Science.gov

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 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.

  3. 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.

  4. 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.

  5. 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 .

  6. 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.

  7. 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.

  8. Magnetic Incommensurability in p-TYPE Cuprate Perovskites

    NASA Astrophysics Data System (ADS)

    Sherman, A.

    2012-07-01

    For the superconducting phase with a d-wave order parameter and zero temperature, the magnetic susceptibility of the t-J model is calculated using the Mori projection operator technique. Conditions for the appearance of an incommensurate magnetic response below the resonance frequency are identified. A fast decay of the tails of the hole coherent peaks and a weak intensity of the hole incoherent continuum near the Fermi level are enough to produce an incommensurate response using different hole dispersions established for p-type cuprates, in which such response was observed. In this case, the nesting of the itinerant-electron theory or the charge modulation of the stripe theory is unnecessary for the incommensurability. The theory reproduces the hourglass dispersion of the susceptibility maxima with their location in the momentum space similar to that observed experimentally. The upper branch of the dispersion stems from the excitations of localized spins, while the lower one is due to the incommensurate maxima of their damping. The narrow and intensive resonance peak arises if the frequency of these excitations at the antiferromagnetic momentum lies below the edge of the two-fermion continuum; otherwise the maximum is broad and less intensive.

  9. 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.

  10. 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).

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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}

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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}.

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  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. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  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. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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…

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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)].

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.}.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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.

  14. 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}.

  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. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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).

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. High performance hybrid magnetic structure for biotechnology applications

    DOEpatents

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

    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.

  17. 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.

  18. 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.

  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. 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.

  1. 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

  2. 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 ).

  3. 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.

  4. 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*.

  5. 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.

  6. 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

  7. 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

  8. 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).

  9. 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.

  10. 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)

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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)

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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.

  14. [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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. Magnetic structures of nanometer scale Dy, Cr and Ni

    SciTech Connect

    Fitzsimmons, M.R.; Robinson, R.A.; Lawson, A.C.; Kwei, G.H.; Sickafus, K.E. ); Eastman, J.A. ); Burkel, E. . Sektion Physik, Lehrstuhl Peisl)

    1992-10-01

    Materials composed of nanometer-sized structures are becoming technologically relevant as the sizes of electronic devices approach the nanometer scale. Questions as to the performance and durability of these devices can be partially addressed through the characterization and understanding of the magnetic structures and properties of nanometer-sized materials. The purpose of the present work is to understand the relationship between the microstructure of nanocrystalline materials and their magnetic structures and properties. This paper summarizes three separate experiments: (1) an X-ray diffraction and anomalous absorption (XANES) study of nanocrystalline Dy, (2) neutron diffraction measurements of the magnetic structure of nanocrystalline Cr, and (3) the measurement of the magnetization density of a single twist grain boundary in Ni.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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…

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. Muslim Education and Its (In)commensurability with Multiculturalism: Some Thoughts on the Imaginative Madrassah

    ERIC Educational Resources Information Center

    Waghid, Yusef; Davids, Nuraan

    2014-01-01

    Muslim education is not incommensurate with multiculturalism and, hence, does not pose a threat to multiculturalism at all. If Muslim education were to be perceived as a risk to multiculturalism then either such a form of education is not conceived appropriately or the claims of multiculturalism are false. Instead, the authors argue that Muslim…

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Magnetic structure of La8Cu7O19

    NASA Astrophysics Data System (ADS)

    Prokeš, K.; Ressouche, E.; Mohan, A.; Wolter, A. U. B.; Büchner, B.; Hess, C.

    2017-01-01

    The magnetic structure of the five-leg ladder compound La8Cu7O19 has been determined using single crystalline neutron diffraction. The material orders antiferromagnetically with the propagation vector q =(1/2 ,1/2 ,0 ) below TN=102.5 (3 ) K . Above this temperature the magnetic susceptibility corresponds indeed to that of a five-leg S =1 /2 spin ladder, assuming isotropic couplings along the rungs and the legs [J /kB=J'/kB=194 (3 ) K ] . Crystallographically, the Cu magnetic moments divide into two subsystems, depending on the environment. Moments situated at centers of octahedra built up by oxygens orient along the b axis and couple to neighboring moments antiferromagnetically, whereas those creating a complicated ribbon structure possess all three Cartesian components. All Cu moments are found to have magnitudes between 0.69 and 1.32 μB . Thus, it is seen that the five-leg ladder La8Cu7O19 exhibits long-range antiferromagnetic ordering and possesses a rather complicated magnetic structure which has a noncollinear character.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Structure and magnetic properties of nanostructured Ni-ferrite

    NASA Astrophysics Data System (ADS)

    Albuquerque, A. S.; Ardisson, J. D.; Macedo, W. A. A.; López, J. L.; Paniago, R.; Persiano, A. I. C.

    2001-05-01

    The structural and magnetic properties of NiFe 2O 4 ultrafine powders synthesized by coprecipitation, a nonconventional method of preparation, were investigated. The samples were obtained by annealing at relatively low temperatures (300-600°C) and characterized by X-ray diffraction, Mössbauer spectroscopy, and vibrating sample magnetometry. The average particle diameter ranges from 4 to 15 nm, as determined by X-ray diffraction. All nanometric powder samples presented strong superparamagnetic relaxation at room temperature and reduced magnetic hyperfine fields at -193°C. Magnetometry measurements indicated different magnetic behavior related with crystallinity of samples, coercivity as high as 168 Oe at 27°C, value that is nearly two times higher than coercivity of bulk Ni-ferrite.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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)

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Microfabricated magnetic structures for future medicine: from sensors to cell actuators.

    PubMed

    Vitol, Elina A; Novosad, Valentyn; Rozhkova, Elena A

    2012-10-01

    In this review, we discuss the prospective medical application of magnetic carriers microfabricated by top-down techniques. Physical methods allow the fabrication of a variety of magnetic structures with tightly controlled magnetic properties and geometry, which makes them very attractive for a cost-efficient mass-production in the fast growing field of nanomedicine. Stand-alone fabricated particles along with integrated devices combining lithographically defined magnetic structures and synthesized magnetic tags will be considered. Applications of microfabricated multifunctional magnetic structures for future medicinal purposes range from ultrasensitive in vitro diagnostic bioassays, DNA sequencing and microfluidic cell sorting to magnetomechanical actuation, cargo delivery, contrast enhancement and heating therapy.

  10. A Novel Integrated Structure with a Radial Displacement Sensor and a Permanent Magnet Biased Radial Magnetic Bearing

    PubMed Central

    Sun, Jinji; Zhang, Yin

    2014-01-01

    In this paper, a novel integrated structure is proposed in order to reduce the axial length of the high speed of a magnetically suspended motor (HSMSM) to ensure the maximum speed, which combines radial displacement sensor probes and the permanent magnet biased radial magnetic bearing in HSMSM. The sensor probes are integrated in the magnetic bearing, and the sensor preamplifiers are placed in the control system of the HSMSM, separate from the sensor probes. The proposed integrated structure can save space in HSMSMs, improve the working frequency, reduce the influence of temperature on the sensor circuit, and improve the stability of HSMSMs. PMID:24469351

  11. A novel integrated structure with a radial displacement sensor and a permanent magnet biased radial magnetic bearing.

    PubMed

    Sun, Jinji; Zhang, Yin

    2014-01-24

    In this paper, a novel integrated structure is proposed in order to reduce the axial length of the high speed of a magnetically suspended motor (HSMSM) to ensure the maximum speed, which combines radial displacement sensor probes and the permanent magnet biased radial magnetic bearing in HSMSM. The sensor probes are integrated in the magnetic bearing, and the sensor preamplifiers are placed in the control system of the HSMSM, separate from the sensor probes. The proposed integrated structure can save space in HSMSMs, improve the working frequency, reduce the influence of temperature on the sensor circuit, and improve the stability of HSMSMs.

  12. Structures of diffusion regions in collisionless magnetic reconnection

    SciTech Connect

    Umeda, Takayuki; Togano, Kentaro; Ogino, Tatsuki

    2010-05-15

    Detailed structures of diffusion regions in two-dimensional collisionless magnetic reconnection are studied by using an electromagnetic Vlasov simulation. It has been well known that plasma number density decreases near the X-point of the reconnection. However, numerical thermal fluctuations exist in particle-in-cell simulations, and there is a possibility that detailed structures near the X-point diffuse numerically when the number of particles per cell is not enough. In the present study, a high-resolution two-dimensional Vlasov simulation is performed. It is found that electron number density in the electron diffusion region decreases to a hundredth of the initial value. Structures of electron diffusion region are determined by the local electron inertial length.

  13. Measurement of the Structural Unit in magnetic dispersions

    NASA Astrophysics Data System (ADS)

    Mercer, T.; Bissell, P. R.

    2013-01-01

    Measurement of the Structural Unit (SU - containing both the solid phase and trapped­fluid within their associated structures) in magnetic dispersions has been carried out using Hindered Settling (HS) analysis that uses scanning column magnetometry and cone & plate rheology techniques. From this, an equivalent Stokes' particle diameter, d, of (5.2 ≤ d ≤ 8.2) microns was determined that is approximately 22 times larger than the iron oxide particles of our formulation. A previous computer simulation based on HS theory produces complete concentration­height profiles of the sedimenting system over time that compare well when using a correspondingly large trapped­liquid fraction of around the 84% of the SU volume determined here, giving confidence in the result. As interest in iron oxide suspensions for potential biomedical and chemical decontamination/catalysis applications continues to grow an understanding of their structures is likely to become increasingly important.

  14. Sharp magnetic structures from dynamos with density stratification

    NASA Astrophysics Data System (ADS)

    Jabbari, Sarah; Brandenburg, Axel; Kleeorin, Nathan; Rogachevskii, Igor

    2017-01-01

    Recent direct numerical simulations (DNS) of large-scale turbulent dynamos in strongly stratified layers have resulted in surprisingly sharp bipolar structures at the surface. Here we present new DNS of helically and non-helically forced turbulence with and without rotation and compare with corresponding mean-field simulations (MFS) to show that these structures are a generic outcome of a broader class of dynamos in density-stratified layers. The MFS agree qualitatively with the DNS, but the period of oscillations tends to be longer in the DNS. In both DNS and MFS, the sharp structures are produced by converging flows at the surface and might be driven in nonlinear stage of evolution by the Lorentz force associated with the large-scale dynamo-driven magnetic field if the dynamo number is at least 2.5 times supercritical.

  15. Cryogenic expansion joint for large superconducting magnet structures

    DOEpatents

    Brown, Robert L.

    1978-01-01

    An expansion joint is provided that accommodates dimensional changes occurring during the cooldown and warm-up of large cryogenic devices such as superconducting magnet coils. Flattened tubes containing a refrigerant such as gaseous nitrogen (N.sub.2) are inserted into expansion spaces in the structure. The gaseous N.sub.2 is circulated under pressure and aids in the cooldown process while providing its primary function of accommodating differential thermal contraction and expansion in the structure. After lower temperatures are reached and the greater part of the contraction has occured, the N.sub.2 liquefies then solidifies to provide a completely rigid structure at the cryogenic operating temperatures of the device.

  16. Constructing the Coronal Magnetic Field by Correlating Parameterized Magnetic Field Lines with Observed Coronal Plasma Structures

    NASA Technical Reports Server (NTRS)

    Allen, Gary G.; Alexander, David

    1999-01-01

    A method is presented for constructing the coronal magnetic field from photospheric magnetograms and observed coronal loops. A set of magnetic field lines generated from magnetogram data is parameterized and then deformed by varying the parameterized values. The coronal flux tubes associated with this field are adjusted until the correlation between the field lines and the observed coronal loops is maximized. A mathematical formulation is described which ensures that (1) the normal component of the photospheric field remains unchanged, (2) the field is given in the entire corona over an active region, (3) the field remains divergence-free, and 4electric currents are introduced into the field. It is demonstrated that a parameterization of a potential field, comprising a radial stretching of the field, can provide a match for a simple bipolar active region, AR 7999, which crossed the central meridian on 1996 November 26. The result is a non-force-free magnetic field with the Lorentz force being of the order of 10(exp -5.5) g per s(exp 2) resulting from an electric current density of 0.79 micro A per m(exp 2). Calculations show that the plasma beta becomes larger than unity at a strong non-radial currents requires low height of about 0.25 solar radii supporting the non-force-free conclusion. The presence of such strong non-radial currents requires large transverse pressure gradients fo maintain a magnetostatic atmosphere, required by the relatively persistent nature of the coronal structures observed in AR 7999. This scheme is an important tool in generating a magnetic field solution consistent with the coronal flux tube observations and the observed photospheric magnetic field.

  17. Increased reliability of nuclear magnetic resonance protein structures by consensus structure bundles.

    PubMed

    Buchner, Lena; Güntert, Peter

    2015-02-03

    Nuclear magnetic resonance (NMR) structures are represented by bundles of conformers calculated from different randomized initial structures using identical experimental input data. The spread among these conformers indicates the precision of the atomic coordinates. However, there is as yet no reliable measure of structural accuracy, i.e., how close NMR conformers are to the "true" structure. Instead, the precision of structure bundles is widely (mis)interpreted as a measure of structural quality. Attempts to increase precision often overestimate accuracy by tight bundles of high precision but much lower accuracy. To overcome this problem, we introduce a protocol for NMR structure determination with the software package CYANA, which produces, like the traditional method, bundles of conformers in agreement with a common set of conformational restraints but with a realistic precision that is, throughout a variety of proteins and NMR data sets, a much better estimate of structural accuracy than the precision of conventional structure bundles.

  18. Atomic simulations of effects of contact size and interfacial interaction strength on superlubricity in incommensurate sliding interface

    NASA Astrophysics Data System (ADS)

    Zhu, Peng-Zhe; Hu, Yuan-Zhong; Ma, Tian-Bao; Li, Rui; Wang, Hui

    2015-01-01

    Understanding the effects of contact size and interfacial interaction strength on superlubricity in incommensurate sliding interface is critically needed for the design and development of nanoscale ultra-low friction devices. This study uses molecular dynamics simulations to explore the sliding friction behaviors of an incommensurate interface consisting of a diamond slider and a silver substrate. The instantaneous relative lattice constant is proposed to quantitatively describe the commensurability of contacting surfaces in the sliding process. It is found that when the contact size is large, the slider exhibits ultra-low friction force. While for small contact size, superlubricity behavior breaks down,which is due to the transition of incommensurate-commensurate interfacial configuration in the local contact region. It is also found that when the interfacial interaction strength is reduced below a critical value, the obvious stick-slip motion observed for the small slider with large interfacial interaction strength disappears and superlubricity behavior occurs, which results from the incommensurate interfacial configuration in the contact region maintained during the sliding process. These results provide a first demonstration that the instantaneous incommensurate-commensurate transition in the local contact region can result in the breakdown of superlubricity in a realistic three-dimensional sliding system. The obtained results not only may guide the design of nanoscale ultra-low friction devices, but also provide some insights into the origins of friction at macroscopic interfaces which usually consists of many small nanoscale contacts.

  19. Defect-induced magnetic structure of CuMnSb

    NASA Astrophysics Data System (ADS)

    Máca, F.; Kudrnovský, J.; Drchal, V.; Turek, I.; Stelmakhovych, O.; Beran, P.; Llobet, A.; Marti, X.

    2016-09-01

    The observed ground state for the CuMnSb alloy is the antiferromagnetic (111) phase as confirmed by neutron diffraction experiments. Ab initio total energy calculations for ideal, defect-free CuMnSb contradict this result and indicate that other magnetic structures can have their total energies lower. It is known that Heusler alloys usually contain various defects depending on the sample preparation. We have therefore investigated magnetic phases of CuMnSb assuming the most common defects which exist in real experimental conditions. The full-potential supercell approach and a Heisenberg model approach using the coherent potential approximation are adopted. The results of the total energy supercell calculations indicate that defects that bring Mn atoms close together promote the antiferromagnetic (111) structure already for a low critical defect concentrations (≈3 %). A detailed study of exchange interactions between Mn moments further supports the above stabilization mechanism. Finally, the stability of the antiferromagnetic (111) order is enhanced by inclusion of electron correlations in narrow Mn bands. The present refinement structure analysis of the neutron scattering experiment supports theoretical conclusions.

  20. Structural and magnetic properties of chromium doped zinc ferrite

    SciTech Connect

    Sebastian, Rintu Mary; Thankachan, Smitha; Xavier, Sheena; Mohammed, E. M.; Joseph, Shaji

    2014-01-28

    Zinc chromium ferrites with chemical formula ZnCr{sub x}Fe{sub 2−x}O{sub 4} (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were prepared by Sol - Gel technique. The structural as well as magnetic properties of the synthesized samples have been studied and reported here. The structural characterizations of the samples were analyzed by using X – Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), and Transmission Electron Microscope (TEM). The single phase spinel cubic structure of all the prepared samples was tested by XRD and FTIR. The particle size was observed to decrease from 18.636 nm to 6.125 nm by chromium doping and induced a tensile strain in all the zinc chromium mixed ferrites. The magnetic properties of few samples (x = 0.0, 0.4, 1.0) were investigated using Vibrating Sample Magnetometer (VSM)

  1. Magnetic field-dependent spin structures of nanocrystalline holmium.

    PubMed

    Szary, Philipp; Kaiser, Daniel; Bick, Jens-Peter; Lott, Dieter; Heinemann, André; Dewhurst, Charles; Birringer, Rainer; Michels, Andreas

    2016-04-01

    The results are reported of magnetic field-dependent neutron diffraction experiments on polycrystalline inert-gas condensed holmium with a nanometre crystallite size (D = 33 nm). At T = 50 K, no evidence is found for the existence of helifan(3/2) or helifan(2) structures for the nanocrystalline sample, in contrast with results reported in the literature for the single crystal. Instead, when the applied field H is increased, the helix pattern transforms progressively, most likely into a fan structure. It is the component of H which acts on the basal-plane spins of a given nanocrystallite that drives the disappearance of the helix; for nanocrystalline Ho, this field is about 1.3 T, and it is related to a characteristic kink in the virgin magnetization curve. For a coarse-grained Ho sample, concomitant with the destruction of the helix phase, the emergence of an unusual angular anisotropy (streak pattern) and the appearance of novel spin structures are observed.

  2. Synthesis, structure, and magnetic characterization of Cr4US8

    NASA Astrophysics Data System (ADS)

    Ward, Matthew D.; Chan, Ian Y.; Malliakas, Christos D.; Lee, Minseong; Choi, Eun Sang; Ibers, James A.

    2016-01-01

    The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P21/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie-Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength.

  3. Low-Dimensional Systems: Structures of Interfaces and Magnetic Chains

    NASA Astrophysics Data System (ADS)

    Shen, Qing

    The solid-solid metal oxide(MO) interface in (100) orientation was modeled and its properties were investigated by molecular Dynamics(MD). MD was used to model temperature dependent geometry in the interface region, using standard interatomic potentials. The lattice structure across the MO-MO interface is found to change continually from one crystal to another. The radial distribution function, average potential energy for each layer, the average interplanar spacing, mean square displacement of the ions and spectrum of the autocorrelation function of velocity were calculated. Results for (100) MgO-CoO and NiO-CoO interfaces are compared with solid-solution and pure-phase data. The solid-solid metal oxide interface of rock -salt structure in (100) orientation was modeled and its properties were investigated by Local Density(LD) theory. Starting with molecular dynamics determined time-average atomic configurations at the interface, self-consistent LD calculations were made to determine electronic structure, spectroscopic and energetic properties of interface atoms. Spectral distributions, bonding mechanisms, charge densities and consequences for the optical band gap were determined. Results are given for (100) MgO-CoO interfaces, rm Mg_{x}Co_{1-x}O alloy and NiO-CoO interface. The magnetic properties of transition-metal based quasi-one dimensional molecular metals show unusual concentration and temperature dependence. Ion magnetization in the one dimensional rm Cu_{1-c}Ni _{c} chain of rm Cu_{1-c}Ni_{c}(pc)I was modeled by Monte Carlo methods, using indirect exchange interaction potentials of variable range. The effects of dilution of Cu spin moments by diamagnetic Ni ions and impurity scattering effects on the electron gas polarization are determined. Results are compared with NMR T-dependent magnetization data for this molecular metal.

  4. Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15.

    PubMed

    Lin, Kun; Zhou, Zhengyang; Liu, Laijun; Ma, Hongqiang; Chen, Jun; Deng, Jinxia; Sun, Junliang; You, Li; Kasai, Hidetaka; Kato, Kenichi; Takata, Masaki; Xing, Xianran

    2015-10-28

    Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What's more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb(2+)-Bi(3+) ordering in the large pentagonal caves, which can suppress the local polarization in x-y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.

