Ye.V. Shcherbakova

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.

Magnetocrystalline anisotropy and exchange interactions in the novel R3(Fe, V)29 compounds (R Y, Nd, Sm)

A type of magnetocrystalline anisotropy and exchange interactions of the novel ternary R3(Fe, V)29 compounds (R  Y, Nd, Sm) have been investigated. The compounds are uniaxial ferromagnets with easy magnetization direction along the [2 0 1] axis of the monoclinic lattice at room temperature. The temperature variations of the magnetic moment and the first anisotropy constant for Y3(Fe, V)29 are presented. The first order magnetization process along the hard magnetization direction takes place for Sm3(Fe, V)29 at T < 120 K. A magnetic anomaly is detected in the temperature dependence of the a.c. susceptibility for Nd3(Fe, V)29 which can be related to a spin reorientation.

Magnetic properties of Sm2(Fe,Ti)17 compounds and their nitrides with Th2Zn17 and Th2Ni17 structures

Abstract In Sm 2 (Fe 1− x Ti x ) 17 compounds ( x =0.02, 0.03, 0.04) the hexagonal Th 2 Ni 17 structure has been stabilized at high temperatures. The type of crystal structure affects the magnetic properties of Sm 2 (Fe,Ti) 17 . For the Th 2 Ni 17 structure, higher values of the Curie temperature and constants of planar magnetocrystalline anisotropy than those for the Th 2 Zn 17 structure are observed. For both structures, the substitution of Ti for Fe leads to growing importance of the anisotropy constants of orders higher than second. No change in the type of structure is found upon nitrogenation. The hexagonal Sm 2 (Fe,Ti) 17 nitrides as well as the rhombohedral nitrides show uniaxial anisotropy at room temperature.

Magnetic phase transitions in the system La(Fe,Co,Ai)13 at high pressures

The magnetic properties and electrical resistivity of La(Fe0.88-xCoxAl0.12)13 alloys (0.009 0.01) and ferromagnetic-antiferromagnetic-paramagnetic transitions (x < 0.01) in the course of heating were studied at both ambient and high pressure. The action of pressure on the magnetic phase transitions is qualitatively similar to a decrease of cobalt concentration in the La(Fe0.88−xCoxAl0.12)13 alloys. Applying pressure results in a decrease in the magnetic phase transition temperatures. For alloys with concentrations in the vicinity of the AF-F transition (x = 0.02-0.04) antiferromagnetic features were observed to occur under pressure. The results are discussed in the context of the instability of the ferromagnetic state in this Invar system.

The formation of Z-phase Sm(Fe,Ti)8.5

Abstract The high-temperature modification Sm 2 (Fe,Ti) 17 of Th 2 Ni 17 type was found to exist in the Sm(Fe 1− x ti x ) y alloy system (0.04⩽ x ⩽0.07 and 8.0⩽ y ⩽9.0) at T ⩾1250 °C. More low-temperature phases Sm(Fe,Ti) 12 and Sm 2 (Fe,Ti) 17 of Th 2 Zn 17 type form from this modification. A ternary Sm(Fe 0.935 Ti 0.065 ) 8.5 compound analogous to the Z-phase Sm(Fe 0.91 V 0.09 ) 8.5 is obtained in the interval 1150–1250 °C. It can be considered to have a new type of a superstructure based on the CaCu 5 -type structure with a monoclinic unit cell having parameters a =0.972 nm, b =0.856 nm, c =1.063 nm, β=96° 50′.

Magnetic phase diagram of La(Fe0.873Co0.007Al0.12)13 cluster intermetallic compound

Abstract The magnetic properties of the La(Fe 0.873 Co 0.007 Al 0.12 ) 13 intermetallic compound have been studied. The compound is a cluster antiferromagnet showing the metamagnetic transition. The magnetic phase diagram of the compound has been constructed. The temperature dependence of the inverse paramagnetic susceptibility of La(Fe 0.873 Co 0.007 Al 0.12 ) 13 obeys the Curie–Weiss law. The large positive paramagnetic Curie point indicates the presence of predominantly ferromagnetic exchange interactions. The Neel temperature can be considered as the temperature of the ferromagnetic ordering of the Fe magnetic moments in clusters coupled antiferromagnetically.

New phases in Tb–Fe–Si system

Abstract The phase composition of the Tb(Fe 1− x Si x ) y alloys, where x =0.09 or 0.15 and y =8.5 or 9.667, has been studied by X-ray diffraction using micromonocrystals. Reflections of the Tb 3 (Fe,Si) 29 phase and of two new previously unknown phases are found. Models of the atomic arrangement in the new phases correlating well with the experimental diffraction patterns are suggested. Both new phases can be formed by the dumb-bell substitution for Tb atoms in the CaCu 5 lattice. According to the models, the compositions of phases are Tb 12 (Fe,Si) 109 and Tb 4 (Fe,Si) 41 .

Peculiarities of the R3(Fe,Si)29 phase formation in the SmFeSi system

Abstract The phase content of the Sm(Fe 1− x Si x ) y alloys (0.05≤ x ≤0.15; 8.5≤ y ≤12) has been studied by X-ray diffraction using micromonocrystals. The compounds Sm 2 (Fe,Si) 17 , Sm(Fe,Si) 12 and a novel Sm 3 (Fe,Si) 29 compound with a monoclinic unit cell are found. The lattice parameters of Sm 3 (Fe,Si) 29 are: a =1.056 nm, b =0.850 nm, c =0.966 nm, β =96.8°. This compound forms as a result of a solid state transformation from the high-temperature Sm 2 (Fe,Si) 17 phase. Diffuse effects observed in rocking photographs suggest transition structures arising from this transformation. The Curie temperatures of Sm 3 (Fe,Si) 29 vary in the interval 496–521 K.

Phase transformations in iron-rich Tb–Fe–Si alloys

The investigated decomposition of solid solutions on the base of the Th2Ni17-type Tb2(Fe,Si)17 compounds is accompanied by formation of the Tb3(Fe,Si)29 or Tb4(Fe,Si)41 compounds. The transformation proceeds by nucleation and growth of the phases throughout the volume of matrix. Simultaneously, the so-called transition structure consisting of a continuous set of regions with different amounts of Fe–Fe(Si) dumbbells was observed. It was concluded that in the transition structure regions the dumbbells form chains oriented along the 〈111〉 direction of the CaCu5 lattice, but the arrangement of the dumbbell chains is different. Low atom mobility in the R–Fe–Si alloys is likely to be responsible for formation of the transition structure.

Intermetallic compounds in the iron-rich SmFeRe alloys

In the iron-rich SmFeRe alloys, novel ternary compounds Sm(Fe,Re)12 of the ThMn12 type and Sm3(Fe,Re)24 with a monoclinic unit cell have been discovered. Both of these compounds are highly anisotropic uniaxial ferromagnets with the anisotropy fields more than 8 MA m−1. The Curie temperatures and saturation magnetization at 4.2 K are equal to 415 K and 92 A m2kg−1 respectivelt for Sm(Fe1−xRex−2)12 and 391 K and 109 A m2kg−1 for Sm3(Fe0.92Re0.09)29. The concentration dependences of the lattice parameters. Curie temperature and saturation magnetization for the substituted Sm2(Fe1−xRex)17 compounds (x ⪕ 0.14) are presented.