Neutron diffraction study of the magnetic ordering in EuAs3

The magnetic structure of one of the two ordered phases has been determined at 5 K. The magnetic structure is found to be antiferromagnetic with a cell doubling in the c direction of the monoclinic nuclear cell. The centering in the nuclear cell is replaced by anticentering. The collinear magnetic moments are parallel to the b axis. The magnetic moment per Eu atom has been found to be 5.74(6)μ_B which leads to the saturation magnetic moment of 6.5μ_B.     

Mesure de la structure hyperfine du niveau 3s2 DE 21Ne

We describe a level-crossing measurement of the hyperfine structure of the 3s₂ level of ²¹Ne optically pumped by a laser beam. The magnetic dipole and electric quadrupole hyperfine interaction constants a and b are obtained: a = -728.0±0.8 MHz, b=-13.4±2.5 MHz.     

Current neutralization and plasma polarization for intense ion beams propagating through magnetized background plasmas in a two-dimensional slab approximation

A two-dimensional electromagnetic Particle-in-Cell （PIC） simulation model is proposed to study the propagation of intense, ion beams with beaIn width wb small compared to the electron skin depth c/wpe through background plaslnas in tile presence of external applied magnetic fields. The effcctive eleetron gyrora,dius wge is found to be an important parameter for ion beam transport in the presence of magnetic fields,In the bealn regions, the background plasmas respond differently to the ion beanl of width wb〈wge and wb 〉 wge for the given magnetic field and beaan encrgy, For the case of beam width wb 〈 wge with relative weak external magnetic fiehts, the rotalion effects of plasma electrons a,re found to be signifieant and contributes to the signitica,nt enilaneeinent of the self electric and seif-magnetic fields. While for the ease of beam width wb 〉 wge with relative strong external magnetic fields, the rotation effects of plasma cleetrons are strongly inhibited and a, well neutraliza, tion of ion beam current can be found. Finally, the influences of diftiuent beam widths. beam energies and magnetic fields on the neutralization of ion bc, anl eurrellt are summarized for the eases of wb 〈 wge〈 c/wpe,wge 〈wb〈c/wbp and wb〈c/wpe〈wge.     

Influence du moment octupôlaire sur le calcul de l'élargissement des raies de la transition O → 2 de HCl comprimé

The importance of the “cross-terms” arising in the interruption function S₂(b), when all interactions involving the octupole moment are taken into account, is analyzed. It is shown that agreement between theoretical linewidth calculations and experimental data is considerably improved for large |m| values, provided all electrostatic contributions to S₂(b) are considered, including the terms which involve ω. A semi-empirical value of ω is then derived.     

Irreversible magnetovolume effect in Nd7Rh3 single crystal

Magnetovolume effect in Nd₇Rh₃ single crystal has been studied by measuring the magnetostriction as a function of external magnetic field at 4.2 K. An irreversible magnetovolume effect having a negative remanent volume magnetostriction was observed when the external magnetic field was applied along the b-axis. The irreversible magnetostrictive effect takes place in the longitudinal magnetostriction along the b-axis. The remanent magnetostriction along the b-axis relaxes after removing external magnetic field for several hours and equilibrium state is stabilized.     

Pinning of spiral fluxons by giant screw dislocations in YBa2Cu3O7 − δ single crystals: Josephson analog of the fishtail effect

By using a highly sensitive homemade AC magnetic susceptibility technique, the magnetic flux penetration has been measured in YBa₂Cu₃O_{7 ? δ} single crystals with giant screw dislocations (having the structure of the Archimedean spirals) exhibiting a = 3 spiral turnings, the pitch b = 18.7 μm and the step height c = 1.2 nm (the last parameter is responsible for creation of extended weak-link structure around the giant defects). The magnetic field applied parallel to the surface enters winding around the weak-link regions of the screw in the form of the so-called spiral Josephson fluxons characterized by the temperature dependent pitch b _f (T). For a given temperature, a stabilization of the fluxon structure occurs when b _f (T) matches b (meaning an optimal pinning by the screw dislocations) and manifests itself as a pronounced low-field peak in the dependence of the susceptibility on magnetic field (applied normally to the surface) in the form resembling the high-field (Abrikosov) fishtail effect.     

Etude par diffraction neutronique de la forme haute pression de FeOOH

A powder sample of iron oxyhydroxide (FeOOH_HP) synthesized under high pressure-high temperature conditions, has been studied by neutron diffraction. The magnetic structure has been determined. The magnetic and chemical unit cells are the same and the antiferromagnetic arrangement is collinear with the spins parallel to the c-axis. The crystallographic structure affinement by the Rietveld method has confirmed that FeOOH_HP is isostructural with InOOH (space group P2₁nm) and has established the positional atomic parameters. The magnetic moment of iron (4.7μ_B at 4.2 K) and the O-H distance in the hydrogen bond (1.11 Å) are discussed with regard to the values obtained for the other forms of iron oxyhydroxide.     

