Half-metallicity in Fe-based Heusler alloys Fe2TiZ (Z = Ga,Ge, As,In, Sn and Sb)

The electronic structure and magnetic properties of new Fe-based Heusler alloys Fe₂TiZ (Z = Ga, Ge, As, In, Sn and Sb) have been studied by first-principles calculations. In these alloys, the 24-electron Fe₂TiGe, Fe₂TiSn are nonmagnetic semiconductors and other compounds are all ferrimagnetic metals. Fe₂TiAs and Fe₂TiSb are predicted to be half-metals with 100% spin polarization. The spin polarization ratio in Fe₂TiGa and Fe₂TiIn is also quite high. The calculated total moment for Fe₂TiAs and Fe₂TiSb is 1 μ_B, which is mainly determined by the Fe partial moment. The half-metallicity of Fe₂TiSb is stable under lattice distortion. The spin polarization of Fe₂TiSb is found to be 100% for the lattice variation in a range of 5.6–6.1 Å, which is attractive in practical applications.     

Mössbauer spectroscopic investigation of tin-doped thiospinels

The tin-doped sulphur-containing compound of composition Fe_1.05Cr_1.90Sn_0.05S₄, in which tin is located on the octahedral sites as Sn^4?+? in the spinel-related structure, has been examined by ¹¹⁹Sn Mössbauer spectroscopy. The data complement results obtained by ⁵⁷Fe Mössbauer spectroscopy and show that tin increases the magnetic ordering temperature of pure FeCr₂S₄.     

Electronic structure and magnetism of disordered bcc Fe alloys

We study the electronic structure and magnetic properties of disordered bcc Co_xFe_1-x, Cr_xFe_1-x and Mn_xFe_1-x alloys in their ferromagnetic phases using the Augmented Space Recursion (ASR) technique coupled with the tight-binding linearized muffin tin orbital (TB-LMTO) method. We calculate the density of states and magnetic moment of these alloys to show the variation upon alloying Fe with the other neighbouring 3d transition metals using arguments based on charge transfer, exchange splitting and hybridization effects. Received 10 April 2001 and Received in final form 15 August 2001     

Magnetic state and properties of the Fe0.5TiSe2 intercalation compound

The Fe_0.5TiSe₂ compound with a monoclinic crystal structure has been prepared by intercalation of Fe atoms between Se-Ti-Se sandwiches in the layered structure of TiSe₂. The crystal and magnetic structures, electrical resistivity, and magnetization of the Fe_0.5TiSe₂ compound have been investigated. According to the neutron diffraction data, the Fe_0.5TiSe₂ compound has a tilted antiferromagnetic structure at temperatures below the Néel temperature of 135 K, in which the magnetic moments of Fe atoms are antiferromagnetically ordered inside layers and located at an angle of approximately 74.4° with respect to the layer plane. The magnetic moment of Fe atoms is equal to (2.98 ± 0.05)μ_B. The antiferromagnetic ordering is accompanied by anisotropic spontaneous magnetostrictive distortions of the crystal lattice, which is associated with the spin-orbit interaction and the effect of the crystal field.     

Local magnetic structure and anomalies of magnetic hyperfine interactions of57Fe and119Sn nuclei in lithium aluminium ferrites

The⁵⁷Fe and¹¹⁹Sn Mossbauer spectra of ordered ferrites Li_0.5Fe_2.5−xAl_xO₄∶Sn for 0.8<x<1.0 (the compensation point region) have been studied. The spin glass type magnetic structure with the spin canting angle depending on temperature and aluminium concentration is established. Anomalies in the temperature dependence of the hyperfine magnetic field at tin nuclei have been found near the compensation point of the ferrites     

Mössbauer spectroscopy of the new iron oxide Fe3B7O13(OH)

In order to investigate the electronic state, the local structure, and the magnetic structure of a new ion oxide Fe₃B₇O₁₃(OH), we have applied ⁵⁷Fe Mössbauer spectroscopy. The room-temperature values of isomer shift and quadrupole splitting are 1.16 mm/s and 3.21 mm/s, respectively, which indicate that the Fe ions are in high spin Fe^2?+? state. The spectrum at 4.2 K is composed of a well-resolved hyperfine sextet with the hyperfine field of 3.6 T. In a trimer, each Fe^2?+? magnetic moment is supposed to be directed from Fe^2?+? to OH^???.     

