceleration of a large U or V-shaped structures. The observed sequence of events is consistent with reconnection across the heliospheric current sheet between previously open magnetic field regions, and the creation of a detached magnetic structure which is open to interplanetary space at both ends. Sunward of the reconnection point, coronal disconnection events would return previously open magnetic flux to the Sun as closed field arches. Here we (1) describe one clear disconnection event (1 June 1989); (2) examine the results of a limited survey of disconnection events; and (3) discuss the potential importance of coronal disconnections for maintaining flux in interplanetary space. 7 refs., 3 figs.

  19. Magnetic structures of the M {sub 2}TbF{sub 6} (M=Li, K, Rb) fluorides: A complex behavior resulting from frustration

    SciTech Connect

    Josse, M.; El-Ghozzi, M. Avignant, D.; Andre, G.; Bouree, F.

    2007-05-15

    Neutron powder diffraction has been performed on Li{sub 2}TbF{sub 6}, K{sub 2}TbF{sub 6} and Rb{sub 2}TbF{sub 6} fluoroterbates. Incommensurate long-range magnetic order is observed below T {sub N}=2.02, 1.60 and 2.07 K. The square-modulating of the magnetic structures can be correlated with the geometric frustration induced by the pseudo-hexagonal packing of the [TbF{sub 6}]{sup 2-} chains in these hexafluorides. This frustration and the magnetic interactions are discussed on the basis of experimental data and topological considerations. The magnetic structures encountered in this series, and the particular thermal evolution of the Li{sub 2}TbF{sub 6} magnetic structure may result from the competition between the magnetic interactions taking place in the chains and the magnetic interactions coupling the chains. - Graphical abstract: Pseudo-hexagonal packing of the [TbF{sub 6}]{sup 2-} chains in Li{sub 2}TbF{sub 6}.

  20. Processing incommensurately modulated protein diffraction data with Eval15

    SciTech Connect

    Porta, Jason; Lovelace, Jeffrey J.; Schreurs, Antoine M. M.; Kroon-Batenburg, Loes M. J.; Borgstahl, Gloria E. O.

    2011-07-01

    Data processing of an incommensurately modulated profilin–actin crystal is described. Recent challenges in biological X-ray crystallography include the processing of modulated diffraction data. A modulated crystal has lost its three-dimensional translational symmetry but retains long-range order that can be restored by refining a periodic modulation function. The presence of a crystal modulation is indicated by an X-ray diffraction pattern with periodic main reflections flanked by off-lattice satellite reflections. While the periodic main reflections can easily be indexed using three reciprocal-lattice vectors a*, b*, c*, the satellite reflections have a non-integral relationship to the main lattice and require a q vector for indexing. While methods for the processing of diffraction intensities from modulated small-molecule crystals are well developed, they have not been applied in protein crystallography. A recipe is presented here for processing incommensurately modulated data from a macromolecular crystal using the Eval program suite. The diffraction data are from an incommensurately modulated crystal of profilin–actin with single-order satellites parallel to b*. The steps taken in this report can be used as a guide for protein crystallographers when encountering crystal modulations. To our knowledge, this is the first report of the processing of data from an incommensurately modulated macromolecular crystal.

  1. Incommensurate Chirality Density Wave Transition in a Hybrid Molecular Framework

    NASA Astrophysics Data System (ADS)

    Hill, Joshua A.; Christensen, Kirsten E.; Goodwin, Andrew L.

    2017-09-01

    Using single-crystal x-ray diffraction we characterize the 235 K incommensurate phase transition in the hybrid molecular framework tetraethylammonium silver(I) dicyanoargentate, [NEt4]Ag3(CN )4 . We demonstrate the transition to involve spontaneous resolution of chiral [NEt4]+ conformations, giving rise to a state in which molecular chirality is incommensurately modulated throughout the crystal lattice. We refer to this state as an incommensurate chirality density wave (XDW) phase, which represents a fundamentally new type of chiral symmetry breaking in the solid state. Drawing on parallels to the incommensurate ferroelectric transition of NaNO2 , we suggest the XDW state arises through coupling between acoustic (shear) and molecular rotoinversion modes. Such coupling is symmetry forbidden at the Brillouin zone center but symmetry allowed for small but finite modulation vectors q =[0 ,0 ,qz]* . The importance of long-wavelength chirality modulations in the physics of this hybrid framework may have implications for the generation of mesoscale chiral textures, as required for advanced photonic materials.

  2. Anisotropic structure equations in magnetized quark stars

    NASA Astrophysics Data System (ADS)

    Manreza Paret, D.; Horvath, J. E.; Perez Martinez, A.

    2015-11-01

    It is well-known that a magnetic field in a fermion system breaks the SO(3) symmetry, giving rise to an anisotropy in the energy-momentum tensor and consequently in the equation of state (EoS). Thus, the stellar structure equations of magnetized quark stars (QS) demand to be derived from a more appropriate cylindrical metric. In this work we obtain these equations considering the magnetized quark matter in two phases: Magnetized Strange Quark Matter (MSQM) and Magnetized Color Flavor Locked Phase (MCFL). The main outcome of our work is the value of the maximum magnetic field that an star can hold, i.e. 1018 G. This upper bound is closely related to the violation of the virial relations and also with the instability associated with parity-violation weak processes during the collapse of supernovae.

  3. Micromagnet structures for magnetic positioning and alignment

    NASA Astrophysics Data System (ADS)

    Zanini, L. F.; Osman, O.; Frenea-Robin, M.; Haddour, N.; Dempsey, N. M.; Reyne, G.; Dumas-Bouchiat, F.

    2012-04-01

    High performance hard magnetic films (NdFeB, SmCo) have been patterned at the micron scale using thermo-magnetic patterning. Both out-of-plane and in-plane magnetized structures have been prepared. These micromagnet arrays have been used for the precise positioning and alignment of superparamagnetic nano- and microparticles. The specific spatial arrangement achieved is shown to depend on both the particle size and the size and orientation of the micromagnets. These micromagnet arrays were used to trap cells magnetically functionalized by endocytosis of 100 nm superparamagnetic particles. These simple, compact, and autonomous structures, which need neither an external magnetic field source nor a power supply, have much potential for use in a wide range of biological applications.

  4. Structure and Magnetism in fcc Magnetic Metals on (001) Diamond

    NASA Astrophysics Data System (ADS)

    Wolf, J. A.; Krebs, J. J.; Idzerda, Y. U.; Prinz, G. A.; Kemner, K. M.

    1996-03-01

    We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co, Ni, Fe) on (001) diamonds, the thickness of the films varying from ~1nm to over 100nm. The crystalline quality and fourfold symmetry of these layers was monitored in-situ during film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex-situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout the entire film. The magnetic characterization of the Co-, Ni- and Fe-films was carried out with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops, yielding information on the cubic anisotropy constant K_1, the magnetic moment M and the magnetization reversal. The Co displays extremely high quality growth and magnetic characteristics up to thicknesses well in excess of 100nm, while the Ni is tetragonally distorted resulting in an out-of-plane anisotropy component. The fcc Fe is only stable up to ~2nm before the transition to the bcc crystal structure starts.

  5. Structural alloys for high field superconducting magnets

    SciTech Connect

    Morris, J.W. Jr.

    1985-08-01

    Research toward structural alloys for use in high field superconducting magnets is international in scope, and has three principal objectives: the selection or development of suitable structural alloys for the magnet support structure, the identification of mechanical phenomena and failure modes that may influence service behavior, and the design of suitable testing procedures to provide engineering design data. This paper reviews recent progress toward the first two of these objectives. The structural alloy needs depend on the magnet design and superconductor type and differ between magnets that use monolithic and those that employ force-cooled or ICCS conductors. In the former case the central requirement is for high strength, high toughness, weldable alloys that are used in thick sections for the magnet case. In the latter case the need is for high strength, high toughness alloys that are used in thin welded sections for the conductor conduit. There is productive current research on both alloy types. The service behavior of these alloys is influenced by mechanical phenomena that are peculiar to the magnet environment, including cryogenic fatigue, magnetic effects, and cryogenic creep. The design of appropriate mechanical tests is complicated by the need for testing at 4/sup 0/K and by rate effects associated with adiabatic heating during the tests. 46 refs.

  6. Superlubric-pinned transition in sliding incommensurate colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Invernizzi, Michele; Paronuzzi, Stella; Manini, Nicola; Tosatti, Erio

    2015-10-01

    Two-dimensional (2D) crystalline colloidal monolayers sliding over a laser-induced optical lattice providing the periodic "corrugation" potential recently emerged as a new tool for the study of friction between ideal crystal surfaces. Here, we focus in particular on static friction, the minimal sliding force necessary to depin one lattice from the other. If the colloid and the optical lattices are mutually commensurate, the colloid sliding is always pinned by static friction; however, when they are incommensurate, the presence or absence of pinning can be expected to depend upon the system parameters, like in one-dimensional (1D) systems. If a 2D analogy to the mathematically established Aubry transition of one-dimensional systems were to hold, an increasing periodic corrugation strength U0 should turn an initially free-sliding, superlubric colloid into a pinned state, where the static friction force goes from zero to finite through a well-defined dynamical phase transition. We address this problem by the simulated sliding of a realistic model 2D colloidal lattice, confirming the existence of a clear and sharp superlubric-pinned transition for increasing corrugation strength. Unlike the 1D Aubry transition, which is continuous, the 2D transition exhibits a definite first-order character, with a jump of static friction. With no change of symmetry, the transition entails a structural character, with a sudden increase of the colloid-colloid interaction energy, accompanied by a compensating downward jump of the colloid-corrugation energy. The transition value for the corrugation amplitude U0 depends upon the misalignment angle θ between the optical and the colloidal lattices, superlubricity surviving until larger corrugations for angles away from the energetically favored orientation, which is itself generally slightly misaligned, as shown in recent work. The observability of the superlubric-pinned colloid transition is proposed and discussed.

  7. On the dielectric susceptibility calculation in the incommensurate phase of K2SeO4

    NASA Astrophysics Data System (ADS)

    Aslanyan, T. A.

    2010-10-01

    It is shown that the thermodynamic potential of the domain-like incommensurate (IC) phase of the K2SeO4crystal (viewed as a model for the IC-C transition) should be supplemented with a term, taking into account the local, Lorentz electric field. The latter qualitatively changes the result of calculation of the dielectric susceptibility for this IC structure by Nattermann and Trimper, J. Phys. C: Solid State Phys. 14, 1603, (1981), and gives phase transition to the ferroelectric IC phase obtained by Aslanyan, Phys. Rev. B 70, 024102, (2004).

  8. Clock-model description of incommensurate ferroelectric films and of nematic-liquid-crystal films

    SciTech Connect

    Srolovitz, D.J.; Scott, J.F.

    1986-08-01

    The transmission electron micrographs of submicrometer-thick specimens of incommensurate barium sodium niobate obtained by Xiao-qing e-italict-italic a-italicl-italic. exhibit textures with lines of disclinations ending in vertices of Friedel index m-italic = +1. These are similar to those observed in nematic-liquid-crystal films with continuously degenerate boundary conditions. The nature of the vertices at which these lines meet permits us to examine the physical and topological basis for the equivalence of the two systems. A four-state clock model, in two dimensions, is shown to predict the observed structure.

  9. Basic study of magnetic microwires for sensor applications: Variety of magnetic structures

    NASA Astrophysics Data System (ADS)

    Chizhik, Alexander; Zhukov, Arcady; Gonzalez, Julian; Stupakiewicz, Andrzej

    2017-01-01

    We examine magnetic glass-coated microwires used for magnetic sensors. Images of domain structures and magnetization reversal were obtained with magneto-optical Kerr microscopy. Of particular importance were temperature-induced transformations of surface magnetic structures. Different surface magnetic domains coexist, characterized by various domain periods, magnetization directions, and nobilities of domain walls.

  10. Magnetic order tuned by Cu substitution in Fe1.1–zCuzTe

    SciTech Connect

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, M. D.; Valdivia, P. N.; Bourret-Courchesne, E.; Gu, Genda; Lee, Dung-Hai; Tranquada, J. M.; Birgeneau, R. J.

    2012-07-02

    We study the effects of Cu substitution in Fe₁.₁Te, the nonsuperconducting parent compound of the iron-based superconductor, Fe₁₊yTe₁₋xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at ~60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate ordering wave vector of (0.5–δ, 0, 0.5) with δ being the incommensurability of 0.02, and correlation length of 12 Å along the a axis and 9 Å along the c axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60 K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first-order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has a large effect on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.

  11. Magnetic texturing due to the partial ordering of Fe+3 and Cu+2 in NdBaCuFeO5

    NASA Astrophysics Data System (ADS)

    Pissas, M.

    2017-06-01

    The crystal and magnetic structure of the oxygen deficient double perovskite NdBaCuFeO5 was studied, using neutron powder diffraction data. The structure was refined from neutron powder diffraction data using the space groups P 4 / mmm and P 4 mm . For 2K ⩽ T ⩽TN2 = 260K three families of magnetic Bragg peaks exist. These peaks can be indexed with commensurate propagation vectors k1 =[1/21/21/2 ] ,k2 =[1/21/2 0 ] and the incommensurate k3 =[1/21/2 0.4 ] . Above TN2 only magnetic Bragg peaks originated from k1 and k2 propagation, were observed. The incommensurate magnetic structure can be attributed to a circular inclined spiral ordering as in YBaCuFeO5 compound.

  12. Stellar magnetic structure and activity /theory/

    NASA Astrophysics Data System (ADS)

    Weiss, N. O.

    Both the overall behavior of the solar cycle and the underlying fine structure of magnetic fields in the sun have been studied mathematically in some detail. These theories are summarized and different phenomenological models of the solar cycle are reviewed. In order to provide a description of the magnetic fields in late-type stars it is necessary to extrapolate boldly from what is known about the sun. In this way field strengths and configurations can be estimated.

  13. Impact structures seen by magnetic anomaly maps

    NASA Astrophysics Data System (ADS)

    Isac, Anca; Mandea, Mioara; Purucker, Michael

    2010-05-01

    The terrestrial planets are open systems and impacting was and it can be a very important process for the planetary evolution. Earth has an active dynamo, however neither Moon and Mars have an active one. The magnetized rocks in their crusts suggest that in their earlier history, dynamos may have been operating in the metallic core of these bodies. Because of its large iron core the possibility of an ancient operating Martian dynamo is more likely, but the small lunar core and the age of the magnetized lunar rocks, have brought in debate a possible dynamo origin of lunar magnetism. The magnetic fields have been observed at global scale only for the Earth, Mars and Moon, and very conspicuous magnetic anomalies have been estimated for these three bodies. For this study, we firstly have used the largest impact structures for the Earth, Mars and Moon. Thereafter, we have extended our work to smaller martian and lunar impact craters (30 km diameters), cataloging them in order to obtain information about the impact crater magnetic signatures, positions, shapes and diameters. We superposed ULCN 2005 or Kaguya 2008 gridded topography on Lunar Prospector magnetic map for Moon and Mars Orbiting Laser Altimeter (MOLA) gridded data on Mars Global Surveyor magnetic data for Mars, as a systematic search for Quasi-Circular Depressions. The results obtain for Mars and Moon, obtained for a larger number of craters allow us to have a statistical view on the indicated parameters.

  14. Structural and magnetic phase transitions in CeCu6-xTx (T = Ag,Pd)

    DOE PAGES

    Poudel, Lekhanath N.; De la cruz, Clarina; Payzant, E. Andrew; ...

    2015-12-15

    The structural and the magnetic properties of CeCu6-xAgx (0 ≤ x ≤ 0.85) and CeCu6-xPdx (0 ≤ x ≤ 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P21/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈ 0.1. The structural transitionmore » in CeCu6-xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x ≈ 0.2 and x ≈ 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ1 0 δ2), where δ1 ~ 0.62, δ2 ~ 0.25, x = 0.125 for CeCu6-xPdx and δ1 ~ 0.64, δ2 ~ 0.3, x = 0.3 for CeCu6-xAgx. As a result, the magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.« less

  15. Nanoscale Magnetic Structure of Non-Joulian Magnets

    NASA Astrophysics Data System (ADS)

    Chandrasena, Ravini; Yang, Weibing; Scholl, Andreas; Minar, Jan; Shafer, Padraic; Arenholz, Elke; Ebert, Hubert; Gray, Alexander; Chopra, Harsh Deep

    Strain dependence of magnetic anisotropy energy produces Joule magnetostriction that is a volume conserving process, whereas sensitivity of isotropic exchange energy to interatomic distance is the cause of volume magnetostriction. In a typical magnet, Joule magnetostriction dominates as the volume fraction occupied by regions of uniform spin alignment (domains) is 2-4 orders of magnitude higher than that which is occupied by regions with magnetoelastic gradients (domain walls). Recently, `giant' non-volume conserving or non-Joulian magnetostriction has been discovered in iron-gallium alloys. Here we show using high-resolution polarization-dependent photoelectron microscopy that non-Joulian magnetism arises from an unusual partition of the crystal into nm-scale lamellar domains and domain walls within highly periodic magnetic microcells. High-resolution x-ray circular dichroism measurements at the Fe and Ga L absorption edges further provide evidence of weak iron-induced magnetism on gallium atoms via negative exchange. The results are in excellent agreement with the state-of-the-art theoretical electronic-structure calculations.

  16. Role of electronic structure in magnetic tunneling

    NASA Astrophysics Data System (ADS)

    Wang, Kuising; Zhang, Shufeng; Levy, Peter M.; Szunyogh, Laszlo; Weinberger, Peter

    1998-11-01

    To assess the effect of electronic structure of magnetic electrodes on the magnetoresistance of tunnel junctions (JMR) we made ab initio calculations of the electronic structure of BCC(1 0 0) Fe, and FCC(1 0 0) Co and Ni electrodes. We treat hopping to and propagation in the barrier as adjustable parameters and discuss features of the JMR attributable to the electronic structure of the electrodes.

  17. Seismic probes of solar interior magnetic structure.

    PubMed

    Hanasoge, Shravan; Birch, Aaron; Gizon, Laurent; Tromp, Jeroen

    2012-09-07

    Sun spots are prominent manifestations of solar magnetoconvection, and imaging their subsurface structure is an outstanding problem of wide physical importance. Travel times of seismic waves that propagate through these structures are typically used as inputs to inversions. Despite the presence of strongly anisotropic magnetic waveguides, these measurements have always been interpreted in terms of changes to isotropic wave speeds and flow-advection-related Doppler shifts. Here, we employ partial-differential-equation-constrained optimization to determine the appropriate parametrization of the structural properties of the magnetic interior. Seven different wave speeds fully characterize helioseismic wave propagation: the isotropic sound speed, a Doppler-shifting flow-advection velocity, and an anisotropic magnetic velocity. The structure of magnetic media is sensed by magnetoacoustic slow and fast modes and Alfvén waves, each of which propagates at a different wave speed. We show that even in the case of weak magnetic fields, significant errors may be incurred if these anisotropies are not accounted for in inversions. Translation invariance is demonstrably lost. These developments render plausible the accurate seismic imaging of magnetoconvection in the Sun.

  18. Core-Shell Structured Magnetic Ternary Nanocubes

    SciTech Connect

    Wang, Lingyan; Wang, Xin; Luo, Jin; Wanjala, Bridgid N.; Wang, Chong M.; Chernova, Natalya; Engelhard, Mark H.; Liu, Yao; Bae, In-Tae; Zhong, Chuan-Jian

    2010-12-01

    While transition metal-doped ferrite nanoparticles constitute an important class of soft magnetic nanomaterials with spinel structures, the ability to control the shape and composition would enable a wide range of applications in homogeneous or heterogeneous reactions such as catalysis and magnetic separation of biomolecules. This report describes novel findings of an investigation of core-shell structured MnZn ferrite nanocubes synthesized in organic solvents by manipulating the reaction temperature and capping agent composition in the absence of the conventionally-used reducing agents. The core-shell structure of the highly-monodispersed nanocubes (~20 nm) are shown to consist of an Fe3O4 core and an (Mn0.5Zn0.5)(Fe0.9, Mn1.1)O4 shell. In comparison with Fe3O4 and other binary ferrite nanoparticles, the core-shell structured nanocubes were shown to display magnetic properties regulated by a combination of the core-shell composition, leading to a higher coercivity (~350 Oe) and field-cool/zero-field-cool characteristics drastically different from many regular MnZn ferrite nanoparticles. The findings are discussed in terms of the unique core-shell composition, the understanding of which has important implication to the exploration of this class of soft magnetic nanomaterials in many potential applications such as magnetic resonance imaging, fuel cells, and batteries.

  19. Quantum Spin Fluctuations for a Distorted Incommensurate Spiral

    SciTech Connect

    Fishman, Randy Scott

    2012-01-01

    Quantum spin fluctuations are investigated for the incommensurate state of a geometrically- frustrated triangular-lattice antiferromagnet. With increasing anisotropy, the average suppression of the spin by quantum fluctuations is reduced but the distorted spiral becomes more elliptical. Quan- tum fluctuations also increase the wavevector of the spin state and enhance the critical anisotropy above which a collinear spin state is stabilized. An experimental technique is proposed to isolate the effect of quantum fluctuations from the classical distortion of the spiral.

  20. Processing incommensurately modulated protein diffraction data with Eval15.

    PubMed

    Porta, Jason; Lovelace, Jeffrey J; Schreurs, Antoine M M; Kroon-Batenburg, Loes M J; Borgstahl, Gloria E O

    2011-07-01

    Recent challenges in biological X-ray crystallography include the processing of modulated diffraction data. A modulated crystal has lost its three-dimensional translational symmetry but retains long-range order that can be restored by refining a periodic modulation function. The presence of a crystal modulation is indicated by an X-ray diffraction pattern with periodic main reflections flanked by off-lattice satellite reflections. While the periodic main reflections can easily be indexed using three reciprocal-lattice vectors a*, b*, c*, the satellite reflections have a non-integral relationship to the main lattice and require a q vector for indexing. While methods for the processing of diffraction intensities from modulated small-molecule crystals are well developed, they have not been applied in protein crystallography. A recipe is presented here for processing incommensurately modulated data from a macromolecular crystal using the Eval program suite. The diffraction data are from an incommensurately modulated crystal of profilin-actin with single-order satellites parallel to b*. The steps taken in this report can be used as a guide for protein crystallographers when encountering crystal modulations. To our knowledge, this is the first report of the processing of data from an incommensurately modulated macromolecular crystal.

  1. Structural characterization of copolymer embedded magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Nedelcu, G. G.; Nastro, A.; Filippelli, L.; Cazacu, M.; Iacob, M.; Rossi, C. Oliviero; Popa, A.; Toloman, D.; Dobromir, M.; Iacomi, F.

    2015-10-01

    Small magnetic nanoparticles (Fe3O4) were synthesized by co-precipitation and coated by emulsion polymerization with poly(methyl methacrylate-co-acrylic acid) (PMMA-co-AAc) to create surface functional groups that can attach drug molecules and other biomolecules. The coated and uncoated magnetite nanoparticles were stored for two years in normal closed ships and than characterized by Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, vibrating sample magnetometry, and electron paramagnetic resonance spectroscopy. The solid phase transformation of magnetite to maghemite, as well as an increase in particle size were evidenced for the uncoated nanoparticles. The coated nanoparticles preserved their magnetite structure and magnetic properties. The influences of monomers and surfactant layers on interactions between the magnetic nanoparticles evidenced that the thickness of the polymer has a significant effect on magnetic properties.

  2. Multiscale Dynamics of Solar Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Uritsky, Vadim M.; Davila, Joseph M.

    2012-03-01

    Multiscale topological complexity of the solar magnetic field is among the primary factors controlling energy release in the corona, including associated processes in the photospheric and chromospheric boundaries. We present a new approach for analyzing multiscale behavior of the photospheric magnetic flux underlying these dynamics as depicted by a sequence of high-resolution solar magnetograms. The approach involves two basic processing steps: (1) identification of timing and location of magnetic flux origin and demise events (as defined by DeForest et al.) by tracking spatiotemporal evolution of unipolar and bipolar photospheric regions, and (2) analysis of collective behavior of the detected magnetic events using a generalized version of the Grassberger-Procaccia correlation integral algorithm. The scale-free nature of the developed algorithms makes it possible to characterize the dynamics of the photospheric network across a wide range of distances and relaxation times. Three types of photospheric conditions are considered to test the method: a quiet photosphere, a solar active region (NOAA 10365) in a quiescent non-flaring state, and the same active region during a period of M-class flares. The results obtained show (1) the presence of a topologically complex asymmetrically fragmented magnetic network in the quiet photosphere driven by meso- and supergranulation, (2) the formation of non-potential magnetic structures with complex polarity separation lines inside the active region, and (3) statistical signatures of canceling bipolar magnetic structures coinciding with flaring activity in the active region. Each of these effects can represent an unstable magnetic configuration acting as an energy source for coronal dissipation and heating.

  3. Multiscale Dynamics of Solar Magnetic Structures

    NASA Technical Reports Server (NTRS)

    Uritsky, Vadim M.; Davila, Joseph M.

    2012-01-01

    Multiscale topological complexity of the solar magnetic field is among the primary factors controlling energy release in the corona, including associated processes in the photospheric and chromospheric boundaries.We present a new approach for analyzing multiscale behavior of the photospheric magnetic flux underlying these dynamics as depicted by a sequence of high-resolution solar magnetograms. The approach involves two basic processing steps: (1) identification of timing and location of magnetic flux origin and demise events (as defined by DeForest et al.) by tracking spatiotemporal evolution of unipolar and bipolar photospheric regions, and (2) analysis of collective behavior of the detected magnetic events using a generalized version of the Grassberger-Procaccia correlation integral algorithm. The scale-free nature of the developed algorithms makes it possible to characterize the dynamics of the photospheric network across a wide range of distances and relaxation times. Three types of photospheric conditions are considered to test the method: a quiet photosphere, a solar active region (NOAA 10365) in a quiescent non-flaring state, and the same active region during a period of M-class flares. The results obtained show (1) the presence of a topologically complex asymmetrically fragmented magnetic network in the quiet photosphere driven by meso- and supergranulation, (2) the formation of non-potential magnetic structures with complex polarity separation lines inside the active region, and (3) statistical signatures of canceling bipolar magnetic structures coinciding with flaring activity in the active region. Each of these effects can represent an unstable magnetic configuration acting as an energy source for coronal dissipation and heating.

  4. Core-shell-structured magnetic ternary nanocubes.

    PubMed

    Wang, Lingyan; Wang, Xin; Luo, Jin; Wanjala, Bridgid N; Wang, Chongmin; Chernova, Natasha A; Engelhard, Mark H; Liu, Yao; Bae, In-Tae; Zhong, Chuan-Jian

    2010-12-22

    We report a novel core-shell-structured ternary nanocube of MnZn ferrite synthesized by controlling the reaction temperature and composition in the absence of conventionally used reducing agents. The highly monodispersed core-shell structure consists of an Fe(3)O(4) core and an MnZn Ferrite shell. The observation of a Moiré pattern indicates that the core and the shell are two highly crystalline materials with slightly different lattice constants that are rotated relative to each other by a small angle. The ternary core-shell nanocubes display magnetic properties regulated by a combination of the core-shell composition and exhibit an increased coercivity and field-cooled/zero-field-cooled characteristics drastically different from those of regular MnZn ferrite nanoparticles. The ability to engineer the spatial nanostructures of ternary magnetic nanoparticles in terms of shape and composition offers atomic-level versatility in fine-tuning the nanoscale magnetic properties.

  5. Mobility edges in one-dimensional bichromatic incommensurate potentials

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Li, Xiaopeng; Das Sarma, S.

    2017-08-01

    We theoretically study a one-dimensional (1D) mutually incommensurate bichromatic lattice system, which has been implemented in ultracold atoms to study quantum localization. It has been universally believed that the tight-binding version of this bichromatic incommensurate system is represented by the well-known Aubry-Andre model capturing all the essential localization physics in the experimental cold atom optical lattice system. Here we establish that this belief is incorrect and that the Aubry-Andre model description, which applies only in the extreme tight-binding limit of a very deep primary lattice potential, generically breaks down near the localization transition due to the unavoidable appearance of single-particle mobility edges (SPME). In fact, we show that the 1D bichromatic incommensurate potential system manifests generic mobility edges, which disappear in the tight-binding limit, leading to the well-studied Aubry-Andre physics. We carry out an extensive study of the localization properties of the 1D incommensurate optical lattice without making any tight-binding approximation. We find that, for the full lattice system, an intermediate phase between completely localized and completely delocalized regions appears due to the existence of the SPME, making the system qualitatively distinct from the Aubry-Andre prediction. Using the Wegner flow approach, we show that the SPME in the real lattice system can be attributed to significant corrections of higher-order harmonics in the lattice potential, which are absent in the strict tight-binding limit. We calculate the dynamical consequences of the intermediate phase in detail to guide future experimental investigations for the observation of 1D SPME and the associated intermediate (i.e., neither purely localized nor purely delocalized) phase. We consider effects of interaction numerically, and conjecture the stability of SPME to weak interaction effects, thus leading to the exciting possibility of an

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

    SciTech Connect

    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 Cu$^{2+}$ 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

  7. High performance hybrid magnetic structure for biotechnology applications

    DOEpatents

    Humphries, David E.; Pollard, Martin J.; Elkin, Christopher J.

    2006-12-12

    The present disclosure provides a high performance hybrid magnetic structure made from a combination of permanent magnets and ferromagnetic pole materials which are assembled in a predetermined array. The hybrid magnetic structure provides for separation and other biotechnology applications involving holding, manipulation, or separation of magnetic or magnetizable molecular structures and targets. Also disclosed are: a method of assembling the hybrid magnetic plates, a high throughput protocol featuring the hybrid magnetic structure, and other embodiments of the ferromagnetic pole shape, attachment and adapter interfaces for adapting the use of the hybrid magnetic structure for use with liquid handling and other robots for use in high throughput processes.

  8. Incommensurate growth of Co thin film on close-packed Ag(111) surface

    NASA Astrophysics Data System (ADS)

    Barman, Sukanta; Menon, Krishna Kumar S. R.

    2016-05-01

    Growth of ultrathin Co layers on close-packed Ag(111)were investigated by means of Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Angle-resolved Photoemission Spectroscopy(ARPES) techniques. The close-packed hexagonal face of Co(0001), exhibits a lattice misfit about 13% with Ag(111) surface which manipulates the growth to be incommensurate up to a certain thickness. The strain field causes aperiodic height undulation in the sub-angstrom regime of the film which was confirmed by p(1 × 1) LEED pattern along with a 6-fold moiré reconstruction pattern in the lower film thickness (up to ˜2ML). The evolution of the LEED pattern was studied with increasing film coverage. Lattice strain was measured with respect to the relative positions of these double spots as a functionof film thickness. Almost a constant strain (˜13%) in the full range of film thickness explains the moiré pattern formation in order to stabilize the incommensurate growth. For higher film coverages, an epitaxial well-ordered commensurate growth was observed. Core level and valance band electronic structures of these films were studied by XPS and ARPES techniques.

  9. Incommensurate growth of Co thin film on close-packed Ag(111) surface

    SciTech Connect

    Barman, Sukanta Menon, Krishna Kumar S. R.

    2016-05-06

    Growth of ultrathin Co layers on close-packed Ag(111)were investigated by means of Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Angle-resolved Photoemission Spectroscopy(ARPES) techniques. The close-packed hexagonal face of Co(0001), exhibits a lattice misfit about 13% with Ag(111) surface which manipulates the growth to be incommensurate up to a certain thickness. The strain field causes aperiodic height undulation in the sub-angstrom regime of the film which was confirmed by p(1 × 1) LEED pattern along with a 6-fold moiré reconstruction pattern in the lower film thickness (up to ∼2ML). The evolution of the LEED pattern was studied with increasing film coverage. Lattice strain was measured with respect to the relative positions of these double spots as a functionof film thickness. Almost a constant strain (∼13%) in the full range of film thickness explains the moiré pattern formation in order to stabilize the incommensurate growth. For higher film coverages, an epitaxial well-ordered commensurate growth was observed. Core level and valance band electronic structures of these films were studied by XPS and ARPES techniques.

  10. Second order incommensurate phase transition in 25L-Ta{sub 2}O{sub 5}

    SciTech Connect

    Audier, M.; Chenevier, B.; Roussel, H.; Lintanf Salauen, A.

    2010-09-15

    A new structural state 25L-Ta{sub 2}O{sub 5}, obtained from sintering and annealing treatments of a Ta{sub 2}O{sub 5} powder, is identified both by electron diffraction and high resolution imaging on a transmission electron microscope (TEM). According to general rules for the different L-Ta{sub 2}O{sub 5} structures proposed by Grey et al. (J. Solid State Chem. 178 (2005) 3308), a structural model is derived from their crystallographic data on 19L-Ta{sub 2}O{sub 5}. This model yields simulated images in agreement with high resolution TEM observations of the structure oriented along its [001] zone axis, but only for a very thin crystal thickness of less than 1.2 nm. Such a limitation is shown to be due to a modulation of the structure along its [001] axis. Actually, from an analysis of a diffuse scattering and of its evolution into satellites reflections as a function of the cooling rate, a second order incommensurate phase transition can be assumed to occur in this compound. The property of single phase samples observed by TEM is also verified by X-ray powder diffraction. In a discussion about studies performed by different authors on incommensurate structures in the system Ta{sub 2}O{sub 5}-WO{sub 3}, it is noticed that TEM results, similar to ours, indicate that phase transitions could be expected in these structures. - Graphical Abstract: Electron diffraction patterns of [100] zone axis, showing a structural change of the 25L-Ta{sub 2}O{sub 5} phase through a variation of the cooling rate from 1000 {sup o}C.

  11. Method and apparatus for control of a magnetic structure

    DOEpatents

    Challenger, Michael P.; Valla, Arthur S.

    1996-06-18

    A method and apparatus for independently adjusting the spacing between opposing magnet arrays in charged particle based light sources. Adjustment mechanisms between each of the magnet arrays and the supporting structure allow the gap between the two magnet arrays to be independently adjusted. In addition, spherical bearings in the linkages to the magnet arrays permit the transverse angular orientation of the magnet arrays to also be adjusted. The opposing magnet arrays can be supported above the ground by the structural support.

  12. Hyperfine field and magnetic structure in the B phase of CeCoIn5

    SciTech Connect

    Graf, Matthias J; Curro, Nicholas J; Young, Ben - Li; Urbano, Ricardo R

    2009-01-01

    We re-analyze Nuclear Magnetic Resonance (NMR) spectra observed at low temperatures and high magnetic fields in the field-induced B-phase of CeCoIn{sub 5}. The NMR spectra are consistent with incommensurate antiferromagnetic order of the Ce magnetic moments. However, we find that the spectra of the In(2) sites depend critically on the direction of the ordered moments, the ordering wavevector and the symmetry of the hyperfine coupling to the Ce spins. Assuming isotropic hyperfine coupling, the NMR spectra observed for H {parallel} [100] are consistent with magnetic order with wavevector Q = {pi}(1+{delta}/a, 1/a, 1/c) and Ce moments ordered antiferromagnetically along the [100] direction in real space. If the hyperfine coupling has dipolar symmetry, then the NMR spectra require Ce moments along the [001] direction. The dipolar scenario is also consistent with recent neutron scattering measurements that find an ordered moment of 0.15{micro}{sub B} along [001] and Q{sub n} = {pi}(1+{delta}/a, 1+{delta}c, 1/c) with incommensuration {delta} = 0.12 for field H {parallel} [1{bar 1}0]. Using these parameters, we find that the hyperfine field is consistent with both experiments. We speculate that the B phase of CeCoIn{sub 5} represents an intrinsic phase of modulated superconductivity and antiferromagnetism that can only emerge in a highly clean system.

  13. The vortex structure of magnetic solitons

    NASA Astrophysics Data System (ADS)

    Kovalev, A. S.

    2017-02-01

    Soliton excitations in the general form are considered using the classical model, in a two-dimensional easy-plane ferromagnet. Equations are derived and solved for small-amplitude two-parameter dynamic solitons. It is demonstrated that they have a vortex structure and that as their amplitude increases, the excitations turn into coupled quadrupole vortex states that are characterized by two dynamic parameters: the soliton velocity and its internal precession frequency. The limit transitions of vortex solitons in the general form into vortex dipoles, magnetic lamps, and magnon droplets, are analyzed. The obtained results are compared against the corresponding information about solitons in one-dimensional magnetic systems.

  14. Anomalous lattice compression and magnetic ordering in CuO at high pressures: A structural study and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Kozlenko, D. P.; DruŻbicki, K.; Kichanov, S. E.; Lukin, E. V.; Liermann, H.-P.; Glazyrin, K. V.; Savenko, B. N.

    2017-02-01

    The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-ray powder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations. Anomalous lattice compression is observed, with enlargement of the lattice parameter a , reaching a maximum at P = 13 GPa , followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at high pressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the square fourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural properties and electronic structure of CuO was successfully elucidated in the framework of full-electronic density functional theory calculations with range-separated HSE06, and meta-generalized gradient approximation hybrid M06 functionals. The antiferromagnetic (AFM) ground state with a propagation vector q = (0.5 , 0 , -0.5 ) remains stable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of the principal superexchange magnetic interactions were analyzed, and the pressure behavior of the Néel temperature as well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic state to the commensurate AFM ground state were evaluated. The estimated upper limit of the Néel temperature at P = 38 GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at room temperature and high pressure.

  15. Magnetic Field Structure in Relativistic Jets

    NASA Astrophysics Data System (ADS)

    Jermak, Helen; Mundell, Carole; Steele, Iain; Harrison, Richard; Kobayashi, Shiho; Lindfors, Elina; Nilsson, Kari; Barres de Almeida, Ulisses

    2013-12-01

    Relativistic jets are ubiquitous when considering an accreting black hole. Two of the most extreme examples of these systems are blazars and gamma-ray bursts (GRBs), the jets of which are thought to be threaded with a magnetic field of unknown structure. The systems are made up of a black hole accreting matter and producing, as a result, relativistic jets of plasma from the poles of the black hole. Both systems are viewed as point sources from Earth, making it impossible to spatially resolve the jet. In order to explore the structure of the magnetic field within the jet we take polarisation measurements with the RINGO polarimeters on the world's largest fully autonomous, robotic optical telescope: The Liverpool Telescope. Using the polarisation degree and angle measured by the RINGO polarimeters it is possible to distinguish between global magnetic fields created in the central engine and random tangled magnetic fields produced locally in shocks. We also monitor blazar sources regularly during quiescence with periods of flaring monitored more intensively. Reported here are the early polarisation results for GRBs 060418 and 090102, along with future prospects for the Liverpool Telescope and the RINGO polarimeters.

  16. High performance hybrid magnetic structure for biotechnology applications

    DOEpatents

    Humphries, David E; Pollard, Martin J; Elkin, Christopher J

    2005-10-11

    The present disclosure provides a high performance hybrid magnetic structure made from a combination of permanent magnets and ferromagnetic pole materials which are assembled in a predetermined array. The hybrid magnetic structure provides means for separation and other biotechnology applications involving holding, manipulation, or separation of magnetizable molecular structures and targets. Also disclosed are: a method of assembling the hybrid magnetic plates, a high throughput protocol featuring the hybrid magnetic structure, and other embodiments of the ferromagnetic pole shape, attachment and adapter interfaces for adapting the use of the hybrid magnetic structure for use with liquid handling and other robots for use in high throughput processes.

  17. High performance hybrid magnetic structure for biotechnology applications

    DOEpatents

    Humphries, David E [El Cerrito, CA; Pollard, Martin J [El Cerrito, CA; Elkin, Christopher J [San Ramon, CA

    2009-02-03

    The present disclosure provides a high performance hybrid magnetic structure made from a combination of permanent magnets and ferromagnetic pole materials which are assembled in a predetermined array. The hybrid magnetic structure provides means for separation and other biotechnology applications involving holding, manipulation, or separation of magnetic or magnetizable molecular structures and targets. Also disclosed are further improvements to aspects of the hybrid magnetic structure, including additional elements and for adapting the use of the hybrid magnetic structure for use in biotechnology and high throughput processes.

  18. Growth of two dimensional silica and aluminosilicate bilayers on Pd(111): from incommensurate to commensurate crystalline.

    PubMed

    Jhang, Jin-Hao; Zhou, Chao; Dagdeviren, Omur E; Hutchings, Gregory S; Schwarz, Udo D; Altman, Eric I

    2017-05-31

    Two-dimensional (2D) silica (SiO2) and aluminosilicate (AlSi3O8) bilayers grown on Pd(111) were fabricated and systematically studied using ultrahigh vacuum surface analysis in combination with theoretical methods, including Auger electron spectroscopy, X-ray photoelectron spectroscopy, low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory. Based on LEED results, both SiO2 and AlSi3O8 bilayers start ordering above 850 K in 2 × 10(-6) Torr oxygen. Both bilayers show hexagonal LEED patterns with a periodicity approximately twice that of the Pd(111) surface. Importantly, the SiO2 bilayer forms an incommensurate crystalline structure whereas the AlSi3O8 bilayer crystallizes in a commensurate structure. The incommensurate crystalline SiO2 structure on Pd(111) resulted in a moiré pattern observed with LEED and STM. Theoretical results show that straining the pure SiO2 bilayer to match Pd(111) would cost 0.492 eV per unit cell; this strain energy is reduced to just 0.126 eV per unit cell by replacing 25% of the Si with Al which softens the material and expands the unstrained lattice. Furthermore, the missing electron created by substituting Al(3+) for Si(4+) is supplied by Pd creating a chemical bond to the AlSi3O8 bilayer, whereas van der Waals interactions predominate for the SiO2 bilayer. The results reveal how the interplay between strain, doping, and charge transfer determine the structure of metal-supported 2D silicate bilayers and how these variables may potentially be exploited to manipulate 2D materials structures.

  19. Magnetic Micro/Nano Structures for Biological Manipulation

    NASA Astrophysics Data System (ADS)

    Huang, Chen-Yu; Hsieh, Teng-Fu; Chang, Wei-Chieh; Yeh, Kun-Chieh; Hsu, Ming-Shinn; Chang, Ching-Ray; Chen, Jiann-Yeu; Wei, Zung-Hang

    2016-05-01

    Biomanipulation based on micro/nano structures is an attractive approach for biotechnology. To manipulate biological systems by magnetic forces, the magnetic labeling technology utilized magnetic nanoparticles (MNPs) as a common rule. Ferrofluid, well-dispersed MNPs, can be used for magnetic modification of the surface or as molds to form organized microstructures. For magnetic-based micro/nano structures, different methods to modulate magnetic field at the microscale have been developed. Specifically, this review focused on a new strategy which uses the concept of micromagnetism of patterned magnetic thin film with specific domain walls configurations to generate stable magnetic poles for cell patterning.

  20. The vector structure of active magnetic fields

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1985-01-01

    Observations are needed to show the form of the strains introduced into the fields above the surface of the Sun. The longitudinal component alone does not provide the basic information, so that it has been necessary in the past to use the filamentary structure observed in H sub alpha to supplement the longitudinal information. Vector measurements provide the additional essential information to determine the strains, with the filamentary structure available as a check for consistency. It is to be expected, then, that vector measurements will permit a direct mapping of the strains imposed on the magnetic fields of active regions. It will be interesting to study the relation of those strains to the emergence of magnetic flux, flares, eruptive prominences, etc. In particular we may hope to study the relaxation of the strains via the dynamical nonequilibrium.

  1. Localization in momentum space of ultracold atoms in incommensurate lattices

    SciTech Connect

    Larcher, M.; Dalfovo, F.; Modugno, M.

