G. M. Makarova

Original magnetic behaviour observed in RNi5−xCux alloys (R = Pr, Gd or Y)

Abstract The Curie temperatures, spontaneous magnetizations and initial susceptibilities were investigated in the temperature interval from 1.5 to 40 K for the pseudobinary alloys RNi5−xCux, where R = Pr, Gd and Y, x ≤ 2.6. It was discovered that the solid solutions PrNi5−xCux between the PrNi5 and PrCu5 Van Vleck paramagnets are ferromagnets for intermediate Cu concentrations. It was shown that the ferromagnetic ordering in PrNi5−xCux alloys can be explained by concentrational enhancement of 3d band susceptibility which in its turn leads to the enhancement of f-f exchange interactions. The maxima on the concentration dependences of both Curie temperatures for the RNi5−xCux ferromagnets with R = Pr, Gd and susceptibility for the YNi5−xCux Pauli paramagnets are manifestations of 3d band magnetism.

Mechanisms controlling magnetic properties of pseudobinary compounds TbNi5−xMx (M=Cu or Al)

Abstract Magnetic properties and heat capacity of the pseudobinary TbNi 5− x Cu x and TbNi 5− x Al x alloys have been studied for x ⩽2.5 and x ⩽1.5, respectively. The substitution of Cu or Al for Ni decreases sharply the spontaneous magnetic moment, increases the magnetic anisotropy in the “easy” basal plane, and leads to strong magnetic domain wall pinning. The Curie temperature T C in TbNi 5− x Cu x depends on x non-monotonously and has a maximum value at x =1, while T C in TbNi 5− x Al x does not depend on composition up to x =1 and sharply decreases at x >1. These results are explained by the effects of random local crystal fields, band magnetism and heterogeneous polarization of the mixed 3d band.

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′.

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.

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.

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.

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.

Phase composition and magnetic properties of nanocrystalline SmFe11 − xGaxC1.25 (2 ≤ x ≤ 5) alloys

As-cast and rapidly quenched alloys (RQAs) SmFe11 − xGaxC1.25 (2 ≤ x ≤ 5) have been studied. The RQAs were prepared by melt spinning on a steel wheel rotating at a velocity V = 10−40 m/s. Fragments of the RQAs were annealed in a vacuum at Tann = 500−850°C. The as-cast alloys are multiphase; the maximum volume fraction in them corresponds to the Sm2(Fe, Ga)17C compound with a rhombohedral structure. The rapid quenching leads to the formation of the Sm(Fe, Ga)11C compound (1: 11) with a tetragonal BaCd11-type structure; the maximum volume fraction of the compound is reached in the alloy with x = 3 quenched to a wheel rotating at V = 30 m/s. The melt spinnins of the alloys with x = 2−4 at V = 40 m/s is accompanied by their substantial amorphization. During annealing, the amorphous phase crystallizes mainly with the formation of the 1: 11 phase. A nonequilibrium phase diagram of the alloys quenched at V = 40 m/s and annealed at Tann = 500−850°C has been constructed. The 1: 11 compound has a single-phase region near x = 3 at Tann ≥ 600°C. As the volume fraction of the 1:11 phase increases, the coercive force Hc of nanocrystalline RQAs increases. The maximum coercive force is observed for the SmFe8Ga3C1.25 alloy quenched at V = 40m/s and subsequently annealed at 700°C; it is 0.8 and 12 kOe at 293 and 50 K, respectively. The high coercive force obtained indicates that the Sm(Fe, Ga)11C phase is magnetically uniaxial and has a high magnetic anisotropy energy. The magnetic anisotropy constant K1 of the compound at T = 50 K was estimated to be 3.1 × 107 erg/cm3.