X-ray absorption and magnetic circular dichroism characterization of Mo1–xFexO2 (x = 0–0.05) thin films grown by pulsed laser ablation

The electronic and magnetic properties of well characterized Mo_1???xFe_xO₂ (x = 0–0.5) thin films that show ferromagnetism at room temperature (RT) have been investigated by the means of near edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments at the O K-, Fe L-, and Mo M-edges. The NEXAFS spectra at O K- and Mo M_3,2 -edges show a strong hybridization of O 2p-4d Mo orbitals, and Mo ions change their symmetry with the substitution of Fe ions into MoO₂ matrix. The Fe 2p NEXAFS/XMCD spectra exhibit multiple absorption peaks and an appreciable XMCD signal that persists even at RT. These results demonstrate that Fe is in a mixed valence state of Fe^2?+?–Fe^3?+?, substituting at the Mo site and that the Fe^2?+?/3?+? ions are ferromagnetically polarized.     

Structure-property relationships in the R-type hexaferrites: Cation distributions and magnetic susceptibilities of MX2Fe4O11

The strong, and heretofore unexplained, dependence of the magnetic properties of the R-type hexaferrites MX₂Fe₄O₁₁ on heat treatment has been investigated by means of⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopy at 297 K.⁵⁷Fe Mössbauer spectra of samples of BaTi₂Fe₄O₁₁, BaSn₂Fe₄O₁₁, and SrSn₂Fe₄O₁₁, annealed at several temperatures consist of three partially resolved quadrupole doublet patterns. The pattern with the very large quadrupole splitting, i.e. 1.3 mm s^–1 E _Q 1.7 mm s^–1, is readily assigned to the trigonal bipyramidal site, and exhibits no dependence of its parameters, including the relative intensity, on heat treatment. The remaining two patterns are assigned to Fe³⁺ ions on octahedral sites, and exhibit relative intensities that are strongly dependent on heat treatment. The¹¹⁹Sn spectrum of BaSn₂Fe₄O₁₁ is a broad, apparently single line that, with the exception of verifying the presence of tin as Sn⁴⁺, provides little insight into the details of the structure. The distributions of the cations over all the lattice sites have been deduced from the Mössbauer spectra and compared with the magnetic susceptibility data. It is concluded that the cation distributions of the Sn-containing phase are not strongly dependent on heat treatment, and the magnetic properties exhibit a similar insensitivity to heat treatment. The Ti analogs exhibit a strong dependence of cation distribution on heat treatment, which is reflected in widely varying magnetic ordering temperatures, a variation that is confirmed by the incipient magnetic hyperfine splitting despite the strong magnetic frustration in the R-type hexaferrites.     

A Mössbauer study of iron and iron–cobalt nanotubes in polymer ion-track membranes

Iron and iron–cobalt nanostructures that were synthesized in polymer ion-track membranes have been studied via Mössbauer spectroscopy combined with raster electron microscopy, energy-dispersion analysis, and X-ray diffraction data. The obtained nanostructures are single-phase bcc Fe_1–xCo_x nanotubes with a high degree of polycrystallinity, whose length is 12 μm; their diameter is 110 ± 3 nm and the wall thickness is 21 ± 2 nm. Fe²⁺ and Fe³⁺ cations were detected in the nanotubes, which belong to iron salts that were used and formed in the electrochemical deposition. The Fe nanotubes exhibit eventual magnetic moment direction distributions of Fe atoms, whereas Fe/Co nanotubes have a partial magnetic structure along the nanotube axis with a mean value of the angle between the magnetic moment and nanotube axis of 34° ± 2°. Substituting the Fe atom with Co in the nearest environment of the Fe atom within the Fe/Co structure of nanotubes leads to a noticeable increase in the hyperfine magnetic field at the ⁵⁷Fe nuclei (by 8.7 ± 0.4 kOe) and to a slight decrease in the shift of the Mössbauer line (by 0.005 ± 0.004 mm/s).     