  5. Structural, magnetic and optical properties of two concomitant molecular crystals

    NASA Astrophysics Data System (ADS)

    Silva, Manuela Ramos; Milne, Bruce; Coutinho, Joana T.; Pereira, Laura C. J.; Martín-Ramos, Pablo; Pereira da Silva, Pedro S.; Martín-Gil, Jesús

    2016-03-01

    A new 1D complex has been prepared and characterized. X-ray single crystal structure confirms that the Cu(II) ions assemble in alternating chains with Cu … Cu distances of 2.5685(4) and 3.1760(4) Å. The temperature dependence of the magnetic susceptibility reveals an antiferromagnetic interaction between the paddle-wheel copper centers with an exchange of -300 cm-1. The exchange integral was also determined by quantum chemical ab-initio calculations, using polarised and unpolarised basis sets reproducing well the experimental value. The second harmonic generation efficiency of a concomitantly crystallized material was evaluated and was found to be comparable to urea.

  6. Collision-Free Structure Using Thin-Film Magnet For Electrostatic Energy Harvester

    NASA Astrophysics Data System (ADS)

    Yoshii, S.; Yamaguchi, K.; Fujita, T.; Kanda, K.; Maenaka, K.

    2016-11-01

    This paper proposes collision-free structure using NdFeB thin-film magnet for vibration energy harvesters. By using stripe shaped NdFeB magnet array on the Si MEMS structure, we finally obtained 3 mN of magnetic repulsive force on 8 × 8 mm2 specimen with 40 μm air-gap.

  7. The Magnetic Field Structure of a Snowflake Divertor

    SciTech Connect

    Ryutov, D D; Cohen, R H; Rognlien, T D; Umansky, M V

    2008-05-30

    The snowflake divertor exploits a tokamak geometry in which the poloidal magnetic field null approaches second order; the name stems from the characteristic hexagonal, snowflake-like, shape of the separatrix for an exact second-order null. The proximity of the poloidal field structure to that of a second-order null substantially modifies edge magnetic properties compared to the standard X-point geometry; this, in turn, affects the edge plasma behavior. Modifications include: (1) The flux expansion near the null-point becomes 2-3 times larger; (2) The connection length between the equatorial plane and divertor plate significantly increases; (3) Magnetic shear just inside the separatrix becomes much larger; and (4) In the open-field-line region, the squeezing of the flux-tubes near the null-point increases, thereby causing stronger decoupling of the plasma turbulence in the divertor legs and in the main SOL. These effects can be used to reduce the power load on the divertor plates and/or to suppress the 'bursty' component of the heat flux. It is emphasized that the snowflake divertor can be created by a relatively simple set of poloidal field coils situated beyond the toroidal field coils. Analysis of the robustness of the proposed divertor configuration with respect to changes of the plasma current distribution is presented and it is concluded that, even if the null is close to the second order, the configuration is quite robust.

  8. Magnetic and structural properties of ferrihydrite/hematite nanocomposites

    NASA Astrophysics Data System (ADS)

    Pariona, N.; Camacho-Aguilar, K. I.; Ramos-González, R.; Martinez, Arturo I.; Herrera-Trejo, M.; Baggio-Saitovitch, E.

    2016-05-01

    A rich variety of ferrihydrite/hematite nanocomposites (NCs) with specific size, composition and properties were obtained in transformation reactions of 2-line ferrihydrite. Transmission electron microscopy (TEM) observations showed that the NCs consist of clusters of strongly aggregated nanoparticles (NPs) similarly to a "plum pudding", where hematite NPs "raisins" are surrounded by ferrihydrite "pudding". Magnetic measurements of the NCs correlate very well with TEM results; i.e., higher coercive fields correspond to greater hematite crystallite size. First order reversal curve (FORC) measurements were used for the characterization of the magnetic components of the NCs. FORC diagrams revealed that the NCs prepared at short times are composed by single domains with low coercivity, and NCs prepared at times larger than 60 min exhibited elongated distribution along the Hc axis. It suggested that these samples consist of mixtures of different kinds of hematite particles, ones with low coercivity and others with coercivity greater than 600 Oe. For NCs prepared at times larger than 60 min, Mossbauer spectroscopy revealed the presence of two sextets, which one was assigned to fine hematite particles and other to hematite particles with hyperfine parameters near to bulk hematite. The correlation of the structural and magnetic properties of the ferrihydrite/hematite NCs revealed important characteristics of these materials which have not been reported elsewhere.

  9. The magnetic structure of EuCu2Sb2

    DOE PAGES

    Ryan, D. H.; Cadogan, J. M.; Anand, V. K.; ...

    2015-05-06

    Antiferromagnetic ordering of EuCu2Sb2 which forms in the tetragonal CaBe2Ge2-type structure (space group P4/nmm #129) has been studied using neutron powder diffraction and 151Eu Mössbauer spectroscopy. The room temperature 151Eu isomer shift of –12.8(1) mm/s shows the Eu to be divalent, while the 151Eu hyperfine magnetic field (Bhf) reaches 28.7(2) T at 2.1 K, indicating a full Eu2+ magnetic moment. Bhf(T) follows a smoothmore » $$S=\\frac{7}{2}$$ Brillouin function and yields an ordering temperature of 5.1(1) K. Refinement of the neutron diffraction data reveals a collinear A-type antiferromagnetic arrangement with the Eu moments perpendicular to the tetragonal c-axis. As a result, the refined Eu magnetic moment at 0.4 K is 7.08(15) μB which is the full free-ion moment expected for the Eu2+ ion with $$S=\\frac{7}{2}$$ and a spectroscopic splitting factor of g = 2.« less

  10. Magnetic susceptibility fabrics in slates: Structural, mineralogical and lithological influences

    NASA Astrophysics Data System (ADS)

    Borradaile, G.; Sarvas, P.

    1990-02-01

    A single, penetrative tectonic deformation of Archean greywackes, accompanied by low grade metamorphism, generated low-field magnetic susceptibility fabrics that are coaxial with the rock's schistosity although there are multiple sources of magnetic susceptibility. Pre-metamorphic magnetite and the metamorphic minerals pyrrhotite, biotite and chlorite (variety thuringite: daphnite-aphrosiderite) are responsible for the anisotropy of susceptibility. These minerals grew with preferred crystallographic orientations influenced by the prevailing stress regime. On its own, rotation cannot be invoked to explain the alignment of the metamorphic minerals. There are varying proportions of at least two of these minerals in most specimens. For 153 specimens the degree of anisotropy increases as the mean susceptibility increases over the range from 100 to 700 (in units of 10 -6 S.I.)- Theory shows that this is to be expected either due to increasing the traces of strongly oriented ferrimagnetics or due to increasing the proportion of chlorite. In the latter case this simultaneously increased its preferred orientation by closer packing. Stress-influenced crystallization of chlorite rapidly achieves saturation alignment and a limiting magnetic anisotropy although strain may continue to increase. Samples taken through individual graded beds show that the susceptibility ellipsoid varies from oblate in slaty rocks to a neutral shape in sandier rocks. However, its orientation is always structurally controlled, with the minimum susceptibility axis perpendicular to schistosity.

  11. Filament shape versus coronal potential magnetic field structure

    NASA Astrophysics Data System (ADS)

    Filippov, B.

    2016-01-01

    Solar filament shape in projection on disc depends on the structure of the coronal magnetic field. We calculate the position of polarity inversion lines (PILs) of coronal potential magnetic field at different heights above the photosphere, which compose the magnetic neutral surface, and compare with them the distribution of the filament material in Hα chromospheric images. We found that the most of the filament material is enclosed between two PILs, one at a lower height close to the chromosphere and one at a higher level, which can be considered as a height of the filament spine. Observations of the same filament on the limb by the Solar Terrestrial Relations Observatory spacecraft confirm that the height of the spine is really very close to the value obtained from the PIL and filament border matching. Such matching can be used for filament height estimations in on-disc observations. Filament barbs are housed within protruding sections of the low-level PIL. On the base of simple model, we show that the similarity of the neutral surfaces in potential and non-potential fields with the same sub-photospheric sources is the reason for the found tendency for the filament material to gather near the potential-field neutral surface.

  12. Octupolar out-of-plane magnetic field structure generation during collisionless magnetic reconnection in a stressed X-point collapse

    SciTech Connect

    Graf von der Pahlen, J.; Tsiklauri, D.

    2014-06-15

    The out-of-plane magnetic field, generated by fast magnetic reconnection, during collisionless, stressed X-point collapse, was studied with a kinetic, 2.5D, fully electromagnetic, relativistic particle-in-cell numerical code, using both closed (flux conserving) and open boundary conditions on a square grid. It was discovered that the well known quadrupolar structure in the out-of-plane magnetic field gains four additional regions of opposite magnetic polarity, emerging near the corners of the simulation box, moving towards the X-point. The emerging, outer, magnetic field structure has opposite polarity to the inner quadrupolar structure, leading to an overall octupolar structure. Using Ampere's law and integrating electron and ion currents, defined at grid cells, over the simulation domain, contributions to the out-of-plane magnetic field from electron and ion currents were determined. The emerging regions of opposite magnetic polarity were shown to be the result of ion currents. Magnetic octupolar structure is found to be a signature of X-point collapse, rather than tearing mode, and factors relating to potential discoveries in experimental scenarios or space-craft observations are discussed.

  13. Long-Range Magnetic Interactions in the Multiferroic Antiferromagnet MnWO4

    SciTech Connect

    Ye, Feng; Fishman, Randy Scott; Fernandez-Baca, Jaime A; Podlesnyak, Andrey A; Ehlers, Georg; Mook Jr, Herbert A; Wang, Y.-Q.; Lorenz, Bernd; Chu, C. W.

    2011-01-01

    The spin-wave excitations of the multiferroic MnWO4 have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These excitations can be well described by a Heisenberg model with competing long-range exchange interactions and a single-ion anisotropy term. We find that the magnetic interactions are strongly frustrated within the zigzag spin chain along c-axis and between chains along the a-axis, while the coupling between spin along the b-axis is much weaker. We argue that the balance of these interactions results in the noncollinear incommensurate spin structure associated with the magnetoelectric effect, and the perturbation of the magnetic interactions leads to the observed rich phase diagrams of the chemically-doped materials. This delicate balance can also be tuned by the application of external electric or magnetic fields to achieve practical magnetoelectric control of this type of materials.

  14. 2000 Lilienfeld Prize Talk - From Model Magnets to High Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Birgeneau, Robert J.

    2000-03-01

    Magnetic materials often provide simple and clean examples of important problems in statistical physics. In recent years, much attention has been focussed on one and two dimensional Heisenberg spin systems in which quantum fluctuations play an essential role. Of particular interest are the two dimensional CuO2 Heisenberg square lattice antiferromagnets which, on doping with holes or electrons, become high temperature superconductors. We will review the results of experiments and quantum Monte Carlo calculations on one and two dimensional quantum magnets. We shall also discuss recent neutron studies of the novel incommensurate magnetic structures that occur in the spin glass and superconducting phases of the doped La2CuO4 system. We shall emphasize, in particular, the newly discovered one dimensional spin modulations in the spin glass phase together with the reorientation transition which coincides with the insulator to superconducting transition.

  15. Ground state of the quasi-1D compound BaVS3 resolved by resonant magnetic x-ray scattering.

    PubMed

    Leininger, Ph; Ilakovac, V; Joly, Y; Schierle, E; Weschke, E; Bunau, O; Berger, H; Pouget, J-P; Foury-Leylekian, P

    2011-04-22

    Resonant magnetic x-ray scattering near the vanadium L2,3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below T(N)=31  K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.226   0.226   ξ) in hexagonal notation, with ξ=0.033. The azimuthal-angle dependence of the scattering signal and time-dependent density functional theory simulations indicate an antiferromagnetic order within the ab plane with the spins polarized along a in the monoclinic structure.

  16. Imaging solar coronal magnetic structures in 3D

    NASA Astrophysics Data System (ADS)

    Cartledge, N. P.

    The study of solar coronal structures and, in particular prominences, is a key part of understanding the highly complex physical mechanisms occurring in the Sun's atmosphere. Solar prominences are important in their own right and some of the most puzzling questions in solar theory have arisen through their study. For example, how do they form and how is their mass continuously replenished? How can the magnetic field provide their continuous support against gravity over time periods of several months? How can such cool, dense material exist in thermal equilibrium in the surrounding coronal environment? Why do they erupt? A study of their structure and that of the surrounding medium is important in determining the nature of the coronal plasma and magnetic field. Also, prominences are closely associated with other key phenomena such as coronal mass ejections and eruptive solar flares which occur as a prominence loses equilibrium and rises from the solar surface. Our current understanding of these fascinating structures is extremely limited and we know very little about their basic global structure. In fact, recent prominence observations have caused our basic paradigms to be challenged (Priest, 1996) and so we must set up new models in order to gain even a fundamental understanding. Prominences are highly nonlinear, three-dimensional structures. Large feet (or barbs) reach out from the main body of a prominence and reach down to the photosphere where the dense material continuously drains away. These provide a real clue to the three-dimensional nature of the coronal field and its relation to the photospheric field. It is important, therefore, to make stereographic observations of prominences in order to gain a basic understanding of their essentially three-dimensional nature and attempt to formulate new paradigms for their structure and evolution. There is no doubt that the study of prominences in three dimensions is a crucial exercise if we are to develop a better

  17. Effect of crystal morphology on magnetic structure of nano-magnetites

    NASA Astrophysics Data System (ADS)

    Chen, Y. H.; Zhang, J. F.

    2017-01-01

    The nano-magnetites with particle, rod, tube, and ring crystal morphologies were synthesized and the differences between macroscopic and microscopic magnetic properties were studied. The macroscopic magnetic properties of nano-magnetites obtained via a superconducting quantum interference device (SQUID) showed that both coercive magnetic field and saturation magnetization per unit volume followed the orders of ring > particle > tube > rod, respectively. This indicated that the crystal morphology affected macroscopic magnetic properties. The particle nano-magnetite contained a single domain while the others contained multiple domains measured by a magnetic force microscope (MFM). However, the domain structure of nano-magnetites calculated from SQUID data showed that all were pseudo-single domains. This suggested that the MFM may be a precise tool to determine magnetic structures. Moreover, the crystal morphology of nano-magnetites affected magnetic properties owing to different magnetic-domain structures.

  18. Critical Phenomena at the Normal-Incommensurate Phase Transition in Rb2ZnCl4

    NASA Astrophysics Data System (ADS)

    Mashiyama, Hiroyuki

    1981-08-01

    The X-ray reflection intensity and the dielectric constant are measured around the normal-incommensurate phase transition. From the temperature dependence of a satellite reflection at \\includegraphics{dummy.eps}, the critical exponent 2β is determined to be 0.69± 0.01. This value is very close to the exponent of the three-dimensional n{=}2-vector model. The dielectric constant along the ferroelectric axis shows a weak anomaly at the transition point, which is discussed with the aid of the remormalization-group method.

  19. 4-d magnetism: Electronic structure and magnetism of some Mo-based alloys

    NASA Astrophysics Data System (ADS)

    Liu, Yong; Bose, S. K.; Kudrnovský, J.

    2017-02-01

    We report results of a first-principles density-functional study of alloys of the 4 d -element Mo with group IV elements Si, Ge and Sn in zinc blende (ZB) and rock salt (RS) structures. The study was motivated by a similar study of ours based on the 4 d -element Tc, which showed the presence of half-metallic states with integer magnetic moment (1μB) per formula unit in TcX (X=C, Si, Ge) alloys. The calculated Curie temperatures for the ferromagnetic (FM) phases were low, around or less than 300 K. Searching for the possibility of 4 d -based alloys with higher Curie temperatures we have carried out the study involving the elements Mo, Ru and Rh. Among these the most promising case appears to be that involving the element Mo. Among the MoX (X=Si, Ge, Sn) alloys in ZB and RS structures, both MoGe and MoSn in ZB structures are found to possess an integer magnetic moment of 2μB per formula unit. ZB MoSn can be classified as a marginal/weak half-metal or a spin gapless semiconductor, while ZB MoGe would be best described as a gapless magnetic semiconductor. The calculated Curie temperatures are in the range 300-700 K. Considering the theoretical uncertainty in the band gaps due not only to the treatment of exchange and correlation effects, but density functional theory itself, these classifications may change somewhat, but both merit investigation from the viewpoint of potential spintronic application. Based on their higher Curie temperatures, Mo-based alloys would serve such purpose better than the previously reported Tc-based ones.

  20. Martensitic transition and structural modulations in the Heusler alloy Ni 2FeGa

    NASA Astrophysics Data System (ADS)

    Li, J. Q.; Liu, Z. H.; Yu, H. C.; Zhang, M.; Zhou, Y. Q.; Wu, G. H.

    2003-05-01

    We have found two distinctive structural modulations altering evidently along with the martensitic transition (MT) in the Ni 2FeGa alloy. The first one ( q1), corresponding to the well-known phonon anomalies in the [ ζζ0] TA 2 branch, occurs along the <110> direction. The second one ( q2), an incommensurate modulation observed for the first time, occurs along the <211>-direction. Both modulations change gradually with the premartensitic phonon softening and discontinuously with the MT. Anomalies in magnetic properties emerging around the MT have been briefly discussed.

  1. Size and thickness effect on magnetic structures of maghemite hollow magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Sayed, Fatima; Labaye, Yvan; Sayed Hassan, Rodaina; El Haj Hassan, Fouad; Yaacoub, Nader; Greneche, Jean-Marc

    2016-09-01

    The effect of surface anisotropy on the magnetic ground state of hollow maghemite nanoparticles is investigated using atomistic Monte Carlo simulation. The computer modeling is carried on hollow nanostructures as a function of size and shell thickness. It is found that the large contribution of the surface anisotropy imposes a "throttled" spin structure where the moments located at the outer surface tend to orient normal to the surface while those located at the inner surface appear to be more aligned. For increasing values of surface anisotropy in the frame of a radial model, the magnetic moments become radially oriented either inward or outward giving rise to a "hedgehog" configuration with nearly zero net magnetization. We also show the effect of the size of hollow nanoparticle on the spin behavior where the spin non-collinearity increases (for fixed value of surface anisotropy) as the diameter of the hollow nanoparticle increases due to the significant increase in surface-to-volume ratio, the thickness being constant. Moreover, the thickness of the hollow nanoparticle shell influences the spin configuration and thus the relation between surface anisotropy and the size or the thickness of the hollow nanoparticle is established.

  2. Switchable bi-stable multilayer magnetic probes for imaging of soft magnetic structures.

    PubMed

    Wren, Tom; Puttock, Robb; Gribkov, Boris; Vdovichev, Sergey; Kazakova, Olga

    2017-03-28

    We present the use of custom-made multilayer (ML) magnetic probes in magnetic force microscopy (MFM) for imaging soft magnetic structures, i.e. nickel submicron disks of different dimensions. One of the main advantages of a custom-made ML probe is that it can be controllably switched between standard (parallel) and low moment (antiparallel) states. We demonstrate that the predicted vortex and stripe domain states in the disks are observed when using the ML probes both in the antiparallel and parallel states. However, while the phase contrast is significantly larger in the parallel state, the images are dominated by strong sample - probe interactions that obscure the image. By comparison of the stripe domain width observed by MFM with the ML probe and those expected from the Kittel model, we show that the resolution of the probe in the AP and P states is ∼30-40nm, i.e. of the order of the probe geometrical apex and thus approaching the limit of spatial resolution. The ML probes are further compared to the commercial standard and low moment ones, showing that the quality of images obtained with the ML probe is superior to both commercial probes.

  3. Magnetic and magnetoresistance studies of nanometric electrodeposited Co films and Co/Cu layered structures: Influence of magnetic layer thickness

    NASA Astrophysics Data System (ADS)

    Zsurzsa, S.; Péter, L.; Kiss, L. F.; Bakonyi, I.

    2017-01-01

    The magnetic properties and the magnetoresistance behavior were investigated for electrodeposited nanoscale Co films, Co/Cu/Co sandwiches and Co/Cu multilayers with individual Co layer thicknesses ranging from 1 nm to 20 nm. The measured saturation magnetization values confirmed that the nominal and actual layer thicknesses are in fairly good agreement. All three types of layered structure exhibited anisotropic magnetoresistance for thick magnetic layers whereas the Co/Cu/Co sandwiches and Co/Cu multilayers with thinner magnetic layers exhibited giant magnetoresistance (GMR), the GMR magnitude being the largest for the thinnest Co layers. The decreasing values of the relative remanence and the coercive field when reducing the Co layer thickness down to below about 3 nm indicated the presence of superparamagnetic (SPM) regions in the magnetic layers which could be more firmly evidenced for these samples by a decomposition of the magnetoresistance vs. field curves into a ferromagnetic and an SPM contribution. For thicker magnetic layers, the dependence of the coercivity (Hc) on magnetic layer thickness (d) could be described for each of the layered structure types by the usual equation Hc=Hco+a/dn with an exponent around n=1. The common value of n suggests a similar mechanism for the magnetization reversal by domain wall motion in all three structure types and hints also at the absence of coupling between magnetic layers in the Co/Cu/Co sandwiches and Co/Cu multilayers.

