Iron Magnetic Moments Research Articles

A Mössbauer spectral study of the NdMn 6− xFe xGe 6 solid solutions

The Mössbauer spectra of the NdMn 6− x Fe x Ge 6 solid solutions, with x = 0.5, 1.0 and 1.5 have been obtained at 4.2, 78 and 295 K. They are analyzed in terms of a binomial distribution of environments for the iron 3 g sites. The 78 K weighted average hyperfine fields vary between 14.7 and 15.3 T. The hyperfine field increases with increasing number of iron near neighbours. The isomer shift decreases with increasing x, in agreement with the concomitant unit-cell contraction. The 78 K quadrupole shift of NdMn 5.5Fe 0.5Ge 6 is different from those of NdMn 5FeGe 6 and NdMn 4.5Fe 1.5Ge 6 and indicates that the iron magnetic moments have a different orientation in the former compound, i.e., they lie in the basal plane of the hexagonal unit cell.

Design and Magnetic Properties of New Compounds Containing Iron 2D Building Blocks of the Perovskite Type.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Design and magnetic properties of new compounds containing iron 2D building blocks of the perovskite type

Using the concept of 2D building blocks we have looked for new compounds containing iron 2D perovskite type building blocks. In that purpose, we have tried to exchange the [Cu 2S 2] 2D building blocks found in Sr 3Fe 2Cu 2S 2O 5 by other isostructural blocks such as [Cu 2Se 2], [Ag 2S 2], [Ag 2Se 2] or [Zn 2P 2]. With a high temperature ceramic method and/or a metathesis reaction we have then succeeded to synthesize Sr 3Fe 2Cu 2Se 2O 5, Sr 3Fe 2Ag 2S 2O 5 and Sr 3Fe 2Ag 2Se 2O 5. Structure refinement from X-ray powder diffraction patterns of Sr 3Fe 2Cu 2Se 2O 5 and Sr 3Fe 2Ag 2S 2O 5 have confirmed that the structure of both compounds results from the expected alternated stacking of perovskite [Sr 3Fe 2O 5] and anti-fluorite [Cu 2Se 2] or [Ag 2S 2] 2D building blocks. Mössbauer spectroscopy measurements for Sr 3Cu 2Fe 2Se 2O 5 revealed the presence of Fe 3+ high spin within the perovskite [Sr 3Fe 2O 5] block and showed that the magnetic moments of iron are ordered at low temperature. Moreover neutron diffraction experiments have revealed an antiferromagnetic structure ( T N ≈ 490 K ) with iron magnetic moments aligned along the a axis.

The effect of iron doping in La0.8Sr0.2Fe0.05Co0.95O3-? perovskite

La0.8Sr0.257Fe0.05Co0.95O3-δ perovskite is investigated by 57Fe transmission and emission Mossbauer spectroscopy, X-ray diffraction, AC magnetic susceptibility and magnetotransport measurements. Temperature dependence of the 57Fe Mossbauer isomer shift, quadrupole splitting, magnetic hyperfine field, line broadening, and relative spectral area is presented in a detailed manner for La0.8Sr0.257Fe0.05Co0.95O3-δ . The oxidation state of iron is determined to be Fe3+, and the presence of preferential electronic charge compensation Fe3+ ↦ Fe4+ over that of Co3+ ↦ Co4+ is excluded. Relaxation of iron magnetic moments reflected by the 57Fe Mossbauer spectra of La0.8Sr0.257Fe0.05Co0.95O3-δ are interpreted as evidence for the existence of superparamagnetic like Co clusters and a corresponding cluster glass magnetic phase formed below T ≈65 K.

