Showing papers on "Magnetic structure published in 1971"

Magnetic Structure of Mn3O4 by Neutron Diffraction

Abstract: Mn3O4 is a tetragonal spinel I41/amd. It is ferromagnetic below Tc = 43°K. At 4.2°K neutron diffraction measurements on powdered samples show the presence of 8 sublattices in a unit cell a, 2a, c which is double the chemical unit cell. These 8 sublattices are arranged as follows: 2 sublattices at tetrahedral sites and 6 sublattices at octahedral sites. At 4.2°K the moments are 4.65 μB on A sites and 3.55 μB on B sites with a resulting moment of 1.85 μB/molecule along the (010) direction. The study of thermal variation of the structure shows that at 33°K a rearrangement of moments occurs such that the chemical and magnetic unit cells become identical.

Antiferromagnetism of γ-Phase Manganese Alloys Containing Ni, Zn, Ga and Ge

Abstract: Manganese-rich γ-phase alloys of Mn-Ni, Mn-Zn, Mn-Ga and Mn-Ge have been investigated with X-ray and neutron diffraction and specific heat measurements. The Mn-Zn, Mn-Ga and Mn-Ge alloys exhibit antiferromagnetism below the transition temperature, at which the cubic lattice is transformed to the tetragonal lattice (the axial ratio c / a 1) at a lower temperature. The magnetic structure for the axial ratio c / a >1 is different from that for the axial ratio c / a <1. The integrated values of the anomalous specific heat are less than the values predicted by the localized moment model of antiferromagnetism.

Magnetic Properties of Cr 1− x Mn x As System

Abstract: Studies on X-ray crystallographic, magnetic, neutron diffraction and transport properties have been made of the system Cr 1- x Mn x As (0≤ x ≤0.9). All the members of the system undergo a transition from MnP structure to NiAs structure. Magnetic measurements have revealed the existence of three distinct magnetic regions and the magnetic structures of these regions have been found from neutron diffraction measurements. On the basis of these experimental data, magnetic and crystallographic phase diagrams have been constructed. In particular, CrAs exhibits a discontinuous change in the lattice constants at the Neel temperature which was obtained to be 265°K. The electrical resistivity and thermoelectric power show a strong anomaly at the temperature where the magnetic order disappears. The observed helical spin arrangement may be stabilized by the distorion of the Fermi surface which is caused by the formation of a new zone boundary.

Magnetic Structure of MnAs and MnAs0·92P0·08

Abstract: The similarity of the ordered magnetic structures of orthorhombic MnAs (stable at high pressure) and orthorhombic MnAs0.92P0.08 has been confirmed using neutron diffraction. Below the magnetic ordering temperature, Tc, a canted spin structure is found for both materials. Neutron diffraction measurements from magnetically ordered and disordered temperature regions show that in these materials the Mn magnetic moment varies with the volume of the Mn atom. The variation of the magnitude of the Mn magnetic moment is explained using the relation between Pauling valence and magnetic moment introduced by Mori and Mitsui. The results are in disagreement with the currently accepted interpretation of the susceptibility data.

The magnetic structure of antiferromagnetic DyVO4

Abstract: The magnetic and crystallographic structure of DyVO4 has been determined by neutron diffraction on a powdered sample. The two observed lambda -type anomalies in the specific heat at 13.8 and 3.0 K are explained by a quadrupole ordering followed by an antiferromagnetic transition. At 3.0 K DyVO4 undergoes a transition to a collinear antiferromagnetically ordered state with the moments parallel to the b axis. The magnetic moment is 9/0 mu B at 1.85 K. The nuclear scattering does not allow for a crystallographic phase transition, either at 13.8 K or at 3.0 K. In order to describe the magnetic structure properly the symmetry has to be reduced, however, to orthorhombic symmetry, space group Imma-D2k28.

Neutron and Magnetic Studies of a Single Crystal of Fe2TiO4

Abstract: Magnetic properties of a single crystal of almost pure Ulvospinel Fe 2.05 Ti 0.95 O 4.00 have been investigated by neutron diffraction and magnetic studies. Fe 2 TiO 4 is a perfect inverse spinel with oxygen parameter of u =0.386±0.001 at room temperature. The crystal becomes weakly ferromagnetic below 142°K. The magnetic structure is of the Neel type with the sublattice magnetic moments of 4.2±0.2µ B on both octahedral and tetrahedral sites at 4.2°K. The moment on the octahedral site decreases with increasing temperature faster than that on the tetrahedral site. The spontaneous weak ferromagnetic moment is induced in one of the direction perpendicular to spins. The spins tend to orient to the direction of the field, only when the magnetic field is applied in the [100] direction. The crystal is suggested to distort tetragonally at low temperatures with the spin along the long axis. The average \bar u parameter at 4.2°K is also 0.386±0.001.