  4. Electronic and magnetic structure of neutral radical FBBO

    NASA Astrophysics Data System (ADS)

    Winter, Stephen M.; Mailman, Aaron; Oakley, Richard T.; Thirunavukkuarasu, Komalavalli; Hill, Stephen; Graf, David E.; Tozer, Stanley W.; Tse, John S.; Mito, Masaki; Yamaguchi, Hiroshi

    2014-06-01

    The fluorinated oxobenzo-bridged bisdithiazolyl radical FBBO was recently observed to undergo a pressure-induced Mott insulator-to-metal transition, suggesting a novel organic system for studying Mott physics. This report describes the electronic structure of this material in relation to the observed magnetic response at low pressures. Through analysis of antiferromagnetic resonance measurements, we identify a layered antiferromagnetic ordered phase below TN=13 K at ambient pressure, which requires strong ferromagnetic coupling between nearest neighbours. The origin of such coupling is elucidated from both molecular and solid-state electronic-structure calculations, which suggest a minimal two-orbital model with strong Hund's-rule coupling. This layered phase is partially frustrated by a second-nearest-neighbor antiferromagnetic coupling, which drives a magnetic phase transition at elevated pressure. On the basis of the two-orbital model, we suggest the pressure-induced Mott transition to proceed via rehybridization of the frontier molecular orbitals, resulting in a half-filled insulator to quarter-filled metal crossover.

  5. Gravitational Influences on Magnetic Field Structure in Accretion Disks*

    NASA Astrophysics Data System (ADS)

    Schneck, K.; Coppi, B.

    2009-11-01

    The structure of the magnetic fields associated with plasma disks surrounding black holes is identified when the effects of gravitational and Lorentz forces on the dynamics of the disk are comparable. The effects of corrections to the radial gravitational force% ρGM*R(R^2+z^2)^3/2 are explored within the geometry of a thin disk. A significant external magnetic field component is considered, along with an internal component due to the azimuthal current configuration. The relation of the resulting configuration to the field structure when the gravitational force can be neglectedfootnotetextB. Coppi, Phys. Plasmas 12, 057302 (2005)^,footnotetextCoppi, B. and Rousseau, F. Astrophysical Journal, 641: 458-470 (2006) is discussed. The relevant equations for the pseudo-Newtonian potentialfootnotetextPaczy'nski, B. and Wiita, P. J. Astron. Astrophys. 88: 23 (1980) describing the physics near the event horizon of the black hole are also derived and the physical consequences are explored. *Sponsored in part by the U.S. Department of Energy and the MIT Undergraduate Research Opportunities Program.

  6. RESOLVING THE INTERNAL MAGNETIC STRUCTURE OF THE SOLAR NETWORK

    SciTech Connect

    Martinez Gonzalez, M. J.; Martinez Pillet, V.; Solanki, S. K.; Barthol, P.; Schmidt, W.

    2012-10-20

    We analyze the spectral asymmetry of Stokes V (circularly polarized) profiles of an individual network patch in the quiet Sun observed by Sunrise/IMaX. At a spatial resolution of 0.''15-0.''18, the network elements contain substructure which is revealed by the spatial distribution of Stokes V asymmetries. The area asymmetry between the red and blue lobes of Stokes V increases from nearly zero at the core of the structure to values close to unity at its edges (single-lobed profiles). Such a distribution of the area asymmetry is consistent with magnetic fields expanding with height, i.e., an expanding magnetic canopy (which is required to fulfill pressure balance and flux conservation in the solar atmosphere). Inversion of the Stokes I and V profiles of the patch confirms this picture, revealing a decreasing field strength and increasing height of the canopy base from the core to the periphery of the network patch. However, the non-roundish shape of the structure and the presence of negative area and amplitude asymmetries reveal that the scenario is more complex than a canonical flux tube expanding with height surrounded by downflows.

  7. Role of nonlinear localized structures and turbulence in magnetized plasma

    NASA Astrophysics Data System (ADS)

    Pathak, Neha; Yadav, Nitin; Uma, R.; Sharma, R. P.

    2016-09-01

    In the present study, we have analyzed the field localization of kinetic Alfvén wave (KAW) due to the presence of background density perturbation, which are assumed to be originated by the three dimensionally propagating low frequency KAW. These localized structures play an important role for energy transportation at smaller scales in the dispersion range of magnetic power spectrum. For the present model, governing dynamic equations of high frequency pump KAW and low frequency KAW has been derived by considering ponderomotive nonlinearity. Further, these coupled equations have been numerically solved to analyze the resulting localized structures of pump KAW and magnetic power spectrum in the magnetopause regime. Numerically calculated spectrum exhibits inertial range having spectral index of -3/2 followed by steeper scaling; this steepening in the turbulent spectrum is a signature of energy transportation from larger to smaller scales. In this way, the proposed mechanism, which is based on nonlinear wave-wave interaction, may be useful for understanding the particle acceleration and turbulence in magnetopause.

  8. Structural and magnetic stability of Fe{sub 2}NiSi

    SciTech Connect

    Gupta, Dinesh C. Bhat, Idris Hamid Chauhan, Mamta

    2014-04-24

    Full-potential ab-initio calculations in the stable F-43m phase have been performed to investigate the structural and magnetic properties of Fe{sub 2}NiSi inverse Heusler alloys. The spin magnetic moment distributions show that present material is ferromagnetic in stable F-43m phase. Further, spin resolved electronic structure calculations show that the discrepancy in magnetic moments of Fe-I and Fe-II depend upon the hybridization of Fe with the main group element. It is found that the main group electron concentration is predominantly responsible in establishing the magnetic properties, formation of magnetic moments and the magnetic order for present alloy.

  9. Electronic structure, magnetic and structural properties of Ni doped ZnO nanoparticles

    SciTech Connect

    Kumar, Shalendra; Vats, Prashant; Gautam, S.; Gupta, V.P.; Verma, K.D.; Chae, K.H.; Hashim, Mohd; Choi, H.K.

    2014-11-15

    Highlights: • XRD, and HR-TEM results show the single phase nature of Ni doped ZnO nanoparticles. • dc magnetization results indicate the RT-FM in Ni doped ZnO nanoparticles. • Ni L{sub 3,2} edge NEXAFS spectra infer that Ni ions are in +2 valence state. • O K edge NEXAFS spectra show that O vacancy increases with Ni doping in ZnO. - Abstract: We report structural, magnetic and electronic structural properties of Ni doped ZnO nanoparticles prepared by auto-combustion method. The prepared nanoparticles were characterized by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and dc magnetization measurements. The XRD and HR-TEM results indicate that Ni doped ZnO nanoparticles have single phase nature with wurtzite lattice and exclude the presence of secondary phase. NEXAFS measurements performed at Ni L{sub 3,2}-edges indicates that Ni ions are in +2 valence state and exclude the presence of Ni metal clusters. O K-edge NEXAFS spectra indicate an increase in oxygen vacancies with Ni-doping, while Zn L{sub 3,2}-edge show the absence of Zn-vacancies. The magnetization measurements performed at room temperature shows that pure and Ni doped ZnO exhibits ferromagnetic behavior.

  10. Anisotropies and spin dynamics in ultrathin magnetic multilayer structures

    NASA Astrophysics Data System (ADS)

    Kardasz, Bartlomiej

    High quality magnetic films were prepared by Molecular Beam Epitaxy (MBE) using Thermal Deposition (TD) and Pulse Laser Deposition (PLD) techniques. Ferromagnetic Resonance (FMR) and Mossbauer studies have shown that the Fe films prepared by PLD exhibited a more intermixed interface lattice structure than those prepared by TD. Dramatic decrease of the in-plane interface uniaxial anisotropy for the PLD films compared to those prepared by TD has shown that the in-plane uniaxial anisotropy is caused by magnetoelasticity driven by the Fe/GaAs(001) interface lattice shear. Magnetization dynamics of the ultrathin Fe/Au,Ag/Fe films was studied using Time-Resolved Magneto-Optical Kerr Effect (TRMOKE) and FMR in the frequency range from 1 to 73 GHz. The Gilbert damping was studied in the Au/Fe/GaAs(001) structures as a function of the Fe and Au layer thickness, respectively. The observed increase in magnetic damping in the Fe film covered with thick Au capping layers was explained by spin pumping at the Fe/Au interface accompanied by spin relaxation and diffusion of the accumulated spin density in the Au layer. The spin diffusion length in Au was found to be 34 nm at room temperature. Significant increase of the Gilbert damping was observed in the Au/Fe/GaAs structures with decreasing Fe film thickness. Its origin lies in the additional damping at the Fe/GaAs interface. Direct detection of the spin current propagating across the Ag spacer in Fe/Ag,Au/Fe/GaAs(001) structures was carried out with stroboscopic TRMOKE measurements. The Fe layer grown on GaAs served as a spin pumping source and the Fe layer grown on the Au,Ag spacer was used as a probe for detection of the spin current propagating across the Au and Ag spacers. The experimental results were interpreted using selfconsistent solution of the Landau Lifshitz Gilbert (LLG) equations of motion with the spin diffusion equation for the accumulated spin density in the Au and Ag spacers. The spin diffusion length in Ag was

  11. Structural, morphological and magnetic analysis of Cd-Co-S dilute magnetic semiconductor nanofilms

    NASA Astrophysics Data System (ADS)

    Kumar, Suresh; Negi, N. S.; Katyal, S. C.; Sharma, Pankaj; Sharma, Vineet

    2014-10-01

    Cd1-xCoxS dilute magnetic semiconductor nanofilms (0≤x≤0.08 at%) deposited by chemical bath deposition have been investigated using grazing angle x-ray diffraction, atomic force microscopy and vibrating sample magnetometer. The introduction of Co2+ ions in CdS structure induces structural disorders and hence, results in degradation of crystallinity. The crystallite size, interplanar spacing and lattice parameter ratio decrease with increasing Co2+ concentration in CdS. The diamagnetic state of CdS disappears with increase in Co concentration and films with x>0.02 exhibit ferromagnetism. This may be explained in terms of the spin-orbit interactions and Co2+ ion induced the lattice defects and phase separation.

  12. Incommensurate Magnetism in FeAs Strips: Neutron Scattering from CaFe4As3

    DTIC Science & Technology

    2010-12-21

    numbers: 75.30.Fv, 64.70.Rh, 61.05.F-, 71.18.+y The recent discovery of superconductivity (SC) in iron pnictides [1] has opened a new chapter in SC research...2, 3] contains interpenetrating FeAs strips, which –as spin-ladders in copper oxides – may provide unique insight into electronic correlations of the...square lattice plane. Similar to the parent compounds of the 1111- and 122- type superconductors, CaFe4As3 is not superconducting down to 1.8 K [2

  13. Structural, magnetic and electronic structure properties of Co doped ZnO nanoparticles

    SciTech Connect

    Kumar, Shalendra; Song, T.K.; Gautam, Sanjeev; Chae, K.H.; Kim, S.S.; Jang, K.W.

    2015-06-15

    Highlights: • XRD and HR-TEM results show the single phase nature of Co doped ZnO nanoparticles. • XMCD and dc magnetization results indicate the RT-FM in Co doped ZnO nanoparticles. • Co L{sub 3,2} NEXAFS spectra infer that Co ions are in 2+ valence state. • O K edge NEXAFS spectra show that O vacancy increases with Co doping in ZnO. - Abstract: We reported structural, magnetic and electronic structure studies of Co doped ZnO nanoparticles. Doping of Co ions in ZnO host matrix has been studied and confirmed using various methods; such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersed X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, magnetic hysteresis loop measurements and X-ray magnetic circular dichroism (XMCD). From the XRD and HR-TEM results, it is observed that Co doped ZnO nanoparticles have single phase nature with wurtzite structure and exclude the possibility of secondary phase formation. FE-SEM and TEM micrographs show that pure and Co doped nanoparticles are nearly spherical in shape. O K edge NEXAFS spectra indicate that O vacancies increase with Co doping. The Co L{sub 3,2} edge NEXAFS spectra revealed that Co ions are in 2+ valence state. DC magnetization hysteresis loops and XMCD results clearly showed the intrinsic origin of temperature ferromagnetism in Co doped ZnO nanoparticles.

  14. Incommensurate charge ordered states in the t–t‧–J model

    NASA Astrophysics Data System (ADS)

    Choubey, Peayush; Tu, Wei-Lin; Lee, Ting-Kuo; Hirschfeld, P. J.

    2017-01-01

    We study the incommensurate charge ordered states in the t{--}{t}\\prime {--}J model using the Gutzwiller mean field theory on large systems. In particular, we explore the properties of incommensurate charge modulated states referred to as nodal pair density waves (nPDW) in the literature. nPDW states intertwine site and bond charge order with modulated d-wave pair order, and are characterized by a nonzero amplitude of uniform pairing; they also manifest a dominant intra-unit cell d-density wave form factor. To compare with a recent scanning tunneling microscopy (STM) study (Hamidian et al 2015 Nat. Phys. 12 150) of the cuprate superconductor BSCCO-2212, we compute the continuum local density of states (LDOS) at a typical STM tip height using the Wannier function based approach. By Fourier transforming Cu and O sub-lattice LDOS we also obtain bias-dependent intra-unit cell form factors and spatial phase difference. We find that in the nPDW state the behavior of form factors and spatial phase difference as a function of energy agrees remarkably well with the experiment.This is in contrast to commensurate charge modulated states, which we show do not agree with experiment. We propose that the nPDW states are good candidates for the charge density wave phase observed in the superconducting state of underdoped cuprates.

  15. Spin incommensurability varies linearly with hole content in single-layer Bi2201 cuprate

    NASA Astrophysics Data System (ADS)

    Tranquada, John; Enoki, M.; Fujita, M.; Nishizaki, T.; Yamada, K.; Iikubo, S.; Singh, D. K.; Chang, S.

    2013-03-01

    We have performed inelastic neutron scattering measurements on the single-layer cuprate Bi2+xSr2-xCuO6+y (Bi2201) with x = 0 . 2 , 0.3, 0.4 and 0.5, a doping range that spans the spin-glass (SG) to superconducting (SC) phase boundary. The doping evolution of low energy spin fluctuations (11 meV) was found to be characterized by a change of incommensurate modulation wave vector from the tetragonal [110] to [100]/[010] directions, while maintaining a linear relation between the incommensurability and the hole concentration, δ ~ p . In the SC regime, the spectral weight is strongly suppressed below ~ 4 meV. Similarities and differences in the spin correlations between Bi2201 and the prototypical single-layer system La2-xSrxCuO4 will be discussed. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  16. Structure and magnetism of epitaxial rare-earth-transition-metal films

    SciTech Connect

    Fullerton, E.E.; Sowers, C.H.; Pearson, J.P.; Bader, S.D.

    1996-10-01

    Growth of epitaxial transition-metal superlattices; has proven essential in elucidating the role of crystal orientation and structure on magnetic properties such as giant magnetoresistance, interlayer coupling, and magnetic surface anisotropies. Extending these studies to the growth of epitaxial rare earth-transition metal (RE-TM) films and superlattices promises to play an equally important role in exploring and optimizing the properties of hard magnets. For instance, Skomski and Coey predict that a giant energy product (120 MG Oe) is possible in multilayer structures consisting of aligned hard-magnet layers exchanged coupled with soft-phase layers with high magnetization. Epitaxy provides one route to synthesizing such exchange-hardened magnets on controlled length scales. Epitaxial growth also allows the magnetic properties to be tailored by controlling the crystal orientation and the anisotropies of the magnetic layers and holds the possibility of stabilizing metastable phases. This paper describes the epitaxy and magnetic properties for several alloys.

  17. Magnetic properties of HoMn2O5

    NASA Astrophysics Data System (ADS)

    Radulov, I.; Lovchinov, V.; Dimitrov, D.; Apostolov, A.; Nizhankovskii, V.; Daszkiewicz, M.

    2007-04-01

    We have investigated the detailed field and temperature dependence of the dielectric constant, dielectric losses, electric polarization, magnetization and magnetostriction (MS) in orthorhombic HoMn2O5 single crystals. HoMn2O5 displays incommensurate antiferromagnetic ordering below 39 K, becoming commensurate on further cooling. The commensurate-incommensurate transition takes place at low temperatures. The inherent magnetic frustration in this material is lifted by a small lattice distortion, primarily involving shifts of the Mn3+ cations and giving rise to a canted antiferroelectric phase. Colossal magnetostriction (CMS) effect was observed and a novel phase transition diagram was build.

  18. Effect of high magnetic field on structure and magnetic properties of evaporated crystalline and amorphous Fe-Sm thin films

    NASA Astrophysics Data System (ADS)

    Li, Guojian; Li, Mengmeng; Wang, Jianhao; Du, Jiaojiao; Wang, Kai; Wang, Qiang

    2017-02-01

    Crystalline and amorphous Fe-Sm thin films have been fabricated by using molecular beam vapor deposition method. Then, the effects of both variation of Sm content and application of high magnetic field during film growth on the structure and magnetic properties of the Fe-Sm films have been explored. The results show that bcc structure of the Fe-Sm films with 5.8% Sm transforms to amorphization with 33.0% Sm. Meanwhile, nanocrystallite is formed in the amorphous Fe-Sm films. However, no Fe-Sm compound exists with the change of Sm content and with the application of high magnetic field. Nevertheless, high magnetic field decreases interplanar spacing. The structural evolution has a significant effect on magnetic properties. Saturation magnetization decreases 290% from 1456 emu/cm3 to 373 emu/cm3 with the increase of Sm content from 5.8% to 33.0%. The coercivity increases 1225% from 20 Oe to 265 Oe. Meanwhile, both the saturation magnetization and coercivity of the films decrease with the application of high magnetic field. The reason has been discussed.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  20. The relationship between microstructure and magnetic properties in high-energy permanent magnets characterized by polytwinned structures

    NASA Astrophysics Data System (ADS)

    This report summarizes the results of a study of the relationship between microstructure and magnetic properties in a unique genre of ferromagnetic material characterized by a polysynthetically twinned structure which arises during solid state transformation. These results stem from the work over a period of approximately 27 months of a nominal 3 year grant period. The report also contains a proposal to extend the research project for an additional 3 years. The polytwinned structures produce an inhomogeneous magnetic medium in which the easy axis of magnetization varies quasi-periodically giving rise to special domain configurations which are expected to markedly influence the mechanism of magnetization reversal and hysteresis behavior of these materials in bulk or thin films. The extraordinary permanent magnet properties exhibited by the well-known Co-Pt alloys as well as the Fe-Pt and Fe-Pd systems near the equiatomic composition derive from the formation of a polytwinned microstructure.

  1. Optical fiber magnetic field sensor based on single-mode-multimode-single-mode structure and magnetic fluid.

    PubMed

    Chen, Yaofei; Han, Qun; Liu, Tiegen; Lan, Xinwei; Xiao, Hai

    2013-10-15

    An optical fiber magnetic field sensor based on the single-mode-multimode-single-mode (SMS) structure and magnetic fluid (MF) is proposed and demonstrated. By using a piece of no-core fiber as the multimode waveguide in the SMS structure and MF sealed in a capillary tube as the magnetic sensitive media, which totally immersing the no-core fiber, an all-fiber magnetic sensor was fabricated. Interrogation of the magnetic field strength can be achieved either by measuring the dip wavelength shift of the transmission spectrum or by detecting the transmission loss at a specific wavelength. A demonstration sensor with sensitivities up to 905 pm/mT and 0.748 dB/mT was fabricated and investigated. A theoretical model for the design of the proposed device was developed and numerical simulations were performed.

  2. Identification of an incommensurate FeAl{sub 2} overlayer on FeAl(110) using x-ray diffraction and reflectivity

    SciTech Connect

    Baddorf, A.P.; Chandavarkar, S.S.

    1995-06-30

    FeAl, like NiAl, crystallizes in the CsCl structure. Consequently the (110) planes contain equal amounts of Fe and Al distributed as interlocking rectangles. Unlike the NiAI(110) surface, which retains the (1{times}l) in-plane symmetry of the bulk, FeAl(l10) reconstructs to form an ordered, incommensurate overlayer. The reconstructed layer introduces x-ray diffraction rods at half-order positions along the [1{bar 1}0] direction, and displaced {plus_minus}0.2905 from integer positions along the [001] direction. Peak widths reveal excellent long range order. Specular reflectivity measurements above and below the Fe K{alpha} edge can be reproduced using a model containing a single reconstructed overlayer with an Fe:Al ratio of 1:2, consistent with FeA{sub I}2.

  3. Periodic vortex pinning by regular structures in Nb thin films: magnetic vs. structural effects

    NASA Astrophysics Data System (ADS)

    Montero, Maria Isabel; Jonsson-Akerman, B. Johan; Schuller, Ivan K.

