G. I. Ryabtsev

Spin-orientation transitions in the system BaFe12−2xCoxTixO19

A neutronographic investigation of the system BaFe12−2xCoxTixO19 (0≤x <- 3.5), was conducted in the 77–800 K temperature interval. The distribution of Co2+ and Ti4+ ions in the crystallographic sublattices was calculated. A magnetic state diagram of the system was constructed in x-T coordinates, based on data from the temperature dependencies of the magnetic reflection intensities. It is shown that a state with a plane of easy magnetization exists in the given system only in narrow intervals of Co ion concentrations and temperatures. Features of the occurrence of spin reorientation in the investigated system are discussed.

Magnetization processes of the first kind in the hexaferrite Co0.62Zn1.38W

The magnetization curves M(H) and derivatives ∂2M/∂H2 of a polycrystalline textured specimen of the compound BaCo0.62Zn1.38Fe16O27 are investigated in the 100–300 K temperature range. It is shown that magnetization processes of the first kind are characteristic for this compound at temperatures below 220 K. The diagram of the magnetic state is analyzed in coordinates of the normalized anisotropy constants X=K2/K1 and Y=K3/K1. Temperature dependences of the three magnetic crystallographic anisotropy constants are computed on the basis of experimental data on the critical magnetization and the field, and hysteresis loop width.

Method of a singular point and determination of fields of anisotropy of polycrystalline hexagonal magnets

A numerical computation is performed on the magnetization curves and their derivatives for magnets of hexagonal syngony for isotropic polycrystalline specimens as well as materials with “sheet” texture in the basis plane. It is shown that investigation of the second derivatives ∂2M/∂H2 for a degree of texture fT > 0.4 permits obtaining information about the magnitude of the anisotropy field independently of its type. The singularities of M(H) and ∂2M/∂H2 are examined for magnetization processes of the first kind. In this case the singular point method permits measuring the magnitude of the critical fields, the critical magnetizations, and the anisotropy field on a textured specimen with fT>0.7, which yields information about the magnitudes of the high order anisotropy constants in the long run.

Influence of anisotropy constants of higher order on the magnetic reversal of uniaxial magnets

Within the framework of a simple model in which only homogeneous states of magnetization are considered, the influence of the constants of magnetic crystallographic anisotropy of higher order on the critical field of domain formation and the hysteresis loops of uniaxial magnets is investigated. It is shown that the critical field depends strongly on both the sign of K1 and on the ratio of the magnitudes and signs of K2/K1 and K3/K1. On the basis of stability analysis for the free energy, hysteresis loops of uniaxial magnets as a function of Ki are calculated.

Effect of heat treatment on the anisotropy of the compound Co2Z

The behavior of the anisotropy field of the hexaferrite Co2Z is studied as a function of the heat treatment regime. It is shown that the change in the magnitude of the anisotropy field and its temperature dependence observed during quenching are determined by the redistribution of Co2+ ions over octahedral positions with different orientations of the spin magnetic moments. The increase in the temperature of the spin-reorientation transition “cone of easy magnetization-plane of easy magnetization” indicates the increasing importance of the higher order anisotropy constants in the heat treatment.

Approach to saturation of porous lithium ferrites

A study was made of how porosity affects the law of approach to saturation with respect to magnetization of porous lithium ferrites. The experimental results obtained are discussed within the framework of the theories of Néel and Schlömann.

Law describing the approach to saturation of porous anisotropic materials

A law is obtained for the approach to saturation with respect to magnetization for anisotropic magnetic materials with inhomogeneous saturation magnetization. In the calculation, the spin-wave formalism is used. The effect of an inhomogeneous exchange interaction on the approach to saturation is taken into account. The relations obtained are generalizations of the already known Neel and Holstein-Primakov formulas.