Electronic Structure and Magnetic States of Crystalline and Fullerene-Like Forms of Nickel Dichloride NiCl[sub 2

The electronic structure and magnetic properties of the crystalline and fullerene-like forms of nickel dichloride NiCl2 are investigated in the framework of the local spin density functional theory. It is demonstrated that the band gap can be reproduced in the energy band spectrum of the NiCl2 compound with inclusion of the magnetic ordering in the calculation of the band structure. The metamagnetic nature of the NiCl2 dichloride (i.e., the transition from an antiferromagnetic phase to a ferromagnetic phase in a weak magnetic field) is explained in terms of a small difference (0.025 eV/cell) between the total energies of the ferromagnetic and antiferromagnetic phases. Polyhedral three-shell nanoparticles of the NiCl2 compound exhibit magnetic properties (the magnetic moment of nickel lies in the range 2.0–2.3 μB). For isostructural nanoparticles of the FeCl2 dichloride, the magnetic moment of iron is larger and falls in the range 4.2–4.5 μB, whereas nanoparticles of the CdCl2 dichloride are found to be nonmagnetic. The results of analyzing the interatomic interactions indicate that the composition of fullerene-like nanoparticles of the dichlorides under investigation can deviate from the 1: 2 stoichiometric composition.

Perpendicular-current giant magnetoresistance of M∕Cu∕M (001) junctions (M=Fe, Co, or Ni): An ab initio study

The electronic structure and magnetic properties of semi-infinite Cu(001)∕M∕Cu∕M∕semi-infinite Cu (001) multilayer systems with M=Fe, Co, or Ni have been studied by means of a first-principle Green’s function technique based on the tight-binding linear muffin-tin orbital method. The results show that at the M∕Cu (M=Fe or Co) interfaces there is a net charge transfer from iron and cobalt atoms to the neighboring paramagnetic copper atoms and an enhancement of the iron magnetic moment while at the Ni∕Cu interface, the nickel magnetic moment is reduced compared with its bulk value. This behavior is explained in terms of the relative positions of the Fermi levels of the magnetic material and copper. The conductance is determined in the ballistic limit, in the current-perpendicular-to-the-plane geometry by means of transmission matrix formulation of Kubo-Landauer formalism. It is shown that the oscillations of the giant magnetoresistance ratio are mainly the result of the oscillations of the minority-spin conductance.

A magnetic and Mössbauer spectral study of SmFe 11Ti, LuFe 11Ti, and their respective hydrides

ac Magnetic susceptibility measurements have been carried out on LuFe 11Ti and LuFe 11TiH and reveal the absence of any spin-reorientation between 4.5 and 293 K. Iron-57 Mössbauer spectral measurements between 4.2 and 295 K have been carried out on SmFe 11Ti and LuFe 11Ti and their respective hydrides, SmFe 11TiH and LuFe 11TiH. The Mössbauer spectra have been analyzed with a model that considers both the orientation of the iron magnetic moments and the distribution of titanium atoms in the near neighbor environment of the three crystallographically distinct iron sites. The assignment and the temperature dependence of the hyperfine fields are in complete agreement with the unit cell volume and its expansion upon hydrogenation and with those observed in the related RFe 11Ti and RFe 11TiH compounds. The site assignments and their temperature dependencies of the isomer shifts are in complete agreement both with the Wigner–Seitz cell volumes of the inequivalent iron sites and the crystallographic changes upon hydrogen insertion.

First principles study of induced magnetic moments in Fe1−xMx disordered alloys and in Fe/M (0 0 1) superlattices with M = V, Nb, Ta, Mo

In this paper, we report on a theoretical study of magnetic couplings in Fe1−xMx disordered bulk alloys and in Fe/M (001) superlattices (with M = V, Nb, Ta and Mo). The calculations were carried out using the charge and spin self-consistent Korringa–Kohn–Rostoker method combined with coherent-potential-approximation (KKR-CPA). For Fe1−xVx, site-decomposed magnetic moments were calculated according to two different models of completely and semi disordered alloys.For all the considered transition metals M, an antiferromagnetic (AF) coupling between the Fe and the M magnetic moments was determined. For small concentrations x (d-impurity in bcc Fe metal), the induced magnetic moment on the M atom is of −1.37μB for V and of about −0.6μB for M = Nb, Ta and Mo. The Fe magnetic moment was found to be 2.31μB, equal to that of pure bcc metal. When x increases up to 0.28, the Fe magnetic moment does not change noticeably, while the induced M magnetic moment decreases more dramatically, e.g. for M = V and Mo.Then, Fe5/M1 and Fe4/M2 multilayered systems were considered. In all cases, an AF coupling between the Fe and M layers was derived, whose strength decreases from V to Mo atoms. The impact of the interface interdiffusion on the induced M and reduced Fe magnetic moments in Fe5/M1 and Fe4/M2 was also studied. The atom interdiffusion leads to an increase in the total and average iron magnetic moments, while the induced magnetic moment increases for M = V and remains constant for the other atoms.