    2001-03-01

    The defects present in a superconducting material can lead to a great variety of static and dynamic vortex phases. In particular, the interaction of the vortex lattice with regular arrays of pinning centers such as holes or magnetic dots gives rise to commensurability effects. These commensurability effects can be observed in the magnetoresistance and in the critical current dependence with the applied field. In recent years, experimental results have shown that there is a dependence of the periodic pinning effect on the properties of the vortex lattice (i.e. vortex-vortex interactions, elastic energy and vortex velocity) and also on the dots characteristics (i.e. dot size, distance between dots, magnetic character of the dot material, etc). However, there is not still a good understanding of the nature of the main pinning mechanisms by the magnetic dots. To clarify this important issue, we have studied and compared the periodic pinning effects in Nb films with rectangular arrays of Ni, Co and Fe dots, as well as the pinning effects in a Nb film deposited on a hole patterned substrate without any magnetic material. We will discuss the differences on pinning energies arising from magnetic effects as compared to structural effects of the superconducting film. This work was supported by NSF and DOE. M.I. Montero acknowledges postdoctoral fellowship by the Secretaria de Estado de Educacion y Universidades (Spain).

  4. BIPOLAR MAGNETIC STRUCTURES DRIVEN BY STRATIFIED TURBULENCE WITH A CORONAL ENVELOPE

    SciTech Connect

    Warnecke, Jörn; Losada, Illa R.; Brandenburg, Axel; Kleeorin, Nathan; Rogachevskii, Igor

    2013-11-10

    We report the spontaneous formation of bipolar magnetic structures in direct numerical simulations of stratified forced turbulence with an outer coronal envelope. The turbulence is forced with transverse random waves only in the lower (turbulent) part of the domain. Our initial magnetic field is either uniform in the entire domain or confined to the turbulent layer. After about 1-2 turbulent diffusion times, a bipolar magnetic region of vertical field develops with two coherent circular structures that live during one turbulent diffusion time, and then decay during 0.5 turbulent diffusion times. The resulting magnetic field strengths inside the bipolar region are comparable to the equipartition value with respect to the turbulent kinetic energy. The bipolar magnetic region forms a loop-like structure in the upper coronal layer. We associate the magnetic structure formation with the negative effective magnetic pressure instability in the two-layer model.

  5. 2D Radiative Transfer in Magnetically Confined Structures

    NASA Astrophysics Data System (ADS)

    Heinzel, P.; Anzer, U.

    2003-01-01

    Magnetically confined structures in the solar atmosphere exhibit a large complexity in their shapes and physical conditions. As an example, we show the case of so-called magnetic dips in prominences which are in magnetohydrostatic equilibria. For such models we solve 2D non-LTE multilevel problem for hydrogen with PRD in Lyman resonance lines. The iterative technique used is based on the MALI approach with simple diagonal ALO and SC formal solver. To compute the hydrogen ionization balance, the preconditioned MALI equations are linearized with respect to atomic level populations and electron density and solved iteratively using the Newton-Raphson scheme. Two additional problems are addressed: (i) an adequate iteration method for cases when the column-mass scale is used in one of the two dimensions but varies along the other dimension (which has a geometrical scaling); and (ii) a possibility of using AMR (Adaptive Mesh Refinement) algorithms to account for steep 2D gradients of selected variables (temperature, density, etc.).

  6. Magnetic properties and electronic structure of Mn-Ni-Ga magnetic shape memory alloys.

    PubMed

    D'Souza, Sunil Wilfred; Roy, Tufan; Barman, Sudipta Roy; Chakrabarti, Aparna

    2014-12-17

    Influence of disorder, antisite defects, martensite transition and compositional variation on the magnetic properties and electronic structure of Mn(2)NiGa and Mn(1+x)Ni(2-x)Ga magnetic shape memory alloys have been studied by using full potential spin-polarized scalar relativistic Korringa-Kohn-Rostocker (FP-SPRKKR) method. Mn(2)NiGa is ferrimagnetic and its total spin moment increases when disorder in the occupancy of MnNi (Mn atom in Ni position) is considered. The moment further increases when Mn-Ga antisite defect [1] is included in the calculation. A reasonable estimate of TC for Mn(2)NiGa is obtained from the exchange parameters for the disordered structure. Disorder influences the electronic structure of Mn(2)NiGa through overall broadening of the density of states and a decrease in the exchange splitting. Inclusion of antisite defects marginally broaden the minority spin partial DOS (PDOS), while the majority spin PDOS is hardly affected. For Mn(1+x)Ni(2-x)Ga where 1 ⩾ x ⩾ 0, as x decreases, Mn(Mn) moment increases while Mn(Ni) moment decreases in both austenite and martensite phases. For x ⩾ 0.25, the total moment of the martensite phase is smaller compared to the austenite phase, which indicates possible occurrence of inverse magnetocaloric effect. We find that the redistribution of Ni 3d- Mn(Ni) 3d minority spin electron states close to the Fermi level is primarily responsible for the stability of the martensite phase in Mn-Ni-Ga.

  7. Nonlinear dynamics of drift structures in a magnetized dissipative plasma

    SciTech Connect

    Aburjania, G. D.; Rogava, D. L.; Kharshiladze, O. A.

    2011-06-15

    A study is made of the nonlinear dynamics of solitary vortex structures in an inhomogeneous magnetized dissipative plasma. A nonlinear transport equation for long-wavelength drift wave structures is derived with allowance for the nonuniformity of the plasma density and temperature equilibria, as well as the magnetic and collisional viscosity of the medium and its friction. The dynamic equation describes two types of nonlinearity: scalar (due to the temperature inhomogeneity) and vector (due to the convectively polarized motion of the particles of the medium). The equation is fourth order in the spatial derivatives, in contrast to the second-order Hasegawa-Mima equations. An analytic steady solution to the nonlinear equation is obtained that describes a new type of solitary dipole vortex. The nonlinear dynamic equation is integrated numerically. A new algorithm and a new finite difference scheme for solving the equation are proposed, and it is proved that the solution so obtained is unique. The equation is used to investigate how the initially steady dipole vortex constructed here behaves unsteadily under the action of the factors just mentioned. Numerical simulations revealed that the role of the vector nonlinearity is twofold: it helps the dispersion or the scalar nonlinearity (depending on their magnitude) to ensure the mutual equilibrium and, thereby, promote self-organization of the vortical structures. It is shown that dispersion breaks the initial dipole vortex into a set of tightly packed, smaller scale, less intense monopole vortices-alternating cyclones and anticyclones. When the dispersion of the evolving initial dipole vortex is weak, the scalar nonlinearity symmetrically breaks a cyclone-anticyclone pair into a cyclone and an anticyclone, which are independent of one another and have essentially the same intensity, shape, and size. The stronger the dispersion, the more anisotropic the process whereby the structures break: the anticyclone is more intense

  8. Radio polarization and magnetic field structure in M 101

    NASA Astrophysics Data System (ADS)

    Berkhuijsen, E. M.; Urbanik, M.; Beck, R.; Han, J. L.

    2016-04-01

    We observed total and polarized radio continuum emission from the spiral galaxy M 101 at λλ 6.2 cm and 11.1 cm with the Effelsberg telescope. The angular resolutions are 2.´ 5 (=5.4 kpc) and 4.´ 4 (=9.5 kpc), respectively. We use these data to study various emission components in M 101 and properties of the magnetic field. Separation of thermal and non-thermal emission shows that the thermal emission is closely correlated with the spiral arms, while the non-thermal emission is more smoothly distributed indicating diffusion of cosmic ray electrons away from their places of origin. The radial distribution of both emissions has a break near R = 16 kpc (=7.´ 4), where it steepens to an exponential scale length of L ≃ 5 kpc, which is about 2.5 times smaller than at R< 16 kpc. The distribution of the polarized emission has a broad maximum near R = 12 kpc and beyond R = 16 kpc also decreases with L ≃ 5 kpc. It seems that near R = 16 kpc a major change in the structure of M 101 takes place, which also affects the distributions of the strength of the random and ordered magnetic field. Beyond R = 16 kpc the radial scale length of both fields is about 20 kpc, which implies that they decrease to about 0.3 μG at R = 70 kpc, which is the largest optical extent. The equipartition strength of the total field ranges from nearly 10 μG at R< 2 kpc to 4 μG at R = 22-24 kpc. As the random field dominates in M 101 (Bran/Bord ≃ 2.4), wavelength-independent polarization is the main polarization mechanism. We show that energetic events causing H i shells of mean diameter < 625 pc could partly be responsible for this. At radii < 24 kpc, the random magnetic field depends on the star formation rate/area, ΣSFR, with a power-law exponent of b = 0.28 ± 0.02. The ordered magnetic field is generally aligned with the spiral arms with pitch angles that are about 8° larger than those of H i filaments. Based on observations with the 100 m telescope of the MPIfR at Effelsberg

  9. Electronic structure and magnetic state of transuranium metals under pressure.

    PubMed

    Lukoyanov, A V; Shorikov, A O; Bystrushkin, V B; Dyachenko, A A; Kabirova, L R; Tsiovkin, Yu Yu; Povzner, A A; Dremov, V V; Korotin, M A; Anisimov, V I

    2010-12-15

    The electronic structures of bcc Np, fcc Pu, Am, and Cm pure metals under pressure have been investigated employing the LDA + U method with spin-orbit coupling (LDA + U + SO). The magnetic state of the actinide ions was analyzed in both LS and jj coupling schemes to reveal the applicability of corresponding coupling bases. It was demonstrated that whereas Pu and Am are well described within the jj coupling scheme, Np and Cm can be described appropriately neither in a {mσ}, nor in a {jmj} basis, due to intermediate coupling scheme realization in these metals that requires some finer treatment. The LDA + U + SO results for the considered transuranium metals reveal band broadening and gradual 5f electron delocalization under pressure.

  10. Nuclear magnetic resonance probes of membrane biophysics: Structure and dynamics

    NASA Astrophysics Data System (ADS)

    Leftin, Avigdor

    The phospholipid membrane is a self-assembled, dynamic molecular system that may exist alone in association with only water, or in complex systems comprised of multiple lipid types and proteins. In this dissertation the intra- and inter-molecular forces responsible for the atomistic, molecular and collective equilibrium structure and dynamics are studied by nuclear magnetic resonance spectroscopy (NMR). The multinuclear NMR measurements and various experimental techniques are able to provide data that enable the characterization of the hierarchical spatio-temporal organization of the phospholipid membrane. The experimental and theoretical studies conducted target membrane interactions ranging from model systems composed of only water and lipids, to multiple component domain forming membranes that are in association with peripheral and trans-membrane proteins. These measurements consisit of frequency spectrum lineshapes and nuclear-spin relaxation rates obtained using 2H NMR, 13C NMR, 31P NMR and 1H NMR. The changes of these experimental observables are interpreted within a statistical thermodynamic framework that allows the membrane structure, activation energies, and correlation times of motion to be determined. The cases presented demonstrate how fundamental principles of NMR spectroscopy may be applied to a host of membranes, leading to the biophysical characterization of membrane structure and dynamics.

  11. Improvement of neutral beam injection heating efficiency with magnetic field well structures in a tokamak with a low magnetic field

    NASA Astrophysics Data System (ADS)

    Kim, S. K.; Na, D. H.; Lee, J. W.; Yoo, M. G.; Kim, H.-S.; Hwang, Y. S.; Hahm, T. S.; Na, Yong-Su

    2016-10-01

    Magnetic well structures are introduced as an effective means to reduce the prompt loss of fast ions, the so-called first orbit loss from neutral beam injection (NBI), which is beneficial to tokamaks with a low magnetic field strength such as small spherical torus devices. It is found by single-particle analysis that this additional field structure can modify the gradient of the magnetic field to reduce the shift of the guiding center trajectory of the fast ion. This result is verified by a numerical calculation of following the fast ion’s trajectory. We apply this concept to the Versatile Experiment Spherical Torus [1], where NBI is under design for the purpose of achieving high-performance plasma, to evaluate the effect of the magnetic well structure on NBI efficiency. A 1D NBI analysis code and the NUBEAM code are employed for detailed NBI calculations. The simulation results show that the orbit loss can be reduced by 70%-80%, thereby improving the beam efficiency twofold compared with the reference case without the well structure. The well-shaped magnetic field structure in the low-field side can significantly decrease orbit loss by broadening the non-orbit loss region and widening the range of the velocity direction, thus improving the heating efficiency. It is found that this magnetic well can also improve orbit loss during the slowing down process.

  12. Magnetic susceptibility, specific heat and magnetic structure of CuNi{sub 2}(PO{sub 4}){sub 2}

    SciTech Connect

    Escobal, Jaione; Pizarro, Jose L.; Mesa, Jose L. . E-mail: joseluis.mesa@ehu.es; Larranaga, Aitor; Fernandez, Jesus Rodriguez; Arriortua, Maria I.; Rojo, Teofilo

    2006-10-15

    CuNi{sub 2}(PO{sub 4}){sub 2} phosphate has been synthesized by the ceramic method at 800 deg. C in air. The crystal structure consists of a three-dimensional skeleton constructed from MO{sub 4} (M{sup II} =Cu and Ni) planar squares and M{sub 2}O{sub 8} dimers with square pyramidal geometry, which are interconnected by (PO{sub 4}){sup 3-} oxoanions with tetrahedral geometry. The magnetic behavior has been studied on powdered sample by using susceptibility, specific heat and neutron diffraction data. The bimetallic copper(II)-nickel(II) orthophosphate exhibits a three-dimensional magnetic ordering at, approximately, 29.8 K. However, its complex crystal structure hampers any parametrization of the J-exchange parameter. The specific heat measurements exhibit a three-dimensional magnetic ordering ({lambda}-type) peak at 29.5 K. The magnetic structure of this phosphate shows ferromagnetic interactions inside the Ni{sub 2}O{sub 8} dimers, whereas the sublattice of Cu(II) ions presents antiferromagnetic couplings along the y-axis. The change of the sign in the magnetic unit-cell, due to the [1/2, 0, 1/2] propagation vector determines a purely antiferromagnetic structure. - Graphical abstract: Magnetic structure of CuNi2(PO4)2.

  13. Nanoscaled Magnetic Electrodeposited Structures on the Basis of Ion Group Metals: Preparation, Structure, Magnetic and Magnetoresistive Properties

    DTIC Science & Technology

    2000-01-01

    anisotropy components. The contribution of the surface anisotropy constant to the perpendicular magnetic anisotropy becomes predominant when the magnetic layer...increase (Fig.4). Additional evidence of the development of perpendicular magnetic anisotropy can be seen from the magnetization reversal curves...films with perpendicular magnetic anisotropy , Phys.Stat.Sol.(a), 25, 359-363. 8. Fedosyuk V.M., Kasyutich 0.1., Sheleg M.U. (1989),J.Electrochem.Soc

  14. Magnetic structure of the spin-1/2 layer compound NaNiO2

    NASA Astrophysics Data System (ADS)

    Darie, C.; Bordet, P.; de Brion, S.; Holzapfel, M.; Isnard, O.; Lecchi, A.; Lorenzo, J. E.; Suard, E.

    2005-01-01

    We have carried out high resolution neutron powder diffraction experiments aiming at a determination of the magnetic structure of the S=1/2 layer compound NaNiO2. The magnetic moments are ferromagnetically aligned in the NiO2 layers and antiparallel between layers. The direction of the magnetic moment has a small component along the a-direction.

  15. Complex long-range magnetic ordering in the Mn-bearing dugganite Pb{sub 3}TeMn{sub 3}P{sub 2}O{sub 14}

    SciTech Connect

    Silverstein, H.J.; Sharma, A.Z.; Cruz-Kan, K.; Zhou, H.D.; Huq, A.; Flacau, R.; Wiebe, C.R.

    2013-08-15

    Spin liquids, multiferroics, and doubly-chiral helical structures are just some of the exotic magnetic states found in the langasite compounds. A subclass of the langasite group, the Te{sup 6+}-containing dugganites, has also shown exotic magnetism including magnetoelectric coupling, coexisting complex long-ranged ordered structures, and low-field induced magnetic transitions. Here, we present the first detailed structural study of Pb{sub 3}TeMn{sub 3}P{sub 2}O{sub 14} as well as the first neutron scattering measurements. This material undergoes long-range magnetic ordering, similar to the multiferroic Ba{sub 3}NbFe{sub 3}Si{sub 2}O{sub 14}, at T{sub N}=6.6 K, which is consistent with previous magnetization measurements. However unlike any other langasite or dugganite studied to date, we present evidence of a large, pseudohexagonal incommensurate supercell that alters the nuclear and magnetic structures away from the langasite ideal. - Graphical abstract: Two geometrically frustrated cationic substructures of the langasites and dugganites have profound effects on the magnetism of these compounds. In Pb{sub 3}TeMn{sub 3}P{sub 2}O{sub 14}, Mn{sup 2+} (S=5/2) isolated trinuclear units are shown in yellow, while the red distorted kagomé network is nonmagnetic. (For interpretation of the references to color the reader is referred to the web version of this article.) Highlights: • Polycrystalline Pb{sub 3}TeMn{sub 3}P{sub 2}O{sub 14} was prepared. • Found evidence of a large, pseudohexagonal supercell that is incommensurate with the subcell. • Long-range antiferromagnetic ordering is observed below T{sub N}=6.6 K similar to Ba{sub 3}NbFe{sub 3}Si{sub 2}O{sub 14}. • Broken symmetry probably causes magnetic peak splitting in this system.

  16. A magnetic-piezoelectric smart material-structure utilizing magnetic force interaction to optimize the sensitivity of current sensing

    NASA Astrophysics Data System (ADS)

    Yeh, Po-Chen; Chung, Tien-Kan; Lai, Chen-Hung; Wang, Chieh-Min

    2016-01-01

    This paper presents a magnetic-piezoelectric smart material-structure using a novel magnetic-force-interaction approach to optimize the sensitivity of conventional piezoelectric current sensing technologies. The smart material-structure comprises a CuBe-alloy cantilever beam, a piezoelectric PZT sheet clamped to the fixed end of the beam, and an NdFeB permanent magnet mounted on the free end of the beam. When the smart material-structure is placed close to an AC conductor, the magnet on the beam of the smart structure experiences an alternating magnetic attractive and repulsive force produced by the conductor. Thus, the beam vibrates and subsequently generates a strain in the PZT sheet. The strain produces a voltage output because of the piezoelectric effect. The magnetic force interaction is specifically enhanced through the optimization approach (i.e., achieved by using SQUID and machining method to reorient the magnetization to different directions to maximize the magnetic force interaction). After optimizing, the beam's vibration amplitude is significantly enlarged and, consequently, the voltage output is substantially increased. The experimental results indicated that the smart material-structure optimized by the proposed approach produced a voltage output of 4.01 Vrms with a sensitivity of 501 m Vrms/A when it was placed close to a conductor with a current of 8 A at 60 Hz. The optimized voltage output and sensitivity of the proposed smart structure were approximately 316 % higher than those (1.27 Vrms with 159 m Vrms/A) of representative piezoelectric-based current sensing technologies presented in other studies. These improvements can significantly enable the development of more self-powered wireless current sensing applications in the future.

  17. Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis

    SciTech Connect

    Zhang, C.; Yamanouchi, M. Ikeda, S.; Sato, H.; Fukami, S.; Matsukura, F.; Ohno, H.

    2014-05-07

    We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.

  18. Structural Electronic and Magnetic Properties of Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Continenza, Alessandra

    1990-01-01

    This work is focussed on the structural, electronic and magnetic properties of semiconductor interfaces. The issues and the interest involved in these particular systems are various and have engaged both the scientific and the technological community for more than three decades. The technological interest toward semiconductors is obviously related to device applications while the scientific interest is mainly focussed on the understanding of some characteristic properties, such as potential barriers, carrier properties and band gaps, and how these can be modified by changing different external factors, such as epitaxial growth, strain effects, junctions and doping. A complete knowledge and understanding of these complex issues is, in fact, the basic requirement necessary in order to achieve the ability to "tune" basic properties "at will" and designing the "ad hoc" material for each different device application. We have performed a study of the magnetic, structural and electronic properties of a few particular examples of semiconductor interfaces and heterojunctions namely, rm Fe_{n}/(ZnSe)_ {m}, rm(InAs)_{n }/(InP)_{n} and rm( alpha-Sn)_{n}/(CdTe)_{n }, using the all-electron full-potential linearized augmented plane wave (FLAPW) method. Together with a study of the interface properties, we present results of calculations performed on all the pure constituents, in order to provide comparisons and to better understand how the bulk properties are modified by the interface. In particular, we have analyzed how the properties of these structures can be tailored by changing quantities such as the superlattice periodicity, the epitaxial strain and the interface morphology. We found that the relevance of these factors changes depending on the particular material under study and that it is possible, indeed, to model the characteristics electronic and transport properties of each structure by properly tuning the growth conditions. Our results are in very good agreement with

  19. Strain-Magnetization Properties and Domain Structures of Silicon Steel Sheets

    NASA Astrophysics Data System (ADS)

    Notoji, Atsushi; Saito, Akihiko; Hayakawa, Motozo

    The effects of tensile stress and strain on magnetization and magnetic domains in silicon steel sheets were investigated. The magnetization of elastic deformation regions decreased with increase of strain and the strain-magnetization properties of plastic deformation regions under stress showed peculiar characteristics. The magnetization increased with decreasing strain. We observed Lancet and other domains in a sample, especially around the boundary of crystal, after removing stress applied to a plastic deformation region. This phenomenon can be explained by changes in the domain structures, which were partly observed. This results obtained in this investigation can be applied to the nondestructive detection of fatigue in metallic magnetic materials.