    2011-01-15

    We characterize the disorder-induced localization in momentum space for ultracold atoms in one-dimensional incommensurate lattices, according to the dual Aubry-Andre model. For low disorder the system is localized in momentum space, and the momentum distribution exhibits time-periodic oscillations of the relative intensity of its components. The behavior of these oscillations is explained by means of a simple three-mode approximation. We predict their frequency and visibility by using typical parameters of feasible experiments. Above the transition the system diffuses in momentum space, and the oscillations vanish when averaged over different realizations, offering a clear signature of the transition.

  2. Emergent incommensurate correlations in frustrated ferromagnetic spin-1 chains

    NASA Astrophysics Data System (ADS)

    Lee, Hyeong Jun; Choi, MooYoung; Jeon, Gun Sang

    2017-01-01

    We study frustrated ferromagnetic spin-1 chains, where the ferromagnetic nearest-neighbor coupling competes with the antiferromagnetic next-nearest-neighbor coupling. We use the density-matrix renormalization group to obtain the ground states. Through the analysis of spin-spin correlations we identify the double Haldane phase as well as the ferromagnetic phase. It is shown that the ferromagnetic coupling leads to incommensurate correlations in the double Haldane phase. Such short-range correlations transform continuously into the ferromagnetic instability at the transition to the ferromagnetic phase. We also compare the results with the spin-1/2 and classical spin systems and discuss the string orders in the system.

  3. Detailed study of the magnetic ordering in FeMnP{sub 0.75}Si{sub 0.25}

    SciTech Connect

    Höglin, Viktor; Hudl, Matthias; Caron, Luana; Beran, Premysl; Sørby, Magnus H.; Nordblad, Per; Andersson, Yvonne; Sahlberg, Martin

    2015-01-15

    Magnetic and crystallographic properties of FeMnP{sub 0.75}Si{sub 0.25} in the hexagonal Fe{sub 2}P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (T{sub C}=250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (q{sub x}=0.363(1), T{sub N}=150 K). - Graphical abstract: The ferromagnetic structure of sample I (a) and the antiferromagnetic and incommensurate (q{sub x}=0.363(1)) low temperature structure of sample II (b). The magnetic moments of the Mn and Fe atoms in (b) are aligned in the basal plane along the a- and the b-axis, respectively, and the amplitude of the moments propagates sinusoidally along the a-axis. - Highlights: • Magnetic and crystallographic properties of FeMnP{sub 0.75}Si{sub 0.25} have been investigated. • Co-existing ferro- and antiferromagnetic ordering arise from two phases of Fe{sub 2}P-type. • A low temperature incommensurate antiferromagnetic structure is revealed.

  4. Chirality-driven orbital magnetic moments as a new probe for topological magnetic structures

    PubMed Central

    dos Santos Dias, Manuel; Bouaziz, Juba; Bouhassoune, Mohammed; Blügel, Stefan; Lounis, Samir

    2016-01-01

    When electrons are driven through unconventional magnetic structures, such as skyrmions, they experience emergent electromagnetic fields that originate several Hall effects. Independently, ground-state emergent magnetic fields can also lead to orbital magnetism, even without the spin–orbit interaction. The close parallel between the geometric theories of the Hall effects and of the orbital magnetization raises the question: does a skyrmion display topological orbital magnetism? Here we first address the smallest systems with nonvanishing emergent magnetic field, trimers, characterizing the orbital magnetic properties from first-principles. Armed with this understanding, we study the orbital magnetism of skyrmions and demonstrate that the contribution driven by the emergent magnetic field is topological. This means that the topological contribution to the orbital moment does not change under continuous deformations of the magnetic structure. Furthermore, we use it to propose a new experimental protocol for the identification of topological magnetic structures, by soft X-ray spectroscopy. PMID:27995909

  5. Symmetry-Based Computational Tools for Magnetic Crystallography

    NASA Astrophysics Data System (ADS)

    Perez-Mato, J. M.; Gallego, S. V.; Tasci, E. S.; Elcoro, L.; de la Flor, G.; Aroyo, M. I.

    2015-07-01

    In recent years, two important advances have opened new doors for the characterization and determination of magnetic structures. Firstly, researchers have produced computer-readable listings of the magnetic or Shubnikov space groups. Secondly, they have extended and applied the superspace formalism, which is presently the standard approach for the description of nonmagnetic incommensurate structures and their symmetry, to magnetic structures. These breakthroughs have been the basis for the subsequent development of a series of computer tools that allow a more efficient and comprehensive application of magnetic symmetry, both commensurate and incommensurate. Here we briefly review the capabilities of these computation instruments and present the fundamental concepts on which they are based, providing various examples. We show how these tools facilitate the use of symmetry arguments expressed as either a magnetic space group or a magnetic superspace group and allow the exploration of the possible magnetic orderings associated with one or more propagation vectors in a form that complements and goes beyond the traditional representation method. Special focus is placed on the programs available online at the Bilbao Crystallographic Server ( http://www.cryst.ehu.es ).

  6. Incommensurate spin resonance in URu2Si2

    SciTech Connect

    Balatsky, A V; Chantis, A; Dahal, Hari; Zhu, J X; Parker, David

    2008-01-01

    We propose to search for the spin resonance in URu{sub 2}Si{sub 2} at {omega}{sub res} = 4-6meV at the incommensurate wavector Q* = (1 {+-} 0.4, 0, 0). We expect that this spin resonance will set in at temperatures below HO transition and the intensity of this peak will scale as {approx} {Delta}{sub HO} {approx} (T{sub HO} - T). The resonance peak is know to occur in the states with superconducting gap and results in the gapping of the electronic spectrum add ref on SrruO and cel 15. In the case of HO the gap {Delta}{sub HO} results in the partially gapped electron spectrum. That appears to be a sufficient condition, as shown by Wiebe et al to produce a gap in spin excitation spectrum. In addition, we predict a peak in the spin excitation spectrum, as spectral weight redistribution produces the resonance feature. To the best of our knowledge, if the predicted resonance peak indeed occurs, it would be the first case where the spin resonance occurs at an incommensurate vector Q*.

  7. Microwave sol–gel synthesis and upconversion photoluminescence properties of CaGd{sub 2}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} phosphors with incommensurately modulated structure

    SciTech Connect

    Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor

    2015-08-15

    CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} phosphors with the doping concentrations of Er{sup 3+} and Yb{sup 3+} (x=Er{sup 3+}+Yb{sup 3+}, Er{sup 3+}=0.05, 0.1, 0.2 and Yb{sup 3+}=0.2, 0.45) have been successfully synthesized by the microwave sol–gel method. The crystal structure of CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 °C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd{sub 2}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd{sub 2}(WO{sub 4}){sub 4} revealed about 12 narrow lines. The strongest band observed at 903 cm{sup −1} was assigned to the ν{sub 1} symmetric stretching vibration of WO{sub 4} tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er{sup 3+} luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at {sup 2}H{sub 11/2}→{sup 4}I{sub 15/2} transition is weak in the range of erbium doping level x{sub Er}=0.05–0.2, while, for transition {sup 4}S{sub 3/2}→{sup 4}I{sub 15/2}, the signs of concentration quenching become pronounced at x{sub Er}=0.2. - Graphical abstract: CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb{sup 3+} phosphors with the doping concentrations of Er{sup 3+} and Yb{sup 3+} (x=Er{sup 3+}+Yb{sup 3+}, Er{sup 3+}=0.05, 0.1, 0.2 and Yb{sup 3+}=0.2, 0.45) have been successfully synthesized by the microwave sol–gel method and the crystal structure refinement, and upconversion photoluminescence properties have been investigated. - Highlights: • CaGd{sub 2−x}(WO{sub 4}){sub 4}:Er{sup 3+}/Yb

  8. Method of using triaxial magnetic fields for making particle structures

    DOEpatents

    Martin, James E.; Anderson, Robert A.; Williamson, Rodney L.

    2005-01-18

    A method of producing three-dimensional particle structures with enhanced magnetic susceptibility in three dimensions by applying a triaxial energetic field to a magnetic particle suspension and subsequently stabilizing said particle structure. Combinations of direct current and alternating current fields in three dimensions produce particle gel structures, honeycomb structures, and foam-like structures.

  9. Lanthanide contraction and magnetism in the heavy rare earth elements.

    PubMed

    Hughes, I D; Däne, M; Ernst, A; Hergert, W; Lüders, M; Poulter, J; Staunton, J B; Svane, A; Szotek, Z; Temmerman, W M

    2007-04-05

    The heavy rare earth elements crystallize into hexagonally close packed (h.c.p.) structures and share a common outer electronic configuration, differing only in the number of 4f electrons they have. These chemically inert 4f electrons set up localized magnetic moments, which are coupled via an indirect exchange interaction involving the conduction electrons. This leads to the formation of a wide variety of magnetic structures, the periodicities of which are often incommensurate with the underlying crystal lattice. Such incommensurate ordering is associated with a 'webbed' topology of the momentum space surface separating the occupied and unoccupied electron states (the Fermi surface). The shape of this surface-and hence the magnetic structure-for the heavy rare earth elements is known to depend on the ratio of the interplanar spacing c and the interatomic, intraplanar spacing a of the h.c.p. lattice. A theoretical understanding of this problem is, however, far from complete. Here, using gadolinium as a prototype for all the heavy rare earth elements, we generate a unified magnetic phase diagram, which unequivocally links the magnetic structures of the heavy rare earths to their lattice parameters. In addition to verifying the importance of the c/a ratio, we find that the atomic unit cell volume plays a separate, distinct role in determining the magnetic properties: we show that the trend from ferromagnetism to incommensurate ordering as atomic number increases is connected to the concomitant decrease in unit cell volume. This volume decrease occurs because of the so-called lanthanide contraction, where the addition of electrons to the poorly shielding 4f orbitals leads to an increase in effective nuclear charge and, correspondingly, a decrease in ionic radii.

  10. Processing, Structure and Magnetism of Bioglass Ceramics

    NASA Astrophysics Data System (ADS)

    Leventouri, Th.; Kis, A. C.; Thompson, J. R.

    2003-03-01

    Ferromagnetic glass-ceramics are multiphase systems with bioactive properties that originate from the calcium phosphate, which forms apatite in a physiological environment. Their magnetic properties have been shown to be effective in hyperthermic treatment of animal bone cancer. A series of ferromagnetic glass-ceramic samples in the system 45(CaO, P_2O_5) _ySiO2 xFe_2O3 has been prepared where x=0.05, 0.10, 0.15 and 0.20 in molar concentration with the addition of 3% Na_2O.The samples were heat treated at temperatures from 600 to 1100 ^oC. Phase development was studied with x-ray diffraction methods as a function of processing parameters. Quantitative analysis from Rietveld refinements will be discussed. Magnetic properties of the systems such as saturation, coersivity and remanence have shown a complicated correlation with their corresponding processing and structural parameters.

  11. Decompositional, incommensurate growth of Ferrocene molecules on a Au(111) surface

    SciTech Connect

    K.-F. Braun, V. Iancu, N. Pertaya, K.-H. Rieder and S.-W. Hla

    2006-07-01

    Deviating from the common growth mode of molecular films of organic molecules where the adsorbates remain intact, we observe an essentially different growth behavior for metalocenes with a low temperature scanning tunneling microscope. Ferrocene molecules adsorb dissociatively and form a two layer structure after being decomposed into fragments. The toplayer unit cell is composed of two tilted cyclopentadienyl rings, while the first layer consists of the remaining fragments. Surprisingly a fourfold symmetry is observed for the top layer while the first layer displays threefold symmetry elements. It is this symmetry mismatch which induces an incommensurability between these layers in all except one surface direction. The toplayer is weakly bonded and has an antiferromagnetic groundstate as calculated by local spin density functional approximation.

  12. 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

  13. How to assign a (3 + 1)-dimensional superspace group to an incommensurately modulated biological macromolecular crystal

    PubMed Central

    2017-01-01

    Periodic crystal diffraction is described using a three-dimensional (3D) unit cell and 3D space-group symmetry. Incommensurately modulated crystals are a subset of aperiodic crystals that need four to six dimensions to describe the observed diffraction pattern, and they have characteristic satellite reflections that are offset from the main reflections. These satellites have a non-integral relationship to the primary lattice and require q vectors for processing. Incommensurately modulated biological macromolecular crystals have been frequently observed but so far have not been solved. The authors of this article have been spearheading an initiative to determine this type of crystal structure. The first step toward structure solution is to collect the diffraction data making sure that the satellite reflections are well separated from the main reflections. Once collected they can be integrated and then scaled with appropriate software. Then the assignment of the superspace group is needed. The most common form of modulation is in only one extra direction and can be described with a (3 + 1)D superspace group. The (3 + 1)D superspace groups for chemical crystallographers are fully described in Volume C of International Tables for Crystallography. This text includes all types of crystallographic symmetry elements found in small-molecule crystals and can be difficult for structural biologists to understand and apply to their crystals. This article provides an explanation for structural biologists that includes only the subset of biological symmetry elements and demonstrates the application to a real-life example of an incommensurately modulated protein crystal. PMID:28808437

  14. Crystal Structure and Magnetic Properties of an oxygen deficient n = 2 Ruddlesden-Popper phase Sr3Co2O5.67

    NASA Astrophysics Data System (ADS)

    Hill, Julienne M.; Mitchell, John F.; Dabrowski, Bogdan

    2006-03-01

    Interest in charge, orbital, and spin state phenomena in perovskite and related cobalt oxides is a growing area of transition metal oxide physics. Recently, J. Matsuno et al. have found that epitaxial films of the n = 1 Ruddlesden-Popper (R-P) phase Sr2CoO4 are metallic ferromagnets with relatively high TC ˜ 250 K. This is particularly interesting in light of the formal oxidation state of Co, Co^4+, offering no clear source of carriers. To extend the materials chemistry and physics of the R-P series of cobaltites, we have synthesized the n = 2 R-P phase Sr3Co2O7-δ in bulk form. The crystal structure [from neutron powder diffraction (NPD) data] of our most oxygen-deficient sample, Sr3Co2O5.67 is orthorhombic Immm with a = 3.94025(9) å, b = 3.67479(9) å and c = 20.6642(5) å. The magnetization versus temperature data show two antiferromagnetic transitions at approximately 170 K and 220 K. To further elucidate the magnetic properties of this material, we have conducted a temperature-dependent NPD study. The low temperature magnetic structure is surprisingly complex and suggestive of an incommensurate ordering wave vector. Full details and results of the NPD study will be given. J. Matsuno et al., PRL 93, 167202 (2004).

  15. Structural and magnetic phase transitions in KMnF3

    NASA Astrophysics Data System (ADS)

    Kizhaev, S. A.; Markova, L. A.

    2011-09-01

    The dielectric and magnetic measurements of the KMnF3 crystals obtained by the Czochralski and Bridgman methods have been performed. Three structural transitions have been observed in the crystals. The mutual arrangement of the temperature of magnetic ordering and the temperature of the lower structural transition determines the number and type of magnetic transitions in these crystals.

  16. Small-angle electron scattering of magnetic fine structures.

    PubMed

    Togawa, Yoshihiko

    2013-06-01

    Magnetic structures in magnetic artificial lattices and chiral magnetic orders in chiral magnets have been quantitatively analyzed in the reciprocal space by means of small-angle electron scattering (SAES) method. Lorentz deflection due to magnetic moments and Bragg diffraction due to periodicity are simultaneously recorded at an angle of the order of or less than 1 × 10(-6) rad, using a camera length of more than 100 m. The present SAES method, together with TEM real-space imaging methods such as in-situ Lorentz microscopy, is very powerful in analyzing magnetic fine structures in magnetic materials. Indeed, the existence of both a chiral helimagnetic structure and a chiral magnetic soliton lattice in a chiral magnet CrNb3S6 has been successfully verified for the first time using the present complementary methods.

  17. Electronic structure and magnetic properties of solids

    NASA Astrophysics Data System (ADS)

    Savrasov, Sergej Y.; Toropova, Antonina; Katsnelson, Mikhail I.; Lichtenstein, Alexander I.; Antropov, Vladimir; Kotliar, Gabriel

    2005-05-01

    We review basic computational techniques for simulations of various magnetic properties of solids. Several applications to compute magnetic anisotropy energy, spin wave spectra, magnetic susceptibilities and temperature dependent magnetisations for a number of real systems are presented for illustrative purposes.

  18. Structural analysis of ITER magnet feeders

    SciTech Connect

    Ilyin, Yuri; Gung, Chen-Yu; Bauer, Pierre; Chen, Yonghua; Jong, Cornelis; Devred, Arnaud; Mitchell, Neil; Lorriere, Philippe; Farek, Jaromir; Nannini, Matthieu

    2012-06-15

    This paper summarizes the results of the static structural analyses, which were conducted in support of the ITER magnet feeder design with the aim of validating certain components against the structural design criteria. While almost every feeder has unique features, they all share many common constructional elements and the same functional specifications. The analysis approach to assess the load conditions and stresses that have driven the design is equivalent for all feeders, except for particularities that needed to be modeled in each case. The mechanical analysis of the feeders follows the sub-modeling approach: the results of the global mechanical model of a feeder assembly are used as input for the detailed models of the feeder' sub-assemblies or single components. Examples of such approach, including the load conditions, stress assessment criteria and solutions for the most critical components, are discussed. It has been concluded that the feeder system is safe in the referential operation scenarios. (authors)

  19. Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn{sub 3−x}Co{sub x}TeO{sub 6}

    SciTech Connect

    Ivanov, S.A.; Mathieu, R.; Nordblad, P.; Ritter, C.; Tellgren, R.; Golubko, N.; Mosunov, A.; Politova, E.D.; Weil, M.

    2014-02-01

    Highlights: • Mn{sub 3}TeO{sub 6} and Co{sub 3}TeO{sub 6} are antiferromagnets with corundum related structures. • The structural and magnetic properties of Mn{sub 3−x}Co{sub x}TeO{sub 6} ceramics were investigated. • All compounds adopt the trigonal structure of Mn{sub 3}TeO{sub 6} up to at least x = 2.4. • The antiferromagnetic transition temperature monotonously increases with x. • NPD data evidences the magnetic structure of the Mn{sub 3−x}Co{sub x}TeO{sub 6} ceramics. - Abstract: The effects of Co{sup 2+} doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn{sub 3}TeO{sub 6} have been investigated. Ceramic samples of the solid solution series Mn{sub 3−x}Co{sub x}TeO{sub 6} were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x ≤ 2.4 adopt the trigonal corundum-related structure of pure Mn{sub 3}TeO{sub 6} (space group R3{sup ¯}) in the temperature range 5–295 K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co{sup 2+} concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co{sup 2+} concentration x. Curie–Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn{sub 3}TeO{sub 6} can be described as an incommensurately modulated magnetic spin state with k = [0, 0, k{sub z}] and an elliptical spin-spiral order of spins within the chains of MnO{sub 6} octahedra. With increasing Co{sup 2+} concentration the propagation vector k{sub z} changes

  20. Mapping the magnetic and crystal structure in cobalt nanowires

    SciTech Connect

    Cantu-Valle, Jesus; Betancourt, Israel; Sanchez, John E.; Ruiz-Zepeda, Francisco; Mendoza-Santoyo, Fernando; Ponce, Arturo; Maqableh, Mazin M.; Stadler, Bethanie J. H.

    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 magnetic properties at the nanometric scale.

  1. EPR lineshape of Mn in BCCD single crystals in the incommensurate phase

    NASA Astrophysics Data System (ADS)

    Heidler, R.; Metz, H.; Windsch, W.

    1994-10-01

    For the interpretation of the Electron Paramagnetic Resonance (EPR) lineshape of incommensurate phases there exist many theoretical models. We suppose a simple physical model to interpret the lineshape of the Mn(2+) EPR spectrum of the first incommensurate phase of betaine calcium chloride dihydrate (BCCD) and discuss it in comparison with other models. Furthermore, we investigate the critical behavior of BCCD at the normal to incommensurate phase transition on the basis of our model. The influence of the Mn(2+) impurities on the phase sequence of BCCD is investigated by dielectric measurements.

  2. Partial spin ordering and complex magnetic structure in BaYFeO4: a neutron diffraction and high temperature susceptibility study.

    PubMed

    Thompson, Corey M; Greedan, John E; Garlea, V Ovidiu; Flacau, Roxana; Tan, Malinda; Nguyen, Phuong-Hieu T; Wrobel, Friederike; Derakhshan, Shahab

    2014-01-21

    The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe(3+) sites, that are alternately corner-shared [FeO5](7-) square pyramids and [FeO6](9-) octahedra, forming into [Fe4O18](24-) rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of short-range magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and high-temperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, (1)/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, ∼0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe(3+) are only of the order ∼3.0 μB, smaller than the expected values near 4.5 μB, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at ∼550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the

  3. Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study

    SciTech Connect

    Thompson, Corey; Greedan, John; Garlea, Vasile O; Flacau, Roxana; Tan, Malinda; Derakhshan, Shahab

    2014-01-01

    The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe3+ sites, that are alternately corner-shared [FeO5]7 square pyramids and [FeO6]9 octahedra, forming into [Fe4O18]24 rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of shortrange magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and hightemperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, 1/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe3+ are only of the order 3.0 B, smaller than the expected values near 4.5 B, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic

  4. Magnetic and nonmagnetic phases in doped AB2 t-J Hubbard chains

    NASA Astrophysics Data System (ADS)

    Montenegro-Filho, R. R.; Coutinho-Filho, M. D.

    2014-09-01

    We discuss the rich phase diagram of doped AB2t-J chains by using data from density matrix renormalization group and exact diagonalization techniques. The J vs δ (hole doping) phase diagram exhibits regions of itinerant ferrimagnetism, incommensurate, resonating valence bond and Nagaoka states, phase separation, and Luttinger liquid (LL) physics. Several features are highlighted, such as the modulated ferrimagnetic structure, the occurrence of Nagaoka spin polarons in the underdoped regime and small values of J =4t2/U, where t is the first-neighbor hopping amplitude and U is the on-site repulsive Coulomb interaction, incommensurate structures with nonzero magnetization, and strong-coupling LL physics in the high-doped regime. We also verify that relevant findings are in agreement with the corresponding findings in square and n-leg ladder lattices. In particular, we mention the instability of Nagaoka ferromagnetism against J and δ.

  5. Re-direction of dc magnetic flux in magnetically isotropic multilayered structures

    NASA Astrophysics Data System (ADS)

    Tarkhanyan, Roland H.; Niarchos, Dimitris G.

    2016-07-01

    Analytical design of a periodic composite structure allowing re-direction (bending) of dc magnetic flux with respect to applied external field is presented using methods of transformation optics. The composite structure is made of micrometer scale alternating layers of two different homogeneous and magnetically isotropic materials. Dependence of the magnetic flux bending angle on geometrical orientation of the layers as well as on the magnetic permeability ratio is examined. Such structures can find use in various devices based on the control and manipulations of the magnetic flux.

  6. Bias structure to efficiently package a magnetic bubble domain device

    NASA Technical Reports Server (NTRS)

    Chen, Thomas T. (Inventor)

    1978-01-01

    A single, compact bias structure to efficiently package a plurality of magnetic bubble domain device chips having different bias requirements. The vertical magnetic field distribution within the bias structure air gap is selectively controlled by a magnetically soft field adjusting assembly suitably attached within the bias structure. The size and configuration of the field adjusting assembly tailors local field variations within the air gap to correspond with the bias requirements of the bubble domain chips disposed therein.

  7. Magnetic Sensor for Building Structural Vibrations

    PubMed Central

    García, Alfonso; Morón, Carlos; Tremps, Enrique

    2014-01-01

    This paper shows a new displacement-to-frequency transducer based on the variation of a coil inductance when a magnetic core is partially or completely inserted inside. This transducer is based on a Colpitts oscillator due its low manufacturing price, behavior and immunity to noise. A tank circuit with a configuration in parallel was used because it can be employed at lower frequencies and it enables it to make a direct analysis. The sensor has a dynamic range equal to the length of the coil. The cores can exchange sensors (coils with its ferromagnetic core) using the same electronic measuring system. In this way, with only an electronic circuit, the core sensor determines the measurement range. The obtained resolution is higher than 1/100,000, and the sensor also allows the measurement and knowing in real time the effect of vibration, thermal expansion, referred overload movements, etc.., that can occur in the structural elements of a building. PMID:24504104

  8. Magnetic sensor for building structural vibrations.

    PubMed

    García, Alfonso; Morón, Carlos; Tremps, Enrique

    2014-02-05

    This paper shows a new displacement-to-frequency transducer based on the variation of a coil inductance when a magnetic core is partially or completely inserted inside. This transducer is based on a Colpitts oscillator due its low manufacturing price, behavior and immunity to noise. A tank circuit with a configuration in parallel was used because it can be employed at lower frequencies and it enables it to make a direct analysis. The sensor has a dynamic range equal to the length of the coil. The cores can exchange sensors (coils with its ferromagnetic core) using the same electronic measuring system. In this way, with only an electronic circuit, the core sensor determines the measurement range. The obtained resolution is higher than 1/100,000, and the sensor also allows the measurement and knowing in real time the effect of vibration, thermal expansion, referred overload movements, etc.., that can occur in the structural elements of a building.

  9. Magnetic resonance imaging structured reporting in infertility.

    PubMed

    Montoliu-Fornas, Guillermina; Martí-Bonmatí, Luis

    2016-06-01

    Our objective was to define and propose a standardized magnetic resonance (MR) imaging structured report in patients with infertility to have clinical completeness on possible diagnosis and severity. Patients should be studied preferable on 3T equipment with a surface coil. Standard MR protocol should include high-resolution fast spin-echo T2-weighted, diffusion-weighted images and gradient-echo T1-weighted fat suppression images. The report should include ovaries (polycystic, endometrioma, tumor), oviduct (hydrosalpinx, hematosalpinx, pyosalpinx, peritubal anomalies), uterus (agenesia, hypoplasia, unicornuate, uterus didelphys, bicornuate, septate uterus), myometrium (leiomyomas, adenomyosis), endometrium (polyps, synechia, atrophy, neoplasia), cervix and vagina (isthmoceles, mucosal-parietal irregularity, stenosis, neoplasia), peritoneum (deep endometriosis), and urinary system-associated abnormalities. To be clinically useful, radiology reports must be structured, use standardized terminology, and convey actionable information. The structured report must comprise complete, comprehensive, and accurate information, allowing radiologists to continuously interact with patients and referring physicians to confirm that the information is used properly to affect the decision making process.

  10. Direct evidence of an incommensurate phase in NaNbO{sub 3} and its implication in NaNbO{sub 3}-based lead-free antiferroelectrics

    SciTech Connect

    Guo, Hanzheng; Randall, Clive A.; Shimizu, Hiroyuki

    2015-09-14

    Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO{sub 3} polycrystalline. In addition to the commonly recognized P (Pbma) → R (Pmnm) → S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P → R transition region) is coincident with a diffused dielectric peak appearing at ∼170 °C, and the latter (in the R → S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phase region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO{sub 3} solid solutions.

  11. Solar Multiple Eruptions from a Confined Magnetic Structure

    NASA Astrophysics Data System (ADS)

    Lee, Jeongwoo; Liu, Chang; Jing, Ju; Chae, Jongchul

    2016-09-01

    How eruption can recur from a confined magnetic structure is discussed based on the Solar Dynamics Observatory observations of the NOAA active region 11444, which produced three eruptions within 1.5 hr on 2012 March 27. The active region (AR) had the positive-polarity magnetic fields in the center surrounded by the negative-polarity fields around. Since such a distribution of magnetic polarity tends to form a dome-like magnetic fan structure confined over the AR, the multiple eruptions were puzzling. Our investigation reveals that this event exhibits several properties distinct from other eruptions associated with magnetic fan structures: (i) a long filament encircling the AR was present before the eruptions; (ii) expansion of the open-closed boundary (OCB) of the field lines after each eruption was suggestive of the growing fan-dome structure, and (iii) the ribbons inside the closed magnetic polarity inversion line evolved in response to the expanding OCB. It thus appears that in spite of multiple eruptions the fan-dome structure remained undamaged, and the closing back field lines after each eruption rather reinforced the fan-dome structure. We argue that the multiple eruptions could occur in this AR in spite of its confined magnetic structure because the filament encircling the AR was adequate for slipping through the magnetic separatrix to minimize the damage to its overlying fan-dome structure. The result of this study provides a new insight into the productivity of eruptions from a confined magnetic structure.

  12. Incommensurate atomic density waves in the high-pressure IVb phase of barium.

    PubMed

    Arakcheeva, Alla; Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Pattison, Phil; Dmitriev, Vladimir; Chapuis, Gervais

    2017-03-01

    The host-guest structures of elements at high pressure discovered a decade ago still leave many open questions due to the lack of precise models based on full exploitation of the diffraction data. This concerns in particular Ba IV, which is stable in the range 12-45 GPa. With the example of phase Ba IVb, which is characterized here for the first time, a systematic analysis is presented of possible host-guest structure models based on high-quality single-crystal diffraction data obtained with synchrotron radiation at six different pressures between 16.5 and 19.6 GPa. It is shown that a new incommensurately modulated (IM) structure model better fits the experimental data. Unlike the composite models which are commonly reported for the Ba IV phases, the IM model reveals a density wave and its pressure-dependent evolution. The crucial role played by the selected model in the interpretation of structure evolution under pressure is discussed. The findings give a new experimental basis for a better understanding of the nature of host-guest structures.

  13. Incommensurate atomic density waves in the high-pressure IVb phase of barium

    PubMed Central

    Arakcheeva, Alla; Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Pattison, Phil; Dmitriev, Vladimir; Chapuis, Gervais

    2017-01-01

    The host–guest structures of elements at high pressure discovered a decade ago still leave many open questions due to the lack of precise models based on full exploitation of the diffraction data. This concerns in particular Ba IV, which is stable in the range 12–45 GPa. With the example of phase Ba IVb, which is characterized here for the first time, a systematic analysis is presented of possible host–guest structure models based on high-quality single-crystal diffraction data obtained with synchrotron radiation at six different pressures between 16.5 and 19.6 GPa. It is shown that a new incommensurately modulated (IM) structure model better fits the experimental data. Unlike the composite models which are commonly reported for the Ba IV phases, the IM model reveals a density wave and its pressure-dependent evolution. The crucial role played by the selected model in the interpretation of structure evolution under pressure is discussed. The findings give a new experimental basis for a better understanding of the nature of host–guest structures. PMID:28250954

  14. Magnetic structure of Sm-Co/Fe Spring Magnets

    NASA Astrophysics Data System (ADS)

    Nickel, B.; Donner, W.; Ruehm, A.; Felcher, G. P.; Jiang, J. S.; Bader, S. D.

    2001-03-01

    Exchange spring magnets are systems with potentially high energy product obtained by coupling a layer of material with high coercivity like Sm-Co (wich has a stoichiometry close to SmCo3) with one of high magnetization, like Fe. For an Fe layer thickness exceeding the thickness of a domain wall ( 50 Å) a rotating magnetic field induces both a longitudinal as well as a transversal component of the magnetization. Polarized neutron reflectivity measurements at the instrument "EVA" at the Institut Laue-Langevin in Grenoble confirmed the non-collinearity of the magnetization, and were in quantitative agreement with a "spring" arrangement of the magnetic moments calculated on the basis of a micromagneic model [1]. Up to a critical value of the applied field the moments of the atomic planes of Fe close to the Sm-Co interface remain aligned along the easy axis, while the Fe close to the free surface align with the field. [1] E.E. Fullerton, J.S. Jiang, M. Grimsditch, C.H. Sowers and S.D. Bader, Phys. Rev. B58, 12193 (1998)

  15. Structural phase transitions in isotropic magnetic elastomers

    SciTech Connect

    Meilikhov, E. Z. Farzetdinova, R. M.

    2016-06-15

    Magnetic elastomers represent a new type of materials that are “soft” matrices with “hard” magnetic granules embedded in them. The elastic forces of the matrix and the magnetic forces acting between granules are comparable in magnitude even under small deformations. As a result, these materials acquire a number of new properties; in particular, their mechanical and/or magnetic characteristics can depend strongly on the polymer matrix filling with magnetic particles and can change under the action of an external magnetic field, pressure, and temperature. To describe the properties of elastomers, we use a model in which the interaction of magnetic granules randomly arranged in space with one another is described in the dipole approximation by the distribution function of dipole fields, while their interaction with the matrix is described phenomenologically. A multitude of deformation, magnetic-field, and temperature effects that are described in this paper and are quite accessible to experimental observation arise within this model.

  16. Incommensurate phases in barium sodium niobate: Transmission-electron-microscopy study

    SciTech Connect

    Barre, S.; Mutka, H.; Roucau, C.

    1988-11-01

    A transmission-electron-microscopy study of barium sodium niobate has confirmed new features of the incommensurate phase. We present here images showing the nucleation of the incommensurate phase when the temperature increases after thermal cycling the sample or annealing in the incommensurate phase. In agreement with previous inferences, in situ annealing either at 230 /sup 0/C near the lock-in transition or at 270 /sup 0/C close to the tetragonal normal phase transition can favor the stability of a unidirectional 1q or a doubly modulated 2q incommensurate phase, respectively. The difference in the orientation of discommensurations, either perpendicular to the orthorhombic a axis or perpendicular to the tetragonal a and b axes, agree with an assignment of the two phases based on theoretical arguments and on x-ray and optical data.

  17. Magnetic structure of NiS2 -xSex

    NASA Astrophysics Data System (ADS)

    Yano, S.; Louca, Despina; Yang, J.; Chatterjee, U.; Bugaris, D. E.; Chung, D. Y.; Peng, L.; Grayson, M.; Kanatzidis, Mercouri G.

    2016-01-01

    NiS2 -2 xSex is revisited to determine the magnetic structure using neutron diffraction and magnetic representational analysis. Upon cooling, the insulating parent compound, NiS2, becomes antiferromagnetic with two successive magnetic transitions. The first transition (M 1 ) occurs at TN˜39 K with Γ1ψ1 symmetry and a magnetic propagation vector of k =(000 ) . The second transition (M 2 ) occurs at TN˜30 K with k =(0.5 ,0.5 ,0.5 ) and a Γ1ψ2 symmetry with face-centered translations, giving rise to four possible magnetic domains. With doping, the system becomes metallic. The transition to the M 2 state is suppressed prior to x =0.4 while the M 1 state persists. The M 1 magnetic structure gradually vanishes by x ˜0.8 at a lower concentration than previously reported. The details of the magnetic structures are provided.

  18. Magnetism and surface structure of atomically controlled ultrathin metal films.

    SciTech Connect

    Shiratsuchi, Yu.; Yamamoto, M.; Bader, S. D.; Materials Science Division; Osaka Univ.

    2007-01-01

    We review the correlation of magnetism and surface structure in ultrathin metal films, including the tailoring of novel magnetic properties using atomic scale control of the nanostructure. We provide an overview of modern fabrication and characterization techniques used to create and explore these fascinating materials, and highlight important phenomena of interest. We also discuss techniques that control and characterize both the magnetic and structural properties on an atomic scale. Recent advances in the development and applications of these techniques allow nanomagnetism to be investigated in an unprecedented manner. A system cannot necessarily retain a two-dimensional structure as it enters the ultrathin region, but it can transform into a three-dimensional, discontinuous structure due to the Volmer-Weber growth mechanism. This structural transformation can give rise to superparamagnetism. During this evolution, competing factors such as interparticle interactions and the effective magnetic anisotropy govern the magnetic state. These magnetic parameters are influenced by the nanostructure of the film. In particular, controlling the magnetic anisotropy is critical for determining the magnetic properties. Surface effects play especially important roles in influencing both the magnitude and direction of the magnetic anisotropy in ultrathin films. By properly altering the surface structure, the strength and direction of the magnetic anisotropy are controlled via spin-orbit and/or dipole interactions.

  19. Oxocuprates: A structural and magnetic zoo

    SciTech Connect

    Ramakrishna, B.L.; Ong, E.W.

    1988-11-15

    We have attempted a magnetostructural correlation for the oxocuprates: Y/sub 2/Cu/sub 2/O/sub 5/, BaCuO/sub 2/, Y/sub 2/BaCuO/sub 5/, and YBa/sub 2/Cu/sub 3/O/sub 6/, all of which are closely related to the new high-T/sub c/ superconductors. It was found that this series of compounds has interesting combinations of ferro- and antiferromagnetic interactions as a consequence of the structural and electronic variety of copper. Y/sub 2/Cu/sub 2/O/sub 5/ and Y/sub 2/BaCuO/sub 5/ were shown to be chain and layer magnetic systems, respectively. BaCuO/sub 2/, a complicated 3D structure, has interesting effects of exchange interaction manifested in the temperature-dependent EPR spectrum. YBa/sub 2/Cu/sub 3/O/sub 6/ has been shown to possess a Neel point at 450 K from EPR intensity variation with temperature.

  20. Structures and Zonal Flows in Magnetized Plasmas

    SciTech Connect

    Jovanovic, D.; Shukla, P. K.

    2010-12-14

    The numerical study of the zonal flows (transport barriers) in the drift-wave turbulence in magnetically confined plasmas is presented. The existence of two distinct mechanisms for their generation is demonstrated. The evolution of a drift wave-zonal flow system, nonlinearly coupled via the Reynolds stress, is described by a nonlinear equation for the slowly varying envelope of the drift waves, and the nonlinear dispersion relation for the modulational instability of a drift wave pump is derived and analyzed. First, an arbitrary spatial distribution of strictly poloidally propagating drift waves is shown to rapidly decay into the array of localized soliton-like structures moving with different speeds. The corresponding zonal flow potential evolves into the sequence of shocks that produces a strong shearing, with many alternating plasma flows. Next, it is demonstrated that the coherent dipolar vortices, that constitute the building blocks of the strong drift-wave turbulence, are unstable in the presence of an electron temperature gradient. The dipolar vortices (or modons) undergo a qualitative modification by the action of the scalar nonlinearity arising from the magnetic {beta} effect. The modons propagating in the direction of the electron diamagnetic drift rapidly topple, disintegrating into two monopoles that propagate independently and rapidly disperse. Conversely, for the modons that initially moved in the direction of the ion diamagnetic drift, the {beta}-effect produces the change of the direction of the propagation, followed by the stretching in the poloidal direction. On a long time scale, such modons expand to a length equal to the size of the computational box, and essentially an one-dimensional zonal flow is created, whose transverse scale is determined by the initial modon size.

  1. Commensurate-incommensurate solid transition in the He4 monolayer on γ-graphyne

    NASA Astrophysics Data System (ADS)

    Ahn, Jeonghwan; Lee, Hoonkyung; Kwon, Yongkyung

    2014-08-01

    Path-integral Monte Carlo calculations have been performed to study the He4 adsorption on γ-graphyne, a planar network of benzene rings connected by acetylene bonds. Assuming the 4He-substrate interaction described by a pairwise sum of empirical 4He-carbon interatomic potentials, we find that unlike α-graphyne, a single sheet of γ-graphyne is not permeable to 4He atoms in spite of its large surface area. One-dimensional density distributions computed as a function of the distance from the graphyne surface reveal a layer-by-layer growth of 4He atoms. A partially-filled 4He monolayer is found to exhibit different commensurate solid structures depending on the helium coverage; it shows a C2/3 commensurate structure at an areal density of 0.0491 Å-2, a C3/3 structure at 0.0736 Å-2, and a C4/3 structure at 0.0982 Å-2. While the promotion to the second layer starts beyond the C4/3 helium coverage, the first 4He layer is found to form an incommensurate triangular solid when compressed with the development of the second layer.

  2. Magnetic shielding structure optimization design for wireless power transmission coil

    NASA Astrophysics Data System (ADS)

    Dai, Zhongyu; Wang, Junhua; Long, Mengjiao; Huang, Hong; Sun, Mingui

    2017-09-01

    In order to improve the performance of the wireless power transmission (WPT) system, a novel design scheme with magnetic shielding structure on the WPT coil is presented in this paper. This new type of shielding structure has great advantages on magnetic flux leakage reduction and magnetic field concentration. On the basis of theoretical calculation of coil magnetic flux linkage and characteristic analysis as well as practical application feasibility consideration, a complete magnetic shielding structure was designed and the whole design procedure was represented in detail. The simulation results show that the coil with the designed shielding structure has the maximum energy transmission efficiency. Compared with the traditional shielding structure, the weight of the new design is significantly decreased by about 41%. Finally, according to the designed shielding structure, the corresponding experiment platform is built to verify the correctness and superiority of the proposed scheme.

  3. Crystal structure and magnetic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy

    SciTech Connect

    Rangi, Manisha; Agarwal, Ashish Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.

    2014-08-15

    Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A{sup 2+} results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe{sup 4+} ruled out by Mössbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi{sub 0.8}Ba{sub 0.2}FeO{sub 3} sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

  4. An instrument for precision magnetic measurements of large magnetic structures

    NASA Astrophysics Data System (ADS)

    Beltrán, D.; Bordas, J.; Campmany, J.; Molins, A.; Perlas, J. A.; Traveria, M.

    2001-02-01

    A high precision-system for measuring the three-dimensional distribution of magnetic fields over large volumes, such as those produced by accelerator magnets, has been designed and commissioned. This instrument can be calibrated to a precision of ±1 G for magnetic fields of up to 1.5 T by means of an NMR system. A moving arm containing a 3D Hall probe scans the volume (up to 500×250×3000 mm 3) with a precision of ±50 μm in any direction. After appropriate identification of the various sources of error, and the optimisation of the various parts of the instrument where they are generated, an overall precision of ±2 G has been achieved, i.e. a relative precision of ±2×10 -4 for a nominal field of 1 T.

  5. Unraveling chromatin structure using magnetic tweezers

    NASA Astrophysics Data System (ADS)

    van Noort, John

    2010-03-01

    The compact, yet dynamic organization of chromatin plays an essential role in regulating gene expression. Although the static structure of chromatin fibers has been studied extensively, the controversy about the higher order folding remains. The compaction of eukaryotic DNA into chromatin has been implicated in the regulation of all DNA processes. To understand the relation between gene regulation and chromatin structure it is essential to uncover the mechanisms by which chromatin fibers fold and unfold. We used magnetic tweezers to probe the mechanical properties of individual nucleosomes and chromatin fibers consisting of a single, well-defined array of 25 nucleosomes. From these studies five major features appeared upon forced extension of chromatin fibers: the elastic stretching of chromatin's higher order structure, the breaking of internucleosomal contacts, unwrapping of the first turn of DNA, unwrapping of the second turn of DNA, and the dissociation of histone octamers. These events occur sequentially at the increasing force. Neighboring nucleosomes stabilize DNA folding into a nucleosome relative to isolated nucleosomes. When an array of nucleosomes is folded into a 30 nm fiber, representing the first level of chromatin condensation, the fiber stretched like a Hookian spring at forces up to 4 pN. Together with a nucleosome-nucleosome stacking energy of 14 kT this points to a solenoid as the underlying topology of the 30 nm fiber. Surprisingly, linker histones do not affect the length or stiffness of the fibers, but stabilize fiber folding up to forces of 7 pN. The stiffness of the folded chromatin fiber points at histone tails that mediate nucleosome stacking. Fibers with a nucleosome repeat length of 167 bp instead of 197 bp are significantly stiffer, consistent with a two-start helical arrangement. The extensive thermal breathing of the chromatin fiber that is a consequence of the observed high compliance provides a structural basis for understanding the

  6. Nonlinear dynamics of breathers in the spiral structures of magnets

    SciTech Connect

    Kiselev, V. V. Raskovalov, A. A.