Abrupt discontinuity of the bulk modulus pressure dependence in Fe64Ni36.

X-ray diffraction and ultrasonic measurements have been carried out simultaneously up to 7 GPa at ambient temperature on a polycrystalline sample of Fe64Ni36 Invar alloy. The bulk modulus is found to increase linearly with pressure with an unusual low value (1.4) of dB/dP up to about 3.1(2) GPa followed by a regular slope (3.6) at higher pressure. The observation of these two distinct regimes is in qualitative agreement with previous results on the variation of the iron magnetic moment, and can be interpreted using the 2gamma-state model in terms of gradual population of low spin-small volume state at the expense of the high spin-large volume state under pressure.

Magnetic and Mössbauer spectral properties of DyFe 11Ti and DyFe 11TiH

The temperature dependence of the AC magnetic susceptibility, between 4.2 and 300 K, and the magnetization, between 300 and 600 K, has been measured for DyFe 11Ti and DyFe 11TiH. Iron-57 Mössbauer spectral measurements between 4.2 and 295 K have also been carried out on DyFe 11Ti and DyFe 11TiH and analyzed with a model which considers both the direction of the magnetization in the different magnetic phases of these compounds and the distribution of titanium atoms in the near-neighbor environment of the three crystallographically distinct iron sites. The magnetic measurements and the Mössbauer spectra of DyFe 11Ti clearly show the influence of the two spin reorientations occurring in this compound and indicate that the iron magnetic moments are oriented along the [1 0 0] direction of the basal plane below 100 K. The magnetic measurements and the Mössbauer spectra of DyFe 11TiH do not show any evidence for spin reorientations and are consistent with a basal magnetic anisotropy between 4.2 and 600 K. Hence, the hydrogen insertion into DyFe 11Ti reinforces the dysprosium magnetic anisotropy. The assignment and the temperature dependencies of the Mössbauer spectral hyperfine fields and isomer shifts are in full agreement with a Wigner–Seitz cell analysis of the three iron sites in DyFe 11Ti and DyFe 11TiH.

A magnetic and Mössbauer spectral study of HoFe 11Ti and HoFe 11TiH

A.c. susceptibility measurements were carried out between 4.2 and 295 K on HoFe 11TiH and reveal a spin-reorientation transition at ∼150 K. Iron-57 Mössbauer spectral measurements between 4.2 and 295 K were carried out on both HoFe 11Ti and HoFe 11TiH. The Mössbauer spectra were analyzed with a model which considers both the orientation of the iron magnetic moments and the distribution of titanium atoms in the near-neighbor environment of the three crystallographically distinct iron sites. The assignment and the temperature dependence of the hyperfine fields is in complete agreement with both the iron magnetic moments measured by neutron diffraction and the changes expected at the spin-reorientation. The assignment and the temperature dependence of the isomer shifts is in complete agreement both with the crystallographic changes occurring at the spin reorientation and upon hydrogen insertion. The changes in hyperfine field and isomer shift with the number of titanium near neighbors for each of the three iron sites are consistent with the values observed for related titanium–iron intermetallic compounds.

Magnetic properties of ThFexAl12x alloys

The results of magnetic properties of ThFexAl12–x powder samples with iron concentration x = 4, 4.5 and 5, studied by means of X-ray (XD) and neutron diffraction (ND) techniques as well as the Mössbauer spectroscopy with the monochromatic circularly polarised source (MCPMS), and magnetisation measurements using vibrating sample magnetometer (VSM) are presented. Unpolarized neutron diffraction pattern leaves no doubts that the modulated magnetic structure is observed in the tetragonal ThFe4Al8 compound. The interpretation of our neutron data requires the presence of non-zero magnetic propagation vectors different from the nuclear one. ThFe4Al8 sample has double spiral structure with moments rotating in a plane perpendicular to the wave vector as well as to . Both of them are temperature independent in the range 1.5 K–70 K. The value of iron magnetic moment is close to 1 μB/Fe atom at 1.5 K.