Synthesis of the new oxocuprate Cu5Bi2B4O14 and investigation of its structural, magnetic, and resonant properties

Single crystals of the new compound Cu₅Bi₂B₄O₁₄ are grown and its structural, magnetic, and resonant properties are investigated for the first time. It is found that the Cu₅Bi₂B₄O₁₄ crystal synthesized has a triclinic symmetry with space group $P\bar 1$ and the unit cell parameters a=10.132 Å, b=9.385 Å, c=3.458 Å, α=105.443°, β=97.405°, γ=107.784°, and Z=1. At a temperature of 24.5 K, the crystal undergoes a magnetic phase transition to the magnetically ordered state. The assumption is made that the ferrimagnetic structure of the Cu₅Bi₂B₄O₁₄ crystal consists of two ferromagnetic sublattices coupled through the antiferromagnetic exchange interaction. The unit cell of the crystal contains five copper ions, of which one ion belongs to the first sublattice and the other four ions form the second sublattice. Analysis of the resonant and magnetic static properties demonstrates that the Cu₅Bi₂B₄O₁₄ crystal exhibits an easy-axis magnetic anisotropy. The direction of the easy axis coincides with the c axis of the crystal, whereas the a and b axes are the hard magnetic axes with saturation fields approximately equal to 25 and 10 kOe, respectively.     

Magnetization measurements and the magnetic inhomogeneity of random metal alloys

It is argued that the straightness or otherwise of plots of M_b² vs (B₀/M_b) (where M_b is the magnetization in a magnetic induction B_o and at approximately zero temperature) for different concentrations in the critical or percolation concentration region for long-range ferromagnetic order in atomically disordered metal alloys is neither a satisfactory measure of the magnetic (and/or metallurgical) homogeneity of the alloys nor is it an acceptable test of the applicability of Landau's theory of phase transitions to such alloy systems.     

Some estimates for magnetic fluctuations in a turbulent medium

A new integral relationship between the fluctuations b(r, t) of a magnetic field and its mean B ₀(r, t) is derived for the steady-state magnetic field in a turbulent medium. This formula provides the estimate 〈b?curlb〉=?B ₀?curlB ₀. Simultaneously, the coefficient of amplification of the mean magnetic field α effect) is obtained: α=(η+β)B ₀? curlB ₀/B ₀ ² . The formula for α allows for a decrease in this coefficient owing to the back action of the magnetic field on the turbulent velocity field. It is shown that the Zel’dovich’s estimate 〈 b ²〉?β/η B ₀ ² for two-dimensional turbulence holds for magnetic fields at the instant the fluctuations 〈a ²〉 of the vector potential, rather than 〈b ²〉, reach a maximum. Here, η and β are the ohmic (molecular) and turbulent diffusion coefficients, respectively. This estimate is refined with allowance made for the fact that the condition for diffusion approximation itself relates the β, b, and B ₀ quantities to each other.     

Response of the electrical resistance of La0.67Ca0.33MnO3(40 nm) films mechanically compressed by the substrate in the course of their formation to electric and magnetic fields

The structure and electrical resistance of La_0.67Ca_0.33MnO₃(40 nm) epitaxial films grown quasicoherently on the surface of LaAlO₃(001) substrates are investigated. Compressive mechanical stresses that are active in the substrate plane during nucleation and growth encourage a decrease in the effective unit cell volume and an increase in the relative concentration of tetravalent manganese ions in the manganite layers. This leads to a decrease in the temperature of the maximum in the temperature dependence of the electrical resistivity of the films by approximately 90 K compared to the Curie temperature for the corresponding stoichiometric bulk crystals. It is found that, at T < 120 K and μ₀ H = 0 (where H is the magnetic field strength), the measuring current depends nonlinearly on the voltage V _b applied to the contacts. An increase in the applied voltage V _b and in the magnetic field strength H favors linearization of the current-voltage characteristics of the films.     

Determination de la structure magnetique de la phase Na5Fe3F14γ

The magnetic structure of the ferrimagnetic fluoride - Na₅Fe₃F₁₄ has been determined. The magnetic moments of the iron atoms in (2a) and (4d) sites are antiparallel and directed along the c axis. The magnetic group is P4₂2′₁2′.     

The optically detected magnetic resonance of dangling bonds at the Si/SiO2 interface

The optically detected magnetic resonance (ODMR) observation of dangling bonds at the Si/SiO₂ interface (P_b centers) is reported in this Communication. A luminescence quenching signal is identified as arising from the P_b center through its axially symmetry g tensor along the <1 1 1#62; direction. The negative sign observed for both the P_b center and the neutral phosphorus donor resonances allows us to interpret the recombination mechanism as a spin dependent electron transfer from the phosphorus donor to the P_b center.     