  20. Study of local structure and magnetism in high-T(sub c) copper oxide superconductors

    NASA Technical Reports Server (NTRS)

    Budnick, J. I.; Tan, Z.; Filipkowski, M.; Niedermayer, CH.; Glueckler, H.; Simon, R.; Golnik, A.; Rauer, M.; Recknagel, E.; Weidinger, A.

    1990-01-01

    The muon spin rotation (MUSR) study of local magnetism of Sr-doped La2CuO4 is reviewed. Emphasis is placed on magnetic order as detected by local and bulk probes with local atomic environments studied by x ray absorption fine structure (XAFS). Correlations between the MUSR study of local magnetic ordering and the bulk magnetization study are presented along with a discussion of the dependence upon oxygen stoichiometry. Results are presented for both superconducting phases and magnetic phases. Recent data which reveals the existence of local magnetic ordering in the hydrogen-doped YBa2Cu3O7 system are also discussed.

  1. Magnetic Field Anomalies Above Large Martian Impact Structures

    NASA Astrophysics Data System (ADS)

    Langlais, B.; Ostanciaux; Thébault, E.

    2008-12-01

    The Mars Global Surveyor NASA mission revealed the complex nature of the lithospheric magnetic field of Mars. Intense anomalies are located above the southern cratered highlands, while the giant impact basins (Hellas, Argyre, Utopia) and the northern smoothed lowlands do not show significant anomalies. Here we study the magnetic signal above large impact craters, with diameters ranging between 100 and 2000 km. Magnetic measurements are carefully screened and selected to avoid non static features. Then the mean magnetic field is evaluated both inside each crater rim and in its immediate vicinity, within one crater radius. The ratio of these two quantities helps to determine which craters modified the magnetic properties of the pre-impact lithosphere. In addition, this technique allows the impacts located in the strongly magnetized Terra Sirenum and Terra Cimmeria to be studied. Results of this study, as well as comparison of the magnetic measurements to predicted ones for different pre-impact magnetization directions will be presented.

  2. Isolated magnetic field structures in Mercury's magnetosheath as possible analogues for terrestrial magnetosheath plasmoids and jets

    NASA Astrophysics Data System (ADS)

    Karlsson, Tomas; Liljeblad, Elisabet; Kullen, Anita; Raines, Jim M.; Slavin, James A.; Sundberg, Torbjörn

    2016-09-01

    We have investigated MESSENGER magnetic field data from the Mercury magnetosheath and near solar wind, to identify isolated magnetic field structures (defined as clear, isolated changes in the field magnitude). Their properties are studied in order to determine if they may be considered as analogues to plasmoids and jets known to exist in Earth's magnetosheath. Both isolated decreases of the magnetic field absolute value ('negative magnetic field structures') and increases ('positive structures') are found in the magnetosheath, whereas only negative structures are found in the solar wind. The similar properties of the solar wind and magnetosheath negative magnetic field structures suggests that they are analogous to diamagnetic plasmoids found in Earth's magnetosheath and near solar wind. The latter have earlier been identified with solar wind magnetic holes. Positive magnetic field structures are only found in the magnetosheath, concentrated to a region relatively close to the magnetopause. Their proximity to the magnetopause, their scale sizes, and the association of a majority of the structures with bipolar magnetic field signatures identify them as flux transfer events (which generally are associated with a decrease of plasma density in the magnetosheath). The positive magnetic field structures are therefore not likely to be analogous to terrestrial paramagnetic plasmoids but possibly to a sub-population of magnetosheath jets. At Earth, a majority of magnetosheath jets are associated with the quasi-parallel bow shock. We discuss some consequences of the findings of the present investigation pertaining to the different nature of the quasi-parallel bow shock at Mercury and Earth.

  3. Multiferroicity and spiral magnetism in FeVO{sub 4} with quenched Fe orbital moments

    SciTech Connect

    Daoud-Aladine, A.; Chapon, L. C.; Kundys, B.; Martin, C.; Simon, C.; Radaelli, P. G.; Brown, P. J.

    2009-12-01

    FeVO{sub 4} has been studied by heat capacity, magnetic susceptibility, electric polarization and single-crystal neutron-diffraction experiments. The triclinic crystal structure is made of S-shaped clusters of six Fe{sup 3+} ions, linked by VO{sub 4}{sup 3-} groups. Two long-range magnetic ordering transitions occur at T{sub N1}=22 K and T{sub N2}=15 K. Both magnetic structures are incommensurate and below T{sub N2}, FeVO{sub 4} becomes weakly ferroelectric coincidentally with the loss of the collinearity of the magnetic structure in a very similar fashion than in the classical TbMnO{sub 3} multiferroic material. However we argue that the symmetry considerations and the mechanisms invoked to explain these properties in TbMnO{sub 3} do not straightforwardly apply to FeVO{sub 4}. First, the magnetic structures, even the collinear structure, are all acentric so that ferroelectricity in FeVO{sub 4} is not correlated with the fact magnetic ordering is breaking inversion symmetry. Regarding the mechanism, FeVO{sub 4} has quenched orbital moments that questions the exact role of the spin-orbit interactions.

  4. Modeling and Measurements by Hall probes of Magnetic Structures of Undulators HU256

    SciTech Connect

    Batrakov, A.; Churkin, I.; Ilyin, I.; Steshov, A.; Vobly, P.; Briquez, F.; Chubar, O.; Dael, A.; Roux, G.; Valleau, M.

    2007-01-19

    The magnetic calculations of the individual dipoles and dipoles in 'undulator environment' were executed by means of Mermaid 3D Code and these results were confirmed by magnetic measurements of the individual dipoles and the assembled undulators. The magnetic parameters of all dipoles were estimated on basis of the mechanical measurement of the dipole characteristics (pole gap, yoke width, coil position) and the main dependences obtained from magnetic calculations and measurements. These parameters were used for optimal placing of the dipoles in undulators (sorting). The special Hall probe system was designed and manufactured for magnetic measurements of the undulators. It allowed us to observe the inner structure of the magnetic fields. At a magnetic field measurement accuracy of {+-} 15 {mu}T the accuracy of the 1st integral calculated on the basis of the measured magnetic fields is {approx} 50 {mu}Tm. All three undulators were magnetically measured at BINP and are being re-measured at Soleil after transportation.

  5. Mapping of the magnetic field structure during the sawtooth instability

    NASA Astrophysics Data System (ADS)

    Pavlenko, Ivan; Weyssow, Boris; Carati, Daniele

    2001-10-01

    The periodic relaxation oscillations of the plasma parameters in the central region of the tokamak discharges (sawtooth oscillations) play an important role in ITER plasma. The well known Kadomtsev model of the magnetic reconnection during sawtooth oscillations is based on the hypothesis of magnetic helicity conservation [Kadomtsev B.B. 1975 Sov. J. Plasma Phys. 1 389]. According to the Kadomtsev model, the sawtooth crash is the result of fast and complete magnetic reconnection of a crescent shaped magnetic island formed inside the q=1 surface. In contrast, the incomplete relaxation model assumes the development of the widespread magnetic turbulence when the magnetic island reaches a critical width. This model keeps the value q=0 below unity after the crash. Sawtooth instabilities cause sudden changes in the magnetic topology. We propose a simple mapping procedure for time evolution of the magnetic field topology during crash phase of the sawtooth oscillations. The time evolution of the safety factor profile is constructed in agreement with the assumption that magnetic helicity is conserved during sawtooth crash. Both Kadomtsev and incomplete relaxation models of the magnetic reconnection can be qualitatively described by the TOKAMAP [Balescu R. et al 1998 Physical Review E 58 951]. In the same time the topology of the magnetic surfaces shows the main features of the magnetic field in real tokamaks.

  6. Variation of magnetic braking by non-axisymmetric magnetic fields depending on the perturbed field structure in the KSTAR tokamak

    NASA Astrophysics Data System (ADS)

    Kim, Kimin; Jeon, Y. M.; Park, J.-K.; Ko, W. H.; In, Y.; Choe, W.; Kim, J.; Lee, S. G.; Yoon, S. W.; Kwak, J. G.; Oh, Y. K.

    2017-03-01

    The variation of a magnetic braking profile by non-axisymmetric magnetic fields has been experimentally demonstrated and numerically validated in the KSTAR tokamak. Two types of n  =  2 non-resonant magnetic fields were applied by changing the relative phase of non-axisymmetric field coils. One is even parity, of which non-resonant fields deeply penetrate into the plasma core, and the other is odd parity localized at the plasma edge. The even and odd parity produced significantly different perturbed magnetic field structures, and thereby drove global and edge-dominant toroidal rotation damping, respectively. These distinct braking profiles are consistently reproduced by drift-kinetic particle simulations, indicating the possibility of the predictive utilization of non-resonant magnetic fields for rotation profile control.

  7. Monte Carlo simulation of magnetic multilayered structures with giant magnetoresistance effects

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskiy, D. E.

    2016-02-01

    Description of giant magnetoresistance effects in magnetic multilayered structures with the use of the anisotropic Heisenberg model for determination of magnetic properties of thin ferromagnetic films forming these structures is given. Monte Carlo simulations of magnetic properties for structures, which are constructed from two ferromagnetic films divided by nonmagnetic film, are carried out. The temperature and magnetic field dependencies are considered for ferromagnetic and antiferromagnetic configurations of these structures. The calculation of the magnetoresistance is carried out for different thicknesses of the ferromagnetic films. It was shown, that the obtained temperature dependence for the magnetoresistance is agreed very well with experimental results, measured for the magnetic multilayered structures similar to structures, which are considered in our investigations.

  8. Magnetization of Rare Earth/Cobalt Permanent Magnets Subsequent to Assembly in Complex Rotor Structures.

    DTIC Science & Technology

    1982-06-01

    Coercive Force with Temperature 2S 11 Magnet Demagnetization Versus Temperature 28 12 Non-recoverable Loss Versus Exposure Temperature 30 13 Magnet...elevated temperature (400-5000 C) and a moderate de- magnetizing field, about 1000 Oe. The cooling rate from this exposure is unimportant. The remagnetized...magnetization is low. The 500 C exposure does not appear to affect the microstructure which controls the remag- netization coercive force. 4

  9. The fragile magnetic structures of Fe/CeH 2- δ multilayers

    NASA Astrophysics Data System (ADS)

    Lohstroh, W.; Schulte, O.; Felsch, W.; Klose, F.; Maletta, H.; Felcher, G. P.; Lauter, H.

    2000-02-01

    Fe/CeH 2- δ multilayers exhibit at room temperature evidence of interlayer exchange coupling. Subsequent Fe layers are either parallel or antiparallel to each other, depending on the Fe and CeH 2- δ layer thickness. However, when both layers have thickness larger than ˜15 Å, the antiferromagnetic structure becomes fragmented into domains laterally limited to a few microns, and the magnetic structures become very fragile. Small magnetic fields of a few Oersteds acting on the samples during growth induce helimagnetic configurations which coexist with antiferromagnetic coupling. The magnetic structures can be permanently destroyed by applying magnetic fields larger than 150 Oe.

  10. BaGe6 and BaGe(6-x): incommensurately ordered vacancies as electron traps.

    PubMed

    Akselrud, Lev; Wosylus, Aron; Castillo, Rodrigo; Aydemir, Umut; Prots, Yurii; Schnelle, Walter; Grin, Yuri; Schwarz, Ulrich

    2014-12-15

    We report the high-pressure high-temperature synthesis of the germanium-based framework compounds BaGe6 (P = 15 GPa, T = 1073 K) and BaGe(6-x) (P = 10 GPa, T = 1073 K) which are metastable at ambient conditions. In BaGe(6-x), partial fragmentation of the BaGe6 network involves incommensurate modulations of both atomic positions and site occupancy. Bonding analysis in direct space reveals that the defect formation in BaGe(6-x) is associated with the establishment of free electron pairs around the defects. In accordance with the electron precise composition of BaGe(6-x) for x = 0.5, physical measurements evidence semiconducting electron transport properties which are combined with low thermal conductivity.

  11. Inhibition of chaotic escape from a potential well by incommensurate escape-suppressing excitations.

    PubMed

    Chacón, R; Martínez, J A

    2002-03-01

    Theoretical results are presented concerning the reduction of chaotic escape from a potential well by means of a harmonic parametric excitation that satisfies an ultrasubharmonic resonance condition with the escape-inducing excitation. The possibility of incommensurate escape-suppressing excitations is demonstrated by studying rational approximations to the irrational escape-suppressing frequency. The analytical predictions for the suitable amplitudes and initial phases of the escape-suppressing excitation are tested against numerical simulations based on a high-resolution grid of initial conditions. These numerical results indicate that the reduction of escape is reliably achieved for small amplitudes and at, and only at, the predicted initial phases. For the case of irrational escape-suppressing frequencies, the effective escape-reducing initial phases are found to lie close to the accumulation points of the set of suitable initial phases that are associated with the complete series of convergents up to the convergent giving the chosen rational approximation.

  12. Elastic anomaly and aging of new type of incommensurate phase transition in ferroelectric barium sodium niobate

    NASA Astrophysics Data System (ADS)

    Christy, Yohanes; Matsumoto, Kazuya; Kojima, Seiji

    2015-07-01

    The lattice instability of the incommensurate (IC) phase transition of uniaxial ferroelectric Ba2NaNb5O15 (BNN) was investigated by micro-Brillouin scattering. Spectra of the longitudinal acoustic (LA) mode were observed from room temperature to 750 K. In the vicinity of the IC phase transition temperature TIC = 573 K, elastic anomalies in the form of a sharp peak in the sound velocity and thermal hysteresis during the heating and cooling cycle were observed. During this transition, the crystal point group changed from tetragonal 4mm to orthorhombic 2mm along with the IC modulation. In order to deepen our understanding of the thermal hysteresis, aging experiment in the IC phase was conducted. We can conclude that the appearance of thermal hysteresis related to the relaxation of ferroelastic strain is related to the feature of the new type III IC phase transition mechanism of BNN.

  13. The interplay of long-range magnetic order and single-ion anisotropy in rare earth nickel germanides

    SciTech Connect

    Islam, Z.

    1999-05-10

    This dissertation is concerned with the interplay of long-range order and anisotropy in the tetragonal RNi{sub 2}Ge{sub 2} (R = rare earth) family of compounds. Microscopic magnetic structures were studied using both neutron and x-ray resonant exchange scattering (XRES) techniques. The magnetic structures of Tb, Dy, Eu and Gd members have been determined using high-quality single-crystal samples. This work has correlated a strong Fermi surface nesting to the magnetic ordering in the RNi{sub 2}Ge{sub 2} compounds. Generalized susceptibility, {chi}{sub 0}(q), calculations found nesting to be responsible for both incommensurate ordering wave vector in GdNi{sub 2}Ge{sub 2}, and the commensurate structure in EuNi{sub 2}Ge{sub 2}. A continuous transition from incommensurate to commensurate magnetic structures via band filling is predicted. The surprisingly higher T{sub N} in EuNi{sub 2}Ge{sub 2} than that in GdNi{sub 2}Ge{sub 2} is also explained. Next, all the metamagnetic phases in TbNi{sub 2}Ge{sub 2} with an applied field along the c axis have been characterized with neutron diffraction measurements. A mixed phase model for the first metamagnetic structure consisting of fully-saturated as well as reduced-moment Tb ions is presented. The moment reduction may be due to moment instability which is possible if the exchange is comparable to the low-lying CEF level splitting and the ground state is a singlet. In such a case, certain Tb sites may experience a local field below the critical value needed to reach saturation.

  14. Effect of milling time on magnetic properties and structures of bulk Sm-Co/{alpha}-(Fe, Co) nanocomposite magnets

    SciTech Connect

    Shen, Y.; Huang, M. Q.; Turgut, Z.; Lucas, M. S.; Michel, E.; Horwath, J. C.

    2012-04-01

    Bulk Sm-Co/{alpha}-(Fe,Co) nanocomposite magnets were fabricated by hot pressing composite powders prepared by high-energy ball milling of magnetically hard SmCo{sub 5} powder and magnetically soft Fe powder. The bulk magnets had a nanocomposite structure consisting of Sm-Co matrix (1:5 H and 1:7 H phases) and {alpha}-(Fe,Co) phases. The Fe-Co particles were distributed uniformly in the Sm-Co matrix. The milling time strongly affects the structures and the magnetic properties of the bulk magnets. Increasing milling time led to a decrease of the amount of 1:5 H phase, an increase in the phase fraction of the 1:7 H phase, and a decrease in the amount of soft phase, which resulted in an increase in magnetization and a decrease in coercivity. Scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) analyses revealed that inter-diffusion took place between the Sm-Co matrix and Fe particles during the processing.

  15. Effect of milling time on magnetic properties and structures of bulk Sm-Co/α-(Fe, Co) nanocomposite magnets

    NASA Astrophysics Data System (ADS)

    Shen, Y.; Huang, M. Q.; Turgut, Z.; Lucas, M. S.; Michel, E.; Horwath, J. C.

    2012-04-01

    Bulk Sm-Co/α-(Fe,Co) nanocomposite magnets were fabricated by hot pressing composite powders prepared by high-energy ball milling of magnetically hard SmCo5 powder and magnetically soft Fe powder. The bulk magnets had a nanocomposite structure consisting of Sm-Co matrix (1:5 H and 1:7 H phases) and α-(Fe,Co) phases. The Fe-Co particles were distributed uniformly in the Sm-Co matrix. The milling time strongly affects the structures and the magnetic properties of the bulk magnets. Increasing milling time led to a decrease of the amount of 1:5 H phase, an increase in the phase fraction of the 1:7 H phase, and a decrease in the amount of soft phase, which resulted in an increase in magnetization and a decrease in coercivity. Scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) analyses revealed that inter-diffusion took place between the Sm-Co matrix and Fe particles during the processing.

  16. Dynamic of the Dust Structures under Magnetic Field Effect in DC Glow Discharges

    SciTech Connect

    Vasiliev, M. M.; D'yachkov, L. G.; Antipov, S. N.; Petrov, O. F.; Fortov, V. E.

    2008-09-07

    In this work, we investigate dust structures in the striation of DC glow discharges under magnetic field actions. The dependence of rotation frequency of dusty plasma structures as a function of the magnetic field was investigated. For various magnetic fields kinetic temperatures of the dust particles, diffusion coefficients, and effective coupling coefficient {gamma}* have been determined. Obtained results are analyzed and compared with theoretical predictions.

  17. Bit patterned media with composite structure for microwave assisted magnetic recording

    NASA Astrophysics Data System (ADS)

    Eibagi, Nasim

    Patterned magnetic nano-structures are under extensive research due to their interesting emergent physics and promising applications in high-density magnetic data storage, through magnetic logic to bio-magnetic functionality. Bit-patterned media is an example of such structures which is a leading candidate to reach magnetic densities which cannot be achieved by conventional magnetic media. Patterned arrays of complex heterostructures such as exchange-coupled composites are studied in this thesis as a potential for next generation of magnetic recording media. Exchange-coupled composites have shown new functionality and performance advantages in magnetic recording and bit patterned media provide unique capability to implement such architectures. Due to unique resonant properties of such structures, their possible application in spin transfer torque memory and microwave assisted switching is also studied. This dissertation is divided into seven chapters. The first chapter covers the history of magnetic recording, the need to increase magnetic storage density, and the challenges in the field. The second chapter introduces basic concepts of magnetism. The third chapter explains the fabrication methods for thin films and various lithographic techniques that were used to pattern the devices under study for this thesis. The fourth chapter introduces the exchanged coupled system with the structure of [Co/Pd] / Fe / [Co/Pd], where the thickness of Fe is varied, and presents the magnetic properties of such structures using conventional magnetometers. The fifth chapter goes beyond what is learned in the fourth chapter and utilizes polarized neutron reflectometry to study the vertical exchange coupling and reversal mechanism in patterned structures with such structure. The sixth chapter explores the dynamic properties of the patterned samples, and their reversal mechanism under microwave field. The final chapter summarizes the results and describes the prospects for future

  18. Static and dynamic properties of incommensurate smectic-A/sub I//sub C/ liquid crystals

    SciTech Connect

    Lubensky, T.C.; Ramaswamy, S.; Toner, J.

    1988-10-15

    We study the elasticity, topological defects, and hydrodynamics of the recently discovered incommensurate smectic (A/sub I//sub C/) phase, characterized by two collinear mass density waves of incommensurate spatial frequency. The low-energy long-wavelength excitations of the system can be described by a displacement field u(x) and a ''phason'' field w(x) associated, respectively, with collective and relative motion of the two constituent density waves. We formulate the elastic free energy in terms of these two variables and find that when w = 0, its functional dependence on u is identical to that of a conventional smectic liquid crystal, while when u = 0, its functional dependence on w is the same as that for the angle variable in a slightly anisotropic XY model. An arbitrariness in the definition of u and w allows a choice that eliminates all relevant couplings between them in the long-wavelength elastic energy. The topological defects of the system are dislocations with nonzero u and w components. We introduce a two-dimensional Burgers lattice for these dislocations, and compute the interaction between them. This has two parts: one arising from the u field that is short ranged and identical to the interaction between dislocations in an ordinary smectic liquid crystal, and one arising from the w field that is long ranged and identical to the logarithmic interaction between vortices in an XY model. The hydrodynamic modes of the A/sub I//sub C/ include first- and second-sound modes whose direction-dependent velocities are identical to those in ordinary smectics.