Magnetic properties of R–T hydrides (Ho, Y)6Fe23H15

Magnetization measurements M(T,H,x) were performed on ferrimagnetic Ho6−xYxFe23H15 (x=0.47 and 0.92) compounds in the 4.2–700K temperature range (Curie temperature TC∼600K) in a magnetic field up to 55kOe. In comparison to parent alloys, absorption of hydrogen leads to a decreasing compensation temperature, a strong increase of the magnetic moments of the compounds in the 200–400K temperature range, and a higher Curie temperature. These results are analyzed within the frame of Herbst and Croat refined-Néel molecular field theory model, taking into account the increase of the iron magnetic moment and the weakening of the magnetic exchange coupling NHo–Fe as compared to their alloys values. The mean canting angle between rare earth and iron sublattices θ (θ⩽10°) is important for the yttrium-substituted compounds, particularly in the vicinity of compositions for which Tcomp∼0K.

Preparation, crystal and magnetic structure of the double perovskite Ba 2 FeWO 6

Single-phase polycrystalline material of the double perovskite Ba2FeWO6 was prepared and characterized by X-ray and neutron powder diffraction (NPD). The crystal structure was tetragonal with lattice parameters a=b=5.7479(4) A and c=8.1444(9) A at room temperature (295 K). NPD data at 10 K shows the evidence of an antiferromagnetic ordering of the Fe atoms. The reverse Monte Carlo powder (RMCPOW) technique was used to find the magnetic structure, which showed that it is based on a unit cell related to that of the nuclear structure by the propagation vector 0\(\frac\Box1\Box\Box2\Box\)\(\frac\Box1\Box\Box2\Box\) . An ordering of collinear spins was found with alternate layers in the c-direction or in the a-b plane. The model was checked by Rietveld refinement and the magnetic moment of iron was found to be 3.39(2)μB at 10 K.

A neutron diffraction and Mössbauer spectral study of the magnetic spinreorientation in Nd6Fe13Si

Powder neutron diffraction and Mössbauer spectral studies havebeen carried out on Nd6Fe13Si between 2–295 K. The nuclearneutron scattering shows that Nd6Fe13Si has the tetragonalI4/mcmcrystal structure at all temperatures. A collinear antiferromagnetic structure with thewavevector q = (0, 0, 1) is observed below the Néel temperature of 421 K. A spin reorientation isobserved at ∼100 K in both the neutron diffraction patterns and the Mössbauer spectra.Above and below 100 K, the magnetic moments of the four iron and the twoneodymium crystallographic sites are ferromagnetically coupled within one block alongthe caxis and the resulting magnetic moment of this block isantiferromagnetically coupled with that of the adjacent block along thecaxis through a layer of silicon atoms. Above and below 100 K, themagnetic moments are found to be parallel or very close to thec axis and within orclose to the (a, b)basal plane of the tetragonal unit cell, respectively. This first-order spontaneouszero-field spin reorientation occurs cooperatively and involves both theneodymium and iron magnetic moments. The powder neutron diffractionbetween 10 and 200 K indicates anisotropic lattice changes associatedwith a change in the magnetoelastic coupling in this compound. TheMössbauer spectral hyperfine parameters are those expected for axial andbasal magnetization directions in Nd6Fe13Si and further indicate theexistence of a 75% basal and 25% axial mixed magnetic phase even at4.2 K, a mixed magnetic phase which results from the influence of thesecondary ferromagnetic Nd2Fe17 phase on the primary Nd6Fe13Si phase.

Interplay between magnetic order and the vibrational state of Fe in FeCr 2S 4

The temperature dependence of the 57Fe Mössbauer recoilless fraction, and that of the local electronic and magnetic state of iron in the chalcogenide spinel FeCr 2S 4 have been studied in detail around the Curie temperature with the help of 57Fe Mössbauer spectroscopy. Ferrimagnetic order was found to break down anomalously at ∼20 K below the Curie temperature in FeCr 2S 4. Magnetic relaxation of iron magnetic moments was observed with increasing relaxation rate above T∼155 K. The local Debye temperature as well as the effective vibrating mass, representative for the local vibrational state of iron, was found to be considerably higher in the paramagnetic state than in the magnetically ordered state. At T=186.5 K long range magnetic order was found to develop in response to 6 T external magnetic field showing that in FeCr 2S 4 short-range magnetic order persists well above the Curie temperature.

