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The crystallographic, magnetic, electrical, and magnetoresistive properties of samples of La0.775Sr0.225Mn1−xSnxO3 synthesized by the sol-gel method are studied. It is shown that introducing tin atoms, with their large size, into the manganese sublattice produces significant deformations of the crystal lattice and enhances the structural and magnetic inhomogeneity of the samples. It is discovered that increasing the tin content leads to a reduction in magnetization, a lowering of the Curie temperature, and an increase in the electrical resistivity. The way the crystallographic parameters change is found to correlate with the character of the changes in the magnetic parameters. It is shown that the low-temperature magnetoresistance increases with x, while the magnetoresistance around room temperature is a nonmonotonic function of the tin concentration and has a maximum at x=0.015.

The temperature (4.5–550K) and angular (in the film plane) dependences of the coercivity field for physically nonpercolated nanogranular (CoFeB)x–(SiO2)1−x films with an oriented intraplane granule anisotropy have some unusual properties compared to those owing to blocking of thermally activated reorientation of the magnetic moments of the granules. At temperatures above the blocking temperature Tb≈350–370K, the dependence of the coercivity on the measurement duration is weak compared to that below Tb. Its angular (in the film plane) dependence differs qualitatively from that expected with blocking of superparamagnetic particles. This behavior is explained by the appearance of superferromagnetic ordering of the granule magnetic moments at T>Tb owing to interactions among them. As the temperature is reduced below 100K, the coercive field Hc for magnetization in the easy direction increases significantly more than expected for a blocked superparamagnetic ensemble. Here Hc≠0 for magnetization along the hard ...

Temperature and field investigations of the magnetic properties of multilayer films, consisting of a sequence of alternating magnetic layers of iron and the rare-earth terbium separated by layers of nonmagnetic gold, are performed. The samples were obtained by electron-beam deposition. The field dependence of the magnetic moment of a film with H∥n are analyzed to determine the characteristics of the uniaxial anisotropy. It is shown that a nonuniform uniaxial anisotropy results in nonlinearity in the magnetization of the film in H∥n. The process of magnetization of a film in H⊥n, when the transition to a single-domain state occurs only as a result of the motion of domain walls, is described. It is shown on the basis of the data on the field dependences of the magnetic moment at low temperatures that the magnetic moments of the Fe and Tb layers are oriented oppositely with respect to one another. A compensation point is observed in the temperature dependence of the magnetization; this indicates the presence...

We study the formation of antiferromagnetic magnetoelastic domains in easy-plane antiferromagnets of the iron-group dihalides, in which the infinite degeneracy of the spatial orientation of the antiferromagnetic vector in the basal plane is lifted on account of the spontaneous magnetostriction. In these crystals the domains differ from each other not only by the direction of the antiferromagnetic vector L in them but also by the related directions of the principal axes of the spontaneous magneostrictive strain. The system of antiferromagnetic domains turns out to be identical to the system of elastic domains. It is shown that the processes of magnetization and the induced striction in a magnetic field in the multidomain antiferromagnetic state are interconnected. Data on the field dependence of the induced magnetostriction in the multidomain state of the easy-plane antiferromagnets CoCl2 and NiCl2 are presented and analyzed. It is shown that although the magnetostriction in the cycles of imposition and re...

An analysis is made of the experimental data on the magnetic-field dependence of the magnetostriction and magnetization of the NiCl2 crystal at its transition from the multidomain antiferromagnetic state to a uniform state. It is shown that their field dependence is determined by the mean orientation of the domains, which is characterized by a domain coalignment parameter. That parameter is used to give a phenomenological description of the multidomain state of the antiferromagnet NiCl2.

Experimental data from measurements of the induced magnetostriction of the easy-plane two-sublattice layered antiferromagnet NiCl2 in the homogeneous and multidomain states at T=4.2 K are analyzed. It is shown that the intersublattice magnetoelastic interactions are dominant in NiCl2. The induced magnetostriction of the crystal in the single-domain state is due to canting of the spins of the sublattices toward the magnetic field direction. The induced magnetostriction in the multidomain state is due to a rearrangement of the domain structure and is independent of the small in-plane anisotropy. In both cases the values of the induced magnetostriction are directly proportional to the square of the value of the external magnetic field.

The features of the transformation of the multidomain state of an easy-plane antiferromagnet in an external magnetic field are investigated in the case of a magnetoelastic origin of the multidomain state. Experimental data are presented on the field dependence of the induced magnetostriction of the easy-plane two-sublattice antiferromagnet CoCl2 at different temperatures. In the discussion of the experiments and in the theoretical description we use the approximation of a continuous distribution of domains in the easy plane. It is shown that the orientational distribution of the domains upon the introduction of a magnetic field depends only on the magnitude and direction of the field and is independent of temperature. These features of the distribution of domains can be explained by a matching of their equilibrium magnetostriction with the elasticity of defects wherein the elasticity of the domains compensates the elasticity of the defects.

A structure is proposed for the magnetoelastic antiferromagnetic domains in easy-plane antiferromagnets of the iron-group dihalides. The proposed structure is made up of a triad of regions with 120° rotation of the antiferromagnetic vector on passing between adjacent regions. This domain structure may be stabilized by defects which are isotropic in the easy plane and which preserve the orientational degeneracy of the directions of the antiferromagnetic vector in the easy plane.

An analysis is made of the experimental magnetic-field curves of the anisotropic (in the easy-plane) magnetostriction of the antiferromagnet CoCl2 at different temperatures in the ordered phase. It is shown that the field dependence of the magnetostriction in a single-domain antiferromagnetic state remains proportional to the square of the applied field over the entire temperature range; this behavior corresponds well to the classic (Neel) scheme of collapse of the sublattice spins (spin flip). The temperature dependences of the intrasublattice and intersublattice contributions to the magnetoelasticity are proportional to each other. The temperature dependence of the spin-flip field obtained from the magnetostriction data agrees with that obtained previously from observations of the antiferromagnetic resonance (AFMR). The temperature dependence of the spontaneous anisotropy of the magnetostriction, obtained by extrapolating the magnetostriction in the single-domain state to zero field, is close to M∼T4.

The magnetic ordering model is considered for a single-lattice spin subsystem with S=1 and a large biquadratic exchange whose energy has the same order of magnitude as the bilinear exchange interaction energy. The expression for free energy is obtained in the microscopic approximation, and the phase states are defined and analyzed. The Landau potential is represented as a power expansion in the model microscopic free energy. This expression is used to describe the peculiarities of the temperature dependences of the magnetic susceptibility and magnetoelastic deformation.

It is shown that the spin Hamiltonian of the spin–spin interactions, written with the use of effective spinons defined on the two lowest doublets of magnetic ions with a partially frozen orbital moment, has a non-Heisenberg form. The Heisenberg contribution is represented by spin–spin terms containing three powers of ion spin projections and is anisotropic and comparable to the bilinear spin–spin interaction.

A thermodynamic analysis of the influence of non-Heisenberg interionic spin-spin interactions on the temperature dependence of the NMR frequency of a NiCl2 crystal is carried out.