  19. First-principles study of interface magnetic structure in Nd2Fe14B /(Fe ,Co ) exchange spring magnets

    NASA Astrophysics Data System (ADS)

    Umetsu, Nobuyuki; Sakuma, Akimasa; Toga, Yuta

    2016-01-01

    The magnetic properties of Nd2Fe14B (NFB)/transition metal (TM = Fe, Co) multilayer systems are studied on the basis of first-principles density functional calculations. Assuming a collinear spin structure, we optimize the model structure under a variety of crystallographic alignments of the NFB layer, and analyze the mechanism of interface magnetic coupling. Improvements in remanent magnetization compared to that of single NFB are observed in NFB(001)/Fe, NFB(110)/Fe, and NFB(100)/Co. On the other hand, in NFB(100)/Fe, remanence degradation due to the antiparallel magnetization alignment between NFB and Fe layers is observed. In this system, which has the shortest optimized interlayer distance among all considered systems, an itinerant electron magnetism is required around the interface to lower the total energy, and accordingly, antiferromagnetic coupling is preferred. The significant difference in property between NFB(100)/Fe and NFB(100)/Co is attributed to the difference between their interface structures, optimized interlayer distances, and magnetic stiffness of TM layers.

  20. Syntheses, structures, magnetism, and optical properties of gadolinium scandium chalcogenides

    SciTech Connect

    Jin Gengbang; Choi, Eun Sang; Albrecht-Schmitt, Thomas E.

    2009-05-15

    Three gadolinium scandium chalcogenides have been synthesized using Sb{sub 2}Q{sub 3} (Q=S, Se) fluxes at 975 deg. C. Gd{sub 3.04}Sc{sub 0.96}S{sub 6}, GdScS{sub 3}, and Gd{sub 1.05}Sc{sub 0.95}Se{sub 3} are crystallized in U{sub 3}ScS{sub 6} type, GdFeO{sub 3} type, and UFeS{sub 3} type structures, respectively. The magnetic susceptibilities for these compounds follow the Curie-Weiss law above their transition temperatures. The effective magnetic moments are close to calculated values for free Gd{sup 3+} ions. The Weiss constants for Gd{sub 3.04}Sc{sub 0.96}S{sub 6}, GdScS{sub 3}, and Gd{sub 1.05}Sc{sub 0.95}Se{sub 3} are determined to be -3.3(1), -4.5(4), and 1.5(1) K, respectively. Gd{sub 3.04}Sc{sub 0.96}S{sub 6} orders antiferromagnetically below 9 K. GdScS{sub 3} exhibits an antiferromagnetic ordering below 3 K with a weak ferromagnetism. Gd{sub 1.05}Sc{sub 0.95}Se{sub 3} undergoes a ferromagnetic transition around 5 K. The optical band gaps for Gd{sub 3.04}Sc{sub 0.96}S{sub 6}, GdScS{sub 3}, and Gd{sub 1.05}Sc{sub 0.95}Se{sub 3} are 1.5, 2.1, and 1.2 eV, respectively. - Graphical abstract: A view of the three-dimensional structure of Gd{sub 3.04}Sc{sub 0.96}S{sub 6} along the c axis.

  1. Detection of Defect-Induced Magnetism in Low-Dimensional ZnO Structures by Magnetophotocurrent.

    PubMed

    Lorite, Israel; Kumar, Yogesh; Esquinazi, Pablo; Zandalazini, Carlos; de Heluani, Silvia Perez

    2015-09-09

    The detection of defect-induced magnetic order in single low-dimensional oxide structures is in general difficult because of the relatively small yield of magnetically ordered regions. In this work, the effect of an external magnetic field on the transient photocurrent measured after light irradiation on different ZnO samples at room temperature is studied. It has been found that a magnetic field produces a change in the relaxation rate of the transient photocurrent only in magnetically ordered ZnO samples. This rate can decrease or increase with field, depending on whether the magnetically ordered region is in the bulk or only at the surface of the ZnO sample. The phenomenon reported here is of importance for the development of magneto-optical low-dimensional oxides devices and provides a new guideline for the detection of magnetic order in low-dimensional magnetic semiconductors.

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

    DOE PAGES

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

    2016-09-06

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

  3. Spin structure factors of Heisenberg spin chain in the presence of anisotropy and magnetic field

    NASA Astrophysics Data System (ADS)

    Rezania, H.

    2017-02-01

    We have theoretically studied the spin structure factors of spin chain in the presence of longitudinal field and transverse anisotropy. The possible effects of easy axis magnetization are investigated in terms of anisotropy in the Heisenberg interactions. This anisotropy is considered for exchange coupling constants perpendicular to magnetic field direction. The original spin model hamiltonian is mapped to a bosonic model via a hard core bosonic transformation where an infinite hard core repulsion is imposed to constrain one boson occupation per site. Using Green's function approach, the energy spectrum of quasiparticle excitation has been obtained. The spectrum of the bosonic gas has been implemented in order to obtain two particle propagator which corresponds to spin structure factor of original Heisenberg chain model Hamiltonian. The results show the position of peak in the longitudinal structure factor at fixed value for anisotropy moves to higher frequency with magnetic field. Also the intensity of dynamical structure factor decreases with magnetic field. A small dependence of longitudinal dynamical spin structure factor on the anisotropy is observed for fixed value of magnetic field. Our results show longitudinal static structure factor is found to be monotonically increasing with magnetic field due to increase of spins aligning along magnetic field. Furthermore the dispersion behaviors of static longitudinal and transverse structure factors for different magnetic fields and anisotropy parameters are addressed.

  4. Multiple magnetization plateaus and magnetic structures in the S =1/2 Heisenberg model on the checkerboard lattice

    NASA Astrophysics Data System (ADS)

    Morita, Katsuhiro; Shibata, Naokazu

    2016-10-01

    We study the ground state of the S =1/2 Heisenberg model on the checkerboard lattice in a magnetic field by the density matrix renormalization group method with the sine-square deformation. We obtain magnetization plateaus at M /Msat=0 ,1/4 ,3/8 ,1/2 , and 3/4 , where Msat is the saturated magnetization. The obtained 3/4 plateau state is consistent with the exact result, and the 1/2 plateau is found to have a four-spin resonating loop structure similar to the six-spin loop structure of the 1/3 plateau of the kagome lattice. Different four-spin loop structures are obtained in the 1/4 and 3/8 plateaus but no corresponding states exist in the kagome lattice. The 3/8 plateau has a unique magnetic structure of three types of four-spin local quantum states in a 4 √{2 }×2 √{2 } magnetic unit cell with a 16-fold degeneracy.

  5. Single crystal magnetic structure and susceptibility of CoSe2O5

    DOE PAGES

    Rodriguez, Efrain E.; Cao, Huibo; Haiges, Ralf; ...

    2015-09-08

    The structure of CoSe2O5 consists of one-dimensional ribbons of edge-sharing CoO6 octahedra bound together by polyanionic subunits of Se2O5. Previous work on polycrystalline samples reported a canted antiferromagnetic arrangement of the magnetic moments below the ordering temperature of 8.5 K. Here, we report a single crystal investigation using variable temperature and field magnetic susceptibility and low-temperature neutron diffraction to more precisely characterize the nature of the magnetic ground state of CoSe2O5. Contrary to previous reports, we find that the single crystal magnetic structure shows no canting of the antiferromagnetic ground state, and in the process have identified several field-induced changesmore » to the magnetization. Lastly, we discuss these results in the context of the revised magnetic structure and highlight the importance of crystal growth for the accurate characterization of these properties.« less

  6. Saturable inductor and transformer structures for magnetic pulse compression

    DOEpatents

    Birx, Daniel L.; Reginato, Louis L.

    1990-01-01

    Saturable inductor and transformer for magnetic compression of an electronic pulse, using a continuous electrical conductor looped several times around a tightly packed core of saturable inductor material.

  7. Study of Magnetic Structure in the Solar Photosphere and Chromosphere

    NASA Technical Reports Server (NTRS)

    Noyes, Robert W.; Avrett, Eugene; Nisenson, Peter; Uitenbroek, Han; vanBallegooijen, Adriaan

    1998-01-01

    This grant funded an observational and theoretical program to study the structure and dynamics of the solar photosphere and low chromosphere, and the spectral signatures that result. The overall goal is to learn about mechanisms that cause heating of the overlying atmosphere, and produce variability of solar emission in spectral regions important for astrophysics and space physics. The program exploited two new ground-based observational capabilities: one using the Swedish Solar Telescope on La Palma for very high angular resolution observations of the photospheric intensity field (granulation) and proxies of the magnetic field (G-band images); and the other using the Near Infrared Magnetograph at the McMath-Pierce Solar Facility to map the spatial variation and dynamic behavior of the solar temperature minimum region using infrared CO lines. We have interpreted these data using a variety of theoretical and modelling approaches, some developed especially for this project. Previous annual reports cover the work done up to 31 May 1997. This final report summarizes our work for the entire period, including the period of no-cost extension from 1 June 1997 through September 30 1997. In Section 2 we discuss observations and modelling of the photospheric flowfields and their consequences for heating of the overlying atmosphere, and in Section 3 we discuss imaging spectroscopy of the CO lines at 4.67 mu.

  8. Structure of the magnetized sheath of a dusty plasma

    SciTech Connect

    Mehdipour, H.; Denysenko, I.; Ostrikov, K.

    2010-12-15

    A three-component fluid model for a dusty plasma-sheath in an oblique magnetic field is presented. The study is carried out for the conditions when the thermophoretic force associated with the electron temperature gradient is one of the most important forces affecting dust grains in the sheath. It is shown that the sheath properties (the sheath size, the electron, ion and dust particle densities and velocities, the electric field potential, and the forces affecting the dust particles) are functions of the neutral gas pressure and ion temperature, the dust size, the dust material density, and the electron temperature gradient. Effects of plasma-dust collisions on the sheath structure are studied. It is shown that an increase in the forces pushing dust particles to the wall is accompanied by a decrease in the sheath width. The results of this work are particularly relevant to low-temperature plasma-enabled technologies, where effective control of nano- and microsized particles near solid or liquid surfaces is required.

  9. Structure and dynamics of the coronal magnetic field

    NASA Technical Reports Server (NTRS)

    VanHoven, Gerard; Schnack, Dalton D.

    1996-01-01

    The last few years have seen a marked increase in the sophistication of models of the solar corona. This has been brought about by a confluence of three key elements. First, the collection of high-resolution observations of the Sun, both in space and time, has grown tremendously. The SOHO (Solar Heliospheric Observatory) mission is providing additional correlated high-resolution magnetic, white-light and spectroscopic observations. Second, the power and availability of supercomputers has made two- and three-dimensional modeling routine. Third, the sophistication of the models themselves, both in their geometrical realism and in the detailed physics that has been included, has improved significantly. The support from our current Space Physics Theory grant has allowed us to exploit this confluence of capabilities. We have carried out direct comparisons between observations and models of the solar corona. The agreement between simulated coronal structure and observations has verified that the models are mature enough for detailed analysis, as we will describe. The development of this capability is especially timely, since observations obtained from three space missions that are underway (Ulysses, WIND and SOHO) offer an opportunity for significant advances in our understanding of the corona and heliosphere. Through this interplay of observations and theory we can improve our understanding of the Sun. Our achievements thus far include progress modeling the large-scale structure of the solar corona, three-dimensional models of active region fields, development of emerging flux and current, formation and evolution of coronal loops, and coronal heating by current filaments.

  10. Multi-scale structures of turbulent magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Nakamura, T. K. M.; Nakamura, R.; Narita, Y.; Baumjohann, W.; Daughton, W.

    2016-05-01

    We have analyzed data from a series of 3D fully kinetic simulations of turbulent magnetic reconnection with a guide field. A new concept of the guide filed reconnection process has recently been proposed, in which the secondary tearing instability and the resulting formation of oblique, small scale flux ropes largely disturb the structure of the primary reconnection layer and lead to 3D turbulent features [W. Daughton et al., Nat. Phys. 7, 539 (2011)]. In this paper, we further investigate the multi-scale physics in this turbulent, guide field reconnection process by introducing a wave number band-pass filter (k-BPF) technique in which modes for the small scale (less than ion scale) fluctuations and the background large scale (more than ion scale) variations are separately reconstructed from the wave number domain to the spatial domain in the inverse Fourier transform process. Combining with the Fourier based analyses in the wave number domain, we successfully identify spatial and temporal development of the multi-scale structures in the turbulent reconnection process. When considering a strong guide field, the small scale tearing mode and the resulting flux ropes develop over a specific range of oblique angles mainly along the edge of the primary ion scale flux ropes and reconnection separatrix. The rapid merging of these small scale modes leads to a smooth energy spectrum connecting ion and electron scales. When the guide field is sufficiently weak, the background current sheet is strongly kinked and oblique angles for the small scale modes are widely scattered at the kinked regions. Similar approaches handling both the wave number and spatial domains will be applicable to the data from multipoint, high-resolution spacecraft observations such as the NASA magnetospheric multiscale (MMS) mission.

  11. Structural geology, petrofabrics and magnetic fabrics (AMS, AARM, AIRM)

    NASA Astrophysics Data System (ADS)

    Borradaile, Graham J.; Jackson, Mike

    2010-10-01

    Anisotropy of magnetic susceptibility (AMS) was recognized as a feature of minerals in 1899, and petrofabric-compatible AMS fabrics were reported from 1942-1958. Shortly thereafter, cleavage and mineral lineation were associated with the principal axes of the AMS ellipsoid. AMS is describable by a magnitude ellipsoid, somewhat similar in concept to the finite strain ellipsoid, with principal susceptibilities (κ MAX, κ INT, κ MIN) as its axes and their average value being the mean susceptibility (κ). Orientations of the AMS axes usually have a reasonably straightforward structural significance but their magnitudes are more difficult to interpret, being the result of mineral abundances and different mineral-AMS. The strain ellipsoid is dimensionless (i.e., of unit-volume) and readily compared from one outcrop to another but the AMS ellipsoid represents the anisotropy of a physical property. Thus, (κ) determines the relative importance of AMS for different specimens, or compared outcrops, or component AMS subfabrics. AMS provides a petrofabric tool, unlike any other, averaging and sampling the orientation-distribution of all minerals and all subfabrics in a specimen. Sophisticated laboratory techniques may isolate the AMS contributions of certain minerals from one another, and of certain subfabrics (e.g. depositional from tectonic). However, suitable data processing of the basic AMS measurements (κ MAX, κ INT, κ MIN magnitudes and orientations, and the mean susceptibility, κ) may provide the same information. Thus, AMS provides the structural geologist with a unique tool that may isolate the orientations of subfabrics of different origins (sedimentary, tectonic, tectonic overprints etc.).

  12. Low temperature magneto-structural transitions in Mn3Ni20P6

    NASA Astrophysics Data System (ADS)

    Cedervall, Johan; Beran, Premysl; Vennström, Marie; Danielsson, Therese; Ronneteg, Sabina; Höglin, Viktor; Lindell, David; Eriksson, Olle; André, Gilles; Andersson, Yvonne; Nordblad, Per; Sahlberg, Martin

    2016-05-01

    X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm 3 barm (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic antiferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k=(0 0 ½) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 ~0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K.

  13. Structural and magnetic properties of Fe2CoGa Heusler nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, Changhai; Casper, Frederick; Gasi, Teuta; Ksenofontov, Vadim; Balke, Benjamin; Fecher, Gerhard H.; Felser, Claudia; Hwu, Yeu-Kuang; Lee, Jeu-Jau

    2012-07-01

    Fe2CoGa Heusler nanoparticles are synthesized by a chemical method. The structure and magnetic properties of Fe2CoGa Heusler nanoparticles are investigated by x-ray diffraction, extended x-ray absorption fine structure and Mössbauer spectroscopy. The crystal structure of Fe2CoGa nanoparticles is described by the X-type structure (prototype: Li2AgSb). Magnetic measurements reveal the presence of small Fe2CoGa nanoparticles and lower magnetic moments compared with the theoretically predicted values.

  14. Structure and magnetic properties of Zn-Ti-substituted Ba-ferrite particles for magnetic recording

    NASA Astrophysics Data System (ADS)

    Wang, C. S.; Wei, F. L.; Lu, M.; Han, D. H.; Yang, Z.

    1998-03-01

    The formation process of Zn-Ti-doped Ba-ferrite particles was investigated by the X-ray diffraction technique, transmission electron microscope and magnetic measurements. The effects of heating temperature Th and the Zn-Ti substitution x on the microstructure and magnetic properties of BaFe 12-2 xZn xTi x O 19 particles with x=0.10-0.80 were studied. The temperature dependence of magnetic properties of these particles was measured.

  15. Achievement of Diverse Domain Structures in Soft Magnetic Thin Film through Adjusting Intrinsic Magnetocrystalline Anisotropy

    NASA Astrophysics Data System (ADS)

    Jiao, Juanying; Wang, Tao; Ma, Tianyong; Wang, Ying; Li, Fashen

    2017-01-01

    Oriented soft magnetic hcp-Co1 - x Ir x films with a fixed thickness of 120 nm were fabricated. All prepared films exhibit soft magnetic properties but various magnetocrystalline anisotropies with the variation of Ir content. The measured data shows that diverse domain structures including the Néel wall, Bloch wall, and stripe domains present in a fixed film thickness. It is singular for the single-layer soft magnetic film to possess diverse domains in a fixed thickness. This phenomenon was explained by introducing intrinsic magnetocrystalline anisotropy energy into soft magnetic films rather than the structural parameters of the film, inner stress, and microstructure effect.

  16. The morphologies and magnetic field structures of six 3CR double radio galaxies

    NASA Astrophysics Data System (ADS)

    Miller, L.

    1985-08-01

    Observations of the regions of low surface brightness in six 3CR double radio galaxies (3C 98, 184.1, 192, 223, 332 and 430) have been made with the Cambridge 5-km telescope. Maps of total and polarized intensity are presented, and the projected magnetic field structures have been deduced. High fractional polarization is seen in these sources, indicating that the magnetic fields are well-ordered. A qualitative model for the formation of the magnetic field structures is presented, in which pressure gradients in the extended lobes cause bulk flow of plasma and consequent large-scale shearing of the magnetic fields.

  17. Achievement of Diverse Domain Structures in Soft Magnetic Thin Film through Adjusting Intrinsic Magnetocrystalline Anisotropy.

    PubMed

    Jiao, Juanying; Wang, Tao; Ma, Tianyong; Wang, Ying; Li, Fashen

    2017-12-01

    Oriented soft magnetic hcp-Co1 - x Ir x films with a fixed thickness of 120 nm were fabricated. All prepared films exhibit soft magnetic properties but various magnetocrystalline anisotropies with the variation of Ir content. The measured data shows that diverse domain structures including the Néel wall, Bloch wall, and stripe domains present in a fixed film thickness. It is singular for the single-layer soft magnetic film to possess diverse domains in a fixed thickness. This phenomenon was explained by introducing intrinsic magnetocrystalline anisotropy energy into soft magnetic films rather than the structural parameters of the film, inner stress, and microstructure effect.

  18. Study on micro-structure and morphological evolution of Fe/Pt nano-magnetic film.

    PubMed

    Ishiguro, S; Ju, D Y; Ogatsu, R; Nakano, T

    2011-10-01

    One of the vertical magnetic recordings medium materials of the hard disk drive (HDD) is a Fe/Pt thin film. The development of ultra-high density magnetic recording medium in next generation is expected the magnetic disks such as HDD with capacity enlargement of the data. In order to study effectiveness of the proposed sputtering method, we evaluated micro structure, magnetic and the mechanical properties of a Fe/Pt thin film by some sputtering process conditions. From research results, effect sputtering conditions on micro-structure and mechanical properties of Fe/Pt nano film are verified.

  19. Magnetic layering transitions in a polyamidoamine (PAMAM) dendrimer nano-structure: Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Ziti, S.; Aouini, S.; Labrim, H.; Bahmad, L.

    2017-02-01

    We study the magnetic layering transitions in a polyamidoamine (PAMAM) dendrimer nano-structure, under the effect of an external magnetic field. We examine the magnetic properties, of this model of the spin S=1 Ising ferromagnetic in real nanostructure used in several scientific domains. For T=0, we give and discuss the ground state phase diagrams. At non null temperatures, we applied the Monte Carlo simulations giving important results summarized in the form of the phase diagrams. We also analyzed the effect of varying the external magnetic field, and found the layering transitions in the polyamidoamine (PAMAM) dendrimer nano-structure.

