G. V. Ivanova

Magnetic properties and crystal structure of novel high anisotropic compounds based on the RFeV system (RY, Nd, Sm, Gd)

Abstract We have investigated the crystal structure and magnetic properties of novel ternary compounds of the composition R 2 (Fe 0.91 V 0.09 ) 17 (R≡Y, Nd, Sm, Gd). X-ray diffraction showed that their crystal structure is a superstructure of a new type based on the CaCu 6 structure, but with lattice parameters five times larger than those of CaCu 5 . The Curie temperature and saturation magnetization of the compounds studied fall into the ranges 440–520 K and 15–30 μ B (f.u.) −1 at 4.2 K respectively. The influence of dissolved cobalt, carbon and nitrogen on the magnetic properties of the compounds R 2 (Fe 0.91 V 0.09 ) 17 has been studied.

The microstructure of a magnetically hard Zr2Co11 alloy

Electron-microscopic and electron-graphic analysis has demonstrated that the Zr2Co11 compound has a complex structure. All grains consist of thin plates of a high-temperature rhombohedral phase, which are parallel to the (0001) crystallographic plane; the crystal lattices in the neighboring regions have a twin orientation relative to each other. The transformation of the rhombohedral phase into a low-temperature orthorhombic phase is accompanied by an additional splitting of these plates into regions in which the [001]orth axes are parallel to the [0001]rhomb axes, and the [010]orth axes are rotated through an angle of about 120°. These twin regions, alternating in the samples, favor the minimization of elastic stresses. In electron-diffraction patterns, there are also observed satellites, which testify the existence of structural incommensurate modulation in the [010] direction of the orthorhombic lattice with a period of modulation equal to 18–19 Å.

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.

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.

Crystal Structure and Magnetic Properties of Novel Compound PrFe8Ga3C

We have synthesized a novel intermetallic compound PrFe8Ga3C and studied its structure and magnetic properties. X-ray diffraction analysis revealed that the compound possesses a tetragonal BaCd11-type structure (space group I41/amd). In this structure Ga atoms occupy the same sites as Fe atoms with preferably filling the 4(b) site. Magnetization curves have been measured on the aligned powder samples. Below the Curie temperature TC = 400 K the easy magnetization direction was found to orient within the (100) plane. At 80 K the compound has a spontaneous magnetization of 97 emu/g and anisotropy constant of 4.2107 erg/cm3. At room temperature these values reduce to 78 emu/g and 4.7106 erg/cm3, respectively.

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%.

Formation of ferromagnetism in pseudobinary PrNi5 − xCux (2.5 ≤ x ≤ 5) solid solutions

The structure and magnetic properties of the PrNi5 − xCux alloys have been studied in a composition range of 2.5 ≤ x ≤ 5. Single-phase solid solutions with a hexagonal structure of the CaCu5 type have been shown to be realized within this composition range. It has been found that upon the introduction of nickel into the Van Vleck paramagnet PrCu5 the ground state of the alloys with x ≤ 4.3 becomes ferromagnetic. All the compositions under study exhibit high magnetocrystalline anisotropy of the “easy-basal-plane” type. With allowance for the literature data available, a complete magnetic phase diagram of the PrNi5 − xCux system was constructed; it is characterized by two maxima in the compositional dependence of the Curie temperature. The earlier suggested model of the effect of local random crystal fields on the magnetic state of Pr3+ ions in alloys with low copper contents was shown to be applicable also for the explanation of magnetic properties of alloys with low nickel contents. The results of this study confirm the hypothesis about the determining role of local irregular crystal fields in the formation of the magnetic properties of the pseudobinary PrNi5 − xCux intermetallic compounds.

Features of the Post-Deformation Hardening of Fe-Cr-Co Hard Magnetic Alloys with W and Ga Additives

The structure, mechanical and magnetic properties have been studied for Fe-Cr-Co-based hard magnetic alloys with W and Ga additives, subjected by the quenching and post-deformation hardening. The alloys combine the properties of the hard magnetic material with outstanding mechanical strength and plasticity. Using X-ray and electron microscopy analysis, the reasons and conditions of formation of these properties have been determined.

Effect of gallium on the crystal structure and magnetic properties of PrFe11 − x GaxCy compounds

A homogeneity range of the PrFe11 − xGaxCy phase was determined. As the gallium content increases, the lattice parameters were shown to increase, whereas the Curie temperature decreases; the type of magnetic anisotropy at room temperature is unchanged. In the alloys with x > 3, the transformation of the tetragonal lattice of the compound into an orthorhombic lattice with the axial ratio a/b ≤ 1.006 is observed. This is likely to be caused by the ability of gallium to form covalent bonds. Gallium atoms were found to occupy preferentially 16j2 and 4e2 sites in the orthorhombic lattice of the FePr6.5Ga4.5C compound. The atoms located in the 16j2 sites form wavy chains along the [010] direction of the orthorhombic lattice, whereas the iron atoms located in the 16j1 sites form analogous chains along the [100] direction. Owing to this fact, one of these directions is likely to become an easy axis. The alloy with x= 4.5 has a low coercive force at room temperature; at 114 K, its coercive force is Hc = 42.4 kA/m.

Novel high anisotropic compounds based on RFeM systems (M Ti, V)

Abstract A new type of the compounds has been discovered in the alloys of the approximate composition R(Fe, M) 8.5 where R  Y, Nd, Sm, Gd and M = V, Ti. Their crystal structure is identified to be monoclinic with the calculated stoichiometry R(Fe, M) 9−9.7 . The magnetic properties of these compounds are presented.