    2016-06-15

    The structure and properties of pulsating solitons (breathers) in the spiral structures of magnets are analyzed within the sine-Gordon model. The breather core pulsations are shown to be accompanied by local shifts and oscillations of the spiral structure with the formation of “precursors” and “tails” in the moving soliton. The possibilities for the observation and excitation of breathers in the spiral structures of magnets and multiferroics are discussed.

  7. The History and Significance of the Incommensurability Thesis

    NASA Astrophysics Data System (ADS)

    Pearce, James Jacob

    The incommensurability thesis (IT) maintains that there are no non-prejudicial means of choosing between competing theories in the empirical sciences. If true, IT would entail that natural science is a fundamentally subjective or irrational activity. Should this latter claim prove justifiable, then empirical science cannot be regarded as an organ of objective knowledge, and "scientific realism" is eo ipso false. I follow the origin of IT from its pre-history in Logical Positivism, through certain preliminary philosophical developments in the work of Karl Popper, W. V. O. Quine, Stephen Toulmin and N. R. Hanson, to the eventual formulation and introduction of IT by Thomas Kuhn and Paul Feyerabend. I then examine the rigorous criticism of IT by various philosophers since about 1964, and discuss different methods of objective theory comparison which have been advanced by such philosophers as Hilary Putnam, W. H. Newton-Smith, Michael Devitt, Hartry Field, Philip Kitcher and Howard Sankey. I conclude by arguing for two counterintuitive claims: (1) Even if true, IT fails to provide evidence against scientific realism. (2) In fact, the truth of IT actually furnishes evidence for a necessary condition for scientific realism, and hence evidence which can be construed as indirectly favorable to scientific realism.

  8. Clues for genesis of magnetic field structure of Mercury

    NASA Astrophysics Data System (ADS)

    Hiremath, K. M.

    2012-07-01

    Recent space observations suggest that Mercury inherits a weak and predominantly large-scale steady dipole like magnetic field structure. Present popular paradigm is to invoke most promising geodynamo like phenomenon that requires the main ingredients such as either a full or partial convection of the interior and fast rotation such that magnetic (Lorentz) and Coriolis forces are of similar order of magnitudes. Hence, the ratio of Lorentz to Coriolis force, called the Elsasser number Λ, must be order of unity. Contrary to the expectation, Mercury rotates so slow that Elsasser number turns out to be << 1. There are also other alternative models to explain genesis of magnetic field structure of Mercury. With the observed constraint of Mercury's atmospheric magnetic field structure, internal magnetic field structure is obtained as a solution of magnetic diffusion equation in the core and a combined multipolar (dipole and quadrupole like magnetic field structures embedded in the uniform field) solution of a current free like magnetic field structure in the mantle and in the atmosphere. Magnetic diffusion time scales are estimated to be ˜ billion years suggesting that present day magnetic field structure might be of primordial origin. In order to reconcile with the experimental fact that, as temperature of Mercury's iron core is above Curie temperature and primordial magnetic field structure must be non-existent, it is proposed that permanency of such a large-scale magnetic field structure of the planet is attained during Mercury's early evolutionary history of heavy bombardments by the asteroids and comets leaving their imprints as craters on this planet. That means the solar system bodies that have heavy bombardments with high density craters during the early epochs of such catastrophic events should have strong magnetic field structures. Is this hypothesis universal? Can this hypothesis gives some clues regarding presence or absence of magnetic field structure of

  9. Incommensurate modulation of calcium barium niobate (CBN28 and Ce:CBN28).

    PubMed

    Graetsch, Heribert A; Pandey, Chandra Shekhar; Schreuer, Jürgen; Burianek, Manfred; Mühlberg, Manfred

    2012-04-01

    The incommensurately modulated crystal structures of Ca(0.28)Ba(0.72)Nb(2)O(6) (CBN28) and Ce(0.02)Ca(0.25)Ba(0.72)Nb(2)O(6) (Ce:CBN28) were refined in the supercentred setting X4bm(AA0,-AA0) of the 3 + 2-dimensional superspace group P4bm(aa½,-aa½). Both compounds are isostructural with a tetragonal tungsten bronze-type structure. The modulation of CBN28 consists of a wavy distribution of Ba and Ca atoms as well as vacancies on the incompletely occupied Me2 site with 15-fold oxygen coordination. The occupational modulation is coupled with a modulation of the atomic displacement parameters and a very weak modulation of the positional parameters of Me2. The surrounding O atoms show strong displacive modulations with amplitudes up to ca 0.2 Å owing to the cooperative tilting of the rigid NbO(6) octahedra. The Me1 site with 12-fold coordination and Nb atoms are hardly affected by the modulations. Only first-order satellites were observed and the modulations are described by first-order harmonics. In Ce:CBN28 cerium appears to be located on both the Me2 and Me1 sites. Wavevectors and structural modulations are only weakly modified upon substitutional incorporation of 0.02 cerium per formula unit of calcium.

  10. Magnetism in structures with ferromagnetic and superconducting layers

    NASA Astrophysics Data System (ADS)

    Zhaketov, V. D.; Nikitenko, Yu. V.; Radu, F.; Petrenko, A. V.; Csik, A.; Borisov, M. M.; Mukhamedzhanov, E. Kh.; Aksenov, V. L.

    2017-01-01

    The influence of superconductivity on ferromagnetism in the layered Ta/V/Fe1- x V x /V/Fe1- x V x /Nb/Si structures consisting of ferromagnetic and superconducting layers is studied using polarized neutron reflection and scattering. It is experimentally shown that magnetic structures with linear sizes from 5 nm to 30 μm are formed in these layered structures at low temperatures. The magnetization of the magnetic structures is suppressed by superconductivity at temperatures below the superconducting transition temperatures in the V and Nb layers. The magnetic states of the structures are shown to undergo relaxation over a wide magnetic-field range, which is caused by changes in the states of clusters, domains, and Abrikosov vortices.

  11. Studies of the magnetic structure at the ferromagnet - antiferromagnet interface

    SciTech Connect

    Scholl, A.; Nolting, F.; Stohr, J.; Luning, J.; Seo, J.W.; Locquet, J.-P.; Anders, S.; Ohldag, H.; Padmore, H.A.

    2001-01-02

    Antiferromagnetic layers are a scientifically challenging component in magneto-electronic devices such as magnetic sensors in hard disk heads, or magnetic RAM elements. In this paper we show that photo-electron emission microscopy (PEEM) is capable of determining the magnetic structure at the interface of ferromagnets and antiferromagnets with high spatial resolution (down to 20 nm). Dichroism effects at the L edges of the magnetic 3d transition metals, using circularly or linearly polarized soft x-rays from a synchrotron source, give rise to a magnetic image contrast. Images, acquired with the PEEM2 experiment at the Advanced Light Source, show magnetic contrast for antiferromagnetic LaFeO{sub 3}, microscopically resolving the magnetic domain structure in an antiferromagnetically ordered thin film for the first time. Magnetic coupling between LaFeO{sub 3} and an adjacent Co layer results in a complete correlation of their magnetic domain structures. From field dependent measurements a unidirectional anisotropy resulting in a local exchange bias of up to 30 Oe in single domains could be deduced. The elemental specificity and the quantitative magnetic sensitivity render PEEM a perfect tool to study magnetic coupling effects in multi-layered thin film samples.

  12. [Assemble of magnetic nanoparticles into the structure of cisplatin liposome].

    PubMed

    Wang, Lu; Yang, Cai-qin; Wang, Jing

    2011-05-01

    Effects of different procedures of magnetic nanoparticles into the liposome structure on the distribution of magnetic particles in the liposome were investigated. Magnetic liposomes with high-encapsulating rate of cisplatin (CDDP) were obtained. Fe3O4 magnetic nanoparticles which was modified by organic functional group on surface was synthesized by an one-step modified hydrothermal method. The CDDP magnetic liposomes were prepared by a film scattering-ultrasonic technique and the concentrations of CDDP in the liposomes were measured by graphite furnace atomic absorbance spectroscopy. Magnetic liposomes with different microstructure were prepared by the two different procedures, where the magnetic particles were combined with phospholipid before the film preparation to form liposome in procedure I, and drug solution and the magnetic particles were mixed before hydrating the lipids film to form liposome in procedure II. The liposome structure was observed by transmission electron microscope (TEM). The CDDP magnetic liposomes were prepared by the optimized method which was selected by orthogonal test. Encapsulation rate of the magnetic particles distributed in the phospholipid bilayer through the procedure I was 34.90%. While liposome, produced by the procedure II technique, contained magnetic particles in the interior aqueous compartment, which encapsulation rate was 28.34%. Encapsulation rates of both I and II were higher than that of conventional liposome. The release profile of all the three different liposomes in vitro fitted with a first-order equation. Because of distribution of magnetic particles in the phospholipid bilayer, the skeleton of phospholipid bilayer was changed. The releasing tl/2 of magnetic liposomes produced by the procedure I technique is 9 h, which is shorter than that of the other two liposomes. Assemble of magnetic nanoparticles into the structure of liposome was succeeded by the procedure I, which showed superiority than by procedure II

  13. Electronic and magnetic structures of magnetic vortex core in an Fe quantum dot

    NASA Astrophysics Data System (ADS)

    Nakamura, Kohji; Ito, Tomonori; Freeman, A. J.

    2003-03-01

    Interest in the magnetism of nano-scale structures have increased in both basic and applied science. In ferromagnetic quantum dot structures, curling magnetic structures are known to form, and the magnetization close to the center of the dot may assume a perpendicular orientation. Although many experimental and theoretical investigations have been performed, little is so far known about the electronic and magnetic structures on an atomic scale. Here, we determine the magnetic vortex core structure, modeled by a rod geometry with 29 Fe atoms, from the first-principles FLAPW method(Wimmer, Krakauer, Weinert and Freeman, PRB 24, 864(1981)) including noncollinear magnetism with no shape approximation of the magnetization density.(Nakamura, Freeman, Wang, Zhong, and Fernandez-de-Castro, PRB 65, 12402(2002)) The self-consistent LSDA calculations demonstrate that a swirling magnetic structure is stabilized, in which the spin directions close to the center turn up along the perpendicular orientation with respect to the swirling plane. We find that a swirling intra-atomic noncollinear magnetism is observed near the center, in which the moments continuously orient in circular directions on a smaller length scale inside the atoms and induce orbital moments along the perpendicular direction.

  14. SOLAR ENERGETIC PARTICLE MODULATIONS ASSOCIATED WITH COHERENT MAGNETIC STRUCTURES

    SciTech Connect

    Trenchi, L.; Bruno, R.; D'amicis, R.; Marcucci, M. F.; Telloni, D.; Zurbuchen, T. H.; Weberg, M.

    2013-06-10

    In situ observations of solar energetic particles (SEPs) often show rapid variations of their intensity profile, affecting all energies simultaneously, without time dispersion. A previously proposed interpretation suggests that these modulations are directly related to the presence of magnetic structures with a different magnetic topology. However, no compelling evidence of local changes in magnetic field or in plasma parameters during SEP modulations has been reported. In this paper, we performed a detailed analysis of SEP events and we found several signatures in the local magnetic field and/or plasma parameters associated with SEP modulations. The study of magnetic helicity allowed us to identify magnetic boundaries, associated with variations of plasma parameters, which are thought to represent the borders between adjacent magnetic flux tubes. It is found that SEP dispersionless modulations are generally associated with such magnetic boundaries. Consequently, we support the idea that SEP modulations are observed when the spacecraft passes through magnetic flux tubes, filled or devoid of SEPs, which are alternatively connected and not connected with the flare site. In other cases, we found SEP dropouts associated with large-scale magnetic holes. A possible generation mechanism suggests that these holes are formed in the high solar corona as a consequence of magnetic reconnection. This reconnection process modifies the magnetic field topology, and therefore, these holes can be magnetically isolated from the surrounding plasma and could also explain their association with SEP dropouts.

  15. Structural and magnetic etch damage in CoFeB

    SciTech Connect

    Krayer, L.; Lau, J. W.; Kirby, B. J.

    2014-05-07

    A detailed understanding of the interfacial properties of thin films used in magnetic media is critical for the aggressive component scaling required for continued improvement in storage density. In particular, it is important to understand how common etching and milling processes affect the interfacial magnetism. We have used polarized neutron reflectometry and transmission electron microscopy to characterize the structural and magnetic properties of an ion beam etched interface of a CoFeB film. We found that the etching process results in a sharp magnetic interface buried under a nanometer scale layer of non-magnetic, compositionally distinct material.

  16. Magnetic coupling at perovskite and rock-salt structured interfaces

    SciTech Connect

    Matvejeff, M.; Ahvenniemi, E.; Takahashi, R.; Lippmaa, M.

    2015-10-05

    We study magnetic coupling between hole-doped manganite layers separated by either a perovskite or a rock-salt barrier of variable thickness. Both the type and the quality of the interface have a strong impact on the minimum critical barrier thickness where the manganite layers become magnetically decoupled. A rock-salt barrier layer only 1 unit cell (0.5 nm) thick remains insulating and is able to magnetically de-couple the electrode layers. The technique can therefore be used for developing high-performance planar oxide electronic devices such as magnetic tunnel junctions and quantum well structures that depend on magnetically and electronically sharp heterointerfaces.

  17. Plane and hemispherical potential structures in magnetically expanding plasmas

    SciTech Connect

    Takahashi, Kazunori; Igarashi, Yuichi; Fujiwara, Tamiya

    2010-07-26

    Two-dimensional potential structures are measured for different gas pressure in expanding argon plasma using permanent magnets, where the magnetic field is about 100 G in the source and several gauss in the diffusion chamber. The plane potential drop is observed near the source exit for 0.35 mTorr, while the potential structure becomes hemispherical when increasing up to 1 mTorr; the hemispherical structure results in the radial divergence of the ion beam. It is found that the trajectories of the accelerated ions and the electrons overcoming the potential drop are dominated by the potential structure and magnetic-field lines, respectively.

  18. Short Large-Amplitude Magnetic Structures (SLAMS) at Venus

    NASA Technical Reports Server (NTRS)

    Collinson, G. A.; Wilson, L. B.; Sibeck, D. G.; Shane, N.; Zhang, T. L.; Moore, T. E.; Coates, A. J.; Barabash, S.

    2012-01-01

    We present the first observation of magnetic fluctuations consistent with Short Large-Amplitude Magnetic Structures (SLAMS) in the foreshock of the planet Venus. Three monolithic magnetic field spikes were observed by the Venus Express on the 11th of April 2009. The structures were approx.1.5->11s in duration, had magnetic compression ratios between approx.3->6, and exhibited elliptical polarization. These characteristics are consistent with the SLAMS observed at Earth, Jupiter, and Comet Giacobini-Zinner, and thus we hypothesize that it is possible SLAMS may be found at any celestial body with a foreshock.

  19. Structural and magnetic properties of Mg substituted Co nanoferrites

    SciTech Connect

    Sharma, Jyoti Parashar, Jyoti; Jadoun, Priya; Saxena, V. K.; Bhatnagar, D.; Sharma, Neha; Yadav, Premlata; Sharma, K. B.

    2016-05-23

    The structural and magnetic properties of magnesium substituted cobalt nano ferrites Co{sub x}Mg{sub 1-x}Fe{sub 2}O{sub 4} (x= 0.2, 0.4 and 1.0) have been investigated. The structural characterization has been done by X-ray diffraction (XRD) technique and transmission electron microscopy (TEM). The magnetic studies indicate that the samples show ferromagnetic behaviour at room temperature as well as at low temperature. The magnetization decreases with Mg content in both the cases due to the less magnetic nature of Mg ions than that of the Co ions.

  20. Photon Transport in One-Dimensional Incommensurately Epitaxial CsPbX 3 Arrays

    DOE PAGES

    Wang, Yiping; Sun, Xin; Shivanna, Ravichandran; ...

    2016-11-16

    One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX3 (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensurate epitaxy,more » paving a way for a universally applicable method to grow a broad family of halide perovskite materials. We have studied the unique photon transport in the one-dimensional structure in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Furthermore, epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.« less

  1. Photon Transport in One-Dimensional Incommensurately Epitaxial CsPbX 3 Arrays

    SciTech Connect

    Wang, Yiping; Sun, Xin; Shivanna, Ravichandran; Yang, Yunbo; Chen, Zhizhong; Guo, Yuwei; Wang, Gwo-Ching; Wertz, Esther; Deschler, Felix; Cai, Zhonghou; Zhou, Hua; Lu, Toh-Ming; Shi, Jian

    2016-11-16

    One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX3 (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensurate epitaxy, paving a way for a universally applicable method to grow a broad family of halide perovskite materials. We have studied the unique photon transport in the one-dimensional structure in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Furthermore, epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.

  2. First principles-based moiré model for incommensurate graphene on BN

    NASA Astrophysics Data System (ADS)

    Spataru, Catalin; Thurmer, Konrad

    Various properties of supported graphene films depend strongly on the exact positions of carbon atoms with respect to the underlying substrate. While density functional theory (DFT) can predict atom position in many systems, it cannot be applied straightforwardly to systems that are incommensurate or have large unit cells, such as graphene on a BN surface. We address these limitations by developing a simple moiré model with parameters derived from DFT calculations for systems strained into commensurate structures with manageable unit cell sizes. Our moiré model, which takes into account the flexural rigidity of graphene and includes the influence of the substrate, is able to reproduce the DFT-relaxed carbon positions with an accuracy of <0.01 Å. We then apply this model to the unstrained C/BN system and predict how structure and energy vary with azimuthal orientation of the graphene sheet with respect to the BN substrate. Work supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Co., for the U.S. DOE under Contract DE-AC04-94AL85000.

  3. Photon Transport in One-Dimensional Incommensurately Epitaxial CsPbX3 Arrays

    DOE PAGES

    Wang, Yiping; Sun, Xin; Shivanna, Ravichandran; ...

    2016-12-01

    One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX3 (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters. Structural analysis reveals that the wire arrays follow the symmetry of mica substrate through incommensurate epitaxy,more » paving a way for a universally applicable method to grow a broad family of halide perovskite materials. The unique photon transport in the one-dimensional structure has been studied in the all-inorganic Cs-based perovskite wires via temperature dependent and spatially resolved photoluminescence. Epitaxy of well oriented wire arrays in halide perovskite would be a promising direction for enabling the circuit-level applications of halide perovskite in high-performance electro-optics and optoelectronics.« less

  4. A Magnetic Field Sensor Based on a Magnetic Fluid-Filled FP-FBG Structure.

    PubMed

    Xia, Ji; Wang, Fuyin; Luo, Hong; Wang, Qi; Xiong, Shuidong

    2016-04-29

    Based on the characteristic magnetic-controlled refractive index property, in this paper, a magnetic fluid is used as a sensitive medium to detect the magnetic field in the fiber optic Fabry-Perot (FP) cavity. The temperature compensation in fiber Fabry-Perot magnetic sensor is demonstrated and achieved. The refractive index of the magnetic fluid varies with the applied magnetic field and external temperature, and a cross-sensitivity effect of the temperature and magnetic field occurs in the Fabry-Perot magnetic sensor and the accuracy of magnetic field measurements is affected by the thermal effect. In order to overcome this problem, we propose a modified sensor structure. With a fiber Bragg grating (FBG) written in the insert fiber end of the Fabry-Perot cavity, the FBG acts as a temperature compensation unit for the magnetic field measurement and it provides an effective solution to the cross-sensitivity effect. The experimental results show that the sensitivity of magnetic field detection improves from 0.23 nm/mT to 0.53 nm/mT, and the magnetic field measurement resolution finally reaches 37.7 T. The temperature-compensated FP-FBG magnetic sensor has obvious advantages of small volume and high sensitivity, and it has a good prospect in applications in the power industry and national defense technology areas.

  5. A Magnetic Field Sensor Based on a Magnetic Fluid-Filled FP-FBG Structure

    PubMed Central

    Xia, Ji; Wang, Fuyin; Luo, Hong; Wang, Qi; Xiong, Shuidong

    2016-01-01

    Based on the characteristic magnetic-controlled refractive index property, in this paper, a magnetic fluid is used as a sensitive medium to detect the magnetic field in the fiber optic Fabry-Perot (FP) cavity. The temperature compensation in fiber Fabry-Perot magnetic sensor is demonstrated and achieved. The refractive index of the magnetic fluid varies with the applied magnetic field and external temperature, and a cross-sensitivity effect of the temperature and magnetic field occurs in the Fabry-Perot magnetic sensor and the accuracy of magnetic field measurements is affected by the thermal effect. In order to overcome this problem, we propose a modified sensor structure. With a fiber Bragg grating (FBG) written in the insert fiber end of the Fabry-Perot cavity, the FBG acts as a temperature compensation unit for the magnetic field measurement and it provides an effective solution to the cross-sensitivity effect. The experimental results show that the sensitivity of magnetic field detection improves from 0.23 nm/mT to 0.53 nm/mT, and the magnetic field measurement resolution finally reaches 37.7 T. The temperature-compensated FP-FBG magnetic sensor has obvious advantages of small volume and high sensitivity, and it has a good prospect in applications in the power industry and national defense technology areas. PMID:27136564

  6. Magnetic instability regions in patterned structures: influence of element shape on magnetization reversal dynamics.

    PubMed

    Han, X F; Grimsditch, M; Meersschaut, J; Hoffmann, A; Ji, Y; Sort, J; Nogués, J; Divan, R; Pearson, J E; Keavney, D J

    2007-04-06

    We report a time-resolved imaging study of the influence of shape on magnetic instabilities in patterned magnetic structures. We find that in rectangular structures magnetization reversal initiates at the ends and interior simultaneously, while in structures with tapered ends the reversal begins in the middle of the structures and spreads out to the ends. The degree of tapering is important for both the switching field and the time required for full reversal. A model based on the concept of local instability regions yields good agreement with the observed location of the reversal onsets.

  7. Magnetic instability regions in patterned structures : influence of element shape on magnetization reversal dynamics.

    SciTech Connect

    Keavney, D. J.; Han, X. F.; Grimsditch, M.; Meersschaut, J.; Hoffmann, A.; Ji, Y.; Sort, J.; Notues, J.; Divan, R.; Pearson, J. E.; Guslienko, K. Y.; Bader, S. D.; Inst. voor Kern-en Stralingsfysica and INPAC; Univ. Autonoma de Barcelona

    2007-04-06

    We report a time-resolved imaging study of the influence of shape on magnetic instabilities in patterned magnetic structures. We find that in rectangular structures magnetization reversal initiates at the ends and interior simultaneously, while in structures with tapered ends the reversal begins in the middle of the structures and spreads out to the ends. The degree of tapering is important for both the switching field and the time required for full reversal. A model based on the concept of local instability regions yields good agreement with the observed location of the reversal onsets.

  8. Helicity, anisotropies, and their competition in a multiferroic magnet: Insight from the phase diagram

    NASA Astrophysics Data System (ADS)

    Gvozdikova, M. V.; Ziman, T.; Zhitomirsky, M. E.

    2016-07-01

    Motivated by the complex phase diagram of MnWO4, we investigate the competition between anisotropy, magnetic field, and helicity for the anisotropic next-nearest-neighbor Heisenberg model. Apart from two competing exchanges, which favor a spiral magnetic structure, the model features the biaxial single-ion anisotropy. The model is treated in the real-space mean-field approximation and the phase diagram containing various incommensurate and commensurate states is obtained for different field orientations. We discuss the similarities and differences of the theoretical phase diagram and the experimental diagram of MnWO4.

  9. Magnetic Structure of the Magnetopause Boundary Layer for Open Magnetosphere

    NASA Astrophysics Data System (ADS)

    Ma, Yonghui; Shen, Chao; Zeng, Gang

    2017-04-01

    Using Cluster and Magnetospheric MultiScale (MMS) spacecraft 4 point magnetic field measurements, we analyzed the magnetic structure of magnetopause boundary layer of the open magnetosphere. It is indicated that the magnetopause boundary layer is very thin under strong magnetic shear and the thickness is usually 0.1 Re. We found that the Rotational Discontinuity (RD) is very important structure at magnetopause when the Interplanetary Magnetic Field (IMF) is southward. Within the boundary layer, the magnetic field has a large rotation. Using curvature calculation method, we got that the minimum curvature radius of magnetic field of RD is 0.02 - 0.1Re, implying that the magnetosphere is open when the IMF is southward. Advanced research showed that the field-aligned currents are common in the magnetopause boundary layer.

  10. Magnetic vs. structural fabrics, Whipple detachment structure, Whipple Wash, California

    NASA Astrophysics Data System (ADS)

    MacDonald, William D.; Elwood, Brooks B.

    1990-12-01

    Orientations of ellipsoids of anisotropy of magnetic susceptibility (AMS) are compared with those of mesoscopic structural features for the breccia and upper mylonite zones for the Whipple detachment zone in Whipple Wash, Whipple Mountains, eastern California. The anisotropy of the breccia, which ranges up to 5%, is much less than that of the mylonitic gneiss, which can exceed 100%. Slight differences in trend are evident between the AMS ellipsoid elongations and those of mineral lineations. Maximum axes (χ 1) of the AMS ellipsoids, for both breccia and mylonite, trend generally SSW-NNE with shallow plunge, whereas mineral 'stretching' lineations in the mylonite gneiss have trends near NE-SW with shallow plunge. Measured fold axes are close to the χ 1 axes, SSW-NNE. χ 1 axes in the breccia show more variation, E-W and SSW-NNE, at different structural levels. Mesoscopic mineral lineations in the breccia were not discernible. For the planar elements, AMS ellipsoid flattening is generally more closely parallel to foliation surfaces in the mylonite than in the breccia. This is evident from overlapping minimum susceptibility axes (χ 3) and foliation pole clusters. χ 3 axes are more scattered than are poles of foliation. The scatter in χ 3 is possibly the superimposed susceptibility effect of several structural surfaces of different ages: joints, small faults, transposed metamorphic foliations, and mylonitic foliation. Especially interesting are the discovery of good χ 1 definitions in the breccia, the apparent lack of correlation of χ 1 axes with the very prominent 'stretching' lineations in the mylonite, and the similarity of the χ 1 axial trends with those of the fold/fracture pole patterns.

  11. Evolving Magnetic Structures and Their Relation to Coronal Mass Ejections

    NASA Technical Reports Server (NTRS)

    Feynman, J.

    1996-01-01

    Solar activity regions are frequently concentrated into cluster which persist for many solar rotations. These activity complexes are associated with weak dispersed magnetic fields which are most apparent after the activity itself has ceased. We call this combination of persistent activity and dispersed Evolving Magnetic Structures (EMS). Here we show examples of EMSs and describe the evolution of an EMS associated with major Coronal Mass Ejections (CME) and other solar and magnetic disturbances.

  12. Fractal structure of the interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.; Klein, L. W.

    1985-01-01

    Under some conditions, time series of the interplanetary magnetic field strength and components have the properties of fractal curves. Magnetic field measurements made near 8.5 AU by Voyager 2 from June 5 to August 24, 1981 were self-similar over time scales from approximately 20 sec to approximately 3 x 100,000 sec, and the fractal dimension of the time series of the strength and components of the magnetic field was D = 5/3, corresponding to a power spectrum P(f) approximately f sup -5/3. Since the Kolmogorov spectrum for homogeneous, isotropic, stationary turbulence is also f sup -5/3, the Voyager 2 measurements are consistent with the observation of an inertial range of turbulence extending over approximately four decades in frequency. Interaction regions probably contributed most of the power in this interval. As an example, one interaction region is discussed in which the magnetic field had a fractal dimension D = 5/3.

  13. Unusual Structure and Magnetism in MnO Nanoclusters

    NASA Astrophysics Data System (ADS)

    Ganguly, Shreemoyee; Kabir, Mukul; Sanyal, Biplab; Mookerjee, Abhijit

    2011-03-01

    We report an unusual structural and magnetic evolution in stoichiometric MnO nanoclusters by an extensive and unbiased search through the potential energy surface within density functional theory. The (MnO)n nanoclusters adopt two-dimensional structures in size ranges in which Mnn nanoclusters are three-dimensional and regardless of the size of the nanocluster, the magnetic coupling is found to be antiferromagnetic, and is strikingly different from Mn-based molecular magnets. Both of these features are explained through the inherent electronic structures of the nanoclusters. We gratefully acknowledge financial support from Swedish Research Links program funded by VR/SIDA and Carl Tryggers Foundation, Sweden.

  14. Influence of magnetic fields on structural martensitic transitions

    SciTech Connect

    Lashley, J C; Cooley, J C; Smith, J L; Fisher, R A; Modic, K A; Yang, X- D; Riseborough, P S; Opeil, C P; Finlayson, T R; Goddard, P A; Silhanek, A V

    2009-01-01

    We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high-magnetic fields. The magnetic field dependence is considered unusual as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical framework which can be used to describe the effect of magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant.

  15. Vertical Structure of Magnetized Accretion Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    Lizano, S.; Tapia, C.; Boehler, Y.; D'Alessio, P.

    2016-01-01

    We model the vertical structure of the magnetized accretion disks that are subject to viscous and resistive heating and irradiation by the central star. We apply our formalism to the radial structure of the magnetized accretion disks that are threaded by the poloidal magnetic field dragged during the process of star formation, which was developed by Shu and coworkers. We consider disks around low-mass protostars, T Tauri, and FU Orionis stars, as well as two levels of disk magnetization: {λ }{sys}=4 (strongly magnetized disks) and {λ }{sys}=12 (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk, and the T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7% of the viscous heating. In these models, the T Tauri disk has a larger aspect ratio, which is consistent with that inferred from observations. All the disks have spatially extended hot atmospheres where the irradiation flux is absorbed, although most of the mass (˜90%-95%) is in the disk midplane. With the advent of ALMA one expects direct measurements of magnetic fields and their morphology at disk scales. It will then be possible to determine the mass-to-flux ratio of magnetized accretion disks around young stars, an essential parameter for their structure and evolution. Our models contribute to the understanding of the vertical structure and emission of these disks.

  16. Local magnetic structure determination using polarized neutron holography

    NASA Astrophysics Data System (ADS)

    Szakál, Alex; Markó, Márton; Cser, László

    2015-05-01

    A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems.

  17. Defective graphene and nanoribbons: electronic, magnetic and structural properties

    NASA Astrophysics Data System (ADS)

    Guerra, Thiago; Azevedo, Sérgio; Machado, Marcelo

    2016-03-01

    We make use of first-principles calculations, based on the density functional theory (DFT), to investigate the alterations at the structural, energetic, electronic and magnetic properties of graphene and zigzag graphene nanoribbons (ZGNRs) due to the inclusion of different types of line and punctual defects. For the graphene it is found that the inclusion of defects breaks the translational symmetry of the crystal with drastic changes at its electronic structure, going from semimetallic to semiconductor and metallic. Regarding the magnetic properties, no magnetization is observed for the defective graphene. We also show that the inclusion of defects at ZGNRs is a good way to create and control pronounced peaks at the Fermi level. Furthermore, defective ZGNRs structures show magnetic moment by supercell up to 2.0 μ B . For the non defective ZGNRs is observed a switch of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferrimagnetic and ferromagnetic configurations.

  18. Local magnetic structure determination using polarized neutron holography

    SciTech Connect

    Szakál, Alex Markó, Márton Cser, László

    2015-05-07

    A unique and important property of the neutron is that it possesses magnetic moment. This property is widely used for determination of magnetic structure of crystalline samples observing the magnetic components of the diffraction peaks. Investigations of diffraction patterns give information only about the averaged structure of a crystal but for discovering of local spin arrangement around a specific (e.g., impurity) nucleus remains still a challenging problem. Neutron holography is a useful tool to investigate the local structure around a specific nucleus embedded in a crystal lattice. The method has been successfully applied experimentally in several cases using non-magnetic short range interaction of the neutron and the nucleus. A mathematical model of the hologram using interaction between magnetic moment of the atom and the neutron spin for polarized neutron holography is provided. Validity of a polarized neutron holographic experiment is demonstrated by applying the proposed method on model systems.

  19. New insight in magnetic saturation behavior of nickel hierarchical structures

    NASA Astrophysics Data System (ADS)

    Ma, Ji; Zhang, Jianxing; Liu, Chunting; Chen, Kezheng

    2017-09-01

    It is unanimously accepted that non-ferromagnetic inclusions in a ferromagnetic system will lower down total saturation magnetization in unit of emu/g. In this study, ;lattice strain; was found to be another key factor to have critical impact on magnetic saturation behavior of the system. The lattice strain determined assembling patterns of primary nanoparticles in hierarchical structures and was intimately related with the formation process of these architectures. Therefore, flower-necklace-like and cauliflower-like nickel hierarchical structures were used as prototype systems to evidence the relationship between assembling patterns of primary nanoparticles and magnetic saturation behaviors of these architectures. It was found that the influence of lattice strain on saturation magnetization outperformed that of non-ferromagnetic inclusions in these hierarchical structures. This will enable new insights into fundamental understanding of related magnetic effects.

  20. Vertical Structure of Magnetized Accretion Disks Around Young Stars

    NASA Astrophysics Data System (ADS)

    Tapia, Carlos; Lizano, Susana

    2016-01-01

    We model the vertical structure of magnetized accretion disks subject to viscous and resistive heating, and irradiation by the central star. We apply our formalism to the radial structure of magnetized accretion disks threaded by a poloidal magnetic field dragged during the process of star formation developed by Shu and coworkers. We consider disks around low mass protostars, T Tauri, and FU Orionis stars. We consider two levels of disk magnetization, λsys = 4 (strongly magnetized disks), and λsys = 12 (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk. The T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7% of the viscous heating. In these models, the T Tauri disk has a larger aspect ratio, consistent with that inferred from observations. All the disks have spatially extended hot atmospheres where the irradiation flux is absorbed, although most of the mass (~ 90 - 95 %) is in the disk midplane.

  1. Magnetic and structural phase transitions of MnBi under high magnetic fields

    PubMed Central

    Koyama, Keiichi; Mitsui, Yoshifuru; Watanabe, Kazuo

    2008-01-01

    High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature TSR(=90 K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of TSR. By applying a magnetic field of 5 T, the parameter a increases by ∼0.05% when Tmagnetic phase transition temperature from the ferromagnetic state to the paramagnetic state increases linearly at a rate of 2 KT−1 with increasing magnetic field up to 14 T. PMID:27877955

  2. Magnetic structure and magnetic properties of nanocrystalline and amorphous Fe-Zr-N films

    NASA Astrophysics Data System (ADS)

    Sheftel, Elena N.; Harin, Eugene V.; Tedzhetov, Valentin A.; Kiryukhantsev-Korneev, Philipp V.; Levashov, Evgeny A.; Perov, Nikolai S.; Titova, Alexandra O.

    2016-08-01

    Data on the magnetic structure and magnetic properties of Fe-Zr-N films, which were prepared by reactive magnetron sputtering of a heated target and deposited on glass substrates, are reported. Depending on the Zr content (from 3 to 35 at%), the film compositions are characterized by Zr-to-N (at%) ratio from 0.3 to 36.5. The magnetic properties (saturation magnetization Ms, coercive field Hc) and magnetic structure (effective local magnetic anisotropy field D1/2Ha, grain size 2Rc, effective anisotropy field of stochastic domain D1/2, relative stochastic domain size RL/Rc) of the films are discussed in interrelation with their phase and structural states. The coercive field of the studied ferromagnetic nanocrystalline films was shown to obey the relationship Hc~(2Rc)6 and depends on not only the grain size but also the local magnetic anisotropy field D1/2Ha. As the grain size of ferromagnetic phase decreases, the contribution of the magnetoelastic component to the coercive field decreases. It was shown, by examples of weak ferromagnetic and superparamagnetic films with amorphous and mixed (amorphous+nanocrystalline) structures containing a nonferromagnetic phase, that the magnetic properties reflect the real structural and phase state of the films, which cannot be revealed by the X-ray diffraction analysis.

  3. Spinful fermionic ladders at incommensurate filling: Phase diagram, local perturbations, and ionic potentials

    SciTech Connect

    Carr, Sam T.; Narozhny, Boris N.; Nersesyan, Alexander A.

    2013-12-15

    We study the effect of external potential on transport properties of the fermionic two-leg ladder model. The response of the system to a local perturbation is strongly dependent on the ground state properties of the system and especially on the dominant correlations. We categorize all phases and transitions in the model (for incommensurate filling) and introduce “hopping-driven transitions” that the system undergoes as the inter-chain hopping is increased from zero. We also describe the response of the system to an ionic potential. The physics of this effect is similar to that of the single impurity, except that the ionic potential can affect the bulk properties of the system and in particular induce true long range order. -- Highlights: •We study low temperature electronic properties of a two leg ladder. •We find a wide variety of phase transitions as a function of model parameters. •We study the effect of impurities on these models. •Conductance may be very sensitive to the structure of these impurities.

  4. Magnetoelectric effect and phase transitions in CuO in external magnetic fields

    PubMed Central

    Wang, Zhaosheng; Qureshi, Navid; Yasin, Shadi; Mukhin, Alexander; Ressouche, Eric; Zherlitsyn, Sergei; Skourski, Yurii; Geshev, Julian; Ivanov, Vsevolod; Gospodinov, Marin; Skumryev, Vassil

    2016-01-01

    Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of ≈50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions. PMID:26776921

  5. Multiscale structures of resistive magnetic reconnection at high magnetic Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Miyoshi, Takahiro; Kusano, Kanya

    Magnetic reconnection is the most important process of explosive phenomena in space plasmas. The magnetic Reynolds number for the space plasmas are extremely high in general since those plasmas are thought to be collisionless or semi-collisional. However, magnetic reconnection rate becomes low as magnetic Reynolds number increases within the framework of a stationary resistive MHD model. Thus, modern models of magnetic reconnection often include kinetic effects such as the Hall effect to explain realistic explosive magnetic reconnection. It is thought, on the other hand, that the MHD approximation is valid for the plasmas within a very wide range of scales since the scale gap between the macro-and micro-scale is quite large, e.g., in the solar corona, the ratio of the macro to micro will be more than 107 . Such multiscale structures of MHD with wide range of scales, however, have not been clarified so far. Therefore, in this paper, resistive magnetic reconnection at high magnetic Reynolds numbers are investigated using very high-resolution MHD simulations. Simulation results show that the magnetic energy at high magnetic Reynolds numbers is explosively released, while that at not-so-high magnetic Reynolds numbers is steadily dissipated. In the case of high magnetic Reynolds numbers, multiple small scale plasmoids are intermittently created and ejected via secondary tearing modes in a nonlinearly developed thin current sheet. It is revealed that a secondary plasmoid is not only accelerated up to a local magnetosonic speed toward the down-stream region but also perturbs the up-stream region. Thus, complicated multiscale structures appear around the magnetic field reversal layer. Perspective for the high-resolution simulation of extremely high magnetic Reynolds numbers will be also discussed.

  6. Magnetic and structural transitions in crystals with a structure of the NaCl type

    NASA Astrophysics Data System (ADS)

    Kassan-Ogly, F. A.; Filippov, B. N.

    2009-04-01

    A model of simultaneous magnetic and structural first-order transitions in antiferromagnets with a strong cubic magnetic anisotropy has been constructed on the basis of a synthesis of magnetic modified 6-state and 8-state Potts models and the theoretical model of structural phase transitions in cubic crystals. A revised scheme has been suggested for the derivation of possible magnetic structures in the fcc lattice with allowance for competing interactions between the nearest and next-nearest neighbors. A calculation of the temperature evolution of high-temperature diffuse magnetic scattering of neutrons has been carried out to show that the mechanism of a magnetic transition at the Néel point is caused by the transformation of diffuse magnetic scattering into magnetic Bragg peaks.

  7. Metastable cobalt nitride structures with high magnetic anisotropy for rare-earth free magnets.

    PubMed

    Zhao, Xin; Ke, Liqin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2016-11-23

    Metastable structures of cobalt nitrides and Fe-substituted cobalt nitrides are explored as possible candidates for rare-earth free permanent magnets. Through crystal structure searches using an adaptive genetic algorithm, new structures of ConN (n = 3…8) are found to have lower energies than those previously discovered by experiments. Some structures exhibit large magnetic anisotropy energy, reaching as high as 200 μeV per Co atom (or 2.45 MJ m(-3)) based on first-principles density functional calculation. Substituting a fraction of Co with Fe helps in stabilizing new structures and at the same time further improves the magnetic properties. Our theoretical predictions provide useful insights into a promising system for the discovery of new rare-earth free magnets by experiment.

  8. Field dependence of magnetic ordering in Kagomé-staircase compound Ni3V2O8

    NASA Astrophysics Data System (ADS)

    Kenzelmann, M.; Harris, A. B.; Aharony, A.; Entin-Wohlman, O.; Yildirim, T.; Huang, Q.; Park, S.; Lawes, G.; Broholm, C.; Rogado, N.; Cava, R. J.; Kim, K. H.; Jorge, G.; Ramirez, A. P.

    2006-07-01

    We present powder and single-crystal neutron diffraction and bulk measurements of the Kagomé-staircase compound Ni3V2O8 (NVO) in fields up to 8.5T applied along the c direction. (The Kagomé plane is the a-c plane.) This system contains two types of Ni ions, which we call “spine” and “cross-tie.” Our neutron measurements can be described with the paramagnetic space group Cmca for T<15K and each observed magnetically ordered phase is characterized by the appropriate irreducible representation(s). Our zero-field measurements show that at TPH=9.1K NVO undergoes a transition to a predominantly longitudinal incommensurate structure in which the spine spins are nearly along the a -axis. At THL=6.3K , there is a transition to an elliptically polarized incommensurate structure with both spine and cross-tie moments in the a-b plane. At TLC=4K the system undergoes a first-order phase transition to a commensurate antiferromagnetic structure with the staggered magnetization primarily along the a -axis and a weak ferromagnetic moment along the c -axis. A specific heat anomaly at TCC'=2.3K indicates an additional transition, which remarkably does not affect Bragg peaks of the commensurate C structure. Neutron, specific heat, and magnetization measurements produce a comprehensive temperature-field phase diagram. The symmetries of the incommensurate magnetic phases are consistent with the observation that only one phase is electrically polarized. The magnetic structures are explained theoretically using a simplified model Hamiltonian, that involves competing nearest- and next-nearest-neighbor exchange interactions, single-ion anisotropy, pseudodipolar interactions, and Dzyaloshinskii-Moriya interactions.

  9. MAGNETIC FIELD STRUCTURES TRIGGERING SOLAR FLARES AND CORONAL MASS EJECTIONS

    SciTech Connect

    Kusano, K.; Bamba, Y.; Yamamoto, T. T.; Iida, Y.; Toriumi, S.; Asai, A.

    2012-11-20

    Solar flares and coronal mass ejections, the most catastrophic eruptions in our solar system, have been known to affect terrestrial environments and infrastructure. However, because their triggering mechanism is still not sufficiently understood, our capacity to predict the occurrence of solar eruptions and to forecast space weather is substantially hindered. Even though various models have been proposed to determine the onset of solar eruptions, the types of magnetic structures capable of triggering these eruptions are still unclear. In this study, we solved this problem by systematically surveying the nonlinear dynamics caused by a wide variety of magnetic structures in terms of three-dimensional magnetohydrodynamic simulations. As a result, we determined that two different types of small magnetic structures favor the onset of solar eruptions. These structures, which should appear near the magnetic polarity inversion line (PIL), include magnetic fluxes reversed to the potential component or the nonpotential component of major field on the PIL. In addition, we analyzed two large flares, the X-class flare on 2006 December 13 and the M-class flare on 2011 February 13, using imaging data provided by the Hinode satellite, and we demonstrated that they conform to the simulation predictions. These results suggest that forecasting of solar eruptions is possible with sophisticated observation of a solar magnetic field, although the lead time must be limited by the timescale of changes in the small magnetic structures.