Si对Nd2Fe14B四方相结构和磁性的影响

本文对Si加入Nd₂Fe₁₄B四方相后所形成的合金相的结构和磁性进行了研究。结果表明,Si加入Nd₂Fe₁₄B四方相后并不破坏它的结构(Si的含量可达B的两倍),而形成Nd₂(Fe,Si)₁₄B赝三元金属间化合物。随着Si含量的增加,晶格常数和饱和磁化强度随之减小,但居里温度则随之增加。Si的加入,并不改变Nd₂Fe₁₄B的室温各向 关键词：     

The evolution of electronic configuration and magnetic characterization of Fe<Subscript>9</Subscript>Ni<Subscript>1</Subscript>, Fe<Subscript>8</Subscript>Ni<Subscript>2</Subscript> alloy in theoretical calculation

To analyze the origin of the magnetic enhancement of Fe-Ni alloy, the electronicconfigurations and magnetic properties were investigated using density functional theorybased on the first-principle. The supercell (5 × 1 × 1) of Fe,Fe₉Ni₁ and Fe₈Ni₂ were constructed. Thedefect formation energy, band structure, density of states and electron density differencewere calculated. The results showed that Ni doping changed the electronic configuration ofFe atoms, resulting in the enhancement of spin polarization of Fe and the larger Bohrmagnetic moment in Fe-Ni alloys (Fe₉Ni₁). The results showed thatthe charge transfer and the atomic spacing between Fe atoms and the dopant Ni atoms playedan important role in determination of magnetic moment. The value of Fe supercell(5 × 1 × 1), Fe₉Ni₁ and Fe₈Ni₂ were 23.14,23.34 and 22.61μ _B, respectively.     

Ab initio study of structural and magnetic properties of cubic Fe4N(0 0 1) surface

First-principles calculations are employed to study the structural and magnetic properties of fully-relaxed cubic Fe₄N(0 0 1) surfaces with both Fe₂- and Fe₂N-termination. The results of surface stability calculations show that the (0 0 1) surface of Fe₄N is most possibly existing with Fe₂N-termination. Slab structures have more localized features in the density of states especially for the Fe₂N-terminated surface due to structure relaxation. The average magnetic moments of Fe atoms increase with increasing thickness of slabs. The calculated interlayer distances indicate that the decreases of d₁₂ and d₂₃ result in stronger hybridization and shorter bond distances between Fe2 atom in the second layer and other atoms in surface or the third layers, which lead to variation of magnetic moments with different slab thicknesses.     

Magnetic-dichroism study of iron silicides formed at the Fe/Si(100) interface

The interplay between the phase composition, electronic structure, and magnetic properties of the Fe/Si(100)2×1 interface has been studied at the initial stages of its formation (at Fe doses up to 8 Å). The experiments were carried out in ultra high vacuum by using high-resolution photoelectron spectroscopy with synchrotron radiation. The interface magnetic properties were examined in terms of magnetic linear dichroism in angle-resolved Fe 3p core-level photoemission. It was found that at room temperature a disordered Fe–Si solid solution is formed at the first stage of Fe deposition (≤3.4 Å). In the coverage range of 3.4–4.3 Å the solid solution transforms into Fe₃Si. However, the in-plane ferromagnetic ordering of the silicide occurs only at 6.8 Å Fe that demonstrates the thickness dependence of the magnetic properties of Fe₃Si. The subsequent sample annealing to 150°C transforms Fe₃Si to ε-FeSi, leading to the disappearance of ferromagnetic behavior.     

