The distribution of magnetization in single-crystal samples of silicon iron made in the form of thin disks after heat treatments under the influence of a magnetic field or mechanical stress was determined by Mössbauer spectroscopy. At contents of 5 and 8 at

Short-range order in soft magnetic FeGa alloys containing from 3 to 25 at

The magnetization distribution in a single-crystalline silicon iron after quenching in the paramagnetic state and after annealing in the ferromagnetic state has been determined by Mössbauer spectroscopy. The specimens containing 5, 6, and 8 at

In this paper, the electron and magnetic state of iron placed either on the surface or in the core of TiO2 nanoparticles were investigated using magnetometric methods, electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. It was demonstrated that the EPR spectra of TiO2 samples with iron atoms localized both on the surface and in the core of specific features depending on the composition and size of the nanoparticles. Theoretical calculations using the density functional theory (DFT) method demonstrated that the localization of Fe atoms on the surface is characterized by a considerably larger set of atomic configurations as compared to that in the core of TiO2 nanoparticles. Mössbauer spectra of the samples doped with Fe atoms both on the surface and in the core can be described quite satisfactorily using two and three doublets with different quadrupole splitting, respectively. This probably demonstrates that the Fe atoms on particle surface and in the bulk are in different unlike local surroundings. All iron ions, both on the surface and in the core, were found to be in the Fe3+ high-spin state.

The atomic structure of soft magnetic iron-aluminum alloys is studied by X-ray diffraction and nuclear gamma-resonance spectroscopy. The concentration dependence of the body-centered cubic lattice constant and the short-range order (SRO) parameters in the region of a disordered solid solution is monitored. It is shown that in the concentration range from 3 to 18 at.% Al, the lattice constant increases almost linearly. Discrete decomposition of nuclear gamma resonance spectra makes it possible to determine such SRO parameters as the relative fractions of contributions from coordinations without Al atoms and with one, two, and three Al atoms in the first and second coordination shells. The deviation of the values of these fractions from the average statistical probabilities indicates the presence of a chemical order in the arrangement of atoms. The largest deviations are observed at 12 and 15 at.% Al. Conditions of preliminary heat treatment, such as quenching from the paramagnetic state and holding in the ferromagnetic state, give very similar values of the SRO parameters. The method is characterized by a high resolution in the hyperfine field, while having a rather high sensitivity for determining the intensity of individual contributions.

The structure and magnetic state of Fe100-xNix alloys (x & LE; 20) quenched from 1100 degrees C have been studied by means of Mo & BULL;ssbauer spectroscopy, X-ray diffraction, transmission electron microscopy, and magnetization measurements. The concentration dependences of the lattice parameter of bcc structure and of spontaneous magnetic moment were measured at room temperature. From the analysis of Mo & BULL;ssbauer spectra, concentration dependences of average hyperfine parameters have been determined. Both isomer shift and hyperfine field increase with increasing Ni content in the alloy. Fitting of the spectra with a set of subspectra gives grounds to conclude that the structure of quenched Fe-Ni samples represents a system of bcc regions of varying content, which is formed as a result of separation of the alloy composition. This conclusion is supported by the data of transmission electron microscopy.

The atomic structure of soft magnetic iron-aluminum alloys is studied by X-ray diffraction and nuclear gamma-resonance spectroscopy. The concentration dependence of the body-centered cubic lattice constant and the short-range order (SRO) parameters in the region of a disordered solid solution is monitored. It is shown that in the concentration range from 3 to 18 at.% Al, the lattice constant increases almost linearly. Discrete decomposition of nuclear gamma resonance spectra makes it possible to determine such SRO parameters as the relative fractions of contributions from coordinations without Al atoms and with one, two, and three Al atoms in the first and second coordination shells. The deviation of the values of these fractions from the average statistical probabilities indicates the presence of a chemical order in the arrangement of atoms. The largest deviations are observed at 12 and 15 at.% Al. Conditions of preliminary heat treatment, such as quenching from the paramagnetic state and holding in the ferromagnetic state, give very similar values of the SRO parameters. The method is characterized by a high resolution in the hyperfine field, while having a rather high sensitivity for determining the intensity of individual contributions Keywords: soft magnetic alloys, disordered Fe-Al solid solution, local ordering, X-ray diffraction, Mossbauer effect, distribution of atoms over coordination shells.