  10. Nonvolatile logic elements based on magnetically coupled FSF structures.

    SciTech Connect

    Belkin, A.; Novosad, V.; Iavarone, M.; Divan, R.; Hiller, J.; Prolier, T.; Pearson, J. E.; Karapetrov, G.; Materials Science Division; Illinois Inst. Tech.; Temple Univ.

    2010-01-01

    We demonstrate the evolution of the anisotropic conductivity in the superconductor that is magnetically coupled with two adjacent ferromagnetic layers. Stripe magnetic domain structure in the ferromagnetic layers results in directional superconducting order parameter in the superconducting layer. The conductance anisotropy strongly depends on the period of the magnetic domains and the strength of the local magnetization. The anisotropic conductivity of up to three orders of magnitude can be achieved with spatial critical temperature modulation of 5% of Tc. The effect could be exploited in low temperature nonvolatile logic and storage elements

  11. Structured rf hydrogen plasma induced by magnetic field.

    SciTech Connect

    Barnat, Edward V.

    2007-11-01

    Images of the spatial structure of a capacitively coupled hydrogen discharge are presented for various strengths of applied magnetic field. With increasing magnetic field, we find that not only does the distribution of emission change because of the confinement of the electrons by the magnetic field, but we also find 'dark-bands' regions that form in the discharge. By using narrowband interference filters (10 nm bandwidth), we examine how the relative optical emission centered on H{sub {alpha}} and H{sub {beta}} (with respect to the total optical emission) change with the applied magnetic field.

  12. Electronic band structure of magnetic bilayer graphene superlattices

    SciTech Connect

    Pham, C. Huy; Nguyen, T. Thuong

    2014-09-28

    Electronic band structure of the bilayer graphene superlattices with δ-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

  13. Shock-induced modifications of magnetic minerals from impact structures

    NASA Astrophysics Data System (ADS)

    Kontny, A. M.

    2013-05-01

    Meteorite impact structures are an important feature of most planetary surfaces. The effects of shock waves on the intrinsic magnetic properties of minerals and rocks are therefore essential for the understanding of magnetization processes related to impact events on Earth and other planetary bodies. Despite numerous observations on natural settings (Carporzen et al. 2005; Mang et al. 2012), and experimental studies (Louzada et al. 2010, 2011; Gattacecca et al 2007; Gilder et al. 2004; Mang et al. 2013) there remain uncertainties concerning the rock magnetic properties and the magnetization process related to natural impact structures on Earth. In general, the magnetic signature of terrestrial impact structures is a combined effect between disrupted main regional magnetic trends due to shock and / or thermal demagnetization and high-amplitude, short-wavelength magnetic anomalies in the centre of intermediate to large impact structures. Some large structures (>40 km) are reported to exhibit central high-amplitude anomalies but the dominant magnetic feature is a magnetic low (Pilkington and Grieve 1992). The latter observation is especially important for the giant non-magnetized impact basins on Mars. Therefore numerous studies focused on the understanding of the demagnetization processes during shock pressure (Gilder et al. 2004; Louzada et al. 2010, 2011; Rochette et al. 2003). Many investigations of terrestrial impact structures, however, demonstrated that a natural remanent magnetization (NRM), which is imprinted into terrestrial rocks by the Earth magnetic field, is the main cause of the observed magnetic anomalies. Magnetic signatures of impact structures on Earth are therefore thought to be a combination of three parameters: (1) composition and magnetic properties of the target rocks, (2) modification of rocks and magnetic minerals (fracturing and melting) due to impact-related p-T conditions, (3) acquisition of new natural remanent magnetization (TRM, SRM or

  14. Spin filtering action in a magnetic-nonmagnetic superlattice structure

    NASA Astrophysics Data System (ADS)

    Pal, Biplab

    2017-05-01

    We propose a spin filter device using a model magnetic-nonmagnetic superlattice structure. The spin-dependent electronic transport has been studied in such a superlattice structure using the transfer matrix method (TMM), and it is shown that such structure is capable of exhibiting a well-defined spin filtering action. Our model superlattice structure is composed of magnetic-nonmagnetic atomic sites placed in an alternating sequence. The magnitude and the direction of the magnetic moments attached to each magnetic atom play an important role in controlling the spin transmission for selective range of energies corresponding to the two spin channels leading to a spin filtering effect in such system. To corroborate the spin filtering action we have also studied the density of states (DOS) corresponding to the two spin channels (components) for our system. Experimental realization of our model can be useful in designing potential nanoscale spin filter devices.

  15. Transformation of Structure, Electrical Conductivity, and Magnetism in AA'Fe2O6-δ, A = Sr, Ca and A' = Sr.

    PubMed

    Hona, Ram Krishna; Huq, Ashfia; Mulmi, Suresh; Ramezanipour, Farshid

    2017-08-21

    The ability to control electrical properties and magnetism by varying the crystal structure using the effect of the A-site cation in oxygen-deficient perovskites has been studied in AA'Fe2O6-δ, where A = Sr, Ca and A' = Sr. The structure of Sr2Fe2O6-δ, synthesized at 1250 °C in air, contains dimeric units of FeO5 square pyramids separated by FeO6 octahedra. Here we show that this ordering scheme can be transformed by changing the A-site cations from Sr to Ca. This leads to a structure where layers of corner-sharing FeO6 octahedra are separated by chains of FeO4 tetrahedra. Through systematic variation of the A-site cations, we have determined the average ionic radius required for this conversion to be ∼1.41 Å. We have demonstrated that the magnetic structure is also transformed. The Sr2 compound has an incommensurate magnetic structure, where magnetic moments are in spin-density wave state, aligning perpendicular to the body diagonal of the unit cell. With the aid of neutron diffraction experiments at 10 and 300 K, we have shown that the magnetic structure is converted into a long-range G-type antiferromagnetic system when one Sr is replaced by Ca. In this G-type ordering scheme, the magnetic moments align in the 001 direction, antiparallel to their nearest neighbors. We have also performed variable-temperature electrical conductivity studies on these materials in the temperature range 298-1073 K. These studies have revealed the transformation of charge transport properties, where the metallic behavior of the Sr2 compound is converted into semiconductivity in the CaSr material. The trend of conductivity as a function of temperature is reversed upon changing the A-site cation. The conductivity of the Sr2 compound shows a downturn, while the conductivity of the CaSr material increases as a function of temperature. We have also shown that the CaSr compound exhibits temperature-dependent behavior typical of a mixed ionic-electronic conducting system.

  16. Rare earth magnetic order in RNi{sub 2}B{sub 2}C and RNiBC

    SciTech Connect

    Skanthakumar, S.; Lynn, J.W.

    1998-07-05

    A review of neutron diffraction experiments on the magnetic order in the RNi{sub 2}B{sub 2}C and RNiBC (R-rare earth) systems is given. The RNi{sub 2}B{sub 2}C materials exhibit a wide variety of commensurate and incommensurate magnetic structures for different rare earths, along with superconductivity that is coupled to the magnetism. Simple commensurate antiferromagnetic structures are observed for R = Pr (T{sub N} = 4.0 K), Nd (T{sub N} = 4.8 K), Ho (T{sub N} = 8.5 K) and Dy (T{sub N} = 4.8 K). In addition, HoNi{sub 2}B{sub 2}C exhibits a c-axis spiral and an a-axis modulated incommensurate structure above 5 K, while both structures collapse in favor of the commensurate structure at low T. A transversely polarized spin density wave (SDW) type incommensurate structure is observed for Er (T{sub N} = 6.8 K) and Tm (T{sub N} = 1.5 K), while a longitudinally polarized SDW structure is observed for Tb (T{sub N} = 15 K). No magnetic ordering of any type is detected for Y, Ce and Yb. HoNiBC is an antiferromagnet (T{sub N} = 9.8 K), ErNiBC is a ferromagnetic (T{sub C} = 4.6 K), while TbNiBC and DyNiBC exhibit both ferromagnetic and antiferromagnetic ordering at 17 K and {approximately} 13 K, respectively.

  17. Structure and Magnetic Properties of Lanthanide Nanocrystals

    SciTech Connect

    Dickerson, James Henry

    2014-06-01

    We have had considerable success on this project, particularly in the understanding of the relationship between nanostructure and magnetic properties in lanthanide nanocrystals. We also have successfully facilitated the doctoral degrees of Dr. Suseela Somarajan, in the Department of Physics and Astronomy, and Dr. Melissa Harrison, in the Materials Science Program. The following passages summarize the various accomplishments that were featured in 9 publications that were generated based on support from this grant. We thank the Department of Energy for their generous support of our research efforts in this area of materials science, magnetism, and electron microscopy.

  18. Manipulation by exchange coupling in layered magnetic structures

    SciTech Connect

    Moskalenko, M. A.; Uzdin, V. M.; Zabel, H.

    2014-02-07

    Exchange coupling in magnetic heterostructures can be modified via introduction of additional magnetic spacer layers at the interfaces. The magnetic characteristics and the spacer layer thickness determine the functional properties of the whole system. We show that the hysteresis loop area of trilayer spring magnets with two different soft magnetic layers (s1, s2) and one hard magnetic layer (h) with the sequence s1/s2/h can be increased as compared to both bilayer structures s1/h and s2/h with the same total thickness of the soft layers and for definite thickness ratios of the soft layers and their sequences. For ferrimagnetic spin valves, the perpendicular exchange bias effect can be tuned via the thickness of non-magnetic spacer layers at the interface, which determine the exchange coupling between ferrimagnets. A simple quasi one-dimensional phenomenological model is able to describe the magnetic hysteresis of even complex layered structures and to predict optimal geometrical and magnetic parameters of such heterostructures.

  19. Freestanding single-crystalline magnetic structures fabricated by ion bombardment

    SciTech Connect

    Schoenherr, P.; Bischof, A.; Boehm, B.; Eib, P.; Grimm, S.; Gross, L.; Allenspach, R.; Alvarado, S. F.

    2015-01-19

    Starting from an ultrathin Fe film grown epitaxially on top of a GaAs(001) substrate, we show that freestanding structures can be created by ion-beam treatment. These structures are single-crystalline blisters and only a few nanometers thick. Anisotropic stress in the rim of a blister induces magnetic domain states magnetized in the direction normal to the blister edge. Experimental evidence is provided that the lateral size can be confined by starting from a nanostructured template.

  20. Modulated anharmonic ADPs are intrinsic to aperiodic crystals: a case study on incommensurate Rb2ZnCl4

    PubMed Central

    Li, Liang; Wölfel, Alexander; Schönleber, Andreas; Mondal, Swastik; Schreurs, Antoine M. M.; Kroon-Batenburg, Loes M. J.; van Smaalen, Sander

    2011-01-01

    A combination of structure refinements, analysis of the superspace MEM density and interpretation of difference-Fourier maps has been used to characterize the incommensurate modulation of rubidium tetrachlorozincate, Rb2ZnCl4, at a temperature of T = 196 K, close to the lock-in transition at T lock-in = 192 K. The modulation is found to consist of a combination of displacement modulation functions, modulated atomic displacement parameters (ADPs) and modulated third-order anharmonic ADPs. Up to fifth-order Fourier coefficients could be refined against diffraction data containing up to fifth-order satellite reflections. The center-of-charge of the atomic basins of the MEM density and the displacive modulation functions of the structure model provide equivalent descriptions of the displacive modulation. Modulations of the ADPs and anharmonic ADPs are visible in the MEM density, but extracting quantitative information about these modulations appears to be difficult. In the structure refinements the modulation parameters of the ADPs form a dependent set, and ad hoc restrictions had to be introduced in the refinements. It is suggested that modulated harmonic ADPs and modulated third-order anharmonic ADPs form an intrinsic part, however small, of incommensurately modulated structures in general. Refinements of alternate models with and without parameters for modulated ADPs lead to significant differences between the parameters of the displacement modulation in these two types of models, thus showing the modulation of ADPs to be important for a correct description of the displacive modulation. The resulting functions do not provide evidence for an interpretation of the modulation by a soliton model. PMID:21586828

  1. Two-dimensional chiral asymmetry in unidirectional magnetic anisotropy structures

    SciTech Connect

    Perna, P. Guerrero, R.; Niño, M. A.; Muñoz, M.; Prieto, J. L.; Miranda, R.; Camarero, J.

    2016-05-15

    We investigate the symmetry-breaking effects of magnetic nanostructures that present unidirectional (one-fold) magnetic anisotropy. Angular and field dependent transport and magnetic properties have been studied in two different exchange-biased systems, i.e. ferromagnetic (FM)/ antiferromagnetic (AFM) bilayer and spin-valve structures. We experimentally show the direct relationships between the magnetoresistance (MR) response and the magnetization reversal pathways for any field value and direction. We demonstrate that even though the MR signals are related to different transport phenomena, namely anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), chiral asymmetries are found around the magnetization hard-axis direction, in both cases originated from the one-fold symmetry of the interfacial exchange coupling. Our results indicate that the chiral asymmetry of transport and magnetic behaviors are intrinsic of systems with an unidirectional contribution.

  2. Two-dimensional chiral asymmetry in unidirectional magnetic anisotropy structures

    NASA Astrophysics Data System (ADS)

    Perna, P.; Ajejas, F.; Maccariello, D.; Cuñado, J. L.; Guerrero, R.; Niño, M. A.; Muñoz, M.; Prieto, J. L.; Miranda, R.; Camarero, J.

    2016-05-01

    We investigate the symmetry-breaking effects of magnetic nanostructures that present unidirectional (one-fold) magnetic anisotropy. Angular and field dependent transport and magnetic properties have been studied in two different exchange-biased systems, i.e. ferromagnetic (FM)/ antiferromagnetic (AFM) bilayer and spin-valve structures. We experimentally show the direct relationships between the magnetoresistance (MR) response and the magnetization reversal pathways for any field value and direction. We demonstrate that even though the MR signals are related to different transport phenomena, namely anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), chiral asymmetries are found around the magnetization hard-axis direction, in both cases originated from the one-fold symmetry of the interfacial exchange coupling. Our results indicate that the chiral asymmetry of transport and magnetic behaviors are intrinsic of systems with an unidirectional contribution.

  3. Laminar wave train structure of collisionless magnetic slow shocks

    NASA Technical Reports Server (NTRS)

    Coroniti, F. V.

    1970-01-01

    The laminar wave train structure of collisionless magnetic slow shocks is investigated using two fluid hydromagnetics with ion cyclotron radius dispersion. For shock strengths less than the maximally strong switch-off shock, in the shock leading edge dispersive steepening forms a magnetic field gradient, while in the downstream flow dispersive propagation forms a trailing wave train; dispersion scale lengths are the ion inertial length if beta is smaller than 1 and the ion cyclotron radius if beta is greater than 1. In the switch-off slow shock leading edge, dispersion only produced rotations of the magnetic field direction; the gradient of the magnetic field magnitude, and hence the shock steepening length, is determined solely by resistive diffusion. The switch-off shock structure consists of a long trailing of magnetic rotations which are gradually damped by resistivity.

  4. Structural and magnetic properties of CrSb compounds: NiAs structure

    NASA Astrophysics Data System (ADS)

    Polesya, S.; Kuhn, G.; Mankovsky, S.; Ebert, H.; Regus, M.; Bensch, W.

    2012-01-01

    The structural and magnetic properties of CrSb compounds with NiAs structure have been studied by means of the Korringa-Kohn-Rostoker (KKR) band structure method. An analysis of the structural and magnetic stability has been performed on the basis of total energy calculations for various magnetic states. The magnetic properties at finite temperature have been investigated by means of Monte Carlo simulations on the basis of a classical Heisenberg Hamiltonian and the exchange coupling parameters calculated from first principles. This approach allowed us to determine the critical temperature in good agreement with experiment.

  5. Structural and magnetic properties of CrSb compounds: NiAs structure.

    PubMed

    Polesya, S; Kuhn, G; Mankovsky, S; Ebert, H; Regus, M; Bensch, W

    2012-01-25

    The structural and magnetic properties of CrSb compounds with NiAs structure have been studied by means of the Korringa-Kohn-Rostoker (KKR) band structure method. An analysis of the structural and magnetic stability has been performed on the basis of total energy calculations for various magnetic states. The magnetic properties at finite temperature have been investigated by means of Monte Carlo simulations on the basis of a classical Heisenberg Hamiltonian and the exchange coupling parameters calculated from first principles. This approach allowed us to determine the critical temperature in good agreement with experiment.

  6. Tuning the competing phases of bilayer ruthenate C a3R u2O7 via dilute Mn impurities and magnetic field

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Peng, J.; Tian, W.; Hong, T.; Mao, Z. Q.; Ke, X.

    2017-04-01

    We have systematically investigated the evolution of the magnetic structure of the bilayer ruthenate C a3(Ru1-xM nx) 2O7 induced upon Mn doping. For 0 structure as that of the parent compound at low temperature, while an incommensurate cycloidal magnetic structure emerges at T slightly above the metal-insulator transition (MIT) temperature (TMIT). In contrast, for x ≥0.04 the ground state becomes a G-type antiferromagnetic Mott insulator. Furthermore, we have observed magnetic-field-induced transitions in C a3(Ru0.96Mn0.04) 2O7 , which is positioned at the phase boundary. Below TMIT, the magnetic transition is accompanied by a structural transition, as well as a dramatic change in the electronic properties from a Mott insulator to a localized phase. On the contrary, an incommensurate-to-commensurate spin structure transition is observed for TMITmagnetic tendencies in this bilayer ruthenate system that are very susceptible to 3 d transition-metal substitution and magnetic field.

  7. Fast magnetization precession for perpendicularly magnetized MnAlGe epitaxial films with atomic layered structures

    NASA Astrophysics Data System (ADS)

    Mizukami, S.; Sakuma, A.; Kubota, T.; Kondo, Y.; Sugihara, A.; Miyazaki, T.

    2013-09-01

    Epitaxial growth and magnetization precessional dynamics for tetragonal MnAlGe films are investigated. The films are grown on MgO (100) with c axis parallel to the film normal and well-ordered layered structures. The film exhibits rectangular hysteresis loop with perpendicular magnetic anisotropy constant of 4.7 Merg/cm3 and saturation magnetization of 250 emu/cm3. Magnetization precession with precession frequency of ˜100 GHz is observed by time-resolved magneto-optical Kerr effect. Further, the Gilbert damping constant is found to be less than ˜0.05, which is much larger than that obtained using the first principles calculations.

  8. Synthesis, Structural, Electrical and Magnetic Studies of Ni- Ferrite Nanoparticles

    NASA Astrophysics Data System (ADS)

    Godbole, Bhavana; Badera, Nitu; Shrivastava, S. B.; Jain, Deepti; Chandra, L. S. Sharath; Ganesan, V.

    Mono-dispersed NiFe2O4 nanoparticles have been synthesized using a stable ferric salt of FeCl3 with co-precipitation technique, for study of their structural, morphological and magnetic properties. The XRD pattern conforms the formation of FCC structure with the lattice constant 8.31Ao. The crystallite size was found to increase with the bath temperature ranging from 33 nm to 55 nm. The AFM results revealed that uniform disc shaped particles were obtained. The resistivity measurements show a metal like to semiconductor transition, which depends on the size of the grains. The magnetic study reveals that saturation magnetization increases with the grain thickness.

  9. Spin pumping due to spin waves in magnetic vortex structure

    NASA Astrophysics Data System (ADS)

    Hasegawa, Norinobu; Kondou, Kouta; Kimata, Motoi; Otani, YoshiChika

    2017-05-01

    We performed spin pumping into a Pt wire by using various spin-wave modes excited in a magnetic vortex structure. Radial and azimuthal modes were excited by applying an in-plane radiofrequency magnetic field with a variable frequency. We observed a mode-dependent sign change in the inverse spin Hall voltage induced along the Pt wire. Micromagnetic simulation revealed that the observed behavior reflected the spatial distribution of the spin wave. These findings suggest that spin pumping can be used for the electrical detection of the spatial distribution of confined spin-wave modes in small magnetic structures.

  10. Model for dynamic self-assembled magnetic surface structures.

    SciTech Connect

    Belkin, M.; Glatz, A.; Snezhko, A.; Aranson, I. S.; Materials Science Division; Northwestern Univ.

    2010-07-07

    We propose a first-principles model for the dynamic self-assembly of magnetic structures at a water-air interface reported in earlier experiments. The model is based on the Navier-Stokes equation for liquids in shallow water approximation coupled to Newton equations for interacting magnetic particles suspended at a water-air interface. The model reproduces most of the observed phenomenology, including spontaneous formation of magnetic snakelike structures, generation of large-scale vortex flows, complex ferromagnetic-antiferromagnetic ordering of the snake, and self-propulsion of bead-snake hybrids.

  11. Magnetic flux rope type structures in the geomagnetic tail

    NASA Astrophysics Data System (ADS)

    Antonova, A. E.; Kropotkin, A. P.

    1991-12-01

    Some structures in the geomagnetic tail observed by the Prognoz 9 and ISEE spacecraft as 'magnetic flux ropes' are identified, and new features are emphasized. The structures are associated with considerable fluxes of energetic ions and electrons. Particles are effectively energized at magnetic field discontinuities, resulting in the generation of spectra extending up to MeV energies. An external field source (i.e., the interplanetary magnetic field) may be of essential importance for the generation of the flux ropes whose axes lie in the cross-tail direction.

  12. Magnetic domain-wall dynamics in a submicrometre ferromagnetic structure.

    PubMed

    Atkinson, Del; Allwood, Dan A; Xiong, Gang; Cooke, Michael D; Faulkner, Colm C; Cowburn, Russell P

    2003-02-01

    As fabrication technology pushes the dimensions of ferromagnetic structures into the nanoscale, understanding the magnetization processes of these structures is of fundamental interest, and key to future applications in hard disk drives, magnetic random access memory and other 'spintronic' devices. Measurements on elongated magnetic nanostructures highlighted the importance of nucleation and propagation of a magnetic boundary, or domain wall, between opposing magnetic domains in the magnetization reversal process. Domain-wall propagation in confined structures is of basic interest and critical to the performance of a recently demonstrated magnetic logic scheme for spintronics. A previous study of a 500-nm-wide NiFe structure obtained very low domain-wall mobility in a three-layer device. Here we report room-temperature measurements of the propagation velocity of a domain wall in a single-layer planar Ni80Fe20 ferromagnetic nanowire 200 nm wide. The wall velocities are extremely high and, importantly, the intrinsic wall mobility is close to that in continuous films, indicating that lateral confinement does not significantly affect the gyromagnetic spin damping parameter to the extreme extent previously suggested. Consequently the prospects for high-speed domain-wall motion in future nanoscale spintronic devices are excellent.

  13. Structure and magnetism in novel group IV element-based magnetic materials

    SciTech Connect

    Tsui, Frank

    2013-08-14

    The project is to investigate structure, magnetism and spin dependent states of novel group IV element-based magnetic thin films and heterostructures as a function of composition and epitaxial constraints. The materials systems of interest are Si-compatible epitaxial films and heterostructures of Si/Ge-based magnetic ternary alloys grown by non-equilibrium molecular beam epitaxy (MBE) techniques, specifically doped magnetic semiconductors (DMS) and half-metallic Heusler alloys. Systematic structural, chemical, magnetic, and electrical measurements are carried out, using x-ray microbeam techniques, magnetotunneling spectroscopy and microscopy, and magnetotransport. The work is aimed at elucidating the nature and interplay between structure, chemical order, magnetism, and spin-dependent states in these novel materials, at developing materials and techniques to realize and control fully spin polarized states, and at exploring fundamental processes that stabilize the epitaxial magnetic nanostructures and control the electronic and magnetic states in these complex materials. Combinatorial approach provides the means for the systematic studies, and the complex nature of the work necessitates this approach.

  14. Magnetic anisotropy and magnetic domain structure in C-doped Mn5Ge3

    NASA Astrophysics Data System (ADS)

    Michez, L.-A.; Virot, F.; Petit, M.; Hayn, R.; Notin, L.; Fruchart, O.; Heresanu, V.; Jamet, M.; Le Thanh, V.

    2015-07-01

    Magnetic properties of Mn5Ge3C0.7 thin films grown by molecular beam epitaxy have been studied. SQUID-VSM measurements and magnetic force microscopy have been used to probe the magnetic state and determine the relevant magnetic parameters. The results are supported by a combination of improved Saito's and Kittel's models. The moderate perpendicular magnetic anisotropy ( Qe x p=2/Ku μ0MSa t 2 ≈0.2 ) leads to a stripe domain structure for film thicknesses above 28 nm. For thinner films, the magnetization lies in-plane. The uniaxial magnetocrystalline constant has been found to be much weaker than in Mn5Ge3 and is assigned to hybridization effect between the Mn and C atoms.

  15. Topological superconductor to Anderson localization transition in one-dimensional incommensurate lattices.

    PubMed

    Cai, Xiaoming; Lang, Li-Jun; Chen, Shu; Wang, Yupeng

    2013-04-26

    We study the competition of disorder and superconductivity for a one-dimensional p-wave superconductor in incommensurate potentials. With the increase in the strength of the incommensurate potential, the system undergoes a transition from a topological superconducting phase to a topologically trivial localized phase. The phase boundary is determined both numerically and analytically from various aspects and the topological superconducting phase is characterized by the presence of Majorana edge fermions in the system with open boundary conditions. We also calculate the topological Z2 invariant of the bulk system and find it can be used to distinguish the different topological phases even for a disordered system.

  16. Static and dynamic properties of incommensurate smectic-A(IC) liquid crystals

    NASA Technical Reports Server (NTRS)

    Lubensky, T. C.; Ramaswamy, Sriram; Toner, John

    1988-01-01

    The elasticity, topological defects, and hydrodynamics of the incommensurate smectic A(IC) phase liquid crystals are studied. The phase is characterized by two colinear mass density waves of incommensurate spatial frequency. The elastic free energy is formulated in terms of a displacement field and a phason field. It is found that the topological defects of the system are dislocations with a nonzero phason field and phason field components. A two-dimensional Burgers lattice for these dislocations is introduced. It is shown that the hydrodynamic modes of the phase include first- and second-sound modes whose direction-dependent velocities are identical to those in ordinary smectics.

  17. X-Ray Diffraction Microscopy of Magnetic Structures

    SciTech Connect

    Turner, J.; Lima, E.; Huang, X.; Krupin, O.; Seu, K.; Parks, D.; Kevan, S.; Kisslinger, K.; McNulty, I.; Gambino, R.; Mangin, S.; Roy, S. and Fischer, P.

    2011-07-14

    We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co L{sub 3} edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.

  18. Phase transitions and magnetic structures in MnW1-x Mo x O4 compounds (x  ⩽  0.2)

    NASA Astrophysics Data System (ADS)

    Hardy, Vincent; Payen, Christophe; Damay, Françoise; Meddar, Lynda; Josse, Michaël; Andre, Gilles

    2016-08-01

    Temperature-dependent specific heat, magnetization and neutron diffraction data have been collected in zero magnetic field for polycrystalline samples of MnW1-x Mo x O4 (x  ⩽  0.2) solid solution whose end-member MnWO4 exhibits a magnetoelectric multiferroic phase (AF2 phase) between T 1  ≈  8 K and T 2  =  12.5 K. In MnW1-x Mo x O4, diamagnetic W6+ are replaced with diamagnetic Mo6+ cations and magnetic couplings among Mn2+ (3d 5, S  =  5/2) ions are modified due the doping-induced tuning of the orbital hybridization between Mn 3d and O 2p states. It was observed that magnetic phase transition temperatures which are associated with the second-order AF3-to-paramagnetic (T N) and AF2-to-AF3 (T 2) transitions in pure MnWO4 slightly increase with the Mo content x. Magnetic specific heat data also indicate that the first-order AF1-to-AF2 phase transition at T 1 survives a weak doping x  ⩽  0.05. This latter phase transition becomes invisible above the base temperature 2 K for higher level of doping x  ⩾  0.10. Neutron powder diffraction datasets collected above 1.5 K for a sample of MnW0.8Mo0.2O4 were analyzed using the Rietveld method. The magnetic structure below  ≈  14 K is a helical incommensurate spin order with a temperature-independent propagation vector k  =  (-0.217(6), 0.5, 0.466(4)). This cycloidal magnetic structure is similar to the polar AF2 structure observed in MnWO4. The AF1 up-up-down-down collinear spin arrangement observed in MnWO4 is absent in our MnW0.8Mo0.2O4 sample.

  19. Magnetic switching and phase competition in the multiferroic antiferromagnet Mn1−xFexWO4

    SciTech Connect

    Ye, Feng; Ren, Y.; Fernandez-Baca, Jaime A; Mook Jr, Herbert A; Lynn, J. W.; Chaudhury, R. P.; Wang, Y. Q.; Lorenz, Bernd; Chu, C. W.

    2008-01-01

    Elastic neutron scattering is used to study the spin correlations in the multiferroic Mn1−xFexWO4 with x=0.035, 0.05, and 0.10. The noncollinear incommensurate ICM magnetic structure associated with the ferroelectric FE phase in pure MnWO4 is suppressed at x=0.035 and completely absent at x=0.10. The ICM spin order and FE phase can be restored by applying a magnetic field along the spin easy axis. The low-T commensurate magnetic structure extends in both H/T with increasing Fe concentration. The systematic evolution of the magnetic and electric properties indicates that the noncollinear ICM spin order results from competing magnetic interactions and its stabilization can be tuned by the internal x or external magnetic-field perturbations.

  20. Synthesis, structure and magnetism in copper chalcochromite spinels

    NASA Astrophysics Data System (ADS)

    Neulinger, Janell Rebecca

    The copper chalcochromites (CuCr2X4 (X = S, Se, Te)) possess a rare combination of magnetic and electronic properties compared to other chalcogenide spinet materials. A precise structural and magnetic investigation of these materials was undertaken in order to facilitate technological exploitation of these unusual properties. CuCr2Se4, several halogenated derivatives of the form CuCr2Se4 -xXx (with X = Cl, Br, or I), and CuCr2S3Cl were prepared via powder methods and chemical vapor transport growth of single crystals. A variety of X-ray diffraction techniques were employed to determine the crystal structures of the synthesis products. The materials adopt a trigonal variation of the spinet structure type; the lower-symmetry structure includes a single threefold roto-inversion axis. Halogen doping introduces systematic changes in the properties of the chalcochromites, and the effects of halogen doping were monitored by magnetometry, soft X-ray spectroscopy, and magnetic microscopy techniques. Bulk magnetic properties were characterized by SQUID and vibrating sample magnetometry, at temperatures from 5 K to above the Curie temperatures. Soft X-ray spectroscopic measurements performed at the Advanced Light Source at Lawrence Berkeley National Laboratory included X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) experiments. Dichroic spectra at the Cr L2,3 and Cu L 2,3 absorption edges confirm a ferrimagnetic model of opposing magnetic sub-lattices localized on the Cr and Cu centers; increasing levels of halogen doping suppress the contribution from the copper sublattice and reduce T C. Magnetic domain imaging using the Photoelectron Electron Microscope (PEEM) at the Advanced Light Source indicates the presence of a variety of domain morphologies, including predominantly stripe domains reflecting the uniaxial symmetry of the trigonal spinel structure. The magnetic and structural features of the copper chalcochromites mark them as robust, tunable, and

  1. Band structure peculiarities of magnetic photonic crystals

    NASA Astrophysics Data System (ADS)

    Gevorgyan, A. H.; Golik, S. S.

    2017-10-01

    In this work we studied light diffraction in magneto-photonic crystals (MPC) having large magneto-optical activity and modulation large depth. The case of arbitrary angles between the direction of the external static magnetic field and the normal to the border of the MPC layer is considered. The problem is solved by Ambartsumian's modified layer addition method. It is found that there is a new type of non-reciprocity, namely, the relation R (α) ≠ R (- α) takes place, where R is the reflection coefficient, and α is the incidence angle. It is shown the formation of new photonic band gap (PBG) at oblique incidence of light, which is not selective for the polarization of the incident light, in the case when the external magnetic field is directed along the medium axis. Such a system can be used as: a tunable polarization filter, polarization mirror, circular (elliptical) polarizer, tunable optical diode, etc.

  2. Magnetically driven flows in arched plasma structures.

    PubMed

    Stenson, E V; Bellan, P M

    2012-08-17

    Laboratory experiments demonstrate high-speed plasma flows from both footpoints of arched magnetic flux tubes, resulting in bulk plasma transport into the flux tube and persistent axial collimation even as the flux tube lengthens and kinks. The measured flows are in agreement with the predictions of hoop force and collimation models involving fundamental MHD forces. These forces are expected to drive plasma acceleration in other open flux configurations with arched geometries, such as those found on the solar surface.

  3. Patterned Magnetic Structures for Micro-/Nanoparticle and Cell Manipulation

    NASA Astrophysics Data System (ADS)

    Vieira, Gregory Butler

    Remote manipulation of fluid-borne magnetic particles on a surface is useful to probe, assemble, and sort microscale and nanoscale objects. By patterning magnetic structures in shapes designed to exploit local heterogeneities in thin film magnetization, we have demonstrated effective trapping mechanisms for superparamagnetic micro- and nanoparticles. The features necessary for trapping are shown to arise at domain walls or indentations in microscale and smaller magnetic wires, at the periphery of magnetized disks, and at corners of magnetized triangles. Weak (<150 Oe) in- and out-of-plane external magnetic fields modify the energy landscape of the trapped particles, allowing for the objects to be remotely maneuvered along selected routes across the surface. The mechanism is multiplexed, allowing for simultaneous manipulation of many trapped particles, and their motion is directed using a handheld user interface. Particles are able to be transported over hundreds of micrometers with velocities of upwards of 200 µm/s and average forces of up to hundreds of picoNewtons. The magnetic fields, their spatial distribution, and resulting forces are estimated by modeling magnetization of the patterned structures using micromagnetic simulation or by approximating the traps as point sources of fields. The quality of these models and their relevance for describing particle manipulation under the experimental conditions is discussed. The applicability of these techniques is demonstrated for various biological, biomolecular, and nanoscale systems. Binding of magnetic particles to cells allows for guided cell transport. Composite micelle nanostructures, only tens of nm across, are simultaneously trapped and maneuvered magnetically and tracked fluorescently, despite their small size. The implications for use of this technology in lab-on-chip devices are discussed.

  4. Magnetic Core-Shell Morphology of Structurally Uniform Magnetite Nanoparticles

    NASA Astrophysics Data System (ADS)

    Krycka, Kathryn

    2011-03-01

    Magnetic nanoscale structures are intriguing, in part, because of the exotic properties that emerge compared with bulk. The reduction of magnetic moment per atom in magnetite with decreasing nanoparticle size, for example, has been hypothesized to originate from surface disordering to anisotropy-induced radial canting, which are difficult to distinguish using conventional magnetometry. Small-angle neutron scattering (SANS) is ideal for probing structure, both chemical and magnetic, from nm to microns across an ensemble of particles. Adding polarization analysis (PASANS) of the neutron spin orientation before and after interaction with the scattering particles allows the magnetic structure to be separated into its vector components. Application of this novel technique to 9 nm magnetite nanoparticles closed-packed into face-centered crystallites with order of a micron revealed that at nominal saturation the missing magnetic moments unexpectedly interacted to form well-ordered shells 1.0 to 1.5 nm thick canted perpendicular to their ferrimagnetic cores between 160 to 320 K. These shells additionally displayed intra-particle ``cross-talk'', selecting a common orientation over clusters of tens of nanoparticles. However, the shells disappeared when the external field was removed and interparticle magnetic interactions were negligible (300 K), confirming their magnetic origin. This work has been carried out in collaboration with Ryan Booth, Julie Borchers, Wangchun Chen, Liv Dedon, Thomas Gentile, Charles Hogg, Yumi Ijiri, Mark Laver, Sara Majetich, James Rhyne, and Shannon Watson.

  5. Magnetic domain structure in small diameter magnetic nanowire arrays [rapid communication

    NASA Astrophysics Data System (ADS)

    Qin, Dong-Huan; Zhang, Hao-Li; Xu, Cai-Ling; Xu, Tao; Li, Hu-Lin

    2005-01-01

    Fe 0.3Co 0.7 alloy nanowire arrays were prepared by ac electrodepositing Fe 2+ and Co 2+ into a porous anodic aluminum oxide (PAO) template with diameter about 50 nm. The surface of the samples were polished by 100 nm diamond particle then chemical polishing to give a very smooth surface (below ±10 nm/μm 2). The morphology properties were characterized by SEM and AFM. The bulk magnetic properties and domain structure of nanowire arrays were investigated by VSM and MFM respectively. We found that such alloy arrays showed strong perpendicular magnetic anisotropy with easy axis parallel to nanowire arrays. Each nanowire was in single domain structure with several opposite single domains surrounding it. Additionally, we investigated the domain structure with a variable external magnetic field applied parallel to the nanowire arrays. The MFM results showed a good agreement with our magnetic hysteresis loop.

  6. Magnetically controlled structures in the ionosphere of Mars

    NASA Astrophysics Data System (ADS)

    Duru, F.; Gurnett, D. A.; Averkamp, T. F.; Kirchner, D. L.; Huff, R. L.; Persoon, A. M.; Plaut, J. J.; Picardi, G.

    2006-12-01

    The ionospheric sounding data obtained by the MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) instrument on the Mars Express spacecraft show that the dayside ionosphere has considerable structure over regions of strong crustal magnetic fields. This structure is typically seen as a hyperbola-shaped trace in a display of echo intensity versus apparent altitude and time. The hyperbola shapes are consistent with oblique reflections from regions of enhanced electron density that are fixed with respect to Mars. Comparisons with the Cain et al. (2003) model for the crustal magnetic field of Mars show that the apexes of the hyperbolas, which identify the closest approach to the regions of enhanced electron density, usually coincide with regions where the crustal magnetic field is strong and nearly vertical. The electron density enhancements, which extend as much as 50 km above the surrounding ionosphere, are believed to arise from increases in the scale height of the ionosphere, possibly due to heating of the ionosphere by solar wind electrons that reach the base of the ionosphere along the nearly vertical (open) magnetic field lines. Statistical analyses of the apparent altitudes of the apexes of the hyperbolas, as well as analyses of repeated passes over the same region, indicate that the electron density enhancements usually consist of horizontal cylinder-like structures rather than isolated hemispherical structures. In many cases the axes of the cylindrical density structures are aligned with the symmetry axes of adjacent cylindrical magnetic field structures with opposite polarity.

  7. Magnetically Controlled Structures in the Ionosphere of Mars

    NASA Astrophysics Data System (ADS)

    Duru, F.; Gurnett, D. A.; Averkamp, T. F.; Kirchner, D. L.; Huff, R. L.; Persoon, A. M.; Plaut, J. J.; Picardi, G.

    2006-12-01

    The ionospheric sounding data obtained by the MARSIS (Mars Advanced Radar for Subsurface and Ionospheric Sounding) instrument on the Mars Express spacecraft show that the dayside ionosphere has considerable structure over regions of strong crustal magnetic fields. This structure is typically seen as a hyperbola-shaped trace in a display of echo intensity versus apparent altitude and time. The hyperbola shapes are consistent with oblique reflections from regions of enhanced electron density that are fixed with respect to Mars. Comparisons with the Cain et al. [2003] model for the crustal magnetic field of Mars show that the apexes of the hyperbolas, which identify the closest approach to the regions of enhanced electron density, usually coincide with regions where the crustal magnetic field is strong and nearly vertical. The electron density enhancements, which extend as much as 50 km above the surrounding ionosphere, are believed to arise from increases in the scale height of the ionosphere, possibly due to heating of the ionosphere by solar wind electrons that reach the base of the ionosphere along the nearly vertical (open) magnetic field lines. Statistical analyses of the apparent altitudes of the apexes of the hyperbolas, as well as analyses of repeated passes over the same region, indicate that the electron density enhancements usually consist of horizontal cylinder-like structures rather than isolated hemispherical structures. In many cases the axes of the cylindrical density structures are aligned with the symmetry axes of adjacent cylindrical magnetic field structures with opposite polarity.

  8. Continuous magnetic and structural phase transitions in Fe1+yTe

    SciTech Connect

    Zalinznyak, I.; Xu, Zhijun; Wen, Jianzhong; Tranquada, John M.; Gu, G. D.; Solovyov, Vyachelslav F; Glazkov, V N; Zheludev, Andrey I; Garlea, Vasile O; Stone, Matthew B

    2012-01-01

    We report a sequence of continuous phase transformations in iron telluride, Fe{sub 1+y}Te with y=0.10(1), which is observed by combining neutron diffraction, magnetic susceptibility, and specific-heat measurements on single-crystal samples. While a gradual increase of magnetic scattering near the wave vector (0.5,0,0.5) is seen below T {approx} 70 K, a temperature where the discontinuous first-order magnetostructural phase transition is found in systems with small y ({approx}<0.06), the reduction of the lattice symmetry in Fe{sub 1.1}Te only occurs at T{sub s} {approx} 63 K. Below T{sub N} {approx} 57.5 K, the long-range magnetic order develops, the incommensurate wave vector Q{sub m} of which varies with temperature. Finally, at T{sub m} {approx}< 45 K, the system enters the low-T phase, where Q{sub m} is locked at {approx}(0.48,0,0.5). We conclude that these instabilities are weak compared to the strength of the underlying interactions, and we suggest that the impact of the Fe interstitials on the transitions can be treated with random-field models.

  9. Continuous magnetic and structural phase transitions in Fe1+yTe

    NASA Astrophysics Data System (ADS)

    Zaliznyak, I. A.; Xu, Z. J.; Wen, J. S.; Tranquada, J. M.; Gu, G. D.; Solovyov, V.; Glazkov, V. N.; Zheludev, A. I.; Garlea, V. O.; Stone, M. B.

    2012-02-01

    We report a sequence of continuous phase transformations in iron telluride, Fe1+yTe with y=0.10(1), which is observed by combining neutron diffraction, magnetic susceptibility, and specific-heat measurements on single-crystal samples. While a gradual increase of magnetic scattering near the wave vector (0.5,0,0.5) is seen below T≈70 K, a temperature where the discontinuous first-order magnetostructural phase transition is found in systems with small y (≲0.06), the reduction of the lattice symmetry in Fe1.1Te only occurs at Ts≈63 K. Below TN≈57.5 K, the long-range magnetic order develops, the incommensurate wave vector Qm of which varies with temperature. Finally, at Tm≲45 K, the system enters the low-T phase, where Qm is locked at ≈(0.48,0,0.5). We conclude that these instabilities are weak compared to the strength of the underlying interactions, and we suggest that the impact of the Fe interstitials on the transitions can be treated with random-field models.

  10. Magnetization processes in core/shell exchange-spring structures.

    SciTech Connect

    Jiang, J. S.

    2015-03-27

    The magnetization reversal processes in cylindrical and spherical soft core/hard shell exchange-spring structures are investigated via the analytical nucleation theory, and are verified with numerical micromagnetic simulations. At small core sizes, the nucleation of magnetic reversal proceeds via the modified bulging mode, where the transverse component of the magnetization is only semi-coherent in direction and the nucleation field contains a contribution from self-demagnetization. For large core sizes, the modified curling mode, where the magnetization configuration is vortex-like, is favored at nucleation. The preference for the modified curling mode is beneficial in that the fluxclosure allows cylindrical and spherical core/shell exchange-spring elements to be densely packed into bulk permanent magnets without affecting the nucleation field, thereby offering the potential for high energy product.

  11. Electronic structure and magnetic anisotropy of CrO2

    NASA Astrophysics Data System (ADS)

    Toropova, Antonina; Savrasov, Sergej; Oudovenko, Viktor

    2005-03-01

    The problem of importance of strong correlations for the electronic structure, transport and magnetic properties of half--metallic ferromagnetic CrO2 is addressed by performing density functional based electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. In both schemes we compute electronic structure, optical conductivity and magnetic anisotropy energy for chromium dioxide. It is shown that the corresponding low-- temperature experimental data are best fitted without accounting for the Hubbard U corrections. We conclude that the ordered phase of CrO2 is weakly correlated.

