A. K. Arzhnikov

Magnetic moment of iron atoms in Fe-Al body-centered cubic alloys as a function of the nearest environment

The Fe-Al systems in the concentration range from 29 to 44 at. % Al are investigated in terms of the density functional theory. It is shown that, in the system under consideration, there can exist three magnetic states with close energies. Two of these three magnetic states have collinear magnetic moments (the ferromagnetic and antiferromagnetic states), and the third is a spin-spiral state. In collinear magnetic structures, the local magnetic moments are determined by the nearest chemical environment and, in the antiferromagnetic state, the iron atoms surrounded by a large number of aluminum atoms in their environment have a negative magnetic moment. The results obtained substantiate the applicability of modified models of the Jaccarino-Walker type for the interpretation of the experimental data obtained for Fe-Al alloys. The results of the calculations also indicate a significant role of Stoner excitations in the formation of magnetic order in these alloys.

Lattice distortions near impurity atoms in α-Fe1−x Six alloys

Lattice distortions near impurity atoms in α-Fe1−xSix alloys (x≈0.05–0.06) are studied both experimentally using x-ray diffraction and theoretically by means of ab initio calculations. It is found that the distortions are more complex than experimental data suggest. The displacements of atoms near impurities are not determined by the concentration dependence of the average lattice constant nor by a difference in the ion radii.

Incommensurate Spin-Density Wave in Two-Dimensional Hubbard Model

We consider the magnetic phase diagram of the two-dimensional Hubbard model ona square lattice.We take into account both spiral and collinear incommensurate magnetic states.The possibility of phase separation of spiral magnetic phases is taken into consideration as well.Our study shows that all the listed phases appear to be the ground state at certain parametersof the model. Relation of the obtained results to real materials, e.g. Cu-based high-temperaturesuperconductors, is discussed.

Magnetoresistance and the hall effect of the ordered alloys Fe100 −xAlx (25 < x < 35 at. %)

The transverse magnetoresistance and the Hall effect of Fe100 −xAlx ordered alloys with x = 26.5−34.1 at. % are studied at temperatures of 77 and 295 K. No saturation is found in the field dependences up to 17 kOe. The magnetoresistance is negative, depends nonmonotonically on the Al concentration, and reaches a maximum |ΔR/R| = 1.6% in the concentration range from 28 to 30 at. %. The coefficient of the anomalous Hall effect depends nonlinearly on the Al concentration and resistivity: it increases to a lesser extent as compared to the resistivity at x = 26–30 at. % and decreases with increasing resistivity at x > 30 at. %. An explanation is proposed for the observed anomalies in the magnetotransport properties in the framework of the model developed for the inhomogeneous magnetic microstructure of the Fe100 −xAlx ordered alloys.

Theoretical Investigation of the Magnetic Order in FeAs

The magnetic structure of the iron monoarsenide FeAs is studied using first-principlescalculations. We consider the collinear and non-collinear (spin-spiral wave) magnetic orderingand magnetic anisotropy. It is analitically shown that a magnetic triaxial anisotropy resultsin a sum of two spin-spiral waves with opposite directions of wave vectors and different spinamplitudes, so that the magnetic moments in two perpendicular directions do not equal eachother.

Probe Mössbauer spectroscopy of the evolution of mechanically alloyed Mo92O8(57Fe) system upon heat treatment

X-ray diffraction and Mögsbauer spectroscopy have been used to study the multistage character of the process of recovery to equilibrium in the course of isochronous (1 h) annealings (300–1300°C) of a mechanically alloyed nanocrystalline Mo92O8 system with 1 at % Mögsbauer isotope 57Fe. Three stages of the recovery to the equilibrium state have been established: at 300–700°C, the stage of structural relaxation; at 700–1100°C, the stage of normal grain growth and formation of a dislocation structure; and at 1100–1300°C, the stage of the formation of a composite Mo9957Fe1/MoO2.

Magnetic moments and hyperfine magnetic fields in ordered and disordered quasi-binary Fe75(Si1−xGex)25 alloys

Disordered and DO3 type-ordered Fe75(Si1−xGex)25 alloys are fabricated and investigated using x-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The variations in the magnetic and Mössbauer characteristics are interpreted using ab initio calculations of the electronic structure, magnetic moments, hyperfine magnetic fields, and isomer shifts. The main differences in the properties are related to the increase in the crystal lattice parameter when Si is replaced by Ge in ordered alloys and to a different behavior of the correlations in the Si and Ge positions in disordered alloys.

Magnetic State of Quasiordered Fe–Al Alloys Doped with Ga and B: Magnetic Phase Separation and Spin Order

Results of structural, magnetic, and Mössbauer studies of quasi ordered alloys Fe65Al35 − xMx (Mx = Ga, B; x = 0, 5 at %) are presented. The magnetic state of examined structurally–single-phase alloys at low temperatures is interpreted from the viewpoint of magnetic phase separation. An explanation is proposed for the observed behavior of magnetic characteristics of Fe65Al35 and Fe65Al30Ga5 in the framework of the model of two magnetic phases, a ferromagnetic-type one and a spin density wave. The boron-doped alloy Fe65Al30B5 is shown to demonstrate behavior that is typical of materials with the ferromagnetic type of ordering.

Canted Spiral Magnetic Order in Layered Systems

Formation of a canted spiral magnetic order is studied in the framework of a mean-field approximation of the Hubbard model. It is revealed that this magnetic state can be stabilized under certain conditions in layered systemswith a relatively small interplane electron hopping. Example of an experimentally observed magnetic structure ofLa

Mössbauer and magnetometric studies of the magnetism of quasi-ordered Fe-Al alloys with Ga, V and Mn admixtures

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