The atomic structure of soft magnetic iron-aluminum alloys is studied by X-ray diffraction and nuclear gamma-resonance spectroscopy. The concentration dependence of the body-centered cubic lattice constant and the short-range order (SRO) parameters in the region of a disordered solid solution is monitored. It is shown that in the concentration range from 3 to 18 at.% Al, the lattice constant increases almost linearly. Discrete decomposition of nuclear gamma resonance spectra makes it possible to determine such SRO parameters as the relative fractions of contributions from coordinations without Al atoms and with one, two, and three Al atoms in the first and second coordination shells. The deviation of the values of these fractions from the average statistical probabilities indicates the presence of a chemical order in the arrangement of atoms. The largest deviations are observed at 12 and 15 at.% Al. Conditions of preliminary heat treatment, such as quenching from the paramagnetic state and holding in the ferromagnetic state, give very similar values of the SRO parameters. The method is characterized by a high resolution in the hyperfine field, while having a rather high sensitivity for determining the intensity of individual contributions Keywords: soft magnetic alloys, disordered Fe-Al solid solution, local ordering, X-ray diffraction, Mossbauer effect, distribution of atoms over coordination shells.

To specify what triggers the magnetostructural transition in CeFe2 doped with silicon, the temperature dependences of the magnetization, as well as the initial magnetic susceptibility and field dependences of the magnetization of the rare-earth intermetallic compounds Ce(Fe1 – xSix)2 with the silicon content x ≤ 0.05, were measured. The transition temperature to the magnetically ordered state and the average magnetic moment at Fe atoms were determined, and the magnetic contribution to the entropy change was estimated. Mössbauer spectra of Ce(Fe1 – xSix)2 (x ≤ 0.05) in the paramagnetic state were measured with a discretization of velocity scale of 512 channels, processing of which served to confirm the earlier suggested local ordering of Si atoms in the Fe sublattice.

The phase boundaries of martensitic transformation in Fe-Ni alloys with the composition in the range of 0 - 20 Ni at.% have been determined by X-ray diffraction, differential scanning calorimetry, measurements of magnetic susceptibility and magnetization. It is shown that the alloys quenched from 1100 degrees C at room temperature are in a single-phase state of alpha 2 martensite, except for Fe 80 Ni 20 , which additionally contains a small amount of gamma phase. It is found that in the Fe 97 Ni 3 alloy, the temperature-induced magnetic and structural transformations occur independently of each other. At a nickel concentration from 5 to 20%, the structural alpha -> gamma transformation upon heating is accompanied by the magnetic transition from the ferromagnetic to the paramagnetic phase, which is a first-order phase transition. When cooling the alloys with x <= 10, the paramagnet - ferromagnet transition starts several degrees ahead of the structural gamma -> alpha transformation. The lattice volume changes and thermal effects upon the martensitic transformation are determined. It is shown that the phase diagram including metastable martensitic transformation can be used together with the equilibrium phase diagram to determine the structural states of the Fe-Ni system.

The effect of manganese alloying on the structure and magnetic properties of CeFe2 has been studied on two isostructural series: quasibinary CeFe2-xMnx and nonstoichiometric CeFe2Mnx alloys. The singlephase bcc MgCu2-type structure is formed at x <= 0.5 in both systems. At x = 0.5, the lattice parameter is increased by similar to 0.3%. The Mn alloying leads to a nonmonotonic variation of magnetic moment and gradual decrease in the Curie temperature from 230 K to 150 K and 167 K for CeFe1.5Mn0.5 and CeFe2Mn0.5, respectively. For x >= 0.3, the magnetization data indicate the formation of noncollinear magnetic structure. The binary CeFe2 and nonstoichiometric CeFe2Mn0.15 have been studied using MoEurossbauer effect and X-ray photoelectron spectroscopy. The Ce valence state remains unchanged upon the Mn alloying. The parameters of hyperfine interactions have been determined in paramagnetic state at room temperature and in magnetically ordered state at 78 K. The MoEurossbauer data revealed a difference in the quadrupole coupling constants of CeFe2 and CeFe2Mn0.15, which is associated with the difference in the local distortions of the lattice. (C) 2020 Elsevier B.V. All rights reserved.

To ascertain the nature of the magnetostructural phase transition in Ce(Fe1-xSix)2 compounds with low silicon content, which crystalize into the structure of cubic Laves phase, we studied local structure peculiarities using high-precision 57Fe Mössbauer spectroscopy (with a high discretization of the velocity reference signal). Unlike the earlier published works on this type of compounds, in the study presented, the occurrence of at least two different types of local surrounding of Fe atoms in the binary compound CeFe2 and non-random Si distribution in the Ce(Fe1-xSix)2 crystal structure is reported for the first time. To specify the type of ordering of Si atoms, the experimental data are compared with results of mathematical simulation of different types of ordering, and, in this way, a conclusion on the mechanism of magnetostructural phase transition is made.

Nanopowders of the binary system of immiscible components Fe and Cu are synthesized by gas condensation of metal vapors. The structure and magnetic properties of nanopowders of various compositions are investigated, and their Mössbauer spectra are analyzed. It is shown that the method allows one to obtain nonequilibrium Fe(Cu) and Cu(Fe) solid solutions, in which the concentration of dissolved elements depends on the synthesis conditions.