  12. Repetitive formation and decay of current sheets in magnetic loops: An origin of diverse magnetic structures

    SciTech Connect

    Kumar, Dinesh; Bhattacharyya, R.; Smolarkiewicz, P. K.

    2015-01-15

    In this work, evolution of an incompressible, thermally homogeneous, infinitely conducting, viscous magnetofluid is numerically explored as the fluid undergoes repeated events of magnetic reconnection. The initial magnetic field is constructed by a superposition of two linear force-free fields and has similar morphology as the magnetic loops observed in the solar corona. The results are presented for computations with three distinct sets of footpoint geometries. To onset reconnection, we rely on numerical model magnetic diffusivity, in the spirit of implicit large eddy simulation. It is generally expected that in a high Lundquist number fluid, repeated magnetic reconnections are ubiquitous and hence can lead to a host of magnetic structures with considerable observational importance. In particular, the simulations presented here illustrate formations of magnetic islands, rotating magnetic helices and rising flux ropes—depending on the initial footpoint geometry but through the common process of repeated magnetic reconnections. Further, we observe the development of extended current sheets in two case studies, where the footpoint reconnections generate favorable dynamics.

  13. 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

  14. Three-Dimensional Magnetic Resonance Imaging of Velopharyngeal Structures

    ERIC Educational Resources Information Center

    Bae, Youkyung; Kuehn, David P.; Sutton, Bradley P.; Conway, Charles A.; Perry, Jamie L.

    2011-01-01

    Purpose: To report the feasibility of using a 3-dimensional (3D) magnetic resonance imaging (MRI) protocol for examining velopharyngeal structures. Using collected 3D MRI data, the authors investigated the effect of sex on the midsagittal velopharyngeal structures and the levator veli palatini (levator) muscle configurations. Method: Ten Caucasian…

  15. Three-Dimensional Magnetic Resonance Imaging of Velopharyngeal Structures

    ERIC Educational Resources Information Center

    Bae, Youkyung; Kuehn, David P.; Sutton, Bradley P.; Conway, Charles A.; Perry, Jamie L.

    2011-01-01

    Purpose: To report the feasibility of using a 3-dimensional (3D) magnetic resonance imaging (MRI) protocol for examining velopharyngeal structures. Using collected 3D MRI data, the authors investigated the effect of sex on the midsagittal velopharyngeal structures and the levator veli palatini (levator) muscle configurations. Method: Ten Caucasian…

  16. Electronic correlation in magnetic contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    For interacting electrons the density of transitions [see http://arxiv.org/abs/1405.2288] replaces the density of states in calculations of structural energies. Extending previous work on paramagnetic metals, this approach is applied to correlation effects on the structural stability of magnetic transition metals. Supported by the H. V. Snyder Gift to the University of Oregon.

  17. Structure and magnetism of Fe-26Cr-12Co-1Si ribbon magnets

    NASA Astrophysics Data System (ADS)

    Xin, Wu; Shao-jing, Bu; Xu-hao, Han; Xiang, Chi; Ji-bing, Sun; Ying, Zhang

    2017-02-01

    This paper provides a new and simple way to obtain thinner ribbon magnets with hard magnetic properties. Fe-26Cr-12Co-1Si ribbons were fabricated by melt-spinning at a speed of 40 m/s and followed by multi-step ageing at 647-540 °C. Phase composition, microstructure, domain structure and magnetic properties of the ribbons were studied. It has been found that the phase transformation of γ+α→α1+α2+ Fe(Si,M)2+σ and element diffusion are dominant respectively during the first stage ageing and later multi-step ageing. Consequently, a spinodal structure containing a majority of α1 and small amount of α2 is formed. Model for microstructure and magnetic structure evolution of the ribbons in the ageing process is established. Hc as high as 1026.6 Oe and Br of 7274.8 Gs can be achieved in the seven-step aged ribbons. Such outstanding magnetic performances may be attributed to five main microstructural and magnetic structural factors.

  18. The interplanetary and solar magnetic field sector structures, 1962 - 1968

    NASA Technical Reports Server (NTRS)

    Jones, D. E.

    1972-01-01

    The interplanetary magnetic field sector structure was observed from late 1962 through 1968. During this time it has been possible to study the manner in which the sector pattern and its relation to the photospheric magnetic field configuration changes from solar minimum to solar maximum. Observations were also made relating sector boundaries to specific regions on the solar disk. These and other observations related to the solar origin of the interplanetary field are briefly reviewed.

  19. Dual-function magnetic structure for toroidal plasma devices

    DOEpatents

    Brown, Robert L.

    1978-01-01

    This invention relates to a support system wherein the iron core and yoke of the plasma current system of a tokamak plasma containment device is redesigned to support the forces of the magnet coils. The containment rings, which occupy very valuable space around the magnet coils, are utilized to serve as yokes for the core such that the conventional yoke is eliminated. The overall result is an improved aspect ratio, reduction in structure, smaller overall size, and improved access to the plasma ring.

  20. The effect of internal magnetic structure on the fishbone instability

    SciTech Connect

    Roberts, D.W.; Powell, E.; Kaita, R.; Bell, R.; Chance, M.; Hatcher, R.; Holland, A.; Kaye, S.; Kessel, C.; Kugel, H.; LeBlanc, B.; Manickam, J.; Okabayashi, M.; Paul, S.; Pomphrey, N.; Sauthoff, N.; Sesnic, S.; Takahashi, H.; White, R.; Levinton, F.; Asakura, N.; Duperrex, P.; Gammel, G.

    1992-01-01

    Plasmas exhibiting the ``fishbone`` instability studied on the PBX-M tokamak show a distinct relationship between the plasma shape, the internal magnetic structure, and the presence or absence of fast ion losses associated with the fishbone mode. We have, for the first time, carried out measurements of the magnetic safety factor profile in fishbone-unstable plasmas, and used the knowledge of the associated experimental equilibria to compare the stability and fast ion loss properties of these plasmas with experimental observations.

  1. The effect of internal magnetic structure on the fishbone instability

    SciTech Connect

    Roberts, D.W.; Powell, E. ); Kaita, R.; Bell, R.; Chance, M.; Hatcher, R.; Holland, A.; Kaye, S.; Kessel, C.; Kugel, H.; LeBlanc, B.; Manickam, J.; Okabayashi, M.; Paul, S.; Pomphrey, N.; Sauthoff, N.; Sesnic, S.; Takahashi, H.; White, R. . Plasma Physics Lab.); Levinton, F. (Fusion Physics and Technologies, Torrance, CA (Uni

    1992-01-01

    Plasmas exhibiting the fishbone'' instability studied on the PBX-M tokamak show a distinct relationship between the plasma shape, the internal magnetic structure, and the presence or absence of fast ion losses associated with the fishbone mode. We have, for the first time, carried out measurements of the magnetic safety factor profile in fishbone-unstable plasmas, and used the knowledge of the associated experimental equilibria to compare the stability and fast ion loss properties of these plasmas with experimental observations.

  2. Structural and Magnetic Properties of Thin Film of Iron Nitride

    NASA Astrophysics Data System (ADS)

    Kayani, Zohra Nazir; Riaz, Saira; Naseem, Shahzad

    2014-12-01

    The nano-crystalline iron nitride films with a mixture of γ-Fe4N, ɛFe3N and αFe2N phases were synthesized on copper substrate by sol-gel technology. The structure, morphology and magnetic properties of the samples were characterized using X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometer. The films are ferromagnetic at room temperature. Magnetic properties such as coercive forces and saturation magnetization were found to be 398 Oestered and 32.92 emu/cm3, respectively.

  3. Structural aspects of magnetic fluid stabilization in aqueous agarose solutions

    NASA Astrophysics Data System (ADS)

    Nagornyi, A. V.; Petrenko, V. I.; Avdeev, M. V.; Yelenich, O. V.; Solopan, S. O.; Belous, A. G.; Gruzinov, A. Yu.; Ivankov, O. I.; Bulavin, L. A.

    2017-06-01

    Structure characterization of magnetic fluids (MFs) synthesized by three different methods in aqueous solutions of agarose was done by means of small-angle neutron (SANS) and synchrotron X-ray scattering (SAXS). The differences in the complex aggregation observed in the studied magnetic fluids were related to different stabilizing procedures of the three kinds of MFs. The results of the analysis of the scattering (mean size of single polydisperse magnetic particles, fractal dimensions of the aggregates) are consistent with the data of transmission electron microscopy (TEM).

  4. Can Light Scattering Detect Lock-In Transitions in Incommensurate Insulators ?

    NASA Astrophysics Data System (ADS)

    Poulet, H.; Pick, R. M.

    The following sections are included: * INTRODUCTION * BCCD AT NORMAL PRESSURE - A BRIEF REVIEW * RAMAN ACTIVITY OF THE PHONONS WITH WAVE VECTOR {overrightarrow q _o * THE b MODES RAMAN ACTIVITY IN THE COMMENSURATE PHASES * RAMAN ACTIVITY OF OTHER PHONONS OF THE INCOMMENSURATE PHASE, CLOSE TO A LOCK-IN TRANSITION * SUMMARY AND DISCUSSION * ACKNOWLEDGMENTS * REFERENCES

  5. Observation of nonequilibrium behavior near the Lifshitz point in ferroelectrics with incommensurate phase

    NASA Astrophysics Data System (ADS)

    Rushchanskii, K. Z.; Molnar, A.; Bilanych, R.; Yevych, R.; Kohutych, A.; Vysochanskii, Yu. M.; Samulionis, V.; Banys, J.

    2016-01-01

    We have investigated nonequilibrium properties of proper uniaxial Sn2P2(SexS1-x) 6 ferroelectrics with the type II incommensurate phase above Lifshitz point xLP˜0.28 . We performed measurements of dielectric susceptibility in cooling and heating regimes with the rate ranging 0.002-0.1 K/min, as well as high-resolution ultrasound investigation and hypersound Brillouin scattering experiments. For samples with x ≥0.28 clear anomalies are observed at incommensurate second-order transition (Ti) and at first-order lock-in transition (Tc) in the regime of very slow cooling rate, whereas the intermediate incommensurate phase is not observed when the rate is faster than 0.1 K/min. In general, increasing the cooling rate leads to smearing of the anomaly at Tc. We relate this effect to cooling rate dependence of domain-wall concentration and their size: domain width decreases when cooling rate increases. At certain conditions, the size of domain is comparable to the incommensurate phase modulation period, which is in the micrometer range in the vicinity of Lifshitz point and leads to pinning of the modulation period by domain walls.

  6. Current induced magnetization dynamics and magnetization switching in superconducting ferromagnetic hybrid ( F |S |F ) structures

    NASA Astrophysics Data System (ADS)

    Acharjee, Saumen; Goswami, Umananda Dev

    2016-12-01

    We investigate the current induced magnetization dynamics and magnetization switching in an unconventional p-wave superconductor sandwiched between two misaligned ferromagnetic layers by numerically solving the Landau-Lifshitz-Gilbert equation modified with current induced Slonczewski's spin torque term. A modified form of the Ginzburg-Landau free energy functional has been used for this purpose. We demonstrated the possibility of current induced magnetization switching in the spin-triplet ferromagnetic superconducting hybrid structures with a strong easy axis anisotropy and the condition for magnetization reversal. The switching time for such arrangement is calculated and is found to be highly dependent on the magnetic configuration along with the biasing current. This study would be useful in designing the practical superconducting-spintronic devices.

  7. Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi{sub 1−x}Ca{sub x}Fe{sub 1−x}Mn{sub x}O{sub 3} ceramics

    SciTech Connect

    Kumar, Pawan; Kar, Manoranjan; Shankhwar, Nisha; Srinivasan, A.

    2015-05-21

    The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO{sub 3} lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO{sub 3} at room temperature is observed to be ∼13.8°. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO{sub 3}. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO{sub 3} measured using UV-Vis spectra was supported by the resonance Raman spectra.

  8. Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy

    NASA Technical Reports Server (NTRS)

    Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.

    2009-01-01

    L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

  9. Generation of magnetic structures on the solar photosphere

    SciTech Connect

    Gangadhara, R. T.; Krishan, V.; Bhowmick, A. K.; Chitre, S. M.

    2014-06-20

    The lower solar atmosphere is a partially ionized plasma consisting of electrons, ions, and neutral atoms. In this, which is essentially a three-fluid system, the Hall effect arises from the treatment of the electrons and ions as two separate fluids and the ambipolar diffusion arises from the inclusion of neutrals as the third fluid. The Hall effect and ambipolar diffusion have been shown to be operational in a region beginning from near the photosphere up to the chromosphere. In a partially ionized plasma, the magnetic induction is subjected to ambipolar diffusion and the Hall drift in addition to the usual resistive dissipation. These nonlinear effects create sharp magnetic structures which then submit themselves to various relaxation mechanisms. A first-principles derivation of these effects in a three-fluid system and an analytic solution to the magnetic induction equation in a stationary state are presented, which in the general case includes the Hall effect, ambipolar diffusion, and ohmic dissipation. The temporal evolution of the magnetic field is then investigated under the combined as well as the individual effects of the Hall drift and ambipolar diffusion to demonstrate the formation of steep magnetic structures and the resultant current sheet formation. These structures have just the right features for the release of magnetic energy into the solar atmosphere.

  10. Generation of Magnetic Structures on the Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Gangadhara, R. T.; Krishan, V.; Bhowmick, A. K.; Chitre, S. M.

    2014-06-01

    The lower solar atmosphere is a partially ionized plasma consisting of electrons, ions, and neutral atoms. In this, which is essentially a three-fluid system, the Hall effect arises from the treatment of the electrons and ions as two separate fluids and the ambipolar diffusion arises from the inclusion of neutrals as the third fluid. The Hall effect and ambipolar diffusion have been shown to be operational in a region beginning from near the photosphere up to the chromosphere. In a partially ionized plasma, the magnetic induction is subjected to ambipolar diffusion and the Hall drift in addition to the usual resistive dissipation. These nonlinear effects create sharp magnetic structures which then submit themselves to various relaxation mechanisms. A first-principles derivation of these effects in a three-fluid system and an analytic solution to the magnetic induction equation in a stationary state are presented, which in the general case includes the Hall effect, ambipolar diffusion, and ohmic dissipation. The temporal evolution of the magnetic field is then investigated under the combined as well as the individual effects of the Hall drift and ambipolar diffusion to demonstrate the formation of steep magnetic structures and the resultant current sheet formation. These structures have just the right features for the release of magnetic energy into the solar atmosphere.

  11. Validation and Benchmarking of a Practical Free Magnetic Energy and Relative Magnetic Helicity Budget Calculation in Solar Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Moraitis, K.; Tziotziou, K.; Georgoulis, M. K.; Archontis, V.

    2014-12-01

    In earlier works we introduced and tested a nonlinear force-free (NLFF) method designed to self-consistently calculate the coronal free magnetic energy and the relative magnetic helicity budgets of observed solar magnetic structures. In principle, the method requires only a single, photospheric or low-chromospheric, vector magnetogram of a quiet-Sun patch or an active region and performs calculations without three-dimensional magnetic and velocity-field information. In this work we strictly validate this method using three-dimensional coronal magnetic fields. Benchmarking employs both synthetic, three-dimensional magnetohydrodynamic simulations and nonlinear force-free field extrapolations of the active-region solar corona. Our time-efficient NLFF method provides budgets that differ from those of more demanding semi-analytical methods by a factor of approximately three, at most. This difference is expected to come from the physical concept and the construction of the method. Temporal correlations show more discrepancies that are, however, soundly improved for more complex, massive active regions, reaching correlation coefficients on the order of, or exceeding, 0.9. In conclusion, we argue that our NLFF method can be reliably used for a routine and fast calculation of the free magnetic energy and relative magnetic helicity budgets in targeted parts of the solar magnetized corona. As explained in this article and in previous works, this is an asset that can lead to valuable insight into the physics and triggering of solar eruptions.

  12. Insight into the Dzyaloshinskii-Moriya interaction through first-principles study of chiral magnetic structures

    NASA Astrophysics Data System (ADS)

    Sandratskii, L. M.

    2017-07-01

    The purpose of the paper is to gain deeper insight into microscopic formation of the Dzyaloshinskii-Moriya interaction (DMI). The paper aims at the development of the physical picture able to address apparently contradicting conclusions of recent studies concerning the location of the DMI energy in the real and reciprocal spaces as well as the relation between values of the atomic moments and the DMI strength. The main tools of our study are the first-principles calculations of the energies of the spiral magnetic states with opposite chiralities. We suggest a method of the calculation of the spiral structures with account for the spin-orbit coupling (SOC). It is based on the application of the generalized Bloch theorem and generalized Bloch functions and allows to reduce the consideration of arbitrary incommensurate spiral to small chemical unit cell. The method neglects the anisotropy in the plane orthogonal to the rotation axis of the spirals that does not influence importantly the DMI energy. For comparison, the supercell calculation with full account for the SOC is performed. The concrete calculations are performed for the Co/Pt bilayer. We consider the distribution of the DMI energy in both real and reciprocal spaces and the dependence of the DMI on the number of electrons. The results of the calculations reveal a number of energy compensations in the formation of the DMI. Thus, the partial atomic contributions as functions of the spiral wave vector q are nonmonotonic and have strongly varying slopes. However, in the total DMI energy these atom-related features compensate each other, resulting in a smooth q dependence. The reason for the peculiar form of the partial DMI contributions is a q -dependent difference in the charge distribution between q and -q spirals. The strongly q -dependent relation between atomic contributions shows that the real-space distribution of the DMI energy obtained for a selected q value cannot be considered as a general

  13. Interplanetary planar magnetic structures associated with expanding active regions

    NASA Technical Reports Server (NTRS)

    Nakagawa, Tomoko; Uchida, Yutaka

    1995-01-01

    Planar magnetic structures are interplanetary objects whose magnetic field cannot be explained by Parker's solar wind model. They are characterized by two-dimensional structure of magnetic field that are highly variable and parallel to a plane which is inclined to the ecliptic plane. They appeared independently of interplanetary compression, solar flares, active prominences nor filament disappearances, but the sources often coincided with active regions. On the other hand, it has been discovered by the Yohkoh Soft X-ray telescope that active-region corona expand outwards at speeds of a few to a few tens of km/s near the Sun. The expansions occurred repeatedly, almost continually, even in the absence of any sizable flares. In the Yohkoh Soft X-ray images, the active-region corona seems to expand out into interplanetary space. Solar sources of interplanetary planar magnetic structures observed by Sakigake were examined by Yohkoh soft X-ray telescope. During a quiet period of the Sun from January 6 to November 11, 1993, there found 5 planar magnetic structures according to the criteria (absolute value of Bn)/(absolute value of B) less than 0.1 for planarity and (dB)/(absolute value of B) greater than 0.7 for variability of magnetic field, where Bn, dB, and the absolute value of B are field component normal to a plane, standard deviation, and average of the magnitude of the magnetic field, respectively. Sources of 4 events were on low-latitude (less than 5 degrees) active regions from which loop-like structures were expanding. The coincidence, 80%, is extremely high with respect to accidental coincidence, 7%, of Sakigake windows of solar wind observation with active regions. The last source was on loop-like features which seemed to be related with a mid-latitude (20 degrees) active region.

  14. Self-Organizing Knotted Magnetic Structures in Plasma

    NASA Astrophysics Data System (ADS)

    Smiet, C. B.; Candelaresi, S.; Thompson, A.; Swearngin, J.; Dalhuisen, J. W.; Bouwmeester, D.

    2015-08-01

    We perform full-magnetohydrodynamics simulations on various initially helical configurations and show that they reconfigure into a state where the magnetic field lines span nested toroidal surfaces. This relaxed configuration is not a Taylor state, as is often assumed for relaxing plasma, but a state where the Lorentz force is balanced by the hydrostatic pressure, which is lowest on the central ring of the nested tori. Furthermore, the structure is characterized by a spatially slowly varying rotational transform, which leads to the formation of a few magnetic islands at rational surfaces. We then obtain analytic expressions that approximate the global structure of the quasistable linked and knotted plasma configurations that emerge, using maps from S3 to S2 of which the Hopf fibration is a special case. The knotted plasma configurations have a highly localized magnetic energy density and retain their structure on time scales much longer than the Alfvénic time scale.

  15. Small magnetic structures near the polar regions of the Sun

    NASA Astrophysics Data System (ADS)

    Cabello, I.; Blanco Rodríguez, J.; Balmaceda, L.; Domingo, V.

    2017-10-01

    The study of the small magnetic structures of the solar photosphere is of great relevance because of their association with concentrations of magnetic field and their possible contribution to the variations of the Total Solar Irradiance. These structures are known to appear close to active regions and ubiquitously in the quiet Sun areas. Numerous studies about their distribution across all over the solar surface have been done with high-resolution instrumentation. However, since the observations have always been carried out from the ecliptic plane, their distribution near the polar regions is not well known. Future missions, like Solar Orbiter, will certainly provide valuable information on these yet unexplored regions. In this work, and in preparation for that moment, we select favorable periods for the observation of the polar regions of the Sun, and study the fraction of covered surface by small magnetic structures and its variation with the solar activity.

  16. Understanding spin structure in metallacrown single-molecule magnets using magnetic compton scattering.

    PubMed

    Deb, Aniruddha; Boron, Thaddeus T; Itou, Masayoshi; Sakurai, Yoshiharu; Mallah, Talal; Pecoraro, Vincent L; Penner-Hahn, James E

    2014-04-02

    The 3d-4f mixed metallacrowns frequently show single-molecule magnetic behavior. We have used magnetic Compton scattering to characterize the spin structure and orbital interactions in three isostructural metallacrowns: Gd2Mn4, Dy2Mn4, and Y2Mn4. These data allow the direct determination of the spin only contribution to the overall magnetic moment. We find that the lanthanide 4f spin in Gd2Mn4 and Dy2Mn4 is aligned parallel to the Mn 3d spin. For Y2Mn4 (manganese-only spin) we find evidence for spin delocalization into the O 2p orbitals. Comparing the magnetic Compton scattering data with SQUID studies that measure the total magnetic moment suggests that Gd2Mn4 and Y2Mn4 have only a small orbital contribution to the moment. In contrast, the total magnetic moment for Dy2Mn4 MCs is much larger than the spin-only moment, demonstrating a significant orbital contribution to the overall magnetic moment. Overall, these data provide direct insight into the correlation of molecular design with molecular magnetic properties.

  17. Active Region Magnetic Structure Observed in the Photosphere and Chromosphere

    NASA Technical Reports Server (NTRS)

    Leka, K. D.; Metcalf, Thomas R.

    2001-01-01

    The magnetic flux above sunspots and plage in NOAA (National Oceanic and Atmospheric Administration) Active Region 8299 has been measured in the photosphere and the chromosphere. We investigate the vertical magnetic structure above the umbrae, penumbrae and plage regions using quantitative statistical comparisons of the photospheric and chromospheric vector magnetic flux data. The results include: (1) a decrease in flux with height, (2) the direct detection of the superpenumbral canopy in the chromosphere, (3) values for dB/dz which are consistent with earlier investigations when derived from a straight difference between the two datasets but quite low when derived from the delta x B = 0 condition, (4) a monolithic structure in the umbra which extends well into the upper chromosphere with a very complex and varied structure in the penumbra and plage, as evidenced by (5) a uniform magnetic scale height in the umbrae with an abrupt jump to widely varying scale heights in the penumbral and plage regions. Further, we find (6) evidence for a very large (delta z approximately equals 3Mm) height difference between the atmospheric layers sampled in the two magnetograms, almost a factor of three larger than that implied by atmospheric models. We additionally test the apropriateness of using photospheric magnetic flux as a boundary for field-line extrapolations, and find a better agreement with observed coronal structure when the chromospheric flux is used as a boundary.

  18. Active Region Magnetic Structure Observed in the Photosphere and Chromosphere

    NASA Technical Reports Server (NTRS)

    Leka, K. D.; Metcalf, Thomas R.

    2001-01-01

    The magnetic flux above sunspots and plage in NOAA (National Oceanic and Atmospheric Administration) Active Region 8299 has been measured in the photosphere and the chromosphere. We investigate the vertical magnetic structure above the umbrae, penumbrae and plage regions using quantitative statistical comparisons of the photospheric and chromospheric vector magnetic flux data. The results include: (1) a decrease in flux with height, (2) the direct detection of the superpenumbral canopy in the chromosphere, (3) values for dB/dz which are consistent with earlier investigations when derived from a straight difference between the two datasets but quite low when derived from the delta x B = 0 condition, (4) a monolithic structure in the umbra which extends well into the upper chromosphere with a very complex and varied structure in the penumbra and plage, as evidenced by (5) a uniform magnetic scale height in the umbrae with an abrupt jump to widely varying scale heights in the penumbral and plage regions. Further, we find (6) evidence for a very large (delta z approximately equals 3Mm) height difference between the atmospheric layers sampled in the two magnetograms, almost a factor of three larger than that implied by atmospheric models. We additionally test the apropriateness of using photospheric magnetic flux as a boundary for field-line extrapolations, and find a better agreement with observed coronal structure when the chromospheric flux is used as a boundary.

  19. Electronic and Magnetic Structure of Octahedral Molecular Sieves

    NASA Astrophysics Data System (ADS)

    Morey-Oppenheim, Aimee M.

    The major part of this research consists of magnetic and electronic studies of metal doped cryptomelane-type manganese oxide octahedral molecular sieves (KOMS-2). The second part of this study involves the magnetic characterization of cobalt doped MCM-41 before and after use in the synthesis of single walled carbon nanotubes. Manganese oxides have been used widely as bulk materials in catalysis, chemical sensors, and batteries due to the wide range of possible stable oxidation states. The catalytic function of manganese oxides is further tuned by doping the material with numerous transition metals. It is of particular interest the oxidation states of Mn present after doping. New titrations to determine the oxidation state of Mn were investigated. To further examine the structure of KOMS-2, the magnetic contribution of dopant metals was also examined. The KOMS-2 structure having both diamagnetic and paramagnetic metal ions substitutions was studied. MCM-41 with the incorporation of cobalt into the structure was analyzed for its magnetic properties. The material undergoes significant structural change during the synthesis of single walled carbon nanotubes. It was the focus of this portion of the research to do a complete magnetic profile of both the before and after reaction material.

  20. Structural and magnetic phase transitions in CeCu6-xTx (T = Ag,Pd)

    SciTech Connect

    Poudel, Lekhanath N.; De la cruz, Clarina; Payzant, E. Andrew; Koehler, Michael R.; May, Andrew F.; Garlea, Vasile O.; Taylor, Alice E.; Parker, David S.; Cao, Huibo B.; McGuire, Michael A.; Tian, Wei; Matsuda, Masaaki; Jeen, Hyoung Jeen; Lee, Ho Nyung; Hong, Tao; Calder, Stuart A.; Lumsden, Mark D.; Zhou, Haidong; Keppens, Veerle; Mandrus, D.; Christianson, Andrew D.

    2015-12-15

    The structural and the magnetic properties of CeCu6-xAgx (0 ≤ x ≤ 0.85) and CeCu6-xPdx (0 ≤ x ≤ 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P21/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (Ts) decreases linearly with Ag concentration and extrapolates to zero at xS ≈ 0.1. The structural transition in CeCu6-xPdx remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x ≈ 0.2 and x ≈ 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (δ1 0 δ2), where δ1 ~ 0.62, δ2 ~ 0.25, x = 0.125 for CeCu6-xPdx and δ1 ~ 0.64, δ2 ~ 0.3, x = 0.3 for CeCu6-xAgx. As a result, the magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  1. Monte Carlo simulation of magnetic domain structure and magnetic properties near the morphotropic phase boundary.

    PubMed

    Wei, Songrui; Yang, Sen; Wang, Dong; Song, Xiaoping; Ke, Xiaoqin; Gao, Yipeng; Liao, Xiaoqi; Wang, Yunzhi

    2017-03-08

    The morphotropic phase boundary (MPB), which is the boundary separating a tetragonal phase from a rhombohedral phase by varying the composition or mechanical pressure in ferroelectrics, has been studied extensively for decades because it can lead to strong enhancement of piezoelectricity. Recently, a parallel ferromagnetic MPB was experimentally reported in the TbCo2-DyCo2 ferromagnetic system and this discovery proposes a new way to develop potential materials with giant magnetostriction. However, the role of magnetic domain switching and spin reorientation near the MPB region is still unclear. For the first time, we combine micromagnetic theory with Monte Carlo simulation to investigate the evolution of magnetic domain structures and the corresponding magnetization properties near the MPB region. It is demonstrated that the magnetic domain structure and the corresponding magnetization properties are determined by the interplay among anisotropy energy, magnetostatic energy and exchange energy. If the anisotropy energy barrier is large compared with the magnetostatic energy barrier and the exchange energy barrier, the MPB region is a T and R mixed structure and magnetic domain switching is the dominant mechanism. If the anisotropy energy barrier is small, the MPB region will also contain M phases and spin reorientation is the dominant mechanism. Our work could provide a guide for the design of advanced ferromagnetic materials with enhanced magnetostriction.

  2. Structure organization and magnetic properties of microscale ferrogels: The effect of particle magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Ryzhkov, Aleksandr V.; Melenev, Petr V.; Balasoiu, Maria; Raikher, Yuriy L.

    2016-08-01

    The equilibrium structure and magnetic properties of a ferrogel object of small size (microferrogel(MFG)) are investigated by coarse-grained molecular dynamics. As a generic model of a microferrogel (MFG), a sample with a lattice-like mesh is taken. The solid phase of the MFG consists of magnetic (e.g., ferrite) nanoparticles which are mechanically linked to the mesh making some part of its nodes. Unlike previous models, the finite uniaxial magnetic anisotropy of the particles, as it is the case for real ferrogels, is taken into account. For comparison, two types of MFGs are considered: MFG-1, which dwells in virtually non-aggregated state independently of the presence of an external magnetic field, and MFG-2, which displays aggregation yet under zero field. The structure states of the samples are analyzed with the aid of angle-resolved radial distribution functions and cluster counts. The results reveal the crucial role of the matrix elasticity on the structure organization as well as on magnetization of both MFGs. The particle anisotropy, which plays insignificant role in MFG-1 (moderate interparticle magnetodipole interaction), becomes an important factor in MFG-2 (strong interaction). There, the restrictions imposed on the particle angular freedom by the elastic matrix result in notable diminution of the particle chain lengths as well as the magnetization of the sample. The approach proposed enables one to investigate a large variety of MFGs, including those of capsule type and to purposefully choose the combination of their magnetoelastic parameters.

  3. Structure organization and magnetic properties of microscale ferrogels: The effect of particle magnetic anisotropy.

    PubMed

    Ryzhkov, Aleksandr V; Melenev, Petr V; Balasoiu, Maria; Raikher, Yuriy L

    2016-08-21

    The equilibrium structure and magnetic properties of a ferrogel object of small size (microferrogel(MFG)) are investigated by coarse-grained molecular dynamics. As a generic model of a microferrogel (MFG), a sample with a lattice-like mesh is taken. The solid phase of the MFG consists of magnetic (e.g., ferrite) nanoparticles which are mechanically linked to the mesh making some part of its nodes. Unlike previous models, the finite uniaxial magnetic anisotropy of the particles, as it is the case for real ferrogels, is taken into account. For comparison, two types of MFGs are considered: MFG-1, which dwells in virtually non-aggregated state independently of the presence of an external magnetic field, and MFG-2, which displays aggregation yet under zero field. The structure states of the samples are analyzed with the aid of angle-resolved radial distribution functions and cluster counts. The results reveal the crucial role of the matrix elasticity on the structure organization as well as on magnetization of both MFGs. The particle anisotropy, which plays insignificant role in MFG-1 (moderate interparticle magnetodipole interaction), becomes an important factor in MFG-2 (strong interaction). There, the restrictions imposed on the particle angular freedom by the elastic matrix result in notable diminution of the particle chain lengths as well as the magnetization of the sample. The approach proposed enables one to investigate a large variety of MFGs, including those of capsule type and to purposefully choose the combination of their magnetoelastic parameters.

  4. Spectropolarimetry of fine magnetized structures in the upper solar atmosphere

    NASA Astrophysics Data System (ADS)

    Schad, Thomas Anthony

    2013-12-01

    One of the earliest indications of magnetic fields acting in the solar atmosphere came at the beginning of the 20th century when George Hale noted a "decided definiteness of structure" in photographs within the Hydrogen Balmer-alpha line core. Fine structure both in the chromosphere and in the corona result from processes that are not well understood but accepted as a consequence of the solar magnetic field. Our knowledge of this field is lacking, and until recently, the assumed relationship between fine thermal structure and the magnetic field remained untested. Here, spectropolarimetric diagnostics of fine structures in the solar chromosphere and cool corona are advanced using the infrared He I triplet at 1083 nm. Precise calibration procedures are developed for the Facility Infrared Spectropolarimeter (FIRS), recently commissioned at the Dunn Solar Telescope. Together with high-order adaptive optics, we simultaneously map fine structures while obtaining a polarimetric sensitivity of up to 2 x 10--4 of the incoming intensity. These instrument improvements result in the first maps of the He I polarized signatures within an active region superpenumbra, where Hale first recognized fine-structuring. Selective absorption and emission processes due to non-equilibrium optical pumping are recognized. Our interpretation, using advanced inversions of the He I triplet, provides confirmation of Hale's initial suspicion---the fine structures of the solar chromosphere are visual markers for the magnetic field. Yet, the fine chromospheric thermal structure is not matched by an equivalently fine magnetic structure. Our ability to measure this field suggests the utility of the He I triplet as an inner boundary condition for the inner heliospheric magnetic field. In the corona itself, we infer the vector properties of a catastrophically-cooled coronal loop, uniting space-based and ground-based instrumentation. We determine how fine loops are anchored in the photosphere via a

  5. Electron vortex magnetic holes: A nonlinear coherent plasma structure

    SciTech Connect

    Haynes, Christopher T. Burgess, David; Sundberg, Torbjorn; Camporeale, Enrico

    2015-01-15

    We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

  6. Electron vortex magnetic holes: A nonlinear coherent plasma structure

    NASA Astrophysics Data System (ADS)

    Haynes, Christopher T.; Burgess, David; Camporeale, Enrico; Sundberg, Torbjorn

    2015-01-01

    We report the properties of a novel type of sub-proton scale magnetic hole found in two dimensional particle-in-cell simulations of decaying turbulence with a guide field. The simulations were performed with a realistic value for ion to electron mass ratio. These structures, electron vortex magnetic holes (EVMHs), have circular cross-section. The magnetic field depression is associated with a diamagnetic azimuthal current provided by a population of trapped electrons in petal-like orbits. The trapped electron population provides a mean azimuthal velocity and since trapping preferentially selects high pitch angles, a perpendicular temperature anisotropy. The structures arise out of initial perturbations in the course of the turbulent evolution of the plasma, and are stable over at least 100 electron gyroperiods. We have verified the model for the EVMH by carrying out test particle and PIC simulations of isolated structures in a uniform plasma. It is found that (quasi-)stable structures can be formed provided that there is some initial perpendicular temperature anisotropy at the structure location. The properties of these structures (scale size, trapped population, etc.) are able to explain the observed properties of magnetic holes in the terrestrial plasma sheet. EVMHs may also contribute to turbulence properties, such as intermittency, at short scale lengths in other astrophysical plasmas.

  7. High-pressure ultrasonic study of the commensurate-incommensurate spin-density-wave transition in an antiferromagnetic Cr-0.3 at. % Ru alloy single crystal

    NASA Astrophysics Data System (ADS)

    Cankurtaran, M.; Saunders, G. A.; Wang, Q.; Ford, P. J.; Alberts, H. L.

    1992-12-01

    A comprehensive experimental study has been made of the elastic and nonlinear acoustic behavior of a dilute Cr alloy as it undergoes a commensurate (C)-incommensurate (I) spin-density-wave transition. Simultaneous measurements of the temperature dependence of ultrasonic wave velocity and attenuation of longitudinal and shear 10-MHz ultrasonic waves propagated along both the [100] and the [110] direction of Cr-0.3 at. % Ru alloy single crystal have been made in the temperature range 200-300 K. The temperature dependence of ultrasonic attenuation for each mode is characterized by a spikelike peak centered at TCI (=238.6 K) (on cooling) and at TIC (=255.6 K) (on warming). The velocities of both longitudinal and shear ultrasonic waves exhibit a large and steep increase at TCI on cooling and a similar drop at TIC on warming with a pronounced hysteresis between TIC and TCI. These observations show that the transition between the commensurate and incommensurate phases is first order. Measurements of the effects of hydrostatic pressure (up to 0.15 GPa) on the velocities of ultrasonic waves, which were made at several fixed temperatures between 248 and 297 K, show similar features: a steep increase at PCI (increasing pressure) and a similar drop at PIC (decreasing pressure) with a well-defined hysteresis. Both TCI and TIC increase strongly and approximately linearly with pressure, the mean values of dTCI/dP and dTIC/dP being (333+/-3) K/GPa and (277+/-5) K/GPa, respectively. The pressure and temperature dependencies of the anomalies in the ultrasonic wave velocity have been used to locate both the C-I and I-C boundaries on the magnetic P-T phase diagram. There is a triple point (at about 315 K and 0.22 GPa) where the paramagnetic, commensurate, and incommensurate spin-density-wave phases coexist. Results for the complete sets of the elastic stiffness tensor components and their hydrostatic pressure derivatives have been used to evaluate the acoustic-mode Gr

  8. Incommensurate Cu/Co Ordering in the TlCo 2- xCu xSe 2 ( x˜1) System

    NASA Astrophysics Data System (ADS)

    Norén, L.; Withers, R. L.; Berger, R.

    2000-05-01

    Cu/Co ordering in TlCo2-xCuxSe2, (x∼1) has been investigated using electron and X-ray powder diffraction. The average structure of the x=1 compound can be indexed on an F-centered orthorhombic cell, a=5.5518(6) Å, b=5.4755(5) Å, and c=13.7387(17) Å. Additional weak satellite reflections characterized by the primary modulation wave vector qi∼0.184a* and indicative of an incommensurate modulated structure are revealed by electron diffraction. Characteristic extinction conditions in conjunction with mmm Laue symmetry and known crystal chemical constraints imply a (3+1)-dimensional superspace group symmetry of Fmmm(α01)00s. The incommensurate modulation is attributed to occupational ordering of the two transition metal atoms and associated structural relaxation. The real space interpretation of the Cu/Co ordering pattern is that copper and cobalt atoms form separate layers in the structure at z={1}/{4} and {3}/{4}, respectively. These layers are periodically interchanged as one moves along the x direction. Two periods of this square-wave-like modulation is close to 11a in length but is non-rational compared with the average structure.

  9. Structural origin of magnetic birefringence in rutile-type antiferromagnets

    NASA Astrophysics Data System (ADS)

    Jauch, W.

    1991-10-01

    The microscopic origin of magnetic birefringence in the rutile-type antiferromagnets XF2 (X=Mn, Fe, Co, or Ni) is analyzed on the basis of the theory of structural birefringence developed by Ewald and Born. The general principles of the Ewald-Born theory are reviewed. The magnetic birefringence can be explained by a small exchange-induced internal displacement of the fluorine atoms. Predictions from theory are compared with accurate crystal-structure analyses based on γ-ray-diffraction data. The agreement found between theory and experiment is excellent.

  10. Internal magnetic field structure of perturbed tokamak equilibria

    NASA Astrophysics Data System (ADS)

    Park, Jong-Kyu; Menard, Jonathan; Boozer, Allen; Glasser, Alan

    2006-10-01

    The 3D magnetic field structure of perturbed tokamak equilibria is important for understanding phenomena such as error field correction and plasma flow damping. Perturbed quantities such as plasma displacement and magnetic field can be obtained by minimizing the total potential energy numerically using codes such as the DCON ideal stability code. For error field correction applications, initial work is focusing on determining which external magnetic perturbations tend to drive magnetic islands. Jumps on the rational surfaces in the radial derivative of the normal magnetic field perturbation give the singular currents that arise in an ideal plasma to prevent an island from opening[C. N"uhrenberg and A. H. Boozer, Phys. Plasmas 10, 2840 (2003)]. These currents serve as a measure of the tendency of a perturbation to open a magnetic island. Additionally as a first step benchmarking exercise, we compare the 3D structure of NSTX instabilities as predicted by the DCON and MARS-F codes in the absence of external error fields. Future applications include examining the interplay between external error fields, plasma rotation, and plasma resistivity using the MARS-F code.

  11. Structure of a Magnetic Flux Annihilation Layer Formed by the Collision of Supersonic, Magnetized Plasma Flows.

    PubMed

    Suttle, L G; Hare, J D; Lebedev, S V; Swadling, G F; Burdiak, G C; Ciardi, A; Chittenden, J P; Loureiro, N F; Niasse, N; Suzuki-Vidal, F; Wu, J; Yang, Q; Clayson, T; Frank, A; Robinson, T S; Smith, R A; Stuart, N

    2016-06-03

    We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counterstreaming, supersonic and magnetized aluminum plasma flows. The antiparallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure-two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (T_{i}∼Z[over ¯]T_{e}, with average ionization Z[over ¯]=7). Analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the inflowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.

  12. Magnetic structure and magnetocalorics of GdPO4

    DOE PAGES

    Palacios, E.; Rodriguez-Velamazsn, J. A.; Evangelisti, Marco; ...

    2014-12-12

    The magnetic ordering structure of GdPO4 is determined at T = 60 mK by diffraction of hot neutrons with wavelength = 0.4696 Å. It corresponds to a non-collinear antiferromagnetic arrangement of the Gd moments with propagation vector k = (1/2, 0, 1/2). This arrangement is found to minimize the dipole-dipole interaction and the crystal field anisotropy energy, the magnetic superexchange being much smaller. The intensity of the magnetic reflections decreases with increasing temperature and vanishes at T ≈ 0.8 K, in agreement with the magnetic ordering temperature TN = 0.77 K, as reported in previous works based on heat capacitymore » and magnetic susceptibility measurements. The magnetocaloric parameters have been determined from heat capacity data at constant applied fields up to 7 T, as well as from isothermal magnetization data. Lastly, the magnetocaloric effect, for a field change ΔB = 0 – 7T, reaches –ΔST = 375.8mJ / cm3K–1 at T = 2.1 K, largely exceeding the maximum values reported to date for Gd-based magnetic refrigerants.« less

  13. Structural, magnetic, and transport properties of Permalloy for spintronic experiments

    SciTech Connect

    Nahrwold, Gesche; Scholtyssek, Jan M.; Motl-Ziegler, Sandra; Albrecht, Ole; Merkt, Ulrich; Meier, Guido

    2010-07-15

    Permalloy (Ni{sub 80}Fe{sub 20}) is broadly used to prepare magnetic nanostructures for high-frequency experiments where the magnetization is either excited by electrical currents or magnetic fields. Detailed knowledge of the material properties is mandatory for thorough understanding its magnetization dynamics. In this work, thin Permalloy films are grown by dc-magnetron sputtering on heated substrates and by thermal evaporation with subsequent annealing. The specific resistance is determined by van der Pauw methods. Point-contact Andreev reflection is employed to determine the spin polarization of the films. The topography is imaged by atomic-force microscopy, and the magnetic microstructure by magnetic-force microscopy. Transmission-electron microscopy and transmission-electron diffraction are performed to determine atomic composition, crystal structure, and morphology. From ferromagnetic resonance absorption spectra the saturation magnetization, the anisotropy, and the Gilbert damping parameter are determined. Coercive fields and anisotropy are measured by magneto-optical Kerr magnetometry. The sum of the findings enables optimization of Permalloy for spintronic experiments.