Magnetic structure analysis and group theory

Abstract: R6sum6. L'analyse de structures magnktiques par la thkorie des groupes (analyse de reprksentations) est baste sur la transformation de vecteurs spins, situks dans une position cristallographique donnee, sous les opkrations de symktrie d'un groupe d'espace G ou sous-groupe Gk du cristal dans lequel se trouve la structure magnktique. Le vecteur d'onde k caracterisant le groupe de translation est deduit de l'expkrience de diffraction neutronique. Les Cquations de transformation linkaires induisent une reprksentation r de G ou de Gk. On reduit en reprksentations irrkductibles (r. i.). Les vecteurs de base, sous-tendant les r. i. decrivent des structures magnktiques possibles de sorte que l'on n'a B comparer qu'un faible nombre de modkles avec I'expkrience. La symktrie de I'hamiltonien (de la reprbentation irrkductible) est gknkralement plus klevee que la symktrie de Shubnikov de la structure magnetique. Quant au schkma de classification d'opechowski, notre schkma (C2) utilise d'une manibre cohQente et exclusive les groupes d'espace, m6me pour des spins sinusoidaux et hklicoldaux alors que dans le schkma Cl' on doit ajouter des groupes non cristallographiques pour une description de ces cas. Abstract. The analysis of magnetic structures by group theory (representation analysis) is based on the transformation of spins on a given lattice site under the symmetry operations of a crystallographic space group G or a subgroup Gk of the crystal in which the magnetic structure is imbedded. The wave vector k labelling the translation group is taken from the neutron diffraction experiment. The linear transformation equations induce a representation r of G or Gk. r is reduced to irreducible representations. Basis vectors, constructed from them, describe possible magnetic structures so that only a small number of models have to be compared with experiment. The symmetry of the hamiltonian (of the irreducible representation) is generally higher than the Shubnikov symmetry of the magnetic structure. As far as Opechowski's classification scheme is concerned our scheme (C2) uses space groups consistently, even for sinusoidal and helical spins whereas in the scheme Cl' one must add non crystallographic groups for a full description of the latter case.

Magnetic Structure of FeOCl

Abstract: Mossbauer spectroscopy has been used to study the magnetic properties of ferric oxychloride FeOCl. A paramagnetic to antiferromagnetic transition occurs at 92°±3°K. Near liquid‐helium temperature the antiferromagnetic structure is noncolinear; at least two sets of nonequivalent Fe3+ sites and a doubling of the unit cell are required. All Fe3+ spins are confined to the bc plane (c

NMR Study of the Magnetic Phase of EuSe

Abstract: The Eu 153 NMR in EuSe has been observed as a function of temperature and applied magnetic field. NMR results in zero applied field support the magnetic structure proposed by Fischer et al. ; EuSe has a structure of the NNSS-type in the antiferromagnetic region (from 4.6 K down to about 2.5 K) and a structure in which there coexist the NNS-and NSNS-types in the ferrimagnetic region (below about 2.5 K). As the applied field is increased, the zerofield magnetic structure changes into an intermediate one and finally into the ferromagnetic one (NNN). The coexistence of a canted spin structure and a ferrimagnetic one is proposed for the intermediate phase.

Magnetic Properties of CeBi, NdBi, TbBi, and DyBi

Abstract: The magnetic properties of four REBi compounds, where RE is Ce, Nd, Tb, and Dy, were investigated by neutron diffraction on powder samples; all of these compounds are antiferromagnetic below Neel temperatures TN of 26, 25, 18, and 13°K, respectively. The magnetic structure of both CeBi and NdBi consists of (001) ferromagnetic planes coupled antiferromagnetically with the spin direction along the [001] axis. TbBi has a magnetic structure which consists of (111) ferromagnetic planes coupled antiferromagnetically with a [111] spin direction. The magnetic structure of DyBi could be either type A or B of MnO; the spin direction could not be determined from the present powder sample. CeBi and NiBi possess antiferromagnetic ordering of the first kind whereas TbBi and DyBi have the second kind. The development of antiferromagnetic ordering below TN follows a Brillouin function for CeBi and NdBi but TbBi and DyBi show considerable deviation. The saturation ordered moments for CeBi and NdBi are 6% less than the calculated values whereas for TbBi and NdBi the moments are 12% less than the expected values.