Magnetic structure of low-dimensional LiCu2O2 multiferroic according to 63,65Cu and 7Li NMR studies

The complex NMR study of the magnetic structure of LiCu₂O₂ multiferroic has been performed. It has been shown that the spin spirals in LiCu₂O₂ are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu²⁺ chains. A magnetic field of H ₀ = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H ₀ ?? b.     

Crystal and magnetic structures of Y2CrS4

Chromium(II) sulfide, Y₂CrS₄, prepared by a solid-state reaction of Y₂S₃ and CrS, showed an antiferromagnetic transition at 65 K. The neutron diffraction patterns at 10 and 90 K were both well refined with the space group Pca2₁. At 90 K, cell parameters were a=12.5518(13) Å, b=7.5245(8) Å, and c=12.4918(13) Å. At 10 K, magnetic peaks were observed, which could be indexed on the same unit cell. Magnetic moments of chromium ions were parallel to the b-axis and antiferromagnetically ordered in each set of the 4a sites.     

Crystal structure and magnetic state of the LaMn1−x VxO3 perovskites

The crystal structure and the magnetic state of polycrystalline LaMn_1?x V_xO₃ (0.1<x<0.9) compounds have been studied by x-ray and neutron diffraction methods, as well as by magnetization and ac susceptibility measurements. It is shown that substitution of vanadium for manganese ions leaves the orthorhombic crystal structure of the compounds (space group Pnma) unchanged. The magnetic structure is observed to change from a canted antiferromagnetic ordering (wavevector k=[0, 0, 0], with the antiferromagnetic moments aligned with the a axis and the ferromagnetic component of the magnetic moment parallel to the b axis) at vanadium concentrations x<0.4 to a collinear antiferromagnetic ordering (with the magnetic moments parallel to the b axis) at x>0.8; at this transition occurs through an intermediate state exhibiting spin-glass properties.     

Magnetoresistance anisotropy of strontium ruthenate films grown coherently on a TiO2-terminated SrTiO3(001) substrate

The SrRuO₃ films with a thickness of 80 nm have been coherently grown on a TiO₂-terminated SrTiO₃(001) substrate. Biaxial mechanical stresses induce a considerable difference between the unit cell parameters of the SrRuO₃ layer in the substrate plane (??3.904 ?) and along the normal to the substrate surface (??3.952 ?). The electrical resistivity of the SrRuO3 film decreases practically linearly with increasing magnetic field strength H when the latter is parallel to the current I _b and the projection of the easy magnetization axis in the substrate plane. At T = 4.2 K, ??₀ H = 14 T, and the magnetic field oriented along the hard magnetization axis, the negative anisotropic magnetoresistance of the grown layers reaches 16% and exerts a notice-able effect on the response of electrical resistivity of the SrRuO₃ film to the magnetic field.     

First-order phase transition in potassium dysprosium tungstate induced by the field renormalization and softening of the elastic moduli in the vicinity of a structural Jahn-Teller-type transition

The magnetostriction of KDy(WO₄)₂ single crystals is measured in an external magnetic field at temperatures below the temperature of a structural phase transition of the Jahn-Teller type. A steplike irreversible variation in the elastic strain is observed to occur with an increase in the magnetic field applied along the a or b axis of the monoclinic cell of the crystal. The residual change in the strain is retained after changing the sign of the magnetic field. The return to the initial state characterized by field-induced jumps in the strain is possible only after thermal cycling well above the structural phase transition temperature. The theory of this phenomenon is developed using a phenomenologically derived thermodynamic potential of the elastic sub-system that takes into account the crystal symmetry and the field renormalization of the elastic moduli. The jumplike transitions are interpreted as being due to the magnetic softening of the elastic moduli in the vicinity of the structural phase transition temperature.     

Structural and magnetic properties of the layered compound Ca2.375La0.125Sr0.5GaMn2O8

The brownmillerite-type layered compound Ca_2.375La_0.125Sr_0.5GaMn₂O₈ has been synthesized. The crystal and magnetic structures have been refined by the Rietveld analysis of the neutron powder diffraction patterns at 300 and 20 K. This compound crystallizes in the orthorhombic symmetry under the space group Pcm2₁ (a = 5.447(2), b = 11.359(4) and c = 5.322(2) Å). The compound is found to be antiferromagnetic at 20 K. The ordered Mn magnetic moment, aligned along the crystallographic b-direction, is derived to be 2.53(5) µ_B per Mn ion at 20 K.