  14. ARIES-CS Magnet Conductor and Structure Evaluation

    SciTech Connect

    Wang, X. R.; Raffary, A. R.; Bromberg, L.; Schultz, J. H.; Ku, L. P.; Lyon, J. F.; Mulang, L.; Waganer, L.; El-GuebalyUniv. Wisco, L.; MartinUniv Wiscons, C.

    2008-10-01

    The ARIES-CS study focusing on the conceptual design and assessment of a compact stellarator power plant identified the important advantages and key issues associated with such a design. The coil configuration and structural support approach represent key design challenges, with the final design and material choices affected by a number of material and geometry constraints. This paper describes the design configuration and analysis and material choices for the ARIES-CS magnets and its structure. To meet aggressive cost and assembly/maintenance goals, the magnets are designed as lifetime components. Due to the very complex geometry, one of the goals of the study was to provide a robust operational design. This decision has significant implications on cost and manufacturing requirements. Concepts with both conventional and advanced superconductors have been explored. The coil structure design approach adopted is to wind all six modular coils of one field period in grooves in one monolithic coil structural shell (one per field period). The coil structural shells are then bolted together to form a strong structural shell to react the net radial forces. Extensive engineering analyses of the coil system have been performed using ANSYS shell and solid modeling. These include electromagnetic (EM) analyses to calculate the magnetic fields and EM forces and structural analyses to evaluate the structural responses and optimize the coil support system, which has a considerable impact on the cost of the ARIES-CS power plant.

  15. CONSEQUENCES OF MAGNETIC FIELD STRUCTURE FOR HEAT TRANSPORT IN MAGNETOHYDRODYNAMICS

    SciTech Connect

    Li Shule; Frank, Adam; Blackman, Eric

    2012-03-20

    Interfaces between hot and cold magnetized plasmas exist in various astrophysical contexts, for example, where hot outflows impinge on an ambient interstellar medium. It is of interest to understand how the structure of the magnetic field spanning the interface affects the temporal evolution of the temperature gradient. Here, we explore the relation between the magnetic field topology and the heat transfer rate by adding various fractions of tangled versus ordered field across a hot-cold interface that allows the system to evolve to a steady state. We find a simple mathematical relation for the rate of heat conduction as a function of the initial ratio of ordered-to-tangled field across the interface. We discuss potential implications for the astrophysical context of magnetized wind blown bubbles around evolved stars.

  16. Structure of the wake of a magnetic obstacle.

    PubMed

    Votyakov, E V; Kolesnikov, Yu; Andreev, O; Zienicke, E; Thess, A

    2007-04-06

    We use a combination of numerical simulations and experiments to elucidate the structure of the flow of an electrically conducting fluid past a localized magnetic field, called magnetic obstacle. We demonstrate that the stationary flow pattern is considerably more complex than in the wake behind an ordinary body. The steady flow is shown to undergo two bifurcations (rather than one) and to involve up to six (rather than just two) vortices. We find that the first bifurcation leads to the formation of a pair of vortices within the region of magnetic field that we call inner magnetic vortices, whereas a second bifurcation gives rise to a pair of attached vortices that are linked to the inner vortices by connecting vortices.

  17. High temperature structural and magnetic properties of cobalt nanorods

    SciTech Connect

    Ait Atmane, Kahina; Zighem, Fatih; Soumare, Yaghoub; Ibrahim, Mona; Boubekri, Rym; Maurer, Thomas; Margueritat, Jeremie; Piquemal, Jean-Yves; Ott, Frederic; Chaboussant, Gregory; Schoenstein, Frederic; Jouini, Noureddine; Viau, Guillaume

    2013-01-15

    We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles ({approx}10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by {mu}{sub 0}H{sub C}=2(K{sub MC}+K{sub shape})/M{sub S} with K{sub MC} the magnetocrystalline anisotropy constant, K{sub shape} the shape anisotropy constant and M{sub S} the saturation magnetization. H{sub C} decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. - Graphical abstract: We present in this paper the structural and magnetic properties of high aspect ratio Co nanorods ({approx}10) at high temperatures (up to 623 K) using in-situ X-ray diffraction and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. Highlights: Black-Right-Pointing-Pointer Ferromagnetic Co nanorods are prepared using the polyol process. Black-Right-Pointing-Pointer The structural and texture properties of the Co nanorods are preserved up to 500 K. Black-Right-Pointing-Pointer The magnetic properties of the Co nanorods are irreversibly altered above 525 K.

  18. 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).

  19. Observations of disconnection of open coronal magnetic structures

    SciTech Connect

    McComas, D.J.; Phillips, J.L. ); Hundhausen, A.J.; Burkepile, J.T. )

    1991-01-01

    The authors have surveyed the Solar Maximum Mission coronagraph/polarimeter observations for evidence of magnetic disconnection of previously open magnetic structures and have identified several sequences of images consistent with this interpretation. Such disconnection occurs when open field lines above helmet streamers reconnect, in contrast to previously suggested disconnections of CMEs into closed plasmoids. In this paper a clear example of open field disconnection is shown in detail. The event, on June 27, 1988, is preceded by compression of a preexisting helmet streamer and the open coronal field around it. The compressed helmet streamer and surrounding open field region detach in a large U-shaped structure which subsequently accelerates outward from the Sun. The observed sequence of events is consistent with reconnection across the heliospheric current sheet and the creation of a detached U-shaped magnetic structure. Unlike CMEs, which may open new magnetic flux into interplanetary space, this process could serve to close off previously open flux, perhaps helping to maintain the roughly constant amount of open magnetic flux observed in interplanetary space.

  20. Crossover from an incommensurate singlet spiral state with a vanishingly small spin gap to a valence-bond solid state in dimerized frustrated ferromagnetic spin chains

    NASA Astrophysics Data System (ADS)

    Agrapidis, Cliò Efthimia; Drechsler, Stefan-Ludwig; van den Brink, Jeroen; Nishimoto, Satoshi

    2017-06-01

    Motivated by the magnetic properties of the spin-chain compounds LiCuSbO4≡LiSbCuO4 and Rb2Cu2Mo3O12 , we study the ground state of the Heisenberg chain with dimerized nearest-neighbor ferromagnetic (FM) (J1,J1'<0 ) and next-nearest-neighbor antiferromagnetic (J2>0 ) couplings. Using the density-matrix renormalization group technique and spin-wave theory, we find a first-order transition between a fully polarized FM and an incommensurate spiral state at 2 α =β /(1 +β ) , where α is the frustration ratio J2/|J1| and β the degree of dimerization J1'/J1 . In the singlet spiral state the spin-gap is vanishingly small in the vicinity of the FM transition, corresponding to a situation of LiCuSbO4. For larger α , corresponding to Rb2Cu2Mo3O12 , and smaller β there is a crossover from this frustration induced incommensurate state to an Affleck-Lieb-Kennedy-Tasaki-type valence-bond solid state with substantial spin gaps.

  1. Magnetic Field in Atypical Prominence Structures: Bubble, Tornado, and Eruption

    NASA Astrophysics Data System (ADS)

    Levens, P. J.; Schmieder, B.; López Ariste, A.; Labrosse, N.; Dalmasse, K.; Gelly, B.

    2016-08-01

    Spectropolarimetric observations of prominences have been obtained with the THEMIS telescope during four years of coordinated campaigns. Our aim is now to understand the conditions of the cool plasma and magnetism in “atypical” prominences, namely when the measured inclination of the magnetic field departs, to some extent, from the predominantly horizontal field found in “typical” prominences. What is the role of the magnetic field in these prominence types? Are plasma dynamics more important in these cases than the magnetic support? We focus our study on three types of “atypical” prominences (tornadoes, bubbles, and jet-like prominence eruptions) that have all been observed by THEMIS in the He i D3 line, from which the Stokes parameters can be derived. The magnetic field strength, inclination, and azimuth in each pixel are obtained by using the inversion method of principal component analysis on a model of single scattering in the presence of the Hanle effect. The magnetic field in tornadoes is found to be more or less horizontal, whereas for the eruptive prominence it is mostly vertical. We estimate a tendency toward higher values of magnetic field strength inside the bubbles than outside in the surrounding prominence. In all of the models in our database, only one magnetic field orientation is considered for each pixel. While sufficient for most of the main prominence body, this assumption appears to be oversimplified in atypical prominence structures. We should consider these observations as the result of superposition of multiple magnetic fields, possibly even with a turbulent field component.

  2. Structural, dielectric, magnetic, and nuclear magnetic resonance studies of multiferroic Y-type hexaferrites

    NASA Astrophysics Data System (ADS)

    Khanduri, H.; Chandra Dimri, M.; Kooskora, H.; Heinmaa, I.; Viola, G.; Ning, H.; Reece, M. J.; Krustok, J.; Stern, R.

    2012-10-01

    The effect of strontium substitution on structural, magnetic, and dielectric properties of a multiferroic Y-type hexaferrite (chemical formula Ba2-xSrxMg2Fe12O22 with 0 ≤ x ≤ 2) was investigated. Y-type hexaferrite phase formation was not affected by strontium substitution for barium, in the range 0 ≤ x ≤ 1.5, confirmed by x-ray diffraction and Raman spectroscopy measured at room temperature. Two intermediate magnetic spin phase transitions (at tempertures TI and TII) and a ferrimagnetic-paramagnetic transition (at Curie temperature TC) were identified from the temperature dependence of the magnetic susceptibility. Magnetic transition temperatures (TI, TII, and TC) increased with increasing strontium content. Magnetic hysteresis measurements indicated that by increasing strontium concentration, the coercivity increases, while the saturation magnetization decreases. The 57Fe NMR spectrum of the Y-type hexaferrite measured at 5 K and in zero magnetic field showed remarkable differences compared to that of other hexaferrites due to their different number of tetrahedral and octahedral iron sites. The temperature and frequency dependence of the dielectric permittivity evidenced broad peaks with frequency dispersion in correspondence of the Curie temperature.

  3. Electronic, magnetic, and geometric structure of metallo-carbohedrenes

    SciTech Connect

    Reddy, B.V.; Khanna, S.N.; Jena, P. )

    1992-12-04

    The energetics and the electronic, magnetic, and geometric structure of the metallocarbohedrene Ti[sub 8]C[sub 12] have been calculated self-consistently in the density functional formulation. The structure of Ti[sub 8]C[sub 12] is a distorted dodecahedron with a binding energy of 6.1 electron volts per atom. The unusual stability is derived from covalent-like bonding between carbon atoms and between titanium and carbon atoms with no appreciable interaction between titanium atoms. The density of states at the Fermi energy is high and is derived from a strong hybridization between titanium 3d and carbon sp electrons. Titanium sites carry a small magnetic moment of 0.35 Bohr magneton per atom and the cluster is only weakly magnetic. 13 refs., 3 figs., 1 tab.

  4. Assessing the Structure of Isotropic and Anisotropic Turbulent Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Fatuzzo, Marco; Holden, Lisa; Grayson, Lindsay; Wallace, Kirk

    2016-10-01

    Turbulent magnetic fields permeate our universe, impacting a wide range of astronomical phenomena across all cosmic scales. A clear example is the magnetic field that threads the interstellar medium (ISM), which impacts the motion of cosmic rays through that medium. Understanding the structure of magnetic turbulence within the ISM and how it relates to the physical quantities that characterize it can thus inform our analysis of particle transport within these regions. Toward that end, we probe the structure of magentic turbulence through the use of Lyapunov exponents for a suite of isotropic and nonisotropic Alfvénic turbulence profiles. Our results provide a means of calculating a “turbulence lengthscale” that can then be connected to how cosmic rays propagate through magentically turbulent environments, and we perform such an analysis for molecular cloud environments.

  5. Pulsating jet-like structures in magnetized plasma

    SciTech Connect

    Goncharov, V. P.; Pavlov, V. I.

    2016-08-15

    The formation of pulsating jet-like structures has been studied in the scope of the nonhydrostatic model of a magnetized plasma with horizontally nonuniform density. We discuss two mechanisms which are capable of stopping the gravitational spreading appearing to grace the Rayleigh-Taylor instability and to lead to the formation of stationary or oscillating localized structures. One of them is caused by the Coriolis effect in the rotating frames, and another is connected with the Lorentz effect for magnetized fluids. Magnetized jets/drops with a positive buoyancy must oscillate in transversal size and can manifest themselves as “radio pulsars.” The estimates of their frequencies are made for conditions typical for the neutron star's ocean.

  6. Pulsating jet-like structures in magnetized plasma

    NASA Astrophysics Data System (ADS)

    Goncharov, V. P.; Pavlov, V. I.

    2016-08-01

    The formation of pulsating jet-like structures has been studied in the scope of the nonhydrostatic model of a magnetized plasma with horizontally nonuniform density. We discuss two mechanisms which are capable of stopping the gravitational spreading appearing to grace the Rayleigh-Taylor instability and to lead to the formation of stationary or oscillating localized structures. One of them is caused by the Coriolis effect in the rotating frames, and another is connected with the Lorentz effect for magnetized fluids. Magnetized jets/drops with a positive buoyancy must oscillate in transversal size and can manifest themselves as "radio pulsars." The estimates of their frequencies are made for conditions typical for the neutron star's ocean.

  7. Magnetic and structural properties of manganese ion implanted silicon

    NASA Astrophysics Data System (ADS)

    Awo-Affouda, Chaffra A.

    2007-12-01

    This thesis focuses on semiconductor based spin electronics. The integration of ferromagnetic regions into semiconductor "spintronic" devices to produce spin polarized current is a dynamic research area. One avenue is to make conventional semiconductors ferromagnetic by doping with a transition metal impurity such as Mn. For this, we first investigated the magnetic properties of Mn-implanted Si. We were able to measure above room temperature ferromagnetic hysteresis loops. The high Curie temperature obtained (>400 K), indicated that the synthesis of a technologically useful Si-based magnetic semiconductor is possible. We then focused on studying the structure of the implanted samples in order to establish a correlation between the magnetic and structural properties. The structural investigation involved secondary ion mass spectrometry, Rutherford backscattering, and transmission electron microscopy (TEM) as the main characterization techniques. The combination of the structural and magnetic studies allowed us to isolate an "active" region from which the ferromagnetism originates. We then found that the magnetic properties of the samples are strongly dependant on the interaction of the Mn atoms with the residual implant damage. The evolution of the Mn concentration profiles was also found to be closely related to the distribution of the Si lattice defects. We also observed the formation of Mn rich secondary phases at high enough annealing temperatures >800°C. However, we argued that theses crystallites cannot account for all the observed magnetic properties due to the low Curie temperature of these compounds in bulk form. We concluded that achieving a room temperature Si-based DMS has great potential but careful synthesis of this material system is needed to prevent secondary phase formation.

  8. Superconducting magnetic energy storage apparatus structural support system

    DOEpatents

    Withers, Gregory J.; Meier, Stephen W.; Walter, Robert J.; Child, Michael D.; DeGraaf, Douglas W.

    1992-01-01

    A superconducting magnetic energy storage apparatus comprising a cylindrical superconducting coil; a cylindrical coil containment vessel enclosing the coil and adapted to hold a liquid, such as liquefied helium; and a cylindrical vacuum vessel enclosing the coil containment vessel and located in a restraining structure having inner and outer circumferential walls and a floor; the apparatus being provided with horizontal compression members between (1) the coil and the coil containment vessel and (2) between the coil containment vessel and the vacuum vessel, compression bearing members between the vacuum vessel and the restraining structure inner and outer walls, vertical support members (1) between the coil bottom and the coil containment vessel bottom and (2) between the coil containment vessel bottom and the vacuum vessel bottom, and external supports between the vacuum vessel bottom and the restraining structure floor, whereby the loads developed by thermal and magnetic energy changes in the apparatus can be accommodated and the structural integrity of the apparatus be maintained.

  9. Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations

    DOE PAGES

    Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; ...

    2015-06-23

    The structures and magnetic properties of Co-Zr-B alloys near the composition of Co5Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the “Co11Zr2” polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the “interruption” sites. First-principles calculations showed that themore » magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co5Zr phase and larger than that of the low-temperature Co5.25Zr phase. As a result, our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.« less

  10. Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations

    SciTech Connect

    Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; Wang, Cai -Zhuang; Ho, Kai -Ming

    2015-06-23

    The structures and magnetic properties of Co-Zr-B alloys near the composition of Co5Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the “Co11Zr2” polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the “interruption” sites. First-principles calculations showed that the magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co5Zr phase and larger than that of the low-temperature Co5.25Zr phase. As a result, our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.

  11. Structures and magnetic properties of Co-Zr-B magnets studied by first-principles calculations

    SciTech Connect

    Zhao, Xin; Ke, Liqin; Nguyen, Manh Cuong; Wang, Cai-Zhuang Ho, Kai-Ming

    2015-06-28

    The structures and magnetic properties of Co-Zr-B alloys near the composition of Co{sub 5}Zr with B at. % ≤6% were studied using adaptive genetic algorithm and first-principles calculations. The energy and magnetic moment contour maps as a function of chemical composition were constructed for the Co-Zr-B magnet alloys through extensive structure searches and calculations. We found that Co-Zr-B system exhibits the same structure motif as the “Co{sub 11}Zr{sub 2}” polymorphs, and such motif plays a key role in achieving strong magnetic anisotropy. Boron atoms were found to be able to substitute cobalt atoms or occupy the “interruption” sites. First-principles calculations showed that the magnetocrystalline anisotropy energies of the boron-doped alloys are close to that of the high-temperature rhombohedral Co{sub 5}Zr phase and larger than that of the low-temperature Co{sub 5.25}Zr phase. Our calculations provide useful guidelines for further experimental optimization of the magnetic performances of these alloys.

  12. Anisotropic magnetic properties and magnetic structure of YbPdSi

    NASA Astrophysics Data System (ADS)

    Tsujii, Naohito; Keller, Lukas; Dönni, Andreas; Kitazawa, Hideaki

    2016-08-01

    YbPdSi with orthorhombic crystal structure (space group Pmmn) exhibits a magnetic transition at {{T}\\text{m}}=8 K, below which a ferromagnetic moment develops with an enhanced electronic specific-heat coefficient γ ˜ 200 mJ K-2 mol-1. We have investigated the magnetization, electrical resistivity, and specific heat of YbPdSi using single crystalline samples as functions of temperature and magnetic field. It has been found that the ferromagnetic moment points to the c-direction, although the magnetic moments have an Ising-like anisotropy along the b-direction above the magnetic-transition temperature. Field dependence of the magnetization and electrical resistivity shows a metamagnetic-like transition at {{H}\\text{m}}=0.3 T when field is applied along the b-axis below T  =  3 K, suggesting the existence of an antiferromagnetic component along this direction. The magnetic structure has been investigated by neutron diffraction using powder samples. The magnetic unit cell is identical to the crystal unit cell. The Rietveld fitting has revealed that Yb at the 2a and 2b positions exhibit a collinear ferromagnetic order along the c-axis, whereas Yb at the 4e position undergoes a non-collinear order, involving the ferromagnetic moment along the c-axis and an antiferromagnetic component along the b-axis. The ferromagnetic moments determined by the neutron diffraction are 0.26, 1.3, and 0.15 {μ\\text{B}} for Yb at the 4e, 2b, and 2a sites, respectively. The reduced moments for the 4e and the 2a sites suggest that the Kondo screening effect is important in YbPdSi.

  13. Probing magnetic turbulence by synchrotron polarimetry: statistics and structure of magnetic fields from Stokes correlators

    NASA Astrophysics Data System (ADS)

    Waelkens, A. H.; Schekochihin, A. A.; Enßlin, T. A.

    2009-10-01

    We describe a novel technique for probing the statistical properties of cosmic magnetic fields based on radio polarimetry data. Second-order magnetic field statistics like the power spectrum cannot always distinguish between magnetic fields with essentially different spatial structure. Synchrotron polarimetry naturally allows certain fourth-order magnetic field statistics to be inferred from observational data, which lifts this degeneracy and can thereby help us gain a better picture of the structure of the cosmic fields and test theoretical scenarios describing magnetic turbulence. In this work we show that a fourth-order correlator of specific physical interest, the tension force spectrum, can be recovered from the polarized synchrotron emission data. We develop an estimator for this quantity based on polarized emission observations in the Faraday rotation free frequency regime. We consider two cases: a statistically isotropic field distribution, and a statistically isotropic field superimposed on a weak mean field. In both cases the tension force power spectrum is measurable; in the latter case, the magnetic power spectrum may also be obtainable. The method is exact in the idealized case of a homogeneous relativistic electron distribution that has a power-law energy spectrum with a spectral index of p = 3, and assumes statistical isotropy of the turbulent field. We carry out numerical tests of our method using synthetic polarized emission data generated from numerically simulated magnetic fields. We show that the method is valid, that it is not prohibitively sensitive to the value of the electron spectral index p, and that the observed tension force spectrum allows one to distinguish between e.g. a randomly tangled magnetic field (a default assumption in many studies) and a field organized in folded flux sheets or filaments.

  14. Magnetic Field Roles in Black-Holes Accretion Disk's Structure

    NASA Astrophysics Data System (ADS)

    Abbassi, S.; Samadi, M.

    2016-09-01

    We study several factors which play remarkable roles in vertical structure and dynamics of hot accretion flows around black holes. These factors are large-scale magnetic field, thermal conduction, outflow and self-gravity. We consider an axisymmetric, rotating, steady viscous-resistive hot accretion flows.

  15. Spin Coherence and Magnetization Transport in Nanometer-Scale Structures

    DTIC Science & Technology

    2005-03-31

    Leveraging IBM’s experimental facilities and using IBM and BU’s established expertise in STM nanoassembly and theoretical modeling of spin dynamics...targeted two main goals: • Establish a fundamental understanding of the spin dynamics of nanoassembled structures • Explore the potential for...of the g value of a single atom • Measure spectrum of spin excitations in nanoassembled magnetic structures. • Build a foundation of knowledge

  16. Electronic Structure and Transport in Magnetic Multilayers

    SciTech Connect

    2008-02-18

    ORNL assisted Seagate Recording Heads Operations in the development of CIPS pin Valves for application as read sensors in hard disk drives. Personnel at ORNL were W. H. Butler and Xiaoguang Zhang. Dr. Olle Heinonen from Seagate RHO also participated. ORNL provided codes and materials parameters that were used by Seagate to model CIP GMR in their heads. The objectives were to: (1) develop a linearized Boltzmann transport code for describing CIP GMR based on realistic models of the band structure and interfaces in materials in CIP spin valves in disk drive heads; (2) calculate the materials parameters needed as inputs to the Boltzmann code; and (3) transfer the technology to Seagate Recording Heads.

  17. Structure of a magnetic flux annihilation layer formed by the collision of supersonic, magnetized plasma flows

    DOE PAGES

    Suttle, L. G.; Hare, J. D.; Lebedev, S. V.; ...

    2016-05-31

    We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counter-streaming, supersonic and magnetized aluminum plasma flows. The anti parallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (Ti~¯ZTe, with average ionization ¯Z=7). Lastly, analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of themore » in-flowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.« less

  18. Structure of a magnetic flux annihilation layer formed by the collision of supersonic, magnetized plasma flows

    SciTech Connect

    Suttle, L. G.; Hare, J. D.; Lebedev, S. V.; Swadling, G. F.; Burdiak, G. C.; Ciardi, A.; Chittenden, J. P.; Loureiro, N. F.; Niasse, N.; Suzuki-Vidal, F.; Wu, J.; Yang, Q.; Clayson, T.; Frank, A.; Robinson, T. S.; Smith, R. A.; Stuart, N.

    2016-05-31

    We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counter-streaming, supersonic and magnetized aluminum plasma flows. The anti parallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (Ti~¯ZTe, with average ionization ¯Z=7). Lastly, analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the in-flowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.

  19. Magnetic field sensing based on magnetic-fluid-clad multimode-singlemode-multimode fiber structures.

    PubMed

    Tang, Jiali; Pu, Shengli; Dong, Shaohua; Luo, Longfeng

    2014-10-14

    Magnetic field sensing based on magnetic-fluid-clad multimode-singlemode- multimode fiber structures is proposed and experimentalized. The structures are fabricated out using fiber fusion splicing techniques. The sensing principle is based on the interference between the core mode and cladding modes. Two interference dips are observed in our spectral range. Experimental results indicate that the magnetic field sensing sensitivities of 215 pm/mT and 0.5742 dB/mT are obtained for interference dip around 1595 nm. For interference dip around 1565 nm, the sensitivities are 60.5 pm/mT and 0.4821 dB/mT. The response of temperature is also investigated. The temperature sensitivity for the dip around 1595 nm is obtained to be 9.93 pm/°C.

  20. Structure of a magnetic flux annihilation layer formed by the collision of supersonic, magnetized plasma flows

    SciTech Connect

    Suttle, L. G.; Hare, J. D.; Lebedev, S. V.; Swadling, G. F.; Burdiak, G. C.; Ciardi, A.; Chittenden, J. P.; Loureiro, N. F.; Niasse, N.; Suzuki-Vidal, F.; Wu, J.; Yang, Q.; Clayson, T.; Frank, A.; Robinson, T. S.; Smith, R. A.; Stuart, N.

    2016-05-31

    We present experiments characterizing the detailed structure of a current layer, generated by the collision of two counter-streaming, supersonic and magnetized aluminum plasma flows. The anti parallel magnetic fields advected by the flows are found to be mutually annihilated inside the layer, giving rise to a bifurcated current structure—two narrow current sheets running along the outside surfaces of the layer. Measurements with Thomson scattering show a fast outflow of plasma along the layer and a high ion temperature (Ti~¯ZTe, with average ionization ¯Z=7). Lastly, analysis of the spatially resolved plasma parameters indicates that the advection and subsequent annihilation of the in-flowing magnetic flux determines the structure of the layer, while the ion heating could be due to the development of kinetic, current-driven instabilities.

  1. Mapping the magnonic landscape in patterned magnetic structures

    NASA Astrophysics Data System (ADS)

    Davies, C. S.; Poimanov, V. D.; Kruglyak, V. V.

    2017-09-01

    We report the development of a hybrid numerical/analytical model capable of mapping the spatially varying distributions of the local ferromagnetic resonance (FMR) frequency and dynamic magnetic susceptibility in a wide class of patterned and compositionally modulated magnetic structures. Starting from the numerically simulated static micromagnetic state, the magnetization is deliberately deflected orthogonally to its equilibrium orientation, and the magnetic fields generated in response to this deflection are evaluated using micromagnetic software. This allows us to calculate the elements of the effective demagnetizing tensor, which are then used within a linear analytical formalism to map the local FMR frequency and dynamic magnetic susceptibility. To illustrate the typical results that one can obtain using this model, we analyze three micromagnetic systems boasting nonuniformity in either one or two dimensions, and successfully explain the spin-wave emission observed in each case, demonstrating the ubiquitous nature of the Schlömann excitation mechanism underpinning the observations. Finally, the developed model of local FMR frequency can be used to explain how spin waves could be confined and steered using magnetic nonuniformities of various origins, rendering it a powerful tool for the mapping of the graded magnonic index in magnonics.

  2. Sunspot magnetic structure and interspot radio source formation

    NASA Astrophysics Data System (ADS)

    Solov'ev, A. A.

    2015-12-01

    The magnetic structure of a typical sunspot is represented as a set of three interacting magnetic fluxes. The first one, F1, escapes upward from the sunspot umbra and closes through the corona on the sunspot of opposite polarity. The second, F2, forms the sunspot penumbra. It includes Evershed flows emerging from the sunspot, the heavy photospheric plasma of which cannot be pulled up to the corona. For this reason, the F2 flux at the outer edge of the penumbra should close on the photosphere adjacent to the sunspot, i.e., here the F2 field changes sign. The third flux, F3, is the external magnetic field flux and has the same polarity as F1. Thus, magnetic fields of different signs occur near the outer boundary of the sunspot penumbra. Magnetic reconnections will inevitably take place there. Smalland multiscale current sheets in which particles are accelerated are formed. The latter fill short and low magnetic loops that connect sunspots of different polarity in the bipolar group and form interspot radio sources at the tops of these loops.

  3. Structure-induced spin reorientation in magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Neumann, Alexander; Frauen, Axel; Vollmers, Julian; Meyer, Andreas; Oepen, Hans Peter

    2016-09-01

    We report on structuring-induced changes of the magnetic anisotropy of cylindrical nanostructures which are carved out of thin Pt/Co/Pt films. The magnetic properties of films and structures with a diameter of about 34 nm were investigated via magneto-optic Kerr effect. The magnetic anisotropy is determined for both films and nanostructures for varying Co thicknesses (0.5-7 nm). In general, the nanostructures exhibit larger perpendicular anisotropy than the films. On thickness increase of the Co layer two spin reorientation transitions at about 2.2 and 5 nm are found. At 2.2 nm the nanostructures exhibit the transition from perpendicular to in-plane orientation of magnetization while at 5 nm the reversed transition is found. The variation of the magnetic anisotropy of the Co nanostructures is not solely caused by the change of shape anisotropy. The net change, corrected for the shape, reveals a reduction of strain in the thinnest Co layers while the increase of the anisotropy of the nanostructures at higher Co thicknesses is caused by a transformation of the Co lattice from fcc to hcp.

  4. Structure and magnetism in fcc magnetic transition metals on (001) diamond (abstract)

    NASA Astrophysics Data System (ADS)

    Wolf, J. A.; Krebs, J. J.; Idzerda, Y. U.; Prinz, G. A.; Kemner, K. M.

    1996-04-01

    We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co,Ni,Fe) on (001) diamonds, the thickness of the films varying between a few tenths of a nanometer to over 100 nm. The crystalline quality and fourfold symmetry of these layers was monitored in situ during the film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated ex situ using X-ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout each entire film. The magnetic characterization was performed with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops. The saturation magnetization of the Co films is only slightly lower than the literature values. The coercive fields are very small (˜25 Oe) and the magnetization reversal very sharp. The FMR yielded a fourfold anisotropy comparable to literature values. The observation of the first standing spinwaves underlines the good quality. The Ni films are tetragonally distorted due to the 1.2% mismatch. The FMR data indicate a significant perpendicular anisotropy slightly smaller than 4πM, the fourfold in-plane anisotropy being comparable to the bulk value. The saturation magnetization is reduced by 30% compared to bulk values, probably due to nickel-carbide which was observed in the XRD data from some samples. Neither the in-plane <110> nor the in-plane <100> axis show an easy axis behavior and both require fields in excess of 6000 Oe to saturate, the coercive fields being about 200 Oe. The RHEED patterns of the Fe films show single crystal growth with a lattice constant comparable to diamond, indicating an fcc structure. A similar structural and magnetic characterization of these films will also be presented.

  5. Commensurate-incommensurate solid transition in the 4He monolayer on a single γ-graphyne sheet

    NASA Astrophysics Data System (ADS)

    Kwon, Yongkyung; Ahn, Jeonghwan

    2014-03-01

    We have performed path-integral Monte Carlo calculations to study 4He adsorption on γ-graphyne. Assuming the 4He-substrate interaction described by a pairwise sum of empirical helium-carbon interatomic potentials, we find that unlike α-graphyne, a single sheet of γ-graphyne is not permeable to 4He atoms despite its large surface area. One-dimensional density distribution shows layer-by-layer growth of 4He on γ-graphyne. Partially-filled 4He monolayers are found to exhibit different commensurate structures depending on the helium coverage; it shows a C2/2 commensurate structure at the areal density of 0.0491 Å-2, a C3/2 structure at 0.0736 Å-2, and a C4/2 structure at 0.0982 Å-2. After going through various domain structures, the 4He monolayer is completed at the areal density of 0.115 Å-2 where 4He adatoms form an incommensurate triangular solid. Possible superfluid response of the 4He monolayer on γ-graphyne is now under investigation.

  6. Concentric Magnetic Structures for Magnetophoretic Bead Collection, Cell Trapping and Analysis of Cell Morphological Changes Caused by Local Magnetic Forces

    PubMed Central

    Huang, Chen-Yu; Wei, Zung-Hang

    2015-01-01

    Concentric magnetic structures (ring and square) with domain wall (DW) pinning geometry are designed for biological manipulation. Magnetic beads collection was firstly demonstrated to analyse the local magnetic field generated by DWs and the effective regions to capture magnetic targets of size 1 μm. Primary mouse embryonic fibroblasts (MEFs) are magnetically labeled by internalizing poly (styrene sulfonic acid) stabilized magnetic nanoparticles (PSS-MNPs) and then are selectively trapped by head-to-tail DWs (HH DWs) or tail-to-tail DWs (TT DWs) to be arranged into linear shape or cross shape. The morphologies and the nuclear geometry of the cells growing on two kinds of concentric magnetic structures are shown to be distinctive. The intracellular magnetic forces generated by the local magnetic field of DWs are found to influence the behaviour of cells. PMID:26270332

  7. Quantum phase transitions and phase diagram for a one-dimensional p-wave superconductor with an incommensurate potential.

    PubMed

    Cai, X

    2014-04-16

    The effect of the incommensurate potential is studied for the one-dimensional p-wave superconductor. It is determined by analyzing various properties, such as the superconducting gap, the long-range order of the correlation function, the inverse participation ratio and the Z2 topological invariant, etc. In particular, two important aspects of the effect are investigated: (1) as disorder, the incommensurate potential destroys the superconductivity and drives the system into the Anderson localized phase; (2) as a quasi-periodic potential, the incommensurate potential causes band splitting and turns the system with certain chemical potential into the band insulator phase. A full phase diagram is also presented in the chemical potential-incommensurate potential strength plane.

  8. Structure and magnetism of antiferromagnetic FeMN thin films

    NASA Astrophysics Data System (ADS)

    Maat, Stefan

    2000-09-01

    The magnetic and electronic structure of bulk fcc Fe 50Mn50 was studied by first principles calculations using the layer-version of the Korringa- Kohn-Rostocker method with the local spin density approximation and the coherent potential approximation to treat chemical disorder. The self-consistent calculations suggest a non-collinear spin-structure for Fe50Mn50 as the magnetic ground state, which can be understood from the electronic structure. Possible spin-structures identified are the 3Q structure with spins pointing along the body diagonals and the 2Q structure with spins pointing along the face diagonals. The collinear 1Q structure with spins pointing along the cube edges was found to be energetically unstable. Epitaxial FeMn/Cu multilayers were grown epitaxially by sputtering onto a thick buffer layer of twinned Cu(111) on H-terminated Si(110). The growth was characterized in situ by Auger electron spectroscopy and electron diffraction techniques and ex situ by X-ray diffraction. Neutron diffraction experiments were performed on these multilayers to investigate the spin structure of thin Fe50Mn50 films. The measurements confirmed that Fe50Mn50 has either a 3Q structure or equally populated domains of 2Q or 1Q structures. Hysteresis loops of polycrystalline and epitaxial exchange-biased Ni 80Fe20/Fe50Mn50 films were measured as a function of Fe50Mn50 layer thickness with the longitudinal Kerr effect. The variation of the loop-shift and the coercivity were observed over a full 360° in plane rotation and Fourier analyzed. Coercivities and loop shifts show a strong dependence on the antiferromagnetic layer thickness. Examination of the angular dependent results within different models of exchange bias verified that the Fourier coefficients obey necessary conditions to achieve energetic stability together with spontaneous magnetization.

  9. Magnetic Excitations in the Geometric Frustrated Multiferroic CuCrO2

    SciTech Connect

    Frontzek, Matthias D; Barilo, Sergei; Christianson, Andrew D; Ehlers, Georg; Fishman, Randy Scott; Haraldsen, Jason T; Podlesnyak, Andrey A; Sefat, A. S.; Matsuda, Masaaki; Shiryaev, Sergei; Qiu, Y.; Copley, J.R.D.

    2011-01-01

    In this paper detailed neutron scattering measurements of the magnetic excitation spectrum of \\CCO\\ in the ordered state below $T_{\\rm{N1}}=24.2$~K are presented. The spectra are analyzed using a model Hamiltonian which includes intralayer-exchange up to the next-next-nearest neighbor and interlayer-exchange. We obtain a definite parameter set and show that exchange interaction terms beyond the next-nearest neighbor are important to describe the inelastic excitation spectrum. The magnetic ground state structure generated with our parameter set is in agreement with the structure proposed for \\CCO\\ from the results of single crystal diffraction experiments previously published. We argue that the role of the interlayer exchange is crucial to understand the incommensurability of the magnetic structure as well as the spin-charge coupling mechanism.

  10. Ulysses Data Analysis: Magnetic Topology of Heliospheric Structures

    NASA Technical Reports Server (NTRS)

    Crooker, Nancy

    2001-01-01

    In this final technical report on research funded by a NASA grant, a project overview is given by way of summaries on nine published papers. Research has included: 1) Using suprathermal electron data to study heliospheric magnetic structures; 2) Analysis of magnetic clouds, coronal mass ejections (CME), and the heliospheric current sheet (HCS); 3) Analysis of the corotating interaction region (CIR) which develop from interactions between solar wind streams of different velocities; 4) Use of Ulysses data in the interpretation of heliospheric events and phenomena.

  11. Structuring Light by Concentric-Ring Patterned Magnetic Metamaterial Cavities.

    PubMed

    Zeng, Jinwei; Gao, Jie; Luk, Ting S; Litchinitser, Natalia M; Yang, Xiaodong

    2015-08-12

    Ultracompact and tunable beam converters pose a significant potential for modern optical technologies ranging from classical and quantum communication to optical manipulation. Here we design and demonstrate concentric-ring patterned structures of magnetic metamaterial cavities capable of tailoring both polarization and phase of light by converting circularly polarized light into a vector beam with an orbital angular momentum. We experimentally illustrate the realization of both radially and azimuthally polarized vortex beams using such concentric-ring patterned magnetic metamaterials. These results contribute to the advanced complex light manipulation with optical metamaterials, making it one step closer to realizing the simultaneous control of polarization and orbital angular momentum of light on a chip.

  12. Magnetic resonance in a Cu-Cr-S structure

    SciTech Connect

    Vorotynov, A. M. Abramova, G. M.; Pankrats, A. I.; Petrakovskii, G. A.; Zharkov, S. M.; Zeer, G. M.; Tugarinov, V. I.; Rautskii, M. V.; Sokolov, V. V.

    2013-11-15

    A layered Cu-Cr-S structure composed of single-crystal CuCrS{sub 2} layers and thin CuCr{sub 2}S{sub 4} plates embedded in them has been investigated by the magnetic resonance and scanning electron microscopy methods. The Curie temperature and saturation magnetization of the spinel phase of the investigated samples have been determined. The thickness of the CuCr{sub 2}S{sub 4} layers has been estimated. The dependence of the growncrystal topology on synthesis conditions has been established. An interpretation of the anomalous behavior of the magnetostatic oscillation intensity is offered.

  13. Tunable conductance of magnetic nanowires with structured domain walls.

    PubMed

    Dugaev, V K; Berakdar, J; Barnaś, J

    2006-02-03

    We show that in a magnetic nanowire with double magnetic domain walls, quantum interference results in spin-split quasistationary states localized mainly between the domain walls. Spin-flip-assisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g., upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomenon is shown to be utilizable to manipulate the spin density in the domain vicinity. The domain wall parameters are readily controllable, and the predicted effect is hence exploitable in spintronic devices.

  14. Strange magnetism and the anapole structure of the proton.

    SciTech Connect

    Hasty, R.; Hawthorne-Allen, A. M.; Averett, T.; Barkhuff, D.; Beck, D. H.; Mueller, B.; SAMPLE Collaboration; Physics; Univ. of Illinois; Virginia Polytechnic Inst. and State Univ.; Coll. of William and Mary; Lab. for Nuclear Science and Department of Physics

    2000-12-15

    The violation of mirror symmetry in the weak force provides a powerful tool to study the internal structure of the proton. Experimental results have been obtained that address the role of strange quarks in generating nuclear magnetism. The measurement reported here provides an unambiguous constraint on strange quark contributions to the proton's magnetic moment through the electron-proton weak interaction. We also report evidence for the existence of a parity-violating electromagnetic effect known as the anapole moment of the proton. The proton's anapole moment is not yet well understood theoretically, but it could have important implications for precision weak interaction studies in atomic systems such as cesium.

  15. Magnetic micromechanical structures based on CoNi electrodeposited alloys

    NASA Astrophysics Data System (ADS)

    Cojocaru, P.; Magagnin, L.; Gomez, E.; Vallés, E.; Liu, F.; Carraro, C.; Maboudian, R.

    2010-12-01

    Electrodeposited CoNi magnetic microstructures compatible with silicon microfabrication technology have been developed using a sulfamate acidic bath, as an alternative to a less environmentally friendly chloride bath. The galvanostatic electrodeposition in the formulated electrolyte allows the deposition of cobalt-rich CoNi films and microstructures defined by photoresist at high deposition rates. Microstructures are adherent to the substrate, with a good lateral definition and resistance to the wet etching for the release of the sacrificial layer. The released structures respond to applied magnetic fields and no breakage occurred during large deformation.

  16. GMAG Student Dissertation Award Talk: Effects of Nanoscale Structure on the Magnetism and Transport Properties of Chromium and Chromium-Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Boekelheide, Zoe

    2011-03-01

    Bulk Cr has an incommensurate spin density wave (ISDW) due to nesting of the Fermi surface which is easily disrupted by perturbation. Thus, the properties of Cr are sensitive to small amounts of dopant atoms, application of pressure, etc. which has been well studied in bulk. We have taken advantage of thin film growth techniques to study the effects of nanoscale structure on the properties of Cr and Cr1-xAlx alloys. The first part of my talk will discuss our research on polycrystalline Cr thin films, where variables such as strain and disorder crucially affect the SDW. We find that Cr thin films can be ISDW like in bulk Cr, or transition to commensurate SDW (CSDW) or mixed depending on deposition conditions and the resulting thin film microstructure. The transport properties are also strongly affected, as quasilocal defect states inside the SDW gap cause resonant scattering. This results in anomalous features such as residual resistivity ranging between 3 and 400 μ O -cm and significant resistivity minima at low temperature. Further evidence of quasilocal states inside the SDW gap is seen in the enhanced electronic density of states (DOS) from specific heat measurements of Cr thin films. The second part of my talk will discuss Cr1-xAlx alloys. The addition of Al to Cr causes the ISDW to transition to CSDW for x = 0.03. Cr1-xAlx also exhibits previously unexplained semiconducting behavior for x = 0.15-0.30. I will discuss our ongoing theoretical and experimental research which suggests that a chemically ordered, rhombohedrally distorted Cr3Al structure occurs in nanosized domains and causes a hybridization gap on part of the Fermi surface. The CSDW causes a gap on another part of the Fermi surface, so that the semiconducting behavior can be explained by a combination of structural and magnetic affects. Supported by the DOE under Contract No. DE-AC02-05CH11231.

  17. The Origins of Magnetic Structure in the Corona and Wind

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro K.

    2010-01-01

    One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at two special locations: photospheric polarity inversions lines. (non-potentiality observed as a filament channel) and coronal hole boundaries, (observed as the slow solar wind). This characteristic feature of the closed-field corona is highly unexpected given that its magnetic field is continuously tangled by photospheric motions. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. I propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries inversion lines and coronal holes, creating both filament channels and the slow wind. We describe how the helicity is injected and transported and calculate the relevant rates. I argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field. This work has been supported by the NASA HTP, SR&T, and LWS programs.

  18. Magnetic and structural instabilities of ultrathin Fe(100) wedges

    SciTech Connect

    Bader, S.D.; Li, Dongqi; Qiu, Z.Q.