New nonstoichiometric compounds CeFe2Mnx with a structure of the cubic Laves phase have been synthesized. The concentration range of Mn solubility has been determined. The structure and elemental composition were studied by means of X-ray powder diffraction and energy-dispersive X-ray spectroscopy. Temperature dependences of magnetization were measured. To determine Curie temperatures, magnetic susceptibility measurements were performed. The results obtained for the samples of different compositions of nonstoichiometric and quasi-binary compounds are analyzed taking into account specific features of electronic structure of Ce atoms.

The short/long-range order formation in Fe1-x-Co-x (x < 0.3) alloys has been studied by the nuclear magnetic resonance (NMR) technique, as well as ab initio based atomistic simulation. The NMR measurements show up the formation of a certain short-range order (SRO) in dilute limit above the Curie temperature T-C and of the D0(3)-type SRO (with the dominance of 3rd Co-Co nearest neighbors) in the concentration range 0.2 < x <0.3 after quenching and subsequent annealing in the ferromagnetic state. The results of Monte Carlo simulations of binary Fe-Co alloys with ab initio interatomic interactions predict SRO in agreement with the experiment for small concentrations of Co (C-Co < 0.1), while the B2-type ordering is preferable in binary alloy in the ferromagnetic state. We demonstrate that the presence of point defects (vacancies, interstitial) can change essentially the ordering in alloys with the Co content 20-30% and result in the D0(3)-type SRO formation in a reasonable agreement with the experiment. (C) 2018 Elsevier B.V. All rights reserved.

ABSTRACT X-ray diffraction, magnetic measurements, and Mössbauer spectroscopy were employed to comparatively analyse the relation of the basic characteristics of highly anisotropic materials– coercive force Hc and Curie temperature TC to the peculiarities of short-range atomic order that forms upon annealing of disordered samples of equaiatomic FePd alloys produced by different techniques (casting, melt-spinning, severe deformation). It is shown that for all samples, independently of methods of their preparation, the ordered states with the maximal values of coercivity are inhomogeneous in the composition of short-ordered regions, type of atomic ordering, and degree of tetragonality. The Curie temperature depends on the temperature and duration of annealing for ordering similarly to the conventional course of coercivity, which is peculiar to these alloys. The behaviour of these macroscopic characteristics (Hc and TC) in the course of annealing is shown to correlate with changes in the local atomic configurations revealed in the Mössbauer spectroscopy experiments.

AbstractA comparative analysis of the magnetic properties and Mössbauer spectra of two Ce_2Fe_17 samples prepared by different methods and demonstrating different magnetic behavior is carried out. A model for processing the spectra is proposed, which gives a good description of the Mössbauer spectra of samples in different magnetic states by a superposition of eight subspectra. It is shown that in the samples in the ferromagnetic state there are regions with antiferromagnetic ordering at the local level. The relative fractions of iron atoms in these regions differs for different samples and increases when approaching the temperature of the transition from the ferromagnetic to the antiferromagnetic state.

A comparative analysis of the magnetic properties and Mössbauer spectra of two Ce 2 Fe 17 samples prepared by different methods and demonstrating different magnetic behavior is carried out. A model for processing the spectra is proposed, which gives a good description of the Mössbauer spectra of samples in different magnetic states by a superposition of eight subspectra. It is shown that in the samples in the ferromagnetic state there are regions with antiferromagnetic ordering at the local level. The relative fractions of iron atoms in these regions differs for different samples and increases when approaching the temperature of the transition from the ferromagnetic to the antiferromagnetic state.

A comparative Mossbauer study of structural inhomogeneities that arise in the course of ?1 L1(0) phase transformation in nondeformed (as cast and quenched from 950 degrees C and melt-spun from the ingot) and severely deformed samples of equiatomic FePd alloy upon ordering annealing at ?=450 degrees C has been performed. According to the known experimental works, the chosen temperature of annealing is optimal for achieving the highest coercive force H-c in both quenched and deformed samples. It is shown that in the high-coercivity state both quenched and deformed samples FePd possess an inhomogeneous tetragonal structure, which is preserved even after quite a prolonged (40-100h) annealing. All the samples contain, along with the configurations of the nearest neighbourhood that are assigned to the ordered L1(0) phase, significant volume fractions of configurations typical of nonequiatomic compositions. This conclusion is inconsistent with the commonly accepted concept on single-phase L1(0) type alloys with maximal values of H-c. An inference is made that the structural inhomogeneities detected in the samples under study result from the mismatch of the position of the point of congruent ?1 L1(0) transformation (approximate to 58 at.% Pd) in the phase diagram of the FePd system to equiatomic composition.