Nd2Fe14B的价电子结构分析和磁性计算

应用固体与分子经验电子理论计算了Nd₂Fe₁₄B的价电子结构、磁矩和居里温度,计算结果与实验值相符.计算表明:该合金的磁性与3d磁电子数成正比.从Fe(c)晶位到Fe(k₂)晶位磁矩增加,其机理源于价电子、哑对电子和3d磁电子之间的转化,有78%的哑对电子和18%的3d共价电子转化成了磁电子.居里温度和磁矩与Fe原子配位数成正比,与加权等同键数I^σ成反比,Nd原子 关键词： 2Fe₁₄B')" href="#">Nd₂Fe₁₄B 价电子结构 居里温度     

Mössbauer investigations of Fe and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles for hyperthermia applications

Magnetic nanoparticles of magnetite Fe₃O₄ and Fe synthesized by physical vapor deposition with a fast highly effective method using a solar energy have been studied. Targets have been prepared from tablets pressed from Fe₃O₄ or Fe powders. Relationships between the structure of nanoparticles and their magnetic properties have been investigated in order to understand principles of the control of the parameters of magnetic nanoparticles. Mössbauer investigations have revealed that the nanoparticles synthesized from tablets of both pure iron and Fe₃O₄ consist of two phases: pure iron and iron oxides (γ-Fe₂O₃ and Fe₃O₄). The high iron oxidability suggests that the synthesized nanoparticles have a core/shell structure, where the core is pure iron and the shell is an oxidized iron layer. Magnetite nanoparticles synthesized at a pressure of 80 Torr have the best parameters for hyperthermia due to their core/shell structure and core-to-shell volume ratio.     

Temperature dependent Mössbauer and neutron diffraction studies of Cu x Fe1−x Cr2S4 compounds

The cation distribution and magnetic structure of Cu _x Fe_1?x Cr₂S₄ (x?=?0.1, 0.2, 0.3, 0.4, and 0.5) has been studied by X-ray and neutron diffraction, vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. The charge state of Fe is found to be ferrous (Fe²⁺) for the x?=?0.1 sample; ferric (Fe³⁺) for the x?=?0.5 sample; mixed state (Fe²⁺, Fe³⁺) for the x?=?0.2, 0.3, and 0.4 samples. The Mössbauer spectra of the x?=?0.1 sample show asymmetric line broadening, which is considered to be due to the Jahn–Teller effect of Cu²⁺ ions, and a symmetrical six-line pattern is shown for the x?=?0.5 sample. The valence state of the Cu ions for the x?=?0.1 and 0.5 samples is found to be divalent and monovalent, respectively. The magnetic structure of the samples was determined to be a ferrimagnetic structure with antiparallel alignment of the Fe and Cr ion magnetic moments.     

Ferromagnetic-to-antiferromagnetic transition in (Hf1−xTix)Fe2 intermetallic compounds induced by geometrical frustration of the Fe(2a) sites

The ferromagnetic-to-antiferromagnetic transition in the hexagonal (Hf_1−xTi_x)Fe₂ (0?x?1) intermetallic compounds has been investigated by ⁵⁷Fe Mössbauer spectroscopy. At 10 K, the transition occurs within rather narrow concentration limits, around x=0.55–0.65. We found that the key factor governing the unexpected quick change of the magnetic structure is the magnetic frustration of the Fe(2a) sites. The magnetic frustration is caused by the noncollinearity of the Fe(6h) magnetic sublattice. The noncollinearity arises from the rotation of the magnetic moments due to the competition between the ferromagnetic exchange interactions and the antiferromagnetic Fe(6h)–Ti–Fe(6h) interaction. In the compounds with x=0.4–0.6, the temperature transitions to the antiferromagnetic state are observed. As an example, the Hf_0.4Ti_0.6Fe₂ compound is completely antiferromagnetic above 200 K.     

Low temperature magnetic ordering in Fe-doped TiO 2 samples

Fe-doped TiO₂ samples with different Fe content prepared by mechanical alloying have been investigated by means of Mössbauer spectroscopy at 300 and 4.2 K. The results indicate the coexistence of Fe^2?+? and Fe^3?+? ions in paramagnetic states at room temperatures in the rutile structure. All samples present magnetic order at 4.3 K. When the Fe concentration increases the Fe ions in the rutile matrix became closer giving the possibility of strong magnetic interactions between them. The temperature evolution of the magnetic order was followed for the 15 at.% of Fe sample. The Fe-doped oxide formed for this composition orders below 20 K reaching an almost totally magnetic ordered state at 4.3 K.