    1994-05-01

    An overview is provided of recent efforts to explore magnetic and related structural issues for ultrathin Fe films grown epitaxially as wedge structures onto Ag(100) and Cu(100). Experiments were carried out utilizing the surface magneto-optic Kerr effect (SMOKE). Ordinary bcc Fe is lattice-matched to the primitive unit cell of the Ag(100) surface. Fe wedges on Ag(100) can be fabricated whose thick end has in-plane magnetic easy axes due to the shape anisotropy, and whose thin end has perpendicular easy axes due to the surface magnetic anisotrophy. A spin-reorientation transition can thus be studied in the center of the wedge where the competing anisotropies cancel. The goal is to test the Mermin-Wagner theorem which states that long-range order is lost at finite temperatures in an isotropic two-dimensional Heisenberg system. Fe wedges on Cu(100) can be studied in like manner, but the lattice matching permits fcc and tetragonally-distorted fcc phases to provide structural complexity in addition to the interplay of competing magnetic anisotropies. The results of these studies are new phase identifications that help both to put previous work into perspective and to define issues to pursue in the future.

  19. Electronic structure and magnetic properties of zigzag blue phosphorene nanoribbons

    SciTech Connect

    Hu, Tao; Hong, Jisang

    2015-08-07

    We investigated the electronic structure and magnetism of zigzag blue phosphorene nanoribbons (ZBPNRs) using first principles density functional theory calculations by changing the widths of ZBPNRs from 1.5 to 5 nm. In addition, the effect of H and O passivation was explored as well. The ZBPNRs displayed intra-edge antiferromagnetic ground state with a semiconducting band gap of ∼0.35 eV; and this was insensitive to the edge structure relaxation effect. However, the edge magnetism of ZBPNRs disappeared with H-passivation. Moreover, the band gap of H-passivated ZBPNRs was greatly enhanced because the calculated band gap was ∼1.77 eV, and this was almost the same as that of two-dimensional blue phosphorene layer. For O-passivated ZBPNRs, we also found an intra-edge antiferromagnetic state. Besides, both unpassivated and O-passivated ZBPNRs preserved almost the same band gap. We predict that the electronic band structure and magnetic properties can be controlled by means of passivation. Moreover, the edge magnetism can be also modulated by the strain. Nonetheless, the intrinsic physical properties are size independent. This feature can be an advantage for device applications because it may not be necessary to precisely control the width of the nanoribbon.

  20. The Origins of Magnetic Structure in the Corona and Wind

    NASA Astrophysics Data System (ADS)

    Antiochos, Spiro K.

    2009-05-01

    One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at two special locations: photospheric polarity inversions lines, (non-potentiality observed as a filament channel) and coronal hole boundaries, (observed as the slow solar wind). This characteristic feature of the closed-field corona is highly unexpected given that its magnetic field is continuously tangled by photospheric motions. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. I propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries, inversion lines and coronal holes, creating both filament channels and the slow wind. We describe how the helicity is injected and transported and calculate the relevant rates. I argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field. This work has been supported by the NASA HTP, SR&T, and LWS programs.

  1. Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41

    SciTech Connect

    Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Abernathy, Douglas L.; Aczel, Adam A.; Zhou, Jianshi; Delaire, Olivier A.; Shi, Li

    2016-10-21

    Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7–1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. Furthermore, these findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.

  2. Effective field model of roughness in magnetic nano-structures

    SciTech Connect

    Lepadatu, Serban

    2015-12-28

    An effective field model is introduced here within the micromagnetics formulation, to study roughness in magnetic structures, by considering sub-exchange length roughness levels as a perturbation on a smooth structure. This allows the roughness contribution to be separated, which is found to give rise to an effective configurational anisotropy for both edge and surface roughness, and accurately model its effects with fine control over the roughness depth without the explicit need to refine the computational cell size to accommodate the roughness profile. The model is validated by comparisons with directly roughened structures for a series of magnetization switching and domain wall velocity simulations and found to be in excellent agreement for roughness levels up to the exchange length. The model is further applied to vortex domain wall velocity simulations with surface roughness, which is shown to significantly modify domain wall movement and result in dynamic pinning and stochastic creep effects.

  3. Magnetic field and electric current structure in the chromosphere

    NASA Technical Reports Server (NTRS)

    Dravins, D.

    1974-01-01

    The three-dimensional vector magnetic field structure in the chromosphere above an active region is deduced by using high-resolution H-alpha filtergrams together with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing field lines that outline the H-alpha structure. The height extent of the field is determined from vertical field-gradient observations around sunspots, from observed fibril heights, and from an assumption that the sources of the field are largely local. The computed electric currents (typically 10 mA/sq m) are found to flow in patterns not similar to observed features and not parallel to magnetic fields. Force structures correspond to observed solar features; the dynamics to be expected include: downward motion in bipolar areas in the lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions, and motion of arch filament systems.

  4. Magnetic Field Structure of Pressure Balanced Structures from Ulysses High Latitudes Observations

    NASA Technical Reports Server (NTRS)

    Yamauchi, Y.; Suess, S. T.; Sakurai, T.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    Ulysses observations showed that pressure balance structures (PBSs) are a common feature in the high-latitude solar winds near the solar minimum. On the other hand, coronal plumes are common in polar coronal holes near the solar minimum. It is therefore considered that the PBSs would be remnants of plumes. Several detailed studies of the PBSs have been made from Ulysses/SWOOPS observations, but study of their magnetic structures has not yet been done. The study of the magnetic structure is important because previous observations and theoretical models of plumes indicate that they are related to the network activity such as magnetic reconnection on the photosphere. We have investigated the magnetic structures of the PBSs with Ulysses magnetometer and SWOOPS data. We have found that magnetic reversals in radial magnetic field take place while the spacecraft passes through most of the PBSs These magnetic reversals have been interpreted as large amplitude Alfv/'enic fluctuations but our results suggest that Ulysses is also traversing current sheets of plasmoids associated with network activity at the base of plumes.

  5. Incommensurate quantum-size oscillations in acene-based molecular wires—Effects of quantum fluctuations

    NASA Astrophysics Data System (ADS)

    Schmitteckert, Peter; Thomale, Ronny; Korytár, Richard; Evers, Ferdinand

    2017-03-01

    Molecular wires of the acene-family can be viewed as a physical realization of a two-rung ladder Hamiltonian. For acene-ladders, closed-shell ab initio calculations and elementary zone-folding arguments predict incommensurate gap oscillations as a function of the number of repetitive ring units, NR, exhibiting a period of about ten rings. Results employing open-shell calculations and a mean-field treatment of interactions suggest anti-ferromagnetic correlations that could potentially open a large gap and wash out the gap oscillations. Within the framework of a Hubbard model with repulsive on-site interaction, U, we employ a Hartree-Fock analysis and the density matrix renormalization group to investigate the interplay of gap oscillations and interactions. We confirm the persistence of incommensurate oscillations in acene-type ladder systems for a significant fraction of parameter space spanned by U and NR.

  6. The role of Human Orbitofrontal Cortex in value comparison for incommensurable objects

    PubMed Central

    FitzGerald, Thomas H.B.; Seymour, Ben; Dolan, Raymond J.

    2009-01-01

    The human orbitofrontal cortex is strongly implicated in appetitive valuation. Whether its role extends to support comparative valuation necessary to explain probabilistic choice patterns for incommensurable goods is unknown. Using a binary choice paradigm we derived the subjective values of different bundles of goods, under conditions of both gain and loss. We demonstrate that orbitofrontal activation reflects the difference in subjective value between available options, an effect evident across valuation for both gains and losses. By contrast activation in dorsal striatum and supplementary motor areas reflects subjects’ choice probabilities. These findings indicate that orbitofrontal cortex plays a pivotal role in valuation for incommensurable goods, a critical component process in human decision making. PMID:19571129

  7. Atomic-scale simulations on the sliding of incommensurate surfaces: The breakdown of superlubricity

    NASA Astrophysics Data System (ADS)

    Kim, Woo Kyun; Falk, Michael L.

    2009-12-01

    Molecular dynamics simulations of frictional sliding in an atomic force microscope (AFM) show a clear dependence of superlubricity between incommensurate surfaces on tip compliance and applied normal force. While the kinetic friction vanishes for rigid tips and low normal force, superlubric behavior breaks down for softer tips and high normal force. The simulations provide evidence that the Frenkel-Kontorova-Tomlinson (FKT) scaling applies equally to a more realistic three-dimensional (3D) incommensurate AFM model except in the limit of very low stiffness and high normal load. Unlike the FKT model in which the breakdown of superlubricity coincides with the emergence of the metastable states, in the 3D model some metastable states appear to reduce frictional force leading to nonmonotonic dependence of force on normal load and tip compliance. Metastable states vary with the slider positions and the relative stabilities of these metastable states result in varying transition mechanisms depending on sliding velocity.

  8. Two Dimensional Incommensurate Spin Excitations and Lattice Fluctuations in La2 - x Bax CuO4

    NASA Astrophysics Data System (ADS)

    Wagman, J. J.; Carlo, J. P.; van Gastel, G.; Zhao, Y.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Savicii, A.; Granroth, G. E.; Yamani, Z.; Tun, Z.; Gaulin, B. D.

    2013-03-01

    'Hour-glass' shaped dispersions of antiferromagnetic (AF) spin fluctuations are a robust feature common to many high temperature superconductors. In 214 cuprates, these phenomena are well known to display a strong dependence on the concentration of holes that are introduced into the copper oxide planes by doping. The incommensurability (IC) of the two dimensional magnetic order in this system is sensitive to hole concentration. Here, we present a series of neutron scattering measurements on single crystals of La2 - x Bax CuO4 (LBCO), with 0 . 035 <= x <= 0 . 095 , a doping range that spans the transition from diagonal to parallel IC ordering wavevectors, and from non-superconducting to superconducting ground states. Our measurements map out the evolution of the spin excitations for energies below ~ 50 meV, and focus on an enhancement in the scattered intensity centered in the 17-20 meV at the AF IC positions. This regime corresponds to the approximate crossing of very dispersive spin excitations and weakly dispersive low lying optic phonons in LBCO. NSERC, Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy

  9. Magnetic apatite for structural insights on the plasma membrane.

    PubMed

    Stanca, Sarmiza E; Müller, Robert; Dellith, Jan; Nietzsche, Sandor; Stöckel, Stephan; Biskup, Christoph; Deckert, Volker; Krafft, Christoph; Popp, Jürgen; Fritzsche, Wolfgang

    2015-01-21

    The iron oxide-hydroxyapatite (FeOxHA) nanoparticles reported here differ from those reported before by their advantage of homogeneity and simple preparation; moreover, the presence of carboxymethyldextran (CMD), together with hydroxyapatite (HA), allows access to the cellular membrane, which makes our magnetic apatite unique. These nanoparticles combine magnetic behavior, Raman label ability and the property of interaction with the cellular membrane; they therefore represent an interesting material for structural differentiation of the cell membrane. It was observed by Raman spectroscopy, scanning electron microscopy (SEM) and fluorescence microscopy that FeOxHA adheres to the plasma membrane and does not penetrate the membrane. These insights make the nanoparticles a promising material for magnetic cell sorting, e.g. in microfluidic device applications.

  10. Nanoscale Magnetic Structure of Ferromagnet/Antiferromagnet Manganite Multilayers

    SciTech Connect

    Niebieskikwiat, D.; Hueso, L. E.; Borchers, J. A.; Mathur, N. D.; Salamon, M. B.

    2007-12-14

    We use polarized neutron reflectometry and dc magnetometry to obtain a comprehensive picture of the magnetic structure of a series of La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/Pr{sub 2/3}Ca{sub 1/3}MnO{sub 3} (LSMO/PCMO) superlattices, with varying thickness of the antiferromagnetic (AFM) PCMO layers (0{<=}t{sub A}{<=}7.6 nm). While LSMO presents a few magnetically frustrated monolayers at the interfaces with PCMO, in the latter a magnetic contribution due to ferromagnetic (FM) inclusions within the AFM matrix is maximized at t{sub A}{approx}3 nm. This enhancement of FM moment occurs at the matching between layer thickness and cluster size, implying the possibility of tuning phase separation by imposing appropriate geometrical constraints which favor the accommodation of FM nanoclusters within the ''non-FM'' material.

  11. Magnetic structures of actinide materials by pulsed neutron diffraction

    SciTech Connect

    Lawson, A.C.; Goldstone, J.A.; Huber, J.G.; Giorgi, A.L.; Conant, J.W.; Severing, A.; Cort, B.; Robinson, R.A.

    1990-01-01

    We describe some attempts to observe magnetic structure in various actinide (5f-electron) materials. Our experimental technique is neutron powder diffraction as practiced at a spallation (pulsed) neutron source. We will discuss our investigations of {alpha}-Pu, {delta}-Pu, {alpha}-UD{sub 3} and {beta}-UD{sub 3}. {beta}-UD{sub 3} is a simple ferromagnet: surprisingly, the moments on the two non-equivalent uranium atoms are the same within experimental error. {alpha}-UD{sub 3}, {alpha}-Pu and {delta}-Pu are non-magnetic, within the limits of our observations. Our work with pulsed neutron diffraction shows that it is a useful technique for research on magnetic materials.

  12. Crystal structure and magnetism of UOsAl

    NASA Astrophysics Data System (ADS)

    Andreev, A. V.; Daniš, S.; Šebek, J.; Henriques, M. S.; Vejpravová, J.; Gorbunov, D. I.; Havela, L.

    2017-04-01

    Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn2 type, space group P63/mmc, with lattice parameters a=536.4 pm, c=845.3 pm. Shortest inter-uranium distance 313 pm (along the c-axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10-8 m3 mol-1 (at T=2 K), which is slightly higher with magnetic field along the a-axis compared to the c-axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ=36 mJ mol-1 K-2.

  13. Magnetic apatite for structural insights on the plasma membrane

    NASA Astrophysics Data System (ADS)

    Stanca, Sarmiza E.; Müller, Robert; Dellith, Jan; Nietzsche, Sandor; Stöckel, Stephan; Biskup, Christoph; Deckert, Volker; Krafft, Christoph; Popp, Jürgen; Fritzsche, Wolfgang

    2015-01-01

    The iron oxide-hydroxyapatite (FeOxHA) nanoparticles reported here differ from those reported before by their advantage of homogeneity and simple preparation; moreover, the presence of carboxymethyldextran (CMD), together with hydroxyapatite (HA), allows access to the cellular membrane, which makes our magnetic apatite unique. These nanoparticles combine magnetic behavior, Raman label ability and the property of interaction with the cellular membrane; they therefore represent an interesting material for structural differentiation of the cell membrane. It was observed by Raman spectroscopy, scanning electron microscopy (SEM) and fluorescence microscopy that FeOxHA adheres to the plasma membrane and does not penetrate the membrane. These insights make the nanoparticles a promising material for magnetic cell sorting, e.g. in microfluidic device applications.

  14. Patient experience and the psychiatric discourse: Attempting to bridge incommensurable worlds

    PubMed Central

    Jacob, K. S.

    2015-01-01

    Divergent worldviews, incommensurable frameworks, contrasting models, distinct foci, dissimilar logic, different realities, disparate cultures, and complex patient-physician interaction impact the clinical process and problematize decision-making. Attempting to understand the disease-illness divide, engage patient perspectives, go beyond the traditional biomedical understanding of mental illness and negotiate a shared plan for treatment are serious challenges for psychiatry. The challenge for psychiatrists is to appreciate patient reality and negotiate a shared plan of treatment. PMID:26816435

  15. Fate of topological states in incommensurate generalized Aubry-André models

    NASA Astrophysics Data System (ADS)

    Cestari, J. C. C.; Foerster, A.; Gusmão, M. A.

    2016-05-01

    We study one-dimensional optical lattices described by generalized Aubry-André models that include both commensurate and incommensurate modulations of the hopping amplitude. This brings together two interesting features of this class of systems: Anderson localization and the existence of topological edge states. We follow changes of the single-particle energy spectrum induced by variations of the system parameters, with focus on the survival of topological states in the localized regime.

  16. Tunable and laser-reconfigurable 2D heterocrystals obtained by epitaxial stacking of crystallographically incommensurate Bi2Se3 and MoS2 atomic layers

    PubMed Central

    Vargas, Anthony; Liu, Fangze; Lane, Christopher; Rubin, Daniel; Bilgin, Ismail; Hennighausen, Zachariah; DeCapua, Matthew; Bansil, Arun; Kar, Swastik

    2017-01-01

    Vertical stacking is widely viewed as a promising approach for designing advanced functionalities using two-dimensional (2D) materials. Combining crystallographically commensurate materials in these 2D stacks has been shown to result in rich new electronic structure, magnetotransport, and optical properties. In this context, vertical stacks of crystallographically incommensurate 2D materials with well-defined crystallographic order are a counterintuitive concept and, hence, fundamentally intriguing. We show that crystallographically dissimilar and incommensurate atomically thin MoS2 and Bi2Se3 layers can form rotationally aligned stacks with long-range crystallographic order. Our first-principles theoretical modeling predicts heterocrystal electronic band structures, which are quite distinct from those of the parent crystals, characterized with an indirect bandgap. Experiments reveal striking optical changes when Bi2Se3 is stacked layer by layer on monolayer MoS2, including 100% photoluminescence (PL) suppression, tunable transmittance edge (1.1→0.75 eV), suppressed Raman, and wide-band evolution of spectral transmittance. Disrupting the interface using a focused laser results in a marked the reversal of PL, Raman, and transmittance, demonstrating for the first time that in situ manipulation of interfaces can enable “reconfigurable” 2D materials. We demonstrate submicrometer resolution, “laser-drawing” and “bit-writing,” and novel laser-induced broadband light emission in these heterocrystal sheets. PMID:28740860

  17. Fabrication, Structure, and Magnetism of Transition Metal and Oxide Nanoclusters

    NASA Astrophysics Data System (ADS)

    Wei, Xiaohui

    Nanoclusters display unusual properties due to the high surface-to-volume atom ratios. Our ability to fabricate nanoclusters with various sizes, structures, compositions and morphologies with a cluster-deposition system provides unique ways to investigate several nanoscale phenomena. In this work, we have investigated the structural and magnetic properties of various transition-metal and oxide clusters. One example is bimetallic MnAu nanoclusters. Annealing induces size dependences for the lattice parameters, tetragonal-distortion ratios, composition, as well as the morphologies. The size dependence for lattice parameters agrees well with density-functional-theory calculations. The size-dependent composition and formation dynamics are in good agreement with previous thermodynamics calculations for similar bimetallic nanoclusters. One especially interesting issue is the formation of L10 MnAu-fcc Mn core-shell clusters. After annealing, with core-shell formation the average magnetic moment is significantly enhanced from 0.17 microB/Mn for the L10 MnAu clusters to 2.1 microB/Mn. The origin of this high magnetic moment is discussed in terms of previous theoretical and experimental work on nanoscale ferromagnetic and ferrimagnetic Mn structures. This size dependence results from Ostwald ripening at high temperature and likely exists for all bimetallic nanoparticles with different mobilities for the two constituent elements. Another class of interesting material is dilute magnetic oxides, the room-temperature ferromagnetism of which has been suggested to be defect-related, especially involving oxygen vacancies. For TiO clusters, both experimental and theoretical work is carried to investigate the role of hydroxyl ions for the ferromagnetism. By utilizing the water dissociative adsorption and creation of hydroxyls at oxygen vacancies, we have shown that the magnetic moment increases initially linearly with increasing exposure time in moisture. Reducing the humidity level

  18. Low-degree Structure in Mercury's Planetary Magnetic Field

    NASA Technical Reports Server (NTRS)

    Anderson, Brian J.; Johnson, Catherine L.; Korth, Haje; Winslow, Reka M.; Borovsky, Joseph E.; Purucker, Michael E.; Slavin, James A.; Solomon, Sean C.; Zuber, Maria T.; McNutt, Ralph L. Jr.

    2012-01-01

    The structure of Mercury's internal magnetic field has been determined from analysis of orbital Magnetometer measurements by the MESSENGER spacecraft. We identified the magnetic equator on 531 low-altitude and 120 high-altitude equator crossings from the zero in the radial cylindrical magnetic field component, Beta (sub rho). The low-altitude crossings are offset 479 +/- 6 km northward, indicating an offset of the planetary dipole. The tilt of the magnetic pole relative to the planetary spin axis is less than 0.8 deg.. The high-altitude crossings yield a northward offset of the magnetic equator of 486 +/- 74 km. A field with only nonzero dipole and octupole coefficients also matches the low-altitude observations but cannot yield off-equatorial Beta (sub rho) = 0 at radial distances greater than 3520 km. We compared offset dipole and other descriptions of the field with vector field observations below 600 km for 13 longitudinally distributed, magnetically quiet orbits. An offset dipole with southward directed moment of 190 nT-R-cube (sub M) yields root-mean-square (RMS) residuals below 14 nT, whereas a field with only dipole and octupole terms tuned to match the polar field and the low-altitude magnetic equator crossings yields RMS residuals up to 68 nT. Attributing the residuals from the offset-dipole field to axial degree 3 and 4 contributions we estimate that the Gauss coefficient magnitudes for the additional terms are less than 4% and 7%, respectively, relative to the dipole. The axial alignment and prominent quadrupole are consistent with a non-convecting layer above a deep dynamo in Mercury's fluid outer core.

  19. Structural and magnetic properties of electrospun FeCoNi magnetic nanofibers with nanogranular phases

    NASA Astrophysics Data System (ADS)

    Park, Ji Hea; Kweon, Soon C.; Kim, Sang Woo

    2012-02-01

    Structural and magnetic properties of silicon/aluminum-added and -free FeCoNi magnetic alloy nanofibers with nanogranular phases prepared by electrospinning and subsequent annealing of the PVP-blended ternary metal precursors in hydrogen atmosphere were investigated. The FeCoNi magnetic alloy nanofibers with evenly distributed nanocrystalline phases were formed, which are identified as γ-Fe1- x Ni x binary phase with face-centered cubic structure and α-CoFe phase with body-centered cubic structure. At elevated temperature, the α → γ structural martensitic transformation in the FeCoNi ternary alloys occurred due to the inhomogeneities in composition of the matrix during annealing of the alloy with metastable α-phase. In the Si/Al-added FeCoNi nanofibers, more than two phases with complicated-boundaries of the grains in and/or outside the nanofibers were formed as crystalline phases and amorphous phase. The amorphous phase consisted of Si and/or Al acted as an inhibitor diminishing α → γ transformation as well as an interparticle insulation layer. At low annealing temperature of 450 °C, the Si/Al-added nanofiber mainly consisted of metastable α-phase with a low-crystallinity surface structure and very small diameter of 13 nm was formed and showed an unexpectedly high coercivity, which attributed to the surface effects and/or high surface/volume ratio.

  20. Phonon and magnon dispersions of incommensurate spin ladder compound Sr14Cu24O41

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Zhou, Jianshi; Delaire, Olivier; Shi, Li

    There are a variety of compounds consisting of two or more interpenetrating sublattices with lattice periods incommensurate at least along one crystal axis. One example is spin ladder compound Sr14Cu24O41 consisting of incommensurate spin ladder and spin chain sublattices. It has been predicted that unique phonon modes occur in these compounds due to the relative motion of the sublattices. In the low-wavelength limit, there is only one longitudinal acoustic mode due to the rigid translation of both sublattices. In addition, one extra pseudo-acoustic mode is present due to relative sliding motions of the two sublattices. Although the theoretical aspects of the lattice dynamics of incommensurate compounds have been studied, there have been few experimental investigations on their phonon dynamics. In this work, single crystals of Sr14Cu24O41are grown by the traveling solvent floating zone method. The phonon dispersion of Sr14Cu24O41 is studied through inelastic neutron scattering measurements in order to better understand its phonon dynamics. In addition, its magnon dispersion is investigated and correlated to the large directional magnon thermal conductivity. The measurements reveal a wealth of intriguing features on phonons and magnons in the spin ladder compound. This work is supported by ARO MURI program under Award # W911NF-14-1-0016.

  1. Energy harvesting from structural vibrations of magnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Farsangi, Mohammad Amin Askari; Cottone, Francesco; Sayyaadi, Hassan; Zakerzadeh, Mohammad Reza; Orfei, Francesco; Gammaitoni, Luca

    2017-03-01

    This letter presents the idea of scavenging energy from vibrating structures through magnetic shape memory alloy (MSMA). To this end, a MSMA specimen made of Ni50Mn28Ga22 is coupled to a cantilever beam through a step. Two permanent magnets installed at the top and bottom of the beam create a bias field perpendicular to the magnetization axis of the specimen. When vibrating the device, a longitudinal axial load applies on the MSMA, which in turn changes the magnetization, due to the martensitic variant reorientation mechanism. A pick-up coil wounded around the MSMA converts this variation into voltage according to the Faraday's law. Experimental test confirms the possibility of generating voltage in a vibrating MSMA. In particular, 15 μW power is harvested for acceleration of 0.3 g RMS at a frequency of 19.1 Hz, which is comparable with piezoelectric energy harvesters. It is also found that the optimum bias magnetic field for maximum voltage is lower than the starting field of pseudo elastic behavior.

  2. Structural and magnetic properties of nickel antimony ferrospinels

    SciTech Connect

    Ivanov, S. A.; Tellgren, R.; Porcher, F.; Andre, G.; Ericsson, T.; Nordblad, P; Sadovskaya, N.; Kaleva, G.; Politova, E.; Baldini, M.; Sun, C.; Arvanitis, D.; Kumar, P. Anil; Mathieu, R.

    2015-05-05

    Spinel-type compounds of Fe–Ni–Sb–O system were synthesized as polycrystalline powders. The crystal and magnetic properties were investigated using X-ray and neutron powder diffraction, Mössbauer and X-ray absorption spectroscopy and magnetization measurements. The samples crystallize in the cubic system, space group Fd – 3 m. The distribution of cations between octahedral and tetrahedral sites was refined from the diffraction data sets using constraints imposed by the magnetic, Mössbauer and EDS results and the ionic radii. The cation distribution and the temperature dependence of the lattice parameter (a) and the oxygen positional parameter (u) were obtained. A chemical formula close to Fe0.8Ni1.8Sb0.4O4 was determined, with Sb5+ cations occupying octahedral sites, and Fe3+ and Ni2+ occupying both tetrahedral and octahedral sites. Fe3+ mainly (85/15 ratio) occupy tetrahedral sites, and conversely Ni2+ mainly reside on octahedral ones. The magnetic unit cell is the same as the crystallographic one, having identical symmetry relations. The results indicate that the compounds have a collinear ferrimagnetic structure with antiferromagnetic coupling between the tetrahedral (A) and octahedral (B) sites. Uniquely, the temperature dependence of the net magnetization of this rare earth free ferrimagnet exhibits a compensation point.

  3. Magnetic Structure and Formation of On-disk Coronal Plumes

    NASA Astrophysics Data System (ADS)

    Antonsson, S.; Tiwari, S. K.; Moore, R. L.; Winebarger, A. R.

    2015-12-01

    "Plumes" are feather-like features found on the solar disk, in the plage-like field concentrations of quiet regions. On-disk plumes are analogous to polar/coronal-hole plumes but have not been studied in detail in the past. We research their formation and characteristics, such as lifetime, intensity and magnetic setting at the feet. Atmospheric Imaging Assembly (AIA) images in the 171 Å filter and Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms, both from the Solar Dynamics Observatory (SDO), are analyzed with the IDL SolarSoftWare package and used to study the plumes. We find that on-disk plumes form at the places of converging magnetic fields, and disappear when those fields disperse. However, plumes disappear after nearby events, such as flares, or with the emergence of opposite polarity. The lifetime of each plume tends to be several days, although some appear and disappear within several hours. On-disk plumes outline magnetic fields close to the sun, allowing a better understanding of fine magnetic structures than before. Additionally, since plumes must be heated to around 600,000 K to be visible in 171 Å, their formation and characteristics could tell about how they, and therefore the corona, are heated.

  4. Magnetic monopole interactions: shell structure of meson and baryon states

    SciTech Connect

    Akers, D.

    1986-12-01

    It is suggested that a low-mass magnetic monopole of Dirac charge g = (137/2)e may be interacting with a c-quark's magnetic dipole moment to produce Zeeman splitting of meson states. The mass M/sub 0/ = 2397 MeV of the monopole is in contrast to the 10/sup 16/-GeV monopoles of grand unification theories (GUT). It is shown that shell structure of energy E/sub n/ = M/sub 0/ + 1/4nM/sub 0/... exists for meson states. The presence of symmetric meson states leads to the identification of the shell structure. The possible existence of the 2397-MeV magnetic monopole is shown to quantize quark masses in agreement with calculations of quantum chromodynamics (QCD). From the shell structure of meson states, the existence of two new mesons is predicted: eta(1814 +/- 50 MeV) with I/sup G/(J/sup PC/) = 0/sup +/(0/sup - +/) and eta/sub c/ (3907 +/- 100 MeV) with J/sup PC/ = 0/sup - +/. The presence of shell structure for baryon states is shown.

  5. Electronic Structure and Magnetic Properties of Mixed Clusters.

    NASA Astrophysics Data System (ADS)

    Reddy, Budda V.

    We have investigated the geometry, electronic structure and magnetic properties of low dimensional structures like the clusters and multi-layers. The first part of this work is devoted to studies on the effect of geometry, size, symmetry and dimensionality on the magnetic properties of transition metal elements. The effect of geometry is studied by performing Monte Carlo Simulations in order to investigate the behavior of magnetic moment as a function of field and temperature in antiferromagnetic Cuboctahedral and Icosahedral clusters. Size and symmetry are exploited to reveal giant magnetic moments in 13-atom 4d-clusters of Rh, Ru and Pd. Further, it is shown that dimensionality and size play a very important role in determining the nature of magnetic coupling in Fe layers separated by the spacer layers of Sc, Ti, V, Cr, Co, Ni and Cu. The later part of the thesis is devoted to the study of Met-Car; an unusually stable cage like structure containing 8 Ti and 12 C atoms. The energetics of Ti_8C _{12} are compared with that of the bulk fcc fragments Ti_{14 }C_{13} and the processes that govern the formation of each are illustrated through studies on small clusters of TiC, TiC_2, Ti_2C_2 and Ti_2C_3. The fragmentation patterns of Ti_8C_{12 } are investigated and a special fragment Ti _4C_{12} is shown to possess a huge electron affinity of 4.8 eV. Towards the end, we point the differences in the formation patterns of metal-carbides and metal-nitrides.

  6. Shifting the Starspot Paradigm: Imaging Global Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Roettenbacher, Rachael M.; Monnier, John D.

    2016-01-01

    Stellar magnetism exists in stars across the HR diagram and fuels stellar activity (e.g. flares and starspots). This magnetism affects measurements of fundamental stellar parameters, such as radius and temperature, leading to inaccurate mass and age estimates. In order to better determine stellar parameters, we aim to understand how magnetically-suppressed convection presents as cool regions across the stellar surface. In the standard "spot paradigm" of localized starspots blemishing an otherwise featureless surface, we use precision Kepler data and light curve inversion to study stellar differential rotation and starspot evolution. Contrastingly, by imaging interferometric data collected with the Michigan Infrared Combiner (MIRC) at GSU's Center for High Angular Resolution Astronomy (CHARA) Array, we detect large-scale magnetic structures across the surface of ζ Andromedae. These global regions of suppressed convection cover a large fraction of the surface, likely changing the atmospheric structure of the photosphere and impacting stellar parameter estimates. The large-scale features are at best ambiguous to interpret via established techniques that rely on rotational modulation of spots (e.g. light curve inversion and Doppler imaging). We seek to identify a class of targets where the "spot paradigm" breaks down and gives new insights into a range of phenomena such as long-term changes in flux for active stars, anomalous proper motion of spots derived from precision photometry, and the nature of the stellar dynamo of stars with large convective envelopes.

  7. Unexpected structural and magnetic depth dependence of YIG thin films

    NASA Astrophysics Data System (ADS)

    Cooper, J. F. K.; Kinane, C. J.; Langridge, S.; Ali, M.; Hickey, B. J.; Niizeki, T.; Uchida, K.; Saitoh, E.; Ambaye, H.; Glavic, A.

    2017-09-01

    We report measurements on yttrium iron garnet (YIG) thin films grown on both gadolinium gallium garnet (GGG) and yttrium aluminum garnet (YAG) substrates, with and without thin Pt top layers. We provide three principal results: the observation of an interfacial region at the Pt/YIG interface, we place a limit on the induced magnetism of the Pt layer, and confirm the existence of an interfacial layer at the GGG/YIG interface. Polarized neutron reflectometry (PNR) was used to give depth dependence of both the structure and magnetism of these structures. We find that a thin film of YIG on GGG is best described by three distinct layers: an interfacial layer near the GGG, around 5 nm thick and nonmagnetic, a magnetic "bulk" phase, and a nonmagnetic and compositionally distinct thin layer near the surface. We theorize that the bottom layer, which is independent of the film thickness, is caused by Gd diffusion. The top layer is likely to be extremely important in inverse spin Hall effect measurements, and is most likely Y2O3 or very similar. Magnetic sensitivity in the PNR to any induced moment in the Pt is increased by the existence of the Y2O3 layer; any moment is found to be less than 0.02 μB/atom .

  8. The structural and magnetic properties of dual phase cobalt ferrite.

    PubMed

    Gore, Shyam K; Jadhav, Santosh S; Jadhav, Vijaykumar V; Patange, S M; Naushad, Mu; Mane, Rajaram S; Kim, Kwang Ho

    2017-05-31

    The bismuth (Bi(3+))-doped cobalt ferrite nanostructures with dual phase, i.e. cubic spinel with space group Fd3m and perovskite with space group R3c, have been successfully engineered via self-ignited sol-gel combustion route. To obtain information about the phase analysis and structural parameters, like lattice constant, Rietveld refinement process is applied. The replacement of divalent Co(2+) by trivalent Bi(3+) cations have been confirmed from energy dispersive analysis of the ferrite samples. The micro-structural evolution of cobalt ferrite powders at room temperature under various Bi(3+) doping levels have been identified from the digital photoimages recorded using scanning electron microscopy. The hyperfine interactions, like isomer shift, quadrupole splitting and magnetic hyperfine fields, and cation distribution are confirmed from the Mossbauer spectra. Saturation magnetization is increased with Bi(3+)-addition up to x = 0.15 and then is decreased when x = 0.2. The coercivity is increased from 1457 to 2277 G with increasing Bi(3+)-doping level. The saturation magnetization, coercivity and remanent ratio for x = 0.15 sample is found to be the highest, indicating the potential of Bi(3+)-doping in enhancing the magnetic properties of cobalt ferrite.

  9. Magnetic Field Structure in Molecular Clouds by Polarization Measurements

    NASA Astrophysics Data System (ADS)

    Chen, W. P.; Su, B. H.; Eswaraiah, C.; Pandey, A. K.; Wang, C. W.; Lai, S. P.; Tamura, M.; Sato, S.

    2015-03-01

    We report on a program to delineate magnetic field structure inside molecular clouds by optical and infrared polarization observations. An ordered magnetic field inside a dense cloud may efficiently align the spinning dust grains to cause a detectable level of optical and near-infrared polarization of otherwise unpolarized background starlight due to dichroic extinction. The near-infrared polarization data were taken by SIRPOL mounted on IRSF in SAAO. Here we present the SIRPOL results in RCW 57, for which the magnetic field is oriented along the cloud filaments, and in Carina Nebula, for which no intrinsic polarization is detected in the turbulent environment. We further describe TRIPOL, a compact and efficient polarimer to acquire polarized images simultaneously at g', r', and i' bands, which is recently developed at Nagoya University for adaption to small-aperture telescopes. We show how optical observations probe the translucent outer parts of a cloud, and when combining with infrared observations probing the dense parts, and with millimeter and submillimeter observations to sutdy the central embedded protostar, if there is one, would yield the magnetic field structure on different length scales in the star-formation process.

  10. Structural, dielectric and magnetic properties of Ni substituted zinc ferrite

    NASA Astrophysics Data System (ADS)

    Kumbhar, S. S.; Mahadik, M. A.; Mohite, V. S.; Rajpure, K. Y.; Kim, J. H.; Moholkar, A. V.; Bhosale, C. H.

    2014-08-01

    NixZn1-xFe2O4 ferrite has been synthesized by the ceramic method using Ni CO3, ZnO, Fe2O3 precursors. The influence of Ni content on the structural, morphological, electrical and magnetic properties of NixZn1-xFe2O4 ferrites is studied. The X-ray diffraction (XRD) analysis reveals that the samples are polycrystalline with spinel cubic structure. The SEM images of NixZn1-xFe2O4 ferrite show that the grain size decreases with an increase in the Ni content. The tetrahedral and octahedral vibrations in the samples are studied by IR spectra. Frequency dependence of dielectric constant shows dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. Conduction mechanism due to polarons has been analyzed by measuring the AC conductivity. Impedance spectroscopy is used to study the electrical behavior. Magnetic properties of NixZn1-xFe2O4 are studied by using hysteresis loop measurement. The maximum value of saturation magnetization of 132.8 emu/g obtained for the composition, x=0.8, is attributed to magnetic moment of Fe3+ ions.

  11. Structural and magnetic properties of L10 -FePt nanoparticles aligned by external magnetic field

    NASA Astrophysics Data System (ADS)

    Tamada, Yoshinori; Yamamoto, Shinpei; Nasu, Saburo; Ono, Teruo

    2008-12-01

    We investigated structural and magnetic properties of the easy-axis aligned L10 -FePt nanoparticles by the combined use of x-ray diffraction (XRD), magnetization, and F57e Mössbauer measurements. The L10 -FePt nanoparticles were fixed in a polystyrene matrix by performing free radical polymerization of styrene under an aligning external magnetic field. Mössbauer spectrum of the L10 -FePt nanoparticles/polystyrene composite showed tremendous decrease in the second and fifth absorption lines under the condition that the incident γ ray was parallel to the aligning field. This result indicates that the easy axes of the L10 -FePt nanoparticles in the composite have a strong preferred orientation with a finite distribution. We estimated the distribution of easy-axis orientation by using the Mössbauer hyperfine parameters, which is in good agreement with that determined by the XRD rocking curve.

  12. Synthesis, structural and magnetic characterization of soft magnetic nanocrystalline ternary FeNiCo particles

    NASA Astrophysics Data System (ADS)

    Toparli, Cigdem; Ebin, Burçak; Gürmen, Sebahattin

    2017-02-01

    The present study focuses on the synthesis, microstructural and magnetic properties of ternary FeNiCo nanoparticles. Nanocrystalline ternary FeNiCo particles were synthesized via hydrogen reduction assisted ultrasonic spray pyrolysis method in single step. The effect of precursor concentration on the morphology and the size of particles was investigated. The syntheses were performed at 800 °C. Structure, morphology and magnetic properties of the as-prepared products were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) studies. Scherer calculation revealed that crystallite size of the ternary particles ranged between 36 and 60 nm. SEM and TEM investigations showed that the particle size was strongly influenced by the precursor concentration and Fe, Ni, Co elemental composition of individual particles was homogeneous. Finally, the soft magnetic properties of the particles were observed to be a function of their size.

  13. Magnetic structure and Magnetic transport Properties of Graphene Nanoribbons With Sawtooth Zigzag Edges

    NASA Astrophysics Data System (ADS)

    Wang, D.; Zhang, Z.; Zhu, Z.; Liang, B.

    2014-12-01

    The magnetic structure and magnetic transport properties of hydrogen-passivated sawtooth zigzag-edge graphene nanoribbons (STGNRs) are investigated theoretically. It is found that all-sized ground-state STGNRs are ferromagnetic and always feature magnetic semiconductor properties, whose spin splitting energy gap Eg changes periodically with the width of STGNRs. More importantly, for the STGNR based device, the dual spin-filtering effect with the perfect (100%) spin polarization and high-performance dual spin diode effect with a rectification ratio about 1010 can be predicted. Particularly, a highly effective spin-valve device is likely to be realized, which displays a giant magnetoresistace (MR) approaching 1010%, which is three orders magnitude higher than the value predicted based on the zigzag graphene nanoribbons and six orders magnitude higher than previously reported experimental values for the MgO tunnel junction. Our findings suggest that STGNRs might hold a significant promise for developing spintronic devices.

  14. Effect of substrate rotation on domain structure and magnetic relaxation in magnetic antidot lattice arrays

    SciTech Connect

    Mallick, Sougata; Mallik, Srijani; Bedanta, Subhankar

    2015-08-28

    Microdimensional triangular magnetic antidot lattice arrays were prepared by varying the speed of substrate rotation. The pre-deposition patterning has been performed using photolithography technique followed by a post-deposition lift-off. Surface morphology taken by atomic force microscopy depicted that the growth mechanism of the grains changes from chain like formation to island structures due to the substrate rotation. Study of magnetization reversal via magneto optic Kerr effect based microscopy revealed reduction of uniaxial anisotropy and increase in domain size with substrate rotation. The relaxation measured under constant magnetic field becomes faster with rotation of the substrate during deposition. The nature of relaxation for the non-rotating sample can be described by a double exponential decay. However, the relaxation for the sample with substrate rotation is well described either by a double exponential or a Fatuzzo-Labrune like single exponential decay, which increases in applied field.

  15. High frequency magnetization dynamics of ferromagnetic nano-structures

    NASA Astrophysics Data System (ADS)

    Zohar, Sioan

    effects of magnetization motion in opposite layers of a NiFe/Cu/CoZr "spin valve" have been isolated using ultrafast time-resolved x-ray magnetic circular dichroism (TR-XMCD), a layer-specific probe of dynamics. We first describe our instrumental advances in TR-XMCD, in which we have applied synchronous detection techniques to speed data acquisition, enabling measurements of weak coupling. In these measurements, we observe the CoZr responds to the NiFe precession with an in phase component, typically attributed to interlayer dipolar coupling, and a pi/2 out of phase component which has been attributed to coupling via pure spin currents. We estimate an effective interface mixing conductance of g↑↓eff of 8.68 +/- 1.74 nm-2, very close to what has been observed in epitaxial Fe-based structures. This identification is made subject to the assumption of a phase offset in the Co layer precession, not explained at present. We close with experiments demonstrating the feasibility of TR-XMCD in sub-micron and patterned structures. Synchronous detection techniques have been applied for the first time to measure domain wall motion in micron scale Ni81Fe19 squares.

  16. FLOWS AND WAVES IN BRAIDED SOLAR CORONAL MAGNETIC STRUCTURES

    SciTech Connect

    Pant, V.; Datta, A.; Banerjee, D.

    2015-03-01

    We study the high frequency dynamics in the braided magnetic structure of an active region (AR 11520) moss as observed by the High-Resolution Coronal Imager (Hi-C). We detect quasi-periodic flows and waves in these structures. We search for high frequency dynamics while looking at power maps of the observed region. We find that shorter periodicities (30–60 s) are associated with small spatial scales which can be resolved by Hi-C only. We detect quasi-periodic flows with a wide range of velocities, from 13–185 km s{sup −1}, associated with braided regions. This can be interpreted as plasma outflows from reconnection sites. We also find short period and large amplitude transverse oscillations associated with the braided magnetic region. Such oscillations could be triggered by reconnection or such oscillations may trigger reconnection.

  17. Observation Technique of Surface Magnetic Structure Using Type-I Magnetic Contrast in the Scanning Electron Microscope

    NASA Astrophysics Data System (ADS)

    Kotera, Masatoshi; Katoh, Misao; Suga, Hiroshi

    1995-12-01

    The type-I magnetic contrast in the scanning electron microscope is simulated. The magnetic flux that leaked from the surface magnetic domain is calculated based on the Maxwell equation. Trajectories of secondary electrons emitted from the surface are traced considering this magnetic field and the electric field generated by the secondary electron detector. On the basis of the characteristic variation of the spatial deviation of electrons arriving at the detector, the original domain structure at the specimen surface is estimated.