  20. Mesoscopic simulation for the structures of magnetic fluids

    NASA Astrophysics Data System (ADS)

    Li, Wuming; Li, Qiang

    2017-02-01

    The microstructures of magnetic fluids are simulated using a dissipative particle dynamics (DPD)-based method and are fundamentally important for controlling the macroscopic properties of magnetic fluids and understanding the corresponding rheological behaviors in diverse engineering applications. The cubic polynomial spline function often used as smoothing function in smoothed particle hydrodynamics (SPH) is employed as the conservative force potential function, which can provide a stronger conservative force weight function than the conventional weight function by choosing properly the cutoff radius between the dissipative particles. By employing the above method, the desired results are obtained for both stronger and weaker magnetic particle-particle interaction under the condition of varying the mass of the dissipative particles. In addition, the influences of the magnetic particle-particle interaction and of the magnetic particle area fraction on the microstructure of magnetic fluids are also investigated, respectively, and the obtained results agree qualitatively well with those in the literature obtained by other numerical approaches and experiments. The numerical solutions of the mean equilibrium velocities of the magnetic and dissipative particles are also calculated and approximate the corresponding theoretical values very well. Therefore the employed DPD-based method is highly effective in the simulation of the microstructure of magnetic fluids.

  1. The magnetization curve of spin chains with superlattice structure

    NASA Astrophysics Data System (ADS)

    Silva-Valencia, J.; Franco, R.

    2006-10-01

    The magnetization curve of the spin superlattices composed of repeat pattern of two spin- {1}/{2} XXZ chains with different anisotropy parameters was calculated using density matrix renormalization group. We observe a nontrivial plateau with magnetization value given by the relative sizes of the subchains.

  2. Structural, optical, magnetic and photocatalytic properties of Co doped CuS diluted magnetic semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Sreelekha, N.; Subramanyam, K.; Amaranatha Reddy, D.; Murali, G.; Ramu, S.; Rahul Varma, K.; Vijayalakshmi, R. P.

    2016-08-01

    Pristine and Co doped covellite CuS nanoparticles were synthesized in aqueous solution by facile chemical co-precipitation method with Ethylene Diamine Tetra Acetic Acid (EDTA) as a stabilizing agent. EDAX measurements confirmed the presence of Co in the CuS host lattice. Hexagonal crystal structure of pure and Co doped CuS nanoparticles were authenticated by XRD patterns. TEM images indicated that sphere-shape of nanoparticles through a size ranging from 5 to 8 nm. The optical absorption edge moved to higher energies with increase in Co concentration as indicated by UV-vis spectroscopy. Magnetic measurements revealed that bare CuS sample show sign of diamagnetic character where as in Co doped nanoparticles augmentation of room temperature ferromagnetism was observed with increasing doping precursor concentrations. Photocatalytic performance of the pure and Co doped CuS nanoparticles were assessed by evaluating the degradation rate of rhodamine B solution under sun light irradiation. The 5% Co doped CuS nanoparticles provide evidence for high-quality photocatalytic activity.

  3. Monte Carlo simulation of multilayer magnetic structures and calculation of the magnetoresistance coefficient

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskii, D. E.

    2015-11-01

    The Monte Carlo study of three-layer and spin-valve magnetic structures with giant magnetoresistance effects has been performed with the application of the Heisenberg anisotropic model to the description of the magnetic properties of thin ferromagnetic films. The dependences of the magnetic characteristics on the temperature and external magnetic field have been obtained for the ferromagnetic and antiferromagnetic configurations of these structures. A Monte Carlo method for determining the magnetoresistance coefficient has been developed. The magnetoresistance coefficient has been calculated for three-layer and spin-valve magnetic structures at various thicknesses of ferromagnetic films. It has been shown that the calculated temperature dependence of the magnetoresistance coefficient is in good agreement with experimental data obtained for the Fe(001)/Cr(001) multilayer structure and the CFAS/Ag/CFAS/IrMn spin valve based on the Co2FeAl0.5Si0.5 (CFAS) Heusler alloy.

  4. Electronic structures and magnetic/optical properties of metal phthalocyanine complexes

    SciTech Connect

    Baba, Shintaro; Suzuki, Atsushi Oku, Takeo

    2016-02-01

    Electronic structures and magnetic / optical properties of metal phthalocyanine complexes were studied by quantum calculations using density functional theory. Effects of central metal and expansion of π orbital on aromatic ring as conjugation system on the electronic structures, magnetic, optical properties and vibration modes of infrared and Raman spectra of metal phthalocyanines were investigated. Electron and charge density distribution and energy levels near frontier orbital and excited states were influenced by the deformed structures varied with central metal and charge. The magnetic parameters of chemical shifts in {sup 13}C-nuclear magnetic resonance ({sup 13}C-NMR), principle g-tensor, A-tensor, V-tensor of electric field gradient and asymmetry parameters derived from the deformed structures with magnetic interaction of nuclear quadruple interaction based on electron and charge density distribution with a bias of charge near ligand under crystal field.

  5. Magnetic structure and phase transition of Ni2Mn1.48Sb0.52 magnetic shape memory compound

    DOE PAGES

    Yang, Y. B.; Liu, S. Q.; Zhao, H.; ...

    2016-02-06

    Here, a comprehensive study of the structural and magnetic properties of the Ni2Mn1.48Sb0.52 compound is presente using neutron diffraction and magnetic measurements. It is found that Mn atoms on 4a and 4 sites are ferrimagnetic coupled in the austenitic phase. At 300 K, the magnetic moments of Mn (4a) an Mn (4b) are determined to be 2.72(3) μB and -2.67(5) μB, respectively. From 260 K to 4 K, the compound is in martensite phase and the magnetic moments of Mn (2a), Mn (2f), Mn (2b), Mn (2e) at 4 K ar 2.2(5) μB, 2.3(5) μB, -2.1(5) μB, and -2.6(5) μB,more » respectively.« less

  6. Structural and magnetic properties of granular CoPd multilayers

    NASA Astrophysics Data System (ADS)

    Vivas, L. G.; Figueroa, A. I.; Bartolomé, F.; Rubín, J.; García, L. M.; Deranlot, C.; Petroff, F.; Ruiz, L.; González-Calbet, J. M.; Brookes, N. B.; Wilhelm, F.; Rogalev, A.; Bartolomé, J.

    2016-02-01

    Multilayers of bimetallic CoPd alloyed and assembled nanoparticles, prepared by room temperature sequential sputtering deposition on amorphous alumina, were studied by means of high-resolution transmission electron microscopy, x-ray diffraction, SQUID-based magnetometry and x-ray magnetic circular dichroism. Alloying between Co and Pd in these nanoparticles gives rise to a high perpendicular magnetic anisotropy. Their magnetic properties are temperature dependent: at low temperature, the multilayers are ferromagnetic with a high coercive field; at intermediate temperature the behavior is of a soft-ferromagnet, and at higher temperature, the perpendicular magnetic anisotropy in the nanoparticles disappears. The magnetic orbital moment to spin moment ratio is enhanced compared with Co bare nanoparticles and Co fcc bulk.

  7. Coercivity enhancement in Ce-Fe-B based magnets by core-shell grain structuring

    NASA Astrophysics Data System (ADS)

    Ito, M.; Yano, M.; Sakuma, N.; Kishimoto, H.; Manabe, A.; Shoji, T.; Kato, A.; Dempsey, N. M.; Givord, D.; Zimanyi, G. T.

    2016-05-01

    Ce-based R2Fe14B (R= rare-earth) nano-structured permanent magnets consisting of (Ce,Nd)2Fe14B core-shell grains separated by a non-magnetic grain boundary phase, in which the relative amount of Nd to Ce is higher in the shell of the magnetic grain than in its core, were fabricated by Nd-Cu infiltration into (Ce,Nd)2Fe14B hot-deformed magnets. The coercivity values of infiltrated core-shell structured magnets are superior to those of as-hot-deformed magnets with the same overall Nd content. This is attributed to the higher value of magnetocrystalline anisotropy of the shell phase in the core-shell structured infiltrated magnets compared to the homogeneous R2Fe14B grains of the as-hot-deformed magnets, and to magnetic isolation of R2Fe14B grains by the infiltrated grain boundary phase. First order reversal curve (FORC) diagrams suggest that the higher anisotropy shell suppresses initial magnetization reversal at the edges and corners of the R2Fe14B grains.

  8. Structural and magnetic properties of samarium iron and related alloys

    NASA Astrophysics Data System (ADS)

    Meacham, Brian Eugene

    There were three research objectives. The first objective was to determine what controls the structural scale of the microstructure in Sm-Fe alloys. The second objective was to study the morphological development of antiphase domains. The last objective was to determine the effect of the microstructural state on the coercivity and magnetization reversal of Sm2Fe 17Nx. The as-solidified alloys had large grains with irregular shape but the metal carbide modified alloys had a refinement of the microstructural scale and improved homogeneous grain shape. The magnitude of the scale reduction depended on the additives. It was determined that an important factor for the refinement was the glass forming ability of the alloy composition. The evidence points to solute segregation at the solidification boundary as the dominant mechanism that controls the grain size. The as-solidified binary alloy had significant strain. As annealing occurs the development of antiphase domains causes the reduction of strain, which reduces the defect density. A similar morphology occurs in the TiC modified alloy. It was discovered that order pattern in the antiphase domains has a twin symmetry. This is a new structural feature that has not been seen in antiphase domains before and is called rebel ordering. The recoil data showed that nucleation of reversed domains causes a peak in the remanent susceptibility curve. However, when domain wall pinning occurs there are fluctuations. It was discovered that as the loop shape improves, the separation between the coercivity and the peak center decreases linearly with either the squareness ratio or the fullness factor. The nitrided binary alloy coercivity decreases with increasing ordering. However, there is a narrow order parameter region where the antiphase structure effectively pins domain walls resulting in an enhancement of the coercivity. The microstructural scale affects the coercivity. The single domain limit was determined to be about 300 nm

  9. Monte Carlo calculations of the magnetoresistance in magnetic multilayer structures with giant magnetoresistance effects

    NASA Astrophysics Data System (ADS)

    Prudnikov, V. V.; Prudnikov, P. V.; Romanovskiy, D. E.

    2016-06-01

    A Monte Carlo study of trilayer and spin-valve magnetic structures with giant magnetoresistance effects is carried out. The anisotropic Heisenberg model is used for description of magnetic properties of ultrathin ferromagnetic films forming these structures. The temperature and magnetic field dependences of magnetic characteristics are considered for ferromagnetic and antiferromagnetic configurations of these multilayer structures. The methodology for determination of the magnetoresistance by the Monte Carlo method is introduced; this permits us to calculate the magnetoresistance of multilayer structures for different thicknesses of the ferromagnetic films. The calculated temperature dependence of the magnetoresistance agrees very well with the experimental results measured for the Fe(0 0 1)-Cr(0 0 1) multilayer structure and CFAS-Ag-CFAS-IrMn spin-valve structure based on the half-metallic Heusler alloy Co2FeAl0.5Si0.5.

  10. Interface-driven noncollinear magnetic structure and phase transition of Fe thin films

    NASA Astrophysics Data System (ADS)

    Kawauchi, Taizo; Miura, Yoshio; Zhang, Xiaowei; Fukutani, Katsuyuki

    2017-01-01

    We investigate the magnetic structure and its temperature dependence of Fe thin films grown on MgO(001) and Al2O3 (0001) surfaces by means of nuclear resonant x-ray scattering. By fabricating Fe films δ -doped with 57Fe at the interface and middle of the film, depth-resolved analysis of the magnetic structure is performed. On MgO(001), the magnetization is dominantly out-of-plane at the interface, whereas it is mainly in-plane at the middle of the film, indicating that the Fe film has a noncollinear magnetic structure. On Al2O3 (0001), on the other hand, the magnetization is mainly in-plane in the entire film. The noncollinear magnetic structure on MgO(001) is confirmed to be energetically stable with the aid of first-principles calculations. We also investigate the temperature dependence of the internal magnetic field in a depth-resolved way. The experimental data suggest the internal magnetic field at the interface is smaller than that of the middle of the film on both substrates, suggesting that the magnetic phase transition starts at the interface at a lower temperature than the entire film.

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

    SciTech Connect

    Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. 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 (δ10 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. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

  12. Complexity in the structural and magnetic properties of almost multiferroic EuTi O3

    NASA Astrophysics Data System (ADS)

    Guguchia, Z.; Salman, Z.; Keller, H.; Roleder, K.; Köhler, J.; Bussmann-Holder, A.

    2016-12-01

    In a number of recent publications hidden magnetic properties at high temperatures have been reported for EuTi O3 (ETO), which orders antiferromagnetically below TN=5.7 K . In addition, structural phase transitions have been discovered which correlate with the magnetic responses and can be tuned by a magnetic field. In order to identify the magnetic properties of ETO at temperatures well above TN, low-energy muon-spin rotation (μSR) experiments have been performed on thin films of ETO which exhibit all properties observed in bulk materials and are thus well suited to conclude about the magnetic order of the bulk. The μSR data reveal anomalies at 282 and 200 K related to the structural phase transitions in accordance with birefringence results. In addition, a transition to some kind of magnetic order below 100 K was observed as previously indirectly deduced from conductivity and dielectric constant measurements.

  13. Imaging nanoscale magnetic structures with polarized soft x-ray photons

    SciTech Connect

    Fischer, P.; Im, M.-Y.

    2010-01-18

    Imaging nanoscale magnetic structures and their fast dynamics is scientifically interesting and technologically of highest relevance. The combination of circularly polarized soft X-ray photons which provide a strong X-ray magnetic circular dichroism effect at characteristic X-ray absorption edges, with a high resolution soft X-ray microscope utilizing Fresnel zone plate optics allows to study in a unique way the stochastical behavior in the magnetization reversal process of thin films and the ultrafast dynamics of magnetic vortices and domain walls in confined ferromagnetic structures. Future sources of fsec short and high intense soft X-ray photon pulses hold the promise of magnetic imaging down to fundamental magnetic length and time scales.

  14. The Flow Structure in the Vicinity of the Inner Lagrangian Point in Magnetic Cataclysmic Variables

    NASA Astrophysics Data System (ADS)

    Isakova, P. B.; Zhilkin, A. G.; Bisikalo, D. V.

    2017-03-01

    The mass transfer between the components of the magnetic cataclysmic variables occurs through the inner Lagrangian point. The results of 3D numerical simulations of the flow structure in magnetic cataclysmic variables show that the magnetic field of the accretor essentially influences the flow structure. In polars (with magnetic fields of 10–100 MG at the surface of the white dwarf) the material streaming from the donor splits into the several flows as soon as it leaves the inner Lagrangian point. These flows move along the magnetic field lines and reach the magnetic poles of the accretor. This picture does not correspond to the classical situation of the flow formation when material flows from the donor into the Roche lobe of the accretor along the ballistic trajectory. The aim of our study is to investigate in detail the features of the flow splitting in the vicinity of the inner Lagrangian point in classic polars.

  15. Tunable magnetic resonance in double layered metallic structures.

    PubMed

    Zhou, L; Zhu, Y Y

    2011-12-01

    Double layered metallic gratings have been investigated both theoretically and experimentally. The authors have reported that tunable magnetic resonance (MR) can be achieved by modulating the vertical chirped width dh which could be controlled conveniently in the common electron and/or ion beam microfabrications. The linear relationship between MR wavelength and dh has been reported. By introducing the difference of electric and magnetic penetration depth, an analytic formula deduced from a modified LC model has shown good agreement with the simulation results, and an effective width for trapezoidal sandwiched microstructures has been presented. Our results may provide an alternative choice for tunable MR and broad bandwidth of magnetic metamaterials.

  16. Fabrication, morphological, structural and magnetic properties of electrodeposited Fe3Pt nanowires and nanotubes

    NASA Astrophysics Data System (ADS)

    Khan, U.; Adeela, N.; Li, Wenjing; Irfan, M.; Javed, K.; Riaz, S.; Han, X. F.

    2017-02-01

    Highly ordered Fe3Pt nanowires (NWs) and nanotubes (NTs) embedded in anodic aluminum oxide (AAO) template have been fabricated by dc electrodeposition method. Response of heat treatment on structural and magnetic properties of the samples has been studied with and without the presence of magnetic field (1 T). X-Ray Diffraction analysis shows chemically ordered L12 face centered cubic (FCC) as the dominant phase for Fe3Pt NWs and heat treatment improves crystallinity with retained its phase. Whereas, Fe3Pt NTs show amorphous behavior with and without magnetic field annealing. Furthermore, magnetic properties of the samples have been investigated by vibrating sample magnetometer (VSM). Magnetic parameters of Fe3Pt including magnetic coercivity, saturation magnetization, squareness and shape of MH-loops have been investigated as a result of simple and MF annealing.

  17. Magnetic properties driven by local structure in quasi-1D Ising chain system cobaltate system

    NASA Astrophysics Data System (ADS)

    Kim, Bongjae; Kim, Beom Hyun; Kim, Kyoo; Choi, Hong Chul; Park, Sang-Yeon; Jeong, Y.-H.; Min, B. I.

    2012-02-01

    Using ab-initio band structure method and the microscopic model calculation, the origins of the large orbital magnetic moment and unique magnetic anisotropy in the quasi-1D magnetic cobaltate, α-CoV2O6, is investigated. Unique crystal electric field effect in α-CoV2O6 is combined with the strong spin-orbit coupling, results in intriguing magnetic properties of the system. Based on the estimated strengths of the intra- and the inter-chain exchange interaction, experimentally found 1/3 magnetization plateau in the MH curve can be attributed to spin-flop mechanism. Origin of the reduced magnetic entropy behavior is found to be the strong uniaxial magnetic anisotropy in the quasi-1D Ising chain system.

  18. Generation of a flare loop structure and ejection of magnetic flux from an erupting laboratory arched magnetic flux rope

    NASA Astrophysics Data System (ADS)

    Tripathi, S.; Gekelman, W. N.

    2011-12-01

    A laboratory plasma experiment has been built to generate an arched magnetic flux rope (AMFR) which is essentially an arch-shaped, current-carrying, magnetized plasma structure. Coronal loops and prominences are the main examples of solar AMFRs that frequently erupt and evolve into more energetic events such as flares and coronal mass ejections. Numerous small-scale AMFRs are also observed in the solar corona. In order to capture the important micro-physics of an erupting AMFR, the laboratory experiment has been designed by careful scaling of the solar plasma parameters. The laboratory AMFR (n ~ 1019 m-3, Te ~ 10 eV, L ~ 0.5 m) is produced using a LaB6 plasma source in presence of an arched vacuum magnetic field (B ~ 1 kG) and it evolves in a large magnetized plasma (1.0 m diameter, 4.5 m long, n ~ 1018 m-3, Te ~ 4 eV, B = 25-150 G). Two laser beams (1064 nm, ~0.5 J/pulse) strike movable carbon targets placed behind the electrodes to generate controlled plasma flows from the footpoints of the AMFR. The laser generated flows can mimic a variety of plasma flow conditions that exist on the sun and they can trigger the AMFR eruption by injecting dense plasma and magnetic flux in the AMFR. The experiment runs continuously with a 0.5 Hz repetition rate and is highly reproducible. Thus, several thousands of identical eruptions are routinely generated and evolution of the magnetic field, density, and plasma temperature is recorded in 3D with a high spatiotemporal resolution ( dx = 1 mm, dt= 20 ns) using movable diagnostic probes. Fast-camera images of the erupting AMFR demonstrate striking similarities between laboratory and solar plasma structures, most notably the observation of a flare-loop like structure following the eruption of the laboratory AMFR. The eruption of the AMFR can be initiated either by the laser generated intense flows or by the presence of a strong background magnetic field (B > 50 G ~ magnetic field at the leading edge of the AMFR). In both scenarios

  19. Long-time variation in magnetic structure of CeIr3Si2: Observation of a nucleation-and-growth process of magnetic domains

    DOE PAGES

    Motoya, Kiyoichiro; Hagihala, Masato; Takabatake, Toshiro; ...

    2016-02-29

    CeIr3Si2 is the first three-dimensional uniform magnet in which the long-time variation in magnetic structure was observed. To clarify the microscopic mechanism of this magnetic structural change, time-resolved neutron scattering measurements have been reinvestigated. Clear time variations in the line widths as well as the amplitudes of magnetic Bragg diffractions have been observed in this improved instrumentation. On the notion of this observation, a nucleation-and-growth model of magnetic structural change has been presented. The numerical calculation with this model reproduces well the observation.