Exchange Reflexions in Low Energy Electron Diffraction from Antiferromagnetic Nickel Oxide Crystal

Abstract: The nature of exchange reflexions in low-energy electron diffraction from antiferromagnetic nickel oxide was studied in particular reference to its dependence on the diffraction condition of electrons, which was, in the present study, changed primarily by rotating the crystal at a fixed electron energy. It was pointed out that the exchange reflexions are subject to the three-dimensional diffraction conditions appropriate to the reciprocal lattice points which correspond to the magnetic structure, and also that the intensities of these weak reflexions may be favourably enhanced by the dynamical diffraction effect under the condition which involves the simultaneous presence of a strong regular reflexion.

Crystal‐Field Splitting and Spin Waves in Antiferromagnetic CeSb

Abstract: The specific heat of crystalline samples of CexY1−xSb (x=1, 0.2, 0.1, and 0) and LaSb was measured for temperatures between 1.5° and 70°K. The Neel temperature of CeSb is found to be 16.0 (±0.2)°K. The magnetic specific heat between 1.5° and 3.8°K is proportional to T2. This temperature dependence is correlated with spin waves in the anisotropic magnetic structure of CeSb. The crystal‐field splitting of the 2F5/2 ground state of the Ce3+ ion in CeSb is 24 (±2)°K.

Electronic and Magnetic Structure of Dilute Iron‐Base Alloys

Abstract: Mossbauer spectroscopy has been used to characterize changes in the electronic and magnetic structure of iron resulting from dilute additions of vanadium, chromium, manganese, nickel, molybdenum, tungsten, rhenium, aluminum, and silicon. The data showed that both the isomer shift and the hyperfine field depend linearly upon the bulk composition of the alloy and the local atomic configuration. This model separates the metallurgical dependence of these electronic and magnetic parameters into a long‐range composition‐dependent component and a short‐range composition‐independent component. The long‐range component of isomer shift in iron‐chromium alloys agrees with the value predicted by x‐ray diffraction measurements of the lattice parameter dilation. The short‐range component correlates qualitatively with the electronegativity of the diluents.

Neutron diffraction study of antiferromagnetic DyAsO4

Abstract: The magnetic structure of DyAsO4 has been determined by neutron diffraction on a powdered sample. DyAsO4 undergoes a transition to a non-collinear antiferromagnetically ordered state at 2.5 K, with an inclination of the magnetic moments of phi b=22 degrees relative to the b axis in the ab plane. The magnetic space group is PI212121 (orthorhombic symmetry). The magnetic moment is 8.6 mu B at 2.2 K. The temperature behaviour of the magnetization is in agreement with an Ising magnet. The crystallographic parameters are determined and possible crystallographic phase transitions are discussed.

Magnetic Structure of Manganese Pyrophosphate, Mn2P2O7

Abstract: The arrangement of the spins in antiferromagnetic manganese pyrophosphate at 4 °K has been determined by neutron diffraction from a powder specimen. The spins are in ferromagnetic sheets with the m...

Proton Magnetic Resonance in Antiferromagnetic Ni(NH3)2Ni(CN)4·2C6H6

Abstract: The magnetic spin structure of the antiferromagnetic Ni(NH 3 ) 2 ·Ni(CN) 4 2C 6 H 6 has been investigated by means of proton nuclear magnetic resonance measurements. From the angular dependence of resonance lines in an external field, an ordered magnetic structure (unit cell dimension, a * = a , b * =2 a and c * =2 c ) is inferred in which ferromagnetic chains parallel to a -axis, are arrayed antiferromagnetically to adjacent chains. The magnitude of internal fields at proton sites could be explained by single domain model. But the rotating diagram of the resonance patterns in the c -plane shows that the substance has antiferromagnetic domains.

Magnetic Structure of α‐Ho2C3

Abstract: The antiferromagnetic structure of α‐Ho2C3 as revealed by neutron powder diffraction is stabilized below 19 ± 1°K and is markedly different from the ordered spin structure of the isostructural α‐Tb2C3 (the cubic body‐centered Pu2C3 type). Two out of four body diagonally linked arrays of Ho atoms become the ferromagnetically ordered chains and the remaining two arrays show one‐dimensional antiferromagnetic alignment. Among three nearest Ho–Ho neighbors bridging between the different body‐diagonal arrays are two antiferromagnetic pairs and one ferromagnetic pair. The moment direction is most likely parallel to one of the ferromagnetic linear arrays. The maximum spontaneous moment is 7.3 ± 0.2 μB which is considerably smaller than the free He3+ value of 10 μB. The temperature dependency of the spontaneous magnetization is approximated by the Brillouin function with S = 1 ± 12 but departs significantly from the free ion function with J(g − 1) = 2. The magnetically ordered phase exhibits a sizeable magnetic di...