V. V. Serikov

Phase Separation in Isostructural Systems between Ordering Alloy and Intermetallic Compound

The results of X-ray diffraction, Mossbauer effect and neutron diffraction studies and also magnetic, thermal and kinetic properties measurements of the ternary alloys PdMn x Fe 1-x are presented. It has been shown that the alloys in the 0.2 < x < 0.8 concentration range realize a micro-inhomogeneous state formed by isostructural phases of the constituent compositions: the ferromagnetic PdFe alloy undergoing atomic ordering and the antiferromagnetic PdMn intermetallic compound.

Structure and magnetic properties of nanocrystalline FeCuNbSiB alloys after a thermomechanical treatment

The peculiarities of the formation of a nanocrystalline structure and induced magnetic anisotropy have been studied in Fe87−xCu1Nb3SixB9 alloys (x = 0, 4, 6, 8, 9.5, 11, 13.5 at. %) after thermomechanical treatment. Differences in the dynamics of the process of phase separation in the initial amorphous state, final phase composition, and magnitude and sign of induced magnetic anisotropy have been revealed depending on the initial content of silicon.

Heterogeneous magnetic state in hydrogen-amorphized GdFe2

Abstract Hydrogen-amorphized GdFe 2 H x were prepared for two different compositions of parent alloy and different hydrogenation temperature. The average hyperfine field grows from 22.5 T for the initial compound up to 33.4 T for the amorphized hydride. Samples amorphized at different temperatures show the same hyperfine field, whereas magnetic moment, compensation temperature and Curie temperature decrease with increasing the hydrogenation temperature. The non-Brillouin behavior of temperature dependence of magnetic moment of Gd sublattice and anomalous high-field magnetization curves were found in amorphous hydrides. The obtained results were interpreted in the assumption of heterogeneous structural state.

Structural State of Mechanically Alloyed Cu–Co Compound with a Considerable Magnetoresistance Effect

The structural state of the Cu 80 Co 20 compound after mechanical alloying and a subsequent thermal treatment has been studied by NMR spectroscopy and X-ray diffraction as well as measurements of magnetic and magnetoresistive properties. The analysis of the data obtained suggests the presence of ultradispersed cobalt particles in the copper matrix. A partial dissolving of cobalt in copper is likely to take place in defect regions. Such a structure is responsible for superparamagnetism of the Cu 80 Co 20 compound at T > 150 K and for a considerable GMR effect (12% at T = 77 K). The shifting of X-ray peaks of the copper matrix can be related to a coherent conjugation of Cu and Co constituents.

High-strength magnetically hard Fe-Cr-Co-Based alloys with reduced content of chromium and cobalt

Structure and magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co-W-Ga alloys with reduced Cr and Co contents have been studied. The compositions studied go beyond the limits of the miscibility gap in the phase diagram for conventional Fe-Cr-Co alloys. It has been established that after cold plastic deformation and low-temperature annealing the alloys are characterized by high values of mechanical and magnetic characteristics, which are significantly higher than those of known analogs. It is demonstrated that the treatment suggested leads to the decomposition of homogeneous solid solution based on α-Fe with the precipitation of disperse particles of a tungsten-rich phase, which promotes strengthening of alloys.

Thermomagnetic and Mössbauer studies of structural transformations caused in the amorphous Nd9Fe85B5 alloy by severe plastic deformation and annealing

Thermomagnetic analysis and Mössbauer spectroscopy were used to study the effect of severe plastic deformation (SPD) by high-pressure torsion (HPT) and subsequent annealing on structural transformations and formation of magnetic properties of rapidly quenched Nd9Fe85B6 alloy. The HPT of the Nd9Fe85B6 amorphous alloy was found to result in the precipitation of α-Fe nanocrystals and in changes in the structural state of the residual amorphous phase A′. In the annealed samples, there was revealed a great amount of nonequilibrium phases with different magnetizations. The total content of nonequilibrium phases depends on the annealing temperature and affects the exchange interaction between magnetically soft α-Fe nanocrystals and Nd2Fe14B nanocrystalline grains. The results obtained in this study can explain the differences between the high level of hysteresis properties of nanocrystalline materials, which was predicted theoretically, and low magnitudes realized in practice.

Structural transformations in high-strength magnetically hard Fe-Cr-Co-W-Ga alloys

Processes leading to a high-coercivity state of W and Ga containing Fe-Cr-Co alloys that possess a required strength and plasticity have been investigated. The effect of W and Ga additions on the structural constituents formed due to the decomposition of a high-temperature solid solution has been studied by the methods of X-ray diffraction, electron microscopy, and Mössbauer spectroscopy. The role of cold deformation preceding low-temperature annealings has been clarified.

Magnetic and Mössbauer study of hydrogen-amorphized GdFe2Hx ferrimagnet

Abstract Changes in the magnetic properties of the intermetallic GdFe 2 compound during hydrogen-induced amorphization have been studied. A sharp decrease in energy of the Gd Fe exchange interaction and an increase in the magnetic moment of iron from 1.6 μ B in the initial compound to 2.2 μ B in an amorphous hydride were established. The results obtained were interpreted from the assumption that a heterophase nanostructure occurs, in which the main amorphous ferrimagnetic phase is enriched in Fe relative to the stoichiometry and is characterized by the non-uniform intersublattice exchange interaction.

Mössbauer Studies of the Magnetic Phase Transition in La(Fe 0.88 Si x Al 0.12 - x ) 13 Compounds

Spectra of the nuclear gamma resonance for La(Fe0.88SixAl0.12 − x)13 compounds with different x values have been measured at 100 K. The compounds exhibit an antiferromagnetic ordering in the range of silicon concentrations x ≤ 0.024 and a ferromagnetic ordering at x > 0.024. Analysis of the spectra has been carried out with the use of a two-core distribution of quadrupole shifts. It has been demonstrated that upon a transition from antiferromagnetic to ferromagnetic ordering, the average hyperfine field at the Fe nuclei increases by almost 40 kOe. It has been found that antiferromagnetic compounds are mainly characterized by a positive quadrupole shift, and ferromagnetic ones by a negative quadrupole shift. A model of the formation of a magnetic structure that explains the appearance of a layered antiferromagnetic ordering in La(Fe0.88SixAl0.12 − x)13 compounds has been proposed.

Effect of tungsten and gallium on the structure and magnetic and mechanical properties of Fe-Cr-Co alloys

Effects of the alloying additions of W and Ga, cold deformation, and regimes of heat treatment on the magnetic and mechanical properties of precipitation-hardening Fe-Cr-Co alloys have been investigated. It has been shown that the alloying with tungsten leads to a strengthening of the α solid solution and an additional jumplike increase in strength after deformation and age hardening. The coercive force grows simultaneously with an increase in strength; the structure of the alloy in this case contains a large concentration of linear defects (dislocations), which indicates an important contribution of magnetoelastic energy to the formation of the high-coercivity state and of elastic strains to the increase in the strength properties. The character of fracture becomes brittle. The modifying of the alloy with gallium leads to an increase in plasticity due to the dispersion of the structure, formation of retained austenite in it, and formation of an interphase layer more uniform in composition. The character of fracture changes from brittle to brittle-ductile. A high-strength magnetically hard material has been obtained with Hc = 90–125 A/cm, σm = 120–130 G cm3/g, Br = 0.6–0.65 T, σ0.2 = 1300–1600 MPa, and δ = 2.0–4.6%.