Transformation of the magnetic structure of FeBO3 under high pressures

The transformation of magnetic structure under hydrostatic and quasi-hydrostatic pressures up to 4 GPa was studied for iron borate FeBO3 by the neutron diffraction method. Under quasi-hydrostatic conditions, the orientation of iron magnetic moments changes at pressures P≥1.4 GPa. Under hydrostatic conditions, no changes in the magnetic structure of iron borate were observed up to 2.1 GPa. This behavior is caused by the influence of the inhomogeneity (in magnitude and direction) of elastic stresses on the configuration of magnetic sublattices.

A study on the nuclear and magnetic structure of the double perovskites A 2FeWO 6 (A = Sr, Ba) by neutron powder diffraction and reverse Monte Carlo modeling

Perovskite-type complex metal oxides A 2FeWO 6 (A=Sr, Ba) were prepared by a standard solid state reaction method. Rietveld analysis of neutron powder diffraction (NPD) data at 295 K shows that the Sr 2FeWO 6 (SFW) compound adopts a monoclinic unit cell (space group P2 1/ n, a=5.6480(4), b=5.6088(4), c=7.9362(6) Å and β=89.99(2)°), and the Ba 2FeWO 6 (BFW) compound is tetragonal (space group I4/ m, a=5.7547(4), c=8.125(1) Å). A combination of a reverse Monte Carlo (RMC) technique and Rietveld analysis shows that the low temperature (10 K) magnetic structures of SFW and BFW are antiferromagnetic based on a unit cell related to that of the nuclear structure by a propagation vector, k=(0 1/2 1/2) . The magnetic moment of iron was found to be 3.86(4) μ B and 3.49(2) μ B at 10 K for the Sr- and the Ba-containing compounds, respectively.

Magnetic properties of ThFe 11C x compounds ( x=1.5, 1.8)

Magnetic measurements are carried out on polycrystalline ThFe 11C x ( x=1.5,1.8) samples between 4 and 900 K and magnetic field up to 7 T. This wide temperature range covers both the ferromagnetically ordered region and the paramagnetic region. Not only the ordering temperature, but also the magnetisation are found to be very sensitive to the carbon concentration. The evolution of the magnetic properties versus the carbon content is discussed. The Curie temperature and the Fe–Fe exchange interactions increase when the carbon concentration increases. The mean ordered iron magnetic moment deduced from saturation magnetisation is also found to depend upon the carbon concentration but in the opposite direction. Mean magnetic moment values of 2.00 and 1.88 μ B per iron atom are observed for ThFe 11C 1.5 and ThFe 11C 1.8, respectively. The effective magnetic moment is found to decrease from 3.91 to 3.73 μ B per iron atom for ThFe 11C 1.5 and ThFe 11C 1.8, respectively. The evolution of the effective magnetic moment is discussed on the basis of the spin fluctuations theory. The iron magnetic state in the ThFe 11C 1.5 and ThFe 11C 1.8 present similarities with that reported for the Fe 3C compound.

The relationship between magnetic interactions and near neighbor interatomic distances in the transition metal sublattice of R(Mn/Fe)6A6 (R=Nd or Sm, A=Ge or Sn)

The magnetic and crystallographic structures of R(Fe/Mn)6A6 (R=Nd or Sm and A=Ge or Sn) intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides (A=Sn) and germanides (A=Ge), the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (x⩽2) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties of the germanides deteriorate rapidly as manganese is replaced by iron. This difference in the dependence of magnetic properties on the iron content between the germanides and stannides is explained using the Bethe–Slater relationship between near neighbor exchange interactions and interatomic distances. Based on the observations described in this article, it is concluded that the critical near neighbor interatomic distance above which manganese/iron moments couple positively in these intermetallics is ∼2.614 Å.