  20. Structural and magnetic properties of magnetoelectric oxide heterostructures deposited by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sterbinsky, George Evan

    There is considerable interest in incorporating magnetic materials into electronic devices to achieve new functions such as nonvolatile memories. Electric field control of magnetism is of much interest for new low power electronic devices because it eliminates the need to apply magnetic fields. One approach to achieving electrical control of magnetism is to exploit magnetoelastic effects in composites of ferromagnetic and ferroelectric materials. Application of an electric field to the composite will induce a strain through the piezo-electric effect, and the strain will alter the magnetization of the ferromagnetic constituent through the magnetoelastic effect. In this work, we examine the relationships between growth, strain, and magnetic properties of epitaxial ferrimagnetic Fe3O4 (magnetite) and ferroelectric BaTiO3 thin film heterostructures. We find that altering the strain state of a magnetite layer deposited on a BaTiO3 substrate has a profound effect on its magnetization. Here, we demonstrate the interaction between strain and magnetization is mediated by magnetic anisotropy and the magnetic domains structure of the films. Epitaxial magnetite films were deposited on MgO, BaTiO3, and SrTiO3 substrates by molecular beam epitaxy between temperatures of 573 and 723 K. Examination of the morphologies of Fe3O 4 films indicates that island growth is favored. Films exhibit in-plane magnetic isotropy and reduced saturation magnetizations with respect to the bulk material, as demonstrated by superconducting quantum interference device magnetometry. Magnetic hysteresis measurements suggest that these differences originate from antiphase boundary defects within the films. The strain in magnetite films deposited on BaTiO3 single crystal substrates was measured by x-ray diffraction. Measurements reveal a dependence of magnetization (M) on strain (epsilon) with discontinuities in magnetization versus temperature curves resulting from changes in the domain structure of the

  1. Magnetic and Orbital Structures in Transition Metal Oxides

    NASA Astrophysics Data System (ADS)

    Khomskii, Daniel

    2002-03-01

    The interplay of different degrees of freedom (charge, spin, orbital, lattice) determine all the rich properties of transition metal oxides. In particular, spin and orbital orderings appear to be especially strongly coupled. At least this is the case in perovskite-like systems with (almost) 180-degree metal-oxygen-metal bonds. The coupled spins and orbitals in this case can be described by the effective Hamiltonian of the type H = A(S*S)+B(T*T)+C(S*S)(T*T), where S and T are the spin and pseudospin of an ion ( describing an orbital occupation). In conventional cases, e.g. in perovskites, the constants A, B, C are of the same order, which determines strong coupling between spins and orbitals. However this electronic mechanism is not the only one leading to orbital ordering. The conventional Jahn-Teller interaction can also contribute to the latter, and it is not always clear which mechanism dominates. In this talk I will consider two questions. The first is the possibility to describe different orbital (and charge) superstructures in oxides, in particular in manganites, using the electron-lattice (elastic) interaction [1]. One can show that due to specific features of these interactions, one can naturally get in this mechanism different superstructures, including stripes. The second question concerns the form which these mechanisms take in systems with more complicated crystal structures - notably in oxides with 90-degree bonds. To these systems belong in particular some systems with geometric frustrations, e.g. some spinels, or LiNiO2, NaNiO2. We show that the exchange interaction in case of orbital degeneracy has for these systems the form much different from the perovskites: spin and orbital degrees of freedom are essentially decoupled, orbital exchange being much stronger even in the absence of electron-lattice interaction. We obtain corresponding exchange Hamiltonian, and consider the orbital and spin structure in systems like LiNiO2 [2], in which, due to a

  2. Synthesis of highly magnetic iron nanoparticles suitable for field structuring using a β-diketone surfactant

    NASA Astrophysics Data System (ADS)

    Huber, Dale L.; Venturini, Eugene L.; Martin, James E.; Provencio, Paula P.; Patel, Rina J.

    2004-07-01

    We describe the synthesis of highly magnetic iron nanoparticles using a novel surfactant, a β-diketone. We have produced 6 nm iron nanoparticles with an unusually high saturation magnetization of more than 80% the value of bulk iron. Additionally, we measured a particle susceptibility of 14 (MKS units), which is far above the value possible for micron-scale spherical particles. These properties will allow for formation of composites that can be highly structured by magnetic fields.

  3. Magnetic resonance in a gallium-doped Cu-Cr-S structure

    NASA Astrophysics Data System (ADS)

    Vorotynov, A. M.; Pankrats, A. I.; Abramova, G. M.; Velikanov, D. A.; Bovina, A. F.; Sokolov, V. V.; Filatova, I. Yu.

    2016-04-01

    A layered Cu-Cr-S structure doped with Ga ions and consisting of single-crystal CuCrS2 layers, embedded with thin plates of spinel phases CuCr2S4 and CuGa x Cr2- x S4, has been studied using the magnetic resonance and magnetic susceptibility methods. The Curie temperature and the saturation magnetization of the spinel phases of the samples have been determined. The spinel phase layer thickness has been estimated.

  4. Observation of a Charge Density Wave Incommensuration Near the Superconducting Dome in Cux TiSe2

    NASA Astrophysics Data System (ADS)

    Kogar, A.; de la Pena, G. A.; Lee, Sangjun; Fang, Y.; Sun, S. X.-L.; Lioi, D. B.; Karapetrov, G.; Finkelstein, K. D.; Ruff, J. P. C.; Abbamonte, P.; Rosenkranz, S.

    2017-01-01

    X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in Cux TiSe2 as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. The results show a CDW incommensuration arising at an intercalation value coincident with the onset of superconductivity at around x =0.055 (5 ) . Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up to x =0.091 (6 ), the highest copper concentration examined in this study. The phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.

  5. Effect of Doping and Pressure on Magnetism and Lattice Structure of Fe-Based Superconductors

    DTIC Science & Technology

    2010-04-14

    ar X iv :1 00 4. 21 60 v1 [ co nd -m at .s up r- co n] 1 3 A pr 2 01 0 Effect of doping and pressure on magnetism and lattice structure of Fe...2010) Using first principles calculations, we analyze structural and magnetic trends as a function of charge doping and pressure in BaFe2As2, and...compare to experimentally established facts. We find that density functional theory, while accurately reproducing the structural and magnetic ordering at

  6. Evolution of the magnetic field structure of the Crab pulsar.

    PubMed

    Lyne, Andrew; Graham-Smith, Francis; Weltevrede, Patrick; Jordan, Christine; Stappers, Ben; Bassa, Cees; Kramer, Michael

    2013-11-01

    Pulsars are highly magnetized rotating neutron stars and are well known for the stability of their signature pulse shapes, allowing high-precision studies of their rotation. However, during the past 22 years, the radio pulse profile of the Crab pulsar has shown a steady increase in the separation of the main pulse and interpulse components at 0.62° ± 0.03° per century. There are also secular changes in the relative strengths of several components of the profile. The changing component separation indicates that the axis of the dipolar magnetic field, embedded in the neutron star, is moving toward the stellar equator. This evolution of the magnetic field could explain why the pulsar does not spin down as expected from simple braking by a rotating dipolar magnetic field.

  7. CONSTRAINING PRIMORDIAL MAGNETIC FIELDS THROUGH LARGE-SCALE STRUCTURE

    SciTech Connect

    Kahniashvili, Tina; Natarajan, Aravind; Battaglia, Nicholas; Maravin, Yurii; Tevzadze, Alexander G.

    2013-06-10

    We study primordial magnetic field effects on the matter perturbations in the universe. We assume magnetic field generation prior to the big bang nucleosynthesis (BBN), i.e., during the radiation-dominated epoch of the universe expansion, but do not limit analysis by considering a particular magnetogenesis scenario. Contrary to previous studies, we limit the total magnetic field energy density and not the smoothed amplitude of the magnetic field at large (of the order of 1 Mpc) scales. We review several cosmological signatures, such as halo abundance, thermal Sunyaev-Zel'dovich effect, and Ly{alpha} data. For a cross-check, we compare our limits with that obtained through the cosmic microwave background faraday rotation effect and BBN. The limits range between 1.5 nG and 4.5 nG for n{sub B} in (- 3; -1.5).

  8. Size dependence of structural stability and magnetization of nickel clusters from real-space pseudopotentials

    NASA Astrophysics Data System (ADS)

    Sakurai, Masahiro; Souto-Casares, Jaime; Chelikowsky, James R.

    2016-07-01

    We examine the structural stability and magnetization for nickel clusters containing up to 500 atoms by performing first-principles calculations based on pseudopotential in real space computed within density-functional theory. After structural relaxation, Ni clusters in this size range favor either an fcc structure, which is a crystal structure in bulk, or an icosahedral structure, which is expected for small clusters. The calculated total magnetic moments per atom of energetically stable clusters agree well with experiment, wherein the moments decrease nonmonotonically toward the bulk value as the cluster size increases. We analyze the spatial distribution of the local magnetic moment, which explains why the magnetic moments of Ni clusters are enhanced compared to their bulk value.

  9. Phonon and magnetic structure in δ-plutonium from density-functional theory.

    PubMed

    Söderlind, Per; Zhou, F; Landa, A; Klepeis, J E

    2015-10-30

    We present phonon properties of plutonium metal obtained from a combination of density-functional-theory (DFT) electronic structure and the recently developed compressive sensing lattice dynamics (CSLD). The CSLD model is here trained on DFT total energies of several hundreds of quasi-random atomic configurations for best possible accuracy of the phonon properties. The calculated phonon dispersions compare better with experiment than earlier results obtained from dynamical mean-field theory. The density-functional model of the electronic structure consists of disordered magnetic moments with all relativistic effects and explicit orbital-orbital correlations. The magnetic disorder is approximated in two ways: (i) a special quasi-random structure and (ii) the disordered-local-moment method within the coherent potential approximation. Magnetism in plutonium has been debated intensely, but the present magnetic approach for plutonium is validated by the close agreement between the predicted magnetic form factor and that of recent neutron-scattering experiments.

  10. Structural and Magnetic Properties of Co-Mn-Sb Thin films

    SciTech Connect

    Meinert, M.; Schmalhorst, J.-M.; Ebke, D.; Liu, N. N.; Thomas, A.; Reiss, G.; Kanak, J.; Stobiecki, T.; Arenholz, E.

    2009-12-17

    Thin Co-Mn-Sb films of different compositions were investigated and utilized as electrodes in alumina based magnetic tunnel junctions with CoFe counterelectrode. The preparation conditions were optimized with respect to magnetic and structural properties. The Co-Mn-Sb/Al-O interface was analyzed by x-ray absorption spectroscopy and magnetic circular dichroism with particular focus on the element-specific magnetic moments. Co-Mn-Sb crystallizes in different complex cubic structures depending on its composition. The magnetic moments of Co and Mn are ferromagnetically coupled in all cases. A tunnel magnetoresistance ratio of up to 24% at 13 K was found and indicates that Co-Mn-Sb is not a ferromagnetic half-metal. These results are compared to recent works on the structure and predictions of the electronic properties.

  11. Phonon and magnetic structure in δ-plutonium from density-functional theory

    PubMed Central

    Söderlind, Per; Zhou, F.; Landa, A.; Klepeis, J. E.

    2015-01-01

    We present phonon properties of plutonium metal obtained from a combination of density-functional-theory (DFT) electronic structure and the recently developed compressive sensing lattice dynamics (CSLD). The CSLD model is here trained on DFT total energies of several hundreds of quasi-random atomic configurations for best possible accuracy of the phonon properties. The calculated phonon dispersions compare better with experiment than earlier results obtained from dynamical mean-field theory. The density-functional model of the electronic structure consists of disordered magnetic moments with all relativistic effects and explicit orbital-orbital correlations. The magnetic disorder is approximated in two ways: (i) a special quasi-random structure and (ii) the disordered-local-moment method within the coherent potential approximation. Magnetism in plutonium has been debated intensely, but the present magnetic approach for plutonium is validated by the close agreement between the predicted magnetic form factor and that of recent neutron-scattering experiments. PMID:26514238

  12. Magnetic behavior of CoPt-AlN granular structure laminated with AlN layers

    NASA Astrophysics Data System (ADS)

    Yu, Youxing; Shi, Ji; Nakamura, Yoshio

    2011-04-01

    The magnetic behavior of CoPt-AlN granular structure laminated with AlN layers has been studied. Ultrathin multilayer structure, [CoPt0.5 nm/AlN0.5nm]4, is used as the precursor of the magnetic layers, which are separated by 5-nm-thick AlN layers. Upon thermal annealing, the ultrathin multilayer transforms into CoPt-AlN granular structure, and the thick AlN layers remain to be spacers. When the film was annealed at 400 °C, the out-of-plane direction becomes the easy axis of magnetization, although the coercivity remains small. TEM observation has proved that CoPt shows disklike shape at such an annealing temperature. When increasing the annealing temperature to 600 °C and above, the films show "isotropic" magnetic behavior due to the formation of equiaxial CoPt particles in the magnetic layers.

  13. X-ray imaging of vortex cores in confined magnetic structures

    SciTech Connect

    Fischer, P; Im, M -Y; Kasai, S; Yamada, K; Ono, T; Thiaville, A

    2011-02-11

    Cores of magnetic vortices in micron-sized NiFe disk structures, with thicknesses between 150 and 50 nm, were imaged and analyzed by high-resolution magnetic soft x-ray microscopy. A decrease of the vortex-core radius was observed from approximately 38 to 18 nm with decreasing disk thickness. By comparing with full three-dimensional micromagnetic simulations showing the well-known barrel structure, we obtained excellent agreement, taking into account instrumental broadening and a small perpendicular anisotropy. The proven magnetic spatial resolution of better than 25 nm was sufficient to identify a negative dip close to the vortex core, originating from stray fields of the core. Magnetic vortex structures can serve as test objects for evaluating sensitivity and spatial resolution of advanced magnetic microscopy techniques.

  14. Phonon and magnetic structure in δ-plutonium from density-functional theory

    SciTech Connect

    Söderlind, Per; Zhou, F.; Landa, A.; Klepeis, J. E.

    2015-10-30

    We present phonon properties of plutonium metal obtained from a combination of density-functional-theory (DFT) electronic structure and the recently developed compressive sensing lattice dynamics (CSLD). The CSLD model is here trained on DFT total energies of several hundreds of quasi-random atomic configurations for best possible accuracy of the phonon properties. The calculated phonon dispersions compare better with experiment than earlier results obtained from dynamical mean-field theory. The density-functional model of the electronic structure consists of disordered magnetic moments with all relativistic effects and explicit orbital-orbital correlations. The magnetic disorder is approximated in two ways: (i) a special quasi-random structure and (ii) the disordered-local-moment (DLM) method within the coherent potential approximation. Magnetism in plutonium has been debated intensely, However, the present magnetic approach for plutonium is validated by the close agreement between the predicted magnetic form factor and that of recent neutron-scattering experiments.

  15. Interface effect of magnetic properties in Ni nanoparticles with a hcp core and fcc shell structure.

    PubMed

    Choo, Seongmin; Lee, Kyujoon; Jo, Younghun; Yoon, Seon-Mi; Choi, Jae-Young; Kim, Jea-Young; Park, Jea-Hoon; Lee, Kyung-Jin; Lee, Jong-Heun; Jung, Myung-Hwa

    2011-07-01

    We have fabricated hexagonal close-packed (hcp) Ni nanoparticles covered by a face-centered cubic (fcc) Ni surface layer by polyol method. The magnetic properties have been investigated as a function of temperature and applied magnetic field. The magnetic behavior reveals that the system should be divided magnetically into three distinct phases with different origins. The fcc Ni phase on the shell contributes to the superparamagnetism through a wide temperature range up to 360 K. The hcp Ni phase at the core is associated with antiferromagnetic nature below 12 K. These observations are in good agreement with the X-ray absorption spectroscopy and magnetic circular dichroism measurements. In our particular case, the unique hcp core and fcc shell structure gives rise to an additional anomaly at 20 K in the zero-field-cooled magnetization curve. Its position is barely affected by the magnetic field but its structure disappears above 30 kOe, showing a metamagnetic transition in the magnetization versus magnetic field curve. This new phase originates from the magnetic exchange at the interface between the hcp and fcc Ni sublattices.

  16. First principle study of structural, electronic and magnetic properties of zigzag boron nitride nanoribbon: Role of vacancies

    SciTech Connect

    Kumar, Arun; Bahadur, Amar; Mishra, Madhukar; Vasudeva, Neena

    2015-05-15

    We study the effect of vacancies on the structural, electronic and magnetic properties of zigzag boron nitride nanoribbon (ZBNNR) by using first principle calculations. We find that the shift of the vacancies with respect to the ribbon edges causes change in the structural geometry, electronic structure and magnetization of ZBNNR. These vacancies also produce band gap modulation and consequently results the magnetization of ZBNNR.

  17. Large-scale magnetic structure formation in three-dimensional magnetohydrodynamic turbulence

    SciTech Connect

    Malapaka, Shiva Kumar; Müller, Wolf-Christian

    2013-11-20

    The inverse cascade of magnetic helicity in three-dimensional magnetohydrodynamic (3D-MHD) turbulence is believed to be one of the processes responsible for large-scale magnetic structure formation in astrophysical systems. In this work, we present an exhaustive set of high-resolution direct numerical simulations of both forced and decaying 3D-MHD turbulence, to understand this structure formation process. It is first shown that an inverse cascade of magnetic helicity in small-scale driven turbulence does not necessarily generate coherent large-scale magnetic structures. The observed large-scale magnetic field, in this case, is severely perturbed by magnetic fluctuations generated by the small-scale forcing. In the decaying case, coherent large-scale structures form similarly to those observed astronomically. Based on the numerical results, the formation of large-scale magnetic structures in some astrophysical systems is suggested to be the consequence of an initial forcing that imparts the necessary turbulent energy into the system, which, after the forcing shuts off, decays to form the large-scale structures. This idea is supported by representative examples, e.g., clusters of galaxies.

  18. Structure and magnetic properties of chromium doped cobalt molybdenum nitrides

    SciTech Connect

    Guskos, Niko; Żołnierkiewicz, Grzegorz; Typek, Janusz; Guskos, Aleksander; Adamski, Paweł; Moszyński, Dariusz

    2016-09-15

    Four nanocomposites containing mixed phases of Co{sub 3}Mo{sub 3}N and Co{sub 2}Mo{sub 3}N doped with chromium have been prepared. A linear fit is found for relation between Co{sub 2}Mo{sub 3}N and chromium concentrations. The magnetization in ZFC and FC modes at different temperatures (2–300 K) and in applied magnetic fields (up to 70 kOe) have been investigated. It has been detected that many magnetic characteristics of the studied four nanocomposites correlate not with the chromium concentration but with nanocrystallite sizes. The obtained results were interpreted in terms of magnetic core-shell model of a nanoparticle involving paramagnetic core with two magnetic sublattices and a ferromagnetic shell related to chromium doping. - Highlights: • A new chromium doped mixed Co-Mn-N nanocomposites were synthesized. • Surface ferromagnetism was detected in a wide temperature range. • Core-shell model was applied to explain nanocomposites magnetism.

  19. MAGNETIC STRUCTURE AND MAGNETIC IMAGING OF RE{sub 2}Fe{sub 14}B (RE=Nd,Pr) PERMANENT MAGNETS

    SciTech Connect

    ZHU,Y.; VOLKOV,V.V.

    2000-04-20

    This chapter aims to review the magnetic structures observed in the RE{sub 2}Fe{sub 14}B (RE = Nd, Pr) system using various TEM magnetic imaging techniques. The authors focus on studies of die-upset Nd-based permanent magnets conducted mainly at Brookhaven National Laboratory in the past several years. Investigations on Nd-Fe-B sintered magnets and single crystals, as well as Pr-Fe-B die-upset magnets also will be covered. In Sec.2 and Sec.3 they review the microstructure, including grain alignment and secondary phases of the materials, and grain boundary structure and composition of the intergranular phase. Sec.4 is devoted to the domain structure, such as the width of domain and domain wall and domain-wall energy. Monte Carlo simulation of the effects of demagnetization fields will be presented in Sec.5. In-situ experiments on the dynamic behavior of domain reorientation as a function of temperature, pinning, grain boundary nucleation related to coercivity under various fields are described in Sec.6. Finally, in Sec.7 the correlation between microstructure and properties are discussed.

  20. Analysis of nuclear-quadrupole-resonance spectrum of incommensurate phases: The case of bis(4-chlorophenyl) sulfone

    NASA Astrophysics Data System (ADS)

    Schneider, J.; Schürrer, C.; Wolfenson, A.; Brunetti, A.

    1998-02-01

    In this work, previous experimental studies of the 35Cl nuclear-quadrupole-resonance (NQR) line shape in the incommensurate phase of bis(4-chlorophenyl) sulfone were extended. The broad spectra in the incommensurate phase (IC) were measured using the Fourier transform of the nuclear signal to avoid systematic errors committed in some studies of this compound. The results were interpreted within the framework of the general treatment developed by Perez-Mato, Walisch, and Petersson. The effects of the incommensurate modulation on the asymmetry parameter of the electric-field gradient were explicitly included in the expression of the NQR frequency. The features of the spectra were adequately reproduced in the whole temperature range, by considering the nonsinusoidal character of the atomic modulations reported by x-ray diffraction. No evidences were found concerning IC wave fluctuations smearing out the singularities of the NQR spectrum. On the other hand, relative intensity of NQR peaks and temperature behavior of some parameters of the plane-wave ``local'' model were explicitly calculated. Comparison of these quantities with the experimental results excludes the applicability of the ``local'' model in the case of bis(4-chlorophenyl) sulfone.