  18. Multiple-q states and the Skyrmion lattice of the triangular-lattice Heisenberg antiferromagnet under magnetic fields.

    PubMed

    Okubo, Tsuyoshi; Chung, Sungki; Kawamura, Hikaru

    2012-01-06

    Ordering of the frustrated classical Heisenberg model on the triangular lattice with an incommensurate spiral structure is studied under magnetic fields by means of a mean-field analysis and a Monte Carlo simulation. Several types of multiple-q states including the Skyrmion-lattice state is observed in addition to the standard single-q state. In contrast to the Dzyaloshinskii-Moriya interaction driven system, the present model allows both Skyrmions and anti-Skyrmions, together with a new thermodynamic phase where Skyrmion and anti-Skyrmion lattices form a domain state.

  19. MAGNETIC STRUCTURE OF RAPIDLY ROTATING FK COMAE-TYPE CORONAE

    SciTech Connect

    Cohen, O.; Drake, J. J.; Kashyap, V. L.; Korhonen, H.; Elstner, D.; Gombosi, T. I.

    2010-08-10

    We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large-scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field, in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular should lead to an improved understanding of mass and angular momentum loss from such systems.

  20. Magnetic properties and magnetic domain structure of grain-oriented Fe-3%Si steel under compression

    NASA Astrophysics Data System (ADS)

    Perevertov, O.; Schäfer, R.

    2016-09-01

    The influence of an applied compressive stress on the magnetic properties and domain structure in Goss-textured (110) [001] Fe-3%Si steel is studied. The magnetic domains and magnetization processes were observed by longitudinal Kerr microscopy at different levels of compressive stress. With stress increase the domain structure without applied field evolves from 180° slab-like domains along the surface-parallel easy axis first into stress pattern I, then into the checkerboard pattern and finally into stress pattern II, in which all internal domains are oriented along the transverse axes. The magnetization process under compression is realized by surface closure [001] domains that grow into the bulk at the expense of transverse domains. The domain evolution by these three stress patterns is not practically noticeable in hysteresis curves above 10 MPa—they change continuously with the same effective field being valid for curves from 10 to 67 MPa. The comparison with previous measurements under different stress/cutting angle combinations shows that for the prediction of a constricted hysteresis loop it is sufficient to consider the energy difference between surface-parallel and transverse easy axes neglecting details of the spatial organization of transverse domains.

  1. Structure and magnetism in Cr-embedded Co nanoparticles.

    PubMed

    Baker, S H; Kurt, M S; Roy, M; Lees, M R; Binns, C

    2016-02-03

    We present the results of an investigation into the atomic structure and magnetism of 2 nm diameter Co nanoparticles embedded in an antiferromagnetic Cr matrix. The nanocomposite films used in this study were prepared by co-deposition directly from the gas phase, using a gas aggregation source for the Co nanoparticles and a molecular beam epitaxy (MBE) source for the Cr matrix material. Co K and Cr K edge extended x-ray absorption fine structure (EXAFS) experiments were performed in order to investigate atomic structure in the embedded nanoparticles and matrix respectively, while magnetism was investigated by means of a vibrating sample magnetometer. The atomic structure type of the Co nanoparticles is the same as that of the Cr matrix (bcc) although with a degree of disorder. The net Co moment per atom in the Co/Cr nanocomposite films is significantly reduced from the value for bulk Co, and decreases as the proportion of Co nanoparticles in the film is decreased; for the sample with the most dilute concentration of Co nanoparticles (4.9% by volume), the net Co moment was 0.25 μ B/atom. After field cooling to below 30 K all samples showed an exchange bias, which was largest for the most dilute sample. Both the structural and magnetic results point towards a degree of alloying at the nanoparticle/matrix interface, leading to a core/shell structure in the embedded nanoparticles consisting of an antiferromagnetic CoCr alloy shell surrounding a reduced ferromagnetic Co core.

  2. Structural, electronic, and magnetic characteristics of Np2Co17

    NASA Astrophysics Data System (ADS)

    Halevy, I.; Hen, A.; Orion, I.; Colineau, E.; Eloirdi, R.; Griveau, J.-C.; Gaczyński, P.; Wilhelm, F.; Rogalev, A.; Sanchez, J.-P.; Winterrose, M. L.; Magnani, N.; Shick, A. B.; Caciuffo, R.

    2012-01-01

    A previously unknown neptunium-transition-metal binary compound Np2Co17 has been synthesized and characterized by means of powder x-ray diffraction, 237Np Mössbauer spectroscopy, superconducting-quantum-interference-device magnetometry, and x-ray magnetic circular dichroism (XMCD). The compound crystallizes in a Th2Ni17-type hexagonal structure with room-temperature lattice parameters a=8.3107(1) Å and c=8.1058(1) Å. Magnetization curves indicate the occurrence of ferromagnetic order below TC>350 K. Mössbauer spectra suggest a Np3+ oxidation state and give an ordered moment of μNp=1.57(4) μB and μNp=1.63(4) μB for the Np atoms located, respectively, at the 2b and 2d crystallographic positions of the P63/mmc space group. Combining these values with a sum-rule analysis of the XMCD spectra measured at the neptunium M4,5 absorption edges, one obtains the spin and orbital contributions to the site-averaged Np moment [μS=-1.88(9) μB, μL=3.48(9) μB]. The ratio between the expectation value of the magnetic-dipole moment and the spin magnetic moment (mmd/μS=+1.36) is positive as predicted for localized 5f electrons and lies between the values calculated in intermediate-coupling (IC) and jj approximations. The expectation value of the angular part of the spin-orbit-interaction operator is in excellent agreement with the IC estimate. The ordered moment averaged over the four inequivalent Co sites, as obtained from the saturation value of the magnetization, is μCo≃1.6 μB. The experimental results are discussed against the predictions of first-principles electronic-structure calculations based on the spin-polarized local-spin-density approximation plus the Hubbard interaction.

  3. Structural and magnetic properties of some AgF + Salts

    NASA Astrophysics Data System (ADS)

    Casteel, William J.; Lucier, George; Hagiwara, Rika; Borrmann, Horst; Bartlett, Neil

    1992-01-01

    New salts of the one-dimensional chain-cation (Ag-F) n n+ have been prepared, the structural and magnetic properties of which indicate that they are metallic. A single-crystal X-ray structure analysis of AgFBF 4 has established a linear cationic chain, the two Ag-F interatomic distances, at 296 K, being 2.002(3) and 2.009(3) Å. Magnetic susceptibility measurements on the poweder from 6 to 280 K show an approximately temperature-independent paramagnetism (χ M˜180×10 -6 emu mole -1) with no evidence of a Peierls transition in that range. Although the previously known salt, AgFAsF 6, has a kinked cationic chain (with, at 166 K, Ag-F-Ag=143.1(1) o, F-Ag-F=175.8(1) o, Ag-F=1.994(2) and 2.001(2) Å), it also exhibits temperature-independent paramagnetism from 280 down to 63 K, but a sharp drop in susceptibility below that temperature may signify a Peierls transition. AgFAuF 6, which is probably isostructural with AgFAsF 6, is similar to it magnetically. The salt AgFAuF 4 probably contains a linear cationic chain, since it is isostructural with CuFAuF 4, but the salt Ag(AuF 4) 2, like its relative Ag(AgF 4) 2, is a magnetically dilute paramagnet, the magnetic susceptibility of which departs very little from the Curie law between 6 and 280 K.

  4. Complex magnetic order in the kagomé staircase compound Co3V2O8

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Lynn, J. W.; Huang, Q.; Woodward, F. M.; Yildirim, T.; Lawes, G.; Ramirez, A. P.; Rogado, N.; Cava, R. J.; Aharony, A.; Entin-Wohlman, O.; Harris, A. B.

    2006-07-01

    Co3V2O8 (CVO) has a different type of geometrically frustrated magnetic lattice, a kagomé staircase, where the full frustration of a conventional kagomé lattice is partially relieved. The crystal structure consists of two inequivalent (magnetic) Co sites, one-dimensional chains of Co(2) spine sites, linked by Co(1) cross-tie sites. Neutron powder diffraction has been used to solve the basic magnetic and crystal structures of this system, while polarized and unpolarized single crystal diffraction measurements have been used to reveal a rich variety of incommensurate phases, interspersed with lock-in transitions to commensurate phases. CVO initially orders magnetically at 11.3K into an incommensurate, transversely polarized, spin density wave state, with wave vector k=(0,δ,0) with δ=0.55 and the spin direction along the a axis. δ is found to decrease monotonically with decreasing temperature and then locks into a commensurate antiferromagnetic structure with δ=(1)/(2) for 6.9magnetic structure becomes incommensurate again, and the presence of higher-order satellite peaks indicates that the magnetic structure deviates from a simple sinusoid. δ continues to decrease with decreasing temperature and locks in again at δ=(1)/(3) over a narrow temperature range (6.2

  5. Electronic structure and magnetic anisotropy of CrO2

    NASA Astrophysics Data System (ADS)

    Toropova, A.; Kotliar, G.; Savrasov, S. Y.; Oudovenko, V. S.

    2005-05-01

    The problem of importance of strong correlations for the electronic structure, transport, and magnetic properties of half-metallic ferromagnetic CrO2 is addressed by performing density functional electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. It is shown that the corresponding low-temperature experimental data are best fitted without accounting for the Hubbard U corrections. We conclude that the ordered phase of CrO2 is weakly correlated.

  6. Magnetic mirror structure for testing shell-type quadrupole coils

    SciTech Connect

    Andreev, N.; Barzi, E.; Bossert, R.; Chlachidze, G.; Kashikhin, V.S.; Kashikhin, V.V.; Lamm, M.J.; Nobrega, F.; Novitski, I.; Tartaglia, N.; Turrioni, D.; /Fermilab

    2009-10-01

    This paper presents magnetic and mechanical designs and analyses of the quadrupole mirror structure to test single shell-type quadrupole coils. Several quadrupole coils made of different Nb{sub 3}Sn strands, cable insulation and pole materials were tested using this structure at 4.5 and 1.9 K. The coils were instrumented with voltage taps, spot heaters, temperature sensors and strain gauges to study their mechanical and thermal properties and quench performance. The results of the quadrupole mirror model assembly and test are reported and discussed.

  7. Non-superconducting magnet structures for near-term, large fusion experimental devices

    SciTech Connect

    File, J.; Knutson, D.S.; Marino, R.E.; Rappe, G.H.

    1980-10-01

    This paper describes the magnet and structural design in the following American tokamak devices: the Princeton Large Torus (PLT), the Princeton Divertor Experiment (PDX), and the Tokamak Fusion Test Reactor (TFTR). The Joint European Torus (JET), also presented herein, has a magnet structure evolved from several European programs and, like TFTR, represents state of the art magnet and structure design.

  8. 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.

  9. Solitary waves and nonlinear dynamic coherent structures in magnetic metamaterials

    NASA Astrophysics Data System (ADS)

    Tankeyev, A. P.; Smagin, V. V.; Borich, M. A.; Zhuravlev, A. S.

    2009-03-01

    Within the framework of the extended nonlinear Schrödinger equation (ENSE), two types of nonlinear states of magnetization in a ferromagnet-dielectric-metal metamagnetic structure have been obtained and investigated. These states have an internal structure; e.g., a periodic sequence of compound solitons is formed by kink-antikink pairs (shock waves), and coherent periodic breather structures are formed by “bright” quasi-solitons. Conditions have been found under which the envelope of these states is described by a modified Korteweg-de Vries (mKdV) equation. It is shown that the compound solitons are described by an mKdV equation with repulsion, and the breather structures, by an mKdV equation with attraction. It is shown also that the characteristic properties of the solutions are determined by the sign of the group-velocity dispersion rather than by the sign of the group velocity itself. The results obtained can be used for searching new nonlinear dynamic coherent structures, e.g., compound solitons and breathers in high-dispersion magnetic metamaterials.

  10. 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.

  11. The Role of Magnetic Helicity in Structuring the Solar Corona

    NASA Technical Reports Server (NTRS)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2017-01-01

    Two of the most widely observed and striking features of the Suns magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure filament channels is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

  12. 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.

  13. Anisotropic crystal structure of magnetized neutron star crust

    NASA Astrophysics Data System (ADS)

    Baiko, D. A.; Kozhberov, A. A.

    2017-09-01

    Although the crystallized neutron star crust is responsible for many fascinating observational phenomena, its actual microscopic structure in tremendous gravitational and magnetic fields is not understood. Here we show that in a non-uniform magnetic field, three-dimensional ionic Coulomb crystals comprising the crust may stretch or shrink while their electrostatic pressure becomes anisotropic. The pressure depends non-linearly on the magnitude of the stretch, so that a continuous magnetic field evolution may result in an abrupt crystal elongation or contraction. This may provide a trigger for magnetar activity. A phonon-mode instability is revealed, which sets the limits of magnetic field variation beyond which the crystal is destroyed. These limits sometimes correspond to surprisingly large deformations. It is not known what happens to crust matter subjected to a pressure anisotropy exceeding these limits. We hypothesize that the ion system then possesses a long-range order only in one or two dimensions, i.e. becomes a liquid crystal.

  14. Dynamical structure of magnetized dissipative accretion flow around black holes

    NASA Astrophysics Data System (ADS)

    Sarkar, Biplob; Das, Santabrata

    2016-09-01

    We study the global structure of optically thin, advection dominated, magnetized accretion flow around black holes. We consider the magnetic field to be turbulent in nature and dominated by the toroidal component. With this, we obtain the complete set of accretion solutions for dissipative flows where bremsstrahlung process is regarded as the dominant cooling mechanism. We show that rotating magnetized accretion flow experiences virtual barrier around black hole due to centrifugal repulsion that can trigger the discontinuous transition of the flow variables in the form of shock waves. We examine the properties of the shock waves and find that the dynamics of the post-shock corona (PSC) is controlled by the flow parameters, namely viscosity, cooling rate and strength of the magnetic field, respectively. We separate the effective region of the parameter space for standing shock and observe that shock can form for wide range of flow parameters. We obtain the critical viscosity parameter that allows global accretion solutions including shocks. We estimate the energy dissipation at the PSC from where a part of the accreting matter can deflect as outflows and jets. We compare the maximum energy that could be extracted from the PSC and the observed radio luminosity values for several supermassive black hole sources and the observational implications of our present analysis are discussed.

  15. Nano-structured magnetic metamaterial with enhanced nonlinear properties.

    PubMed

    Kobljanskyj, Yuri; Melkov, Gennady; Guslienko, Konstantin; Novosad, Valentyn; Bader, Samuel D; Kostylev, Michael; Slavin, Andrei

    2012-01-01

    Nano-structuring can significantly modify the properties of materials. We demonstrate that size-dependent modification of the spin-wave spectra in magnetic nano-particles can affect not only linear, but also nonlinear magnetic response. The discretization of the spectrum removes the frequency degeneracy between the main excitation mode of a nano-particle and the higher spin-wave modes, having the lowest magnetic damping, and reduces the strength of multi-magnon relaxation processes. This reduction of magnon-magnon relaxation for the main excitation mode leads to a dramatic increase of its lifetime and amplitude, resulting in the intensification of all the nonlinear processes involving this mode. We demonstrate this experimentally on a two-dimensional array of permalloy nano-dots for the example of parametric generation of a sub-harmonic of an external microwave signal. The characteristic lifetime of this sub-harmonic is increased by two orders of magnitude compared to the case of a continuous magnetic film, where magnon-magnon relaxation limits the lifetime.

  16. Nano-structured magnetic metamaterial with enhanced nonlinear properties

    PubMed Central

    Kobljanskyj, Yuri; Melkov, Gennady; Guslienko, Konstantin; Novosad, Valentyn; Bader, Samuel D.; Kostylev, Michael; Slavin, Andrei

    2012-01-01

    Nano-structuring can significantly modify the properties of materials. We demonstrate that size-dependent modification of the spin-wave spectra in magnetic nano-particles can affect not only linear, but also nonlinear magnetic response. The discretization of the spectrum removes the frequency degeneracy between the main excitation mode of a nano-particle and the higher spin-wave modes, having the lowest magnetic damping, and reduces the strength of multi-magnon relaxation processes. This reduction of magnon-magnon relaxation for the main excitation mode leads to a dramatic increase of its lifetime and amplitude, resulting in the intensification of all the nonlinear processes involving this mode. We demonstrate this experimentally on a two-dimensional array of permalloy nano-dots for the example of parametric generation of a sub-harmonic of an external microwave signal. The characteristic lifetime of this sub-harmonic is increased by two orders of magnitude compared to the case of a continuous magnetic film, where magnon-magnon relaxation limits the lifetime. PMID:22745899

  17. CHARACTERISTIC DEPENDENCE OF UMBRAL DOTS ON THEIR MAGNETIC STRUCTURE

    SciTech Connect

    Watanabe, H.; Kitai, R.; Ichimoto, K.

    2009-09-10

    Umbral dots (UDs) were observed in a stable sunspot in NOAA 10944 by the Hinode Solar Optical Telescope on 2007 March 1. The observation program consisted of blue continuum images and spectropolarimetric profiles of Fe I 630 nm line. An automatic detection algorithm for UDs was applied to the 2 hr continuous blue continuum images, and using the obtained data, the lifetime, size, and proper motion of UDs were calculated. The magnetic structure of the sunspot was derived through the inversion of the spectropolarimetric profiles. We calculated the correlations between UD's parameters (size, lifetime, occurrence rate, proper motion) and magnetic fields (field strength, inclination, azimuth), and obtained the following results. (1) Both the lifetime and size of UDs are almost constant regardless of the magnetic field strength at their emergence site. (2) The speed of UDs increases as the field inclination angle at their emergence site gets larger. (3) The direction of movement of UDs is nearly parallel to the direction of the horizontal component of magnetic field in the region with strongly inclined field, while UDs in the region with weakly inclined field show virtually no proper motion. Our results describe the basic properties of magnetoconvection in sunspots. We will discuss our results in comparison to recent magnetohydrodynamic simulations by Schuessler and Voegler and Rempel et al.

  18. Effect of Ta additions on the magnetic structure of permalloy

    NASA Astrophysics Data System (ADS)

    Moghadam, Nassrin Y.; Stocks, G. Malcolm; Kowalewski, M.; Butler, W. H.

    2000-03-01

    Tantalum is widely used in magnetic devices as a buffer layer. However, Ta has deleterious effects on the magnetic properties. Our earlier studies of Ni-rich Ni-Ta alloys using the KKR-CPA method (H. Winter and G. M. Stocks, Phys. Rev.) 27 882 (1983), B. L. Gyorffy, D. D. Johnson, F. J. Pinski, D. M. Nicholson, and G. M. Stocks in Alloy Phase Stability Vol. 163 of NATO ASI Series E: Applied Sciences edited by G. M. Stocks and A. Gonis (Kluwer, Dordrecht) show that, in the ideal random alloy limit, the average magnetic moment vanishes at 12% Ta. Additional studies of a Ta impurity embedded in pure Ni indicate increased supression of the moments on neighboring Ni atoms. Here we present studies of the effect of Ta on moment formation in permalloy (Ni_.8Fe_.2 solid solution) using the KKR-CPA method. We also study the magnetic structure of Ta impurities embedded in permalloy using large supercell models. The calculations are performed using the locally-self-consistent multiple-scattering method (Y. Wang, G. M. Stocks, W. A. Shelton and D. M. C. Nicholson, Phys. Rev. Lett.) 75 2867 (1995).

  19. A facile route to synthesize core/shell structured carbon/magnetic nanoparticles hybrid and their magnetic properties

    SciTech Connect

    Qi, Xiaosi; Xu, Jianle; Zhong, Wei; Du, Youwei

    2015-07-15

    Graphical abstract: Controllable synthesis of core/shell structured carbon/magnetic nanoparticles hybrid and their tunable magnetic properties. - Highlights: • The paper reports a simple route for core/shell structured carbon/magnetic nanoparticles hybrid. • By controlling the temperature, Fe{sub 3}O{sub 4}@CNCs, Fe@HCNTs and Fe@LCNTs were produced selectively. • The magnetic properties of the obtained core/shell structured hybrid could be tuned effectively. - Abstract: By controlling the pyrolysis temperature, core/shell structured Fe{sub 3}O{sub 4}/carbon nanocages, Fe/helical carbon nanotubes and Fe/low helicity of carbon nanotubes could be synthesized selectively over Fe{sub 2}O{sub 3} nanotubes generated by a hydrothermal method. The transmission electron microscopic and scanning electron microscopic investigations revealed that the efficiency of generating core/shell structured hybrid was high, exceeding 90%. Because of the magnetic nanoparticles tightly wrapped in graphitic layers, the obtained core/shell structured hybrids showed high stability and good magnetic properties. And the magnetic properties of the obtained core/shell structured hybrid could be tuned by the decomposition temperature and time. Therefore, a simple, inexpensive and environment-benign route was proposed to produce magnetism-tunable core/shell structured hybrid in large quantities.

  20. Feedback magnetization of ultra-low index irradiative structure

    NASA Astrophysics Data System (ADS)

    Rybin, Oleg; Shulga, Sergey

    2015-10-01

    Ultra-low refractive index irradiative structure is considered. The structure consists of a patch antenna with the metamaterial slab located on top of the antenna, as superstrate. In this study, ultra-low index phenomenon of the irradiative system is associated with improving the directivity of the patch antenna by putting the metamaterial slab on top of the antenna. The last phenomenon, in turn, is associated with the feedback partial magnetization of Iron inclusions of the slab caused by the radiation from the antenna. Mathematical model for evaluating the complex effective relative permittivity of the irradiative structure is developed. Numerical calculations for complex effective relative permittivity of the irradiative structure and real part of the complex effective relative permeability of the metamaterial slab are done in the study.

  1. STRUCTURE OF PROMINENCE LEGS: PLASMA AND MAGNETIC FIELD

    SciTech Connect

    Levens, P. J.; Labrosse, N.; Schmieder, B.; Ariste, A. López

    2016-02-10

    We investigate the properties of a “solar tornado” observed on 2014 July 15, and aim to link the behavior of the plasma to the internal magnetic field structure of the associated prominence. We made multi-wavelength observations with high spatial resolution and high cadence using SDO/AIA, the Interface Region Imaging Spectrograph (IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT) instrument. Along with spectropolarimetry provided by the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires telescope we have coverage of both optically thick emission lines and magnetic field information. AIA reveals that the two legs of the prominence are strongly absorbing structures which look like they are rotating, or oscillating in the plane of the sky. The two prominence legs, which are both very bright in Ca ii (SOT), are not visible in the IRIS Mg ii slit-jaw images. This is explained by the large optical thickness of the structures in Mg ii, which leads to reversed profiles, and hence to lower integrated intensities at these locations than in the surroundings. Using lines formed at temperatures lower than 1 MK, we measure relatively low Doppler shifts on the order of ±10 km s{sup −1} in the tornado-like structure. Between the two legs we see loops in Mg ii, with material flowing from one leg to the other, as well as counterstreaming. It is difficult to interpret our data as showing two rotating, vertical structures that are unrelated to the loops. This kind of “tornado” scenario does not fit with our observations. The magnetic field in the two legs of the prominence is found to be preferentially horizontal.

  2. Structure of Prominence Legs: Plasma and Magnetic Field

    NASA Astrophysics Data System (ADS)

    Levens, P. J.; Schmieder, B.; Labrosse, N.; López Ariste, A.

    2016-02-01

    We investigate the properties of a “solar tornado” observed on 2014 July 15, and aim to link the behavior of the plasma to the internal magnetic field structure of the associated prominence. We made multi-wavelength observations with high spatial resolution and high cadence using SDO/AIA, the Interface Region Imaging Spectrograph (IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT) instrument. Along with spectropolarimetry provided by the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires telescope we have coverage of both optically thick emission lines and magnetic field information. AIA reveals that the two legs of the prominence are strongly absorbing structures which look like they are rotating, or oscillating in the plane of the sky. The two prominence legs, which are both very bright in Ca ii (SOT), are not visible in the IRIS Mg ii slit-jaw images. This is explained by the large optical thickness of the structures in Mg ii, which leads to reversed profiles, and hence to lower integrated intensities at these locations than in the surroundings. Using lines formed at temperatures lower than 1 MK, we measure relatively low Doppler shifts on the order of ±10 km s-1 in the tornado-like structure. Between the two legs we see loops in Mg ii, with material flowing from one leg to the other, as well as counterstreaming. It is difficult to interpret our data as showing two rotating, vertical structures that are unrelated to the loops. This kind of “tornado” scenario does not fit with our observations. The magnetic field in the two legs of the prominence is found to be preferentially horizontal.

  3. Magnetic ordering and dielectric relaxation in the double perovskite YBaCuFeO5.

    PubMed

    Lai, Yen-Chung; Du, Chao-Hung; Lai, Chun-Hao; Liang, Yu-Hui; Wang, Chin-Wei; Rule, Kirrily C; Wu, Hung-Cheng; Yang, Hung-Duen; Chen, Wei-Tin; Shu, G J; Chou, F-C

    2017-04-12

    Using magnetization, dielectric constant, and neutron diffraction measurements on a high quality single crystal of YBaCuFeO5 (YBCFO), we demonstrate that the crystal shows two antiferromagnetic transitions at [Formula: see text] K and [Formula: see text] K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at T N2. It does not show the evidence of the electric polarization for the crystal used for this study. The transition at T N1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Upon cooling, at T N2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of ([Formula: see text] [Formula: see text] [Formula: see text]), where [Formula: see text], [Formula: see text], and [Formula: see text] are odd, and the incommensurability δ is temperature dependent. Around the transition boundary at T N2, both commensurate and incommensurate spin ordering coexist.

  4. Magnetic ordering and dielectric relaxation in the double perovskite YBaCuFeO5

    NASA Astrophysics Data System (ADS)

    Lai, Yen-Chung; Du, Chao-Hung; Lai, Chun-Hao; Liang, Yu-Hui; Wang, Chin-Wei; Rule, Kirrily C.; Wu, Hung-Cheng; Yang, Hung-Duen; Chen, Wei-Tin; Shu, G. J.; Chou, F.-C.

    2017-04-01

    Using magnetization, dielectric constant, and neutron diffraction measurements on a high quality single crystal of YBaCuFeO5 (YBCFO), we demonstrate that the crystal shows two antiferromagnetic transitions at {{T}N1}∼ 475 K and {{T}N2}∼ 175 K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at T N2. It does not show the evidence of the electric polarization for the crystal used for this study. The transition at T N1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Upon cooling, at T N2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of (\\frac{h}{2} \\frac{k}{2} \\frac{l}{2}+/- δ ), where h , k , and l are odd, and the incommensurability δ is temperature dependent. Around the transition boundary at T N2, both commensurate and incommensurate spin ordering coexist.

  5. Magnetic structures in potential multiferroic GdCrO3

    NASA Astrophysics Data System (ADS)

    Manuel, Pascal; Chapon, Laurent; Khalyavin, Dmitry; Xueyun, Wang; Cheong, Sang-Wook

    2015-03-01

    For the past decade, multiferroics materials have atracted a lot of attention in the condensed matter community because of potential applications for devices. A somewhat ambiguous addition to the multiferroics family was recently reported in the peroskite based GdCrO3 in both bulk and thin film samples. Indeed, ferroelectricity was evidenced by a strong enhancement of the capacitance in a field but significant leakage and no well developed P-E hysteresis blurred the picture. Our own measurements clearly indicate the existence of a polar phase below 2K. To complete the understanding of this material, the determination of the magnetic structure is required but is hampered by the fact Gd is a strong neutron absorber. We will present some neutron diffraction data collected on an isotopic 160GdCrO3 sample at the WISH diffractometer at ISIS which confirm the presence of three successive magnetic phases, previously only seen by magnetization, as a function of temperature. We will compare our determined structures against predictions based on group theoretical considerations and experimental work on other rare-earth ortho-chromates and discuss the mechanism for multiferroicity.

  6. Magnetic and structural aspects of semiconducting perovskites RVO 3

    NASA Astrophysics Data System (ADS)

    Onoda, Masashige; Nagasawa, Hiroshi

    1996-08-01

    Magnetic and structural aspects of the perovskite system RVO 3 ( R = La, Ce, Pr and Nd) with V 3+ ions have been studied by the measurements of X-ray diffraction, electrical resistivity and magnetization. In LaVO 3, besides the antiferromagnetic transition at 147 K and the sharp change in the lattice constants around 140 K, there existed anomalies at 270 K and 670 K for the paramagnetic state. A high temperature series expansion analysis gave the antiferromagnetic exchange constant of 43 K. In CeVO 3, PrVO 3 and NdVO 3, the remanent magnetization essentially originated from the antisymmetric interaction of V ions appeared at about 150 K. There was the gradual change in the lattice constants of the last two compounds between 130 K and 200 K. Unusual temperature dependence of the remanence was observed and qualitatively understood from the molecular field of canted moment acting on the 4 f spins of R ions. At low temperatures, there was observed the peak of reversible susceptibility in CeVO 3 and PrVO 3 that was suggestive of additional structural transition.

  7. Electronic structure theory of wide gap dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Ye, Linhui; Freeman, A. J.

    2007-03-01

    The recent exciting reports that wide gap semiconductors, most notably ZnO, TiO2 and GaN, when doped with transition metal elements, may have Tc's that are higher than room temperature have attracted great interest. When interpreted with care, highly precise first principles FLAPW calculations such as used here, are now providing insights into the nature of their strong ferromagnetism (FM). Here, we present an analysis to the electronic structures of several typical wide gap DMS's and illustrate how first principles calculations can lead to correct predictions of their magnetic properties for both Cr:TiO2 and Mn:GaN. The results demonstrate the importance of defect compensation in the determination of the magnetism. A comparison between Mn:ZnO and Co:ZnO highlights the fundamental difference in their electronic structures which explains why their FM is dependent on carriers of different polarity. Correct predictions of their magnetism are found to be due to the correct treatment of the LDA band gap problem. Finally, we provide semi-quantitative discussions of Co doped TiO2, and illustrate why it is highly non- trivial to fully explain its FM based on first principles calculations. E.Wimmer,H.Krakauer,M.Weinert,A.J.Freeman, PRB 24, 864(1981)

  8. Welding process selection for fabrication of a superconducting magnet structure

    SciTech Connect

    Goodwin, G.M.

    1985-08-01

    The magnets that will provide containment of the intensely hot plasma in fusion reactors must be wound with superconductors to enable these reactors to produce more energy than they consume (Ref. 1). With current superconductor technology, this requires the use of liquid helium at its boiling point (about 4 K, or -269/sup 0/C) as a coolant. At this temperature, all other known materials are solid. Austenitic stainless steels are the most widely used alloys for structural applications below 77 K (-196/sup 0/C) (Ref. 2). Their physical properties offer advantages over those of competing materials; the elastic modulus is high, and the thermal expansion, magnetic permeability, and electrical and thermal conductivities are low. Their mechanical properties, including strength, ductility and fracture toughness, are generally adequate to withstand the large forces imposed on magnet structures reliably. A possible exception to this statement arises in the case of weldments; the limited 4 K (-269/sup 0/C) fracture toughness data for austenitic stainless steel weld metal show a wide range of values, with no obvious explanation for the large differences. This report summarizes the data available in the literature, contributes new data for three different welding processes - gas tungsten arc (GTAW), shielded metal arc (SMAW) and flux cored arc (FCAW) - and offers some observations of the fracture morphology.

  9. Effect of annealing on magnetic properties and structure of Fe-Ni based magnetic microwires

    NASA Astrophysics Data System (ADS)

    Zhukova, V.; Korchuganova, O. A.; Aleev, A. A.; Tcherdyntsev, V. V.; Churyukanova, M.; Medvedeva, E. V.; Seils, S.; Wagner, J.; Ipatov, M.; Blanco, J. M.; Kaloshkin, S. D.; Aronin, A.; Abrosimova, G.; Orlova, N.; Zhukov, A.

    2017-07-01

    We studied the magnetic properties and domain wall (DW) dynamics of Fe47.4Ni26.6Si11B13C2 and Fe77.5Si7.5B15 microwires. Both samples present rectangular hysteresis loop and fast magnetization switching. Considerable enhancement of DW velocity is observed in Fe77.5Si7.5B15, while DW velocity of samples Fe47.4Ni26.6Si11B13C2 is less affected by annealing. The other difference is the magnetic field range of the linear region on dependence of domain wall velocity upon magnetic field: in Fe47.4Ni26.6Si11B13C2 sample is considerably shorter and drastically decreases after annealing. We discussed the influence of annealing on DW dynamics considering different magnetoelastic anisotropy of studied microwires and defects within the amorphous state in Fe47.4Ni26.6Si11B13C2. Consequently we studied the structure of Fe47.4Ni26.6Si11B13C2 sample using X-ray diffraction and the atom probe tomography. The results obtained using the atom probe tomography supports the formation of the B-depleted and Si-enriched precipitates in the metallic nucleus of Fe-Ni based microwires.

  10. Structural and Magnetic Response in Bimetallic Core/Shell Magnetic Nanoparticles

    PubMed Central

    Nairan, Adeela; Khan, Usman; Iqbal, Munawar; Khan, Maaz; Javed, Khalid; Riaz, Saira; Naseem, Shahzad; Han, Xiufeng

    2016-01-01

    Bimagnetic monodisperse CoFe2O4/Fe3O4 core/shell nanoparticles have been prepared by solution evaporation route. To demonstrate preferential coating of iron oxide onto the surface of ferrite nanoparticles X-ray diffraction (XRD), High resolution transmission electron microscope (HR-TEM) and Raman spectroscopy have been performed. XRD analysis using Rietveld refinement technique confirms single phase nanoparticles with average seed size of about 18 nm and thickness of shell is 3 nm, which corroborates with transmission electron microscopy (TEM) analysis. Low temperature magnetic hysteresis loops showed interesting behavior. We have observed large coercivity 15.8 kOe at T = 5 K, whereas maximum saturation magnetization (125 emu/g) is attained at T = 100 K for CoFe2O4/Fe3O4 core/shell nanoparticles. Saturation magnetization decreases due to structural distortions at the surface of shell below 100 K. Zero field cooled (ZFC) and Field cooled (FC) plots show that synthesized nanoparticles are ferromagnetic till room temperature and it has been noticed that core/shell sample possess high blocking temperature than Cobalt Ferrite. Results indicate that presence of iron oxide shell significantly increases magnetic parameters as compared to the simple cobalt ferrite. PMID:28335200

  11. Structural and Magnetic Response in Bimetallic Core/Shell Magnetic Nanoparticles.

    PubMed

    Nairan, Adeela; Khan, Usman; Iqbal, Munawar; Khan, Maaz; Javed, Khalid; Riaz, Saira; Naseem, Shahzad; Han, Xiufeng

    2016-04-14

    Bimagnetic monodisperse CoFe₂O₄/Fe₃O₄ core/shell nanoparticles have been prepared by solution evaporation route. To demonstrate preferential coating of iron oxide onto the surface of ferrite nanoparticles X-ray diffraction (XRD), High resolution transmission electron microscope (HR-TEM) and Raman spectroscopy have been performed. XRD analysis using Rietveld refinement technique confirms single phase nanoparticles with average seed size of about 18 nm and thickness of shell is 3 nm, which corroborates with transmission electron microscopy (TEM) analysis. Low temperature magnetic hysteresis loops showed interesting behavior. We have observed large coercivity 15.8 kOe at T = 5 K, whereas maximum saturation magnetization (125 emu/g) is attained at T = 100 K for CoFe₂O₄/Fe₃O₄ core/shell nanoparticles. Saturation magnetization decreases due to structural distortions at the surface of shell below 100 K. Zero field cooled (ZFC) and Field cooled (FC) plots show that synthesized nanoparticles are ferromagnetic till room temperature and it has been noticed that core/shell sample possess high blocking temperature than Cobalt Ferrite. Results indicate that presence of iron oxide shell significantly increases magnetic parameters as compared to the simple cobalt ferrite.

  12. The Structure of the Separatix in Collisionless Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Daughton, W.; Scudder, J.; Karimabadi, H.

    2005-12-01

    Recent kinetic simulations of magnetic reconnection indicate the formation of intense electrostatic fields that start at the x-point and form sheet-like structures that extend outward for large distances along the separatrices. In the presence of a significant guide field, the characteristic thickness of these layers is on the order of the local electron gyroradius and there are significant deviations from charge neutrality within the layer. The resulting electrostatic fields are primarily perpendicular and may exceed the reconnection electric field by a factor of 20. A serious impediment to understanding the possible role of these structures is the use of periodic boundary conditions typically employed in kinetic simulations. In particular, the strong outward electron flow generated along one leg of a separatrix is allowed to circulate back through the system along the opposite side. This recirculation may artificially enhance beam driven instabilities and/or strongly modify the structure of the separatrix. In this work, we describe initial efforts to employ open boundary conditions in 2D fully kinetic PIC simulations, with the goal of better understanding the structure and role of the separatrix in collisionless magnetic reconnection.

  13. Regulated magnetic domains and high-frequency property in magnetic materials with columnar structure

    NASA Astrophysics Data System (ADS)

    Zhou, Cai; Wei, Wenwen; Jiang, Changjun

    2015-10-01

    The regulation of magnetic domains and high-frequency property in Fe20Ni80 thin films sputtered on anodic aluminum oxide (AAO) substrates with different apertures and a Si substrate were investigated. The obvious stripe domain structure was observed in FeNi thin film sputtered on AAO (pore in diameter d ~ 20 nm) substrate. The distinct cross-sectional columnar structures prepared on three different substrates and measured by scanning electron microscope were shown, which arose from different growth mechanisms on various kinds of substrates. The structure of AAO substrate could modulate the growth mechanism of thin films and the appearance of stripe domains structure. In addition, the resonant frequency was enhanced in FeNi thin film prepared on AAO ( d ~ 20 nm) substrate.

  14. X-ray studies of flaring magnetic structures

    NASA Astrophysics Data System (ADS)

    Goff, Christopher Philip

    This thesis studies non-thermal emission from flaring magnetic structures by looking at HXR emission from flare footpoints at a faint X-ray source above a flare loop and finally at radio emission generated by eruptions. By complementing high quality data from recent missions with data from older instrumentation, studies were performed to compare with accepted models. The relation between Hard X-ray footpoint emission and magnetic field strength in a sample of 32 flares was studied in order to investigate the effects of the magnetic field on the transport of accelerated electrons. It was found that one third of compact flares studied had stronger footpoints in stronger magnetic regions whereas the reverse is anticipated from magnetic trapping arguments. On 16th April 2002, a limb flare was studied in many wavelengths. This provided an opportunity to study an erupting filament from the low corona and into interplanetary space. RHESSI identified a moving X-ray source associated with a rising filament, confirming the plasmoid definition of Tsuneta (1997). The velocity profile of the filament was determined along with its exponential acceleration. This suggested that an instability was responsible for eruption, possibly the kink instability. Doppler shifts were observed on either side of the filament as it crossed the slit field of view, suggesting helical flows and thus a flux rope. A succession of quadrupolar flares, followed by an LDE were then studied. An associated CME was seen and appeared linked to the quadrupolar flares which should re main confined. The flaring region triggered loop expansion, which interacted with a neighbouring large-scale streamer. This led to a fast CME front, which weakened the restraining field above the active region filaments allowing a partial filament eruption. Although at first glance the observations appeared contradictory it was demonstrated that the quadrupolar flares remained confined while triggering a large-scale eruption.

  15. Electronic structure and magnetic phase transition in MnSi

    NASA Astrophysics Data System (ADS)

    Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.

    2017-07-01

    Temperature variations of the amplitude of zero-point and thermal spin fluctuations in a helicoidal ferromagnetic (MnSi) are characterized using the electronic structure model that follows from ab initio LDA + U + SO calculations. It is found that a drastic reduction in the amplitude of zero-point spin fluctuations at temperature T S (in the vicinity of the magnetic phase transition) leads to ferromagnetic solution instability (a change in the sign of the intermode interaction parameter). The observed magnetovolume effect and a sharp change in the radius of spin correlations have the same underlying cause. The results of calculation of the volumetric coefficient of thermal expansion agree well with the observed anomaly in the region of the magnetic phase transition.

  16. Magnetic field adjustment structure and method for a tapered wiggler

    DOEpatents

    Halbach, Klaus

    1988-03-01

    An improved method and structure is disclosed for adjusting the magnetic field generated by a group of electromagnet poles spaced along the path of a charged particle beam to compensate for energy losses in the charged particles which comprises providing more than one winding on at least some of the electromagnet poles; connecting one respective winding on each of several consecutive adjacent electromagnet poles to a first power supply, and the other respective winding on the electromagnet pole to a different power supply in staggered order; and independently adjusting one power supply to independently vary the current in one winding on each electromagnet pole in a group whereby the magnetic field strength of each of a group of electromagnet poles may be changed in smaller increments.

  17. Magnetic field adjustment structure and method for a tapered wiggler

    SciTech Connect

    Halbach, Klaus

    1988-01-01

    An improved method and structure is disclosed for adjusting the magnetic field generated by a group of electromagnet poles spaced along the path of a charged particle beam to compensate for energy losses in the charged particles which comprises providing more than one winding on at least some of the electromagnet poles; connecting one respective winding on each of several consecutive adjacent electromagnet poles to a first power supply, and the other respective winding on the electromagnet pole to a different power supply in staggered order; and independently adjusting one power supply to independently vary the current in one winding on each electromagnet pole in a group whereby the magnetic field strength of each of a group of electromagnet poles may be changed in smaller increments.

  18. Structure of ferrofluid nanofilms in homogeneous magnetic fields.

    PubMed

    Jordanovic, Jelena; Klapp, Sabine H L

    2009-02-01

    We report molecular dynamics simulations results for model ferrofluid films subject to an external, homogeneous magnetic field directed parallel or perpendicular to the film surfaces. The interactions between the magnetic nanoparticles are modeled via the Stockmayer potential. In a previous study [J. Jordanovic and S. H. L. Klapp, Phys. Rev. Lett. 101, 038302 (2008)] we have shown that an external field can control the number and internal structure of the layers characterizing the fluid films, in qualitative agreement with experiments. Here we explore the dependence of the layering effects on thermodynamic conditions, and we analyze the results from an energetic (microscopic and macroscopic) perspective. As a special case we investigate a monolayer to bilayer transition induced via a perpendicular field.

  19. Structure of ferrofluid nanofilms in homogeneous magnetic fields

    NASA Astrophysics Data System (ADS)

    Jordanovic, Jelena; Klapp, Sabine H. L.

    2009-02-01

    We report molecular dynamics simulations results for model ferrofluid films subject to an external, homogeneous magnetic field directed parallel or perpendicular to the film surfaces. The interactions between the magnetic nanoparticles are modeled via the Stockmayer potential. In a previous study [J. Jordanovic and S. H. L. Klapp, Phys. Rev. Lett. 101, 038302 (2008)] we have shown that an external field can control the number and internal structure of the layers characterizing the fluid films, in qualitative agreement with experiments. Here we explore the dependence of the layering effects on thermodynamic conditions, and we analyze the results from an energetic (microscopic and macroscopic) perspective. As a special case we investigate a monolayer to bilayer transition induced via a perpendicular field.

  20. The Role of Magnetic Helicity in Structuring the Solar Corona

    NASA Astrophysics Data System (ADS)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2017-01-01

    Two of the most widely observed and striking features of the Sun's magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure—filament channels—is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.