Vol 83, No 7 (2019)

The temperature dependences of the magnetic susceptibility in magnetic fields applied parallel and perpendicular to axis с of a Mn_0.89Mg_1.11BO₄ single crystal were measured. Spin ordering typical of an antiferromagnetic with an easy magnetization axis was observed below 16 K. The Dzyaloshinskii–Moriya interaction between spins of manganese ions in Mn_0.89Mg_1.11BO₄ was estimated by analyzing the EPR linewidth.

The effect additives of TbAl₃ hydride have on the magnetic properties and structure of sintered permanent magnets based on Pr–Fe–Co–Cu–B alloy with increased temperature stability is studied. Such magnetic properties as B_r = 1.07 T, ВН_max = 216 kJ m⁻³, _jH_c = 2000 kA m⁻¹, H_k = 1680 kA m⁻¹, H_k/_jH_c = 0.84, and α = −0.030% °С⁻¹ (in the temperature range of 20–100°C) are achieved.

The magnetization and slow steady-state deformation oscillations of a droplet of a magnetic fluid in an alternating magnetic field are investigated theoretically. The drop is suspended in another magnetic fluid with which it is immiscible. The change in the magnetic field is so slow that approximations of a quasi-stationary magnetic field and a quasi-steady flow can be used.

Three-dimensional numerical modeling of static domain structures in a Co(0001) film is performed for different values of an external magnetic field perpendicular to the surface of the film or lying in the plane of the film. Changes in the fine structure of domain walls, associated with the appearance, motion, and disappearance of Bloch lines and Bloch points, are considered in detail.

The effect mechanical stress has on the magnetic structure of permalloy microparticles is studied. The particles are square with sides of 25 μm and heights of 15 to 50 nm from sample to sample. It is shown that mechanical stress alters the magnetic structure and forms characteristic bridges between magnetic domains. The lengths of the bridges can be used to quantitatively characterize the tension in a particle.

Directions of the focusing of exchange spin waves inside crystals with an FCC lattice of the rock-salt type are determined. Using the example of ferromagnetic semiconductors EuO and EuS, it is shown that neither an external magnetic field nor dimensional effects are required for focusing in such systems. The directions in the crystal and the necessary conditions for the formation of magnon caustics are determined.

A theory of acoustic spin pumping in a bulk acoustic wave resonator with a ZnO-YIG-GGG-YIG/Pt structure is presented, with allowance for the exchange contribution to the formation of a coupled magnetoelastic wave spectrum, and the back action of acoustically excited magnetic dynamics in YIG films on the elastic subsystem in all layers. Good agreement is achieved between the theoretical and experimental frequency–field dependences of the resonant frequencies of the resonator and the voltage magnitude of the inverse spin Hall effect in Pt.

The magnetic and magneto-optical properties of (Со₄₀Fe₄₀B₂₀)_x(SiO₂)_100x nanocomposites with x = 30–72 at % are studied. The results reveal the inhomogeneous structure of the nanocomposites, which exhibit both large granules and small particles that make independent contributions of different nature to the magnetic properties of the materials. Specific features of the coercive force near the percolation threshold indicate superferromagnetic ordering in the composites at low temperatures.

A Monte Carlo study of the magnetic properties of simulated amorphous alloys of the Re–Gd system is performed using the Heisenberg model. The temperature dependences of spontaneous magnetization, magnetic susceptibility, and the Edwards–Anderson order parameter are calculated. The dependence of the temperature of the transition to the spin-glass state on the concentration of gadolinium atoms is constructed. The transition to the spin-glass state in Re–Gd amorphous alloys occurs only above the percolation threshold in this system.

A two-dimensional anisotropic Ising model with competing interactions on a square lattice is investigated using the Monte Carlo approach, based on the Wang–Landau algorithm. The curves of the density-of-states distribution and the order parameter are obtained. It is shown that the density-of-states distribution jumps sharply when |J₁/J| = 0.6, due to strong degeneration of the modulated state. Sharp jumps are also observed on the distributions of the order parameter when |J₁/J| > 0.2, testifying to the system’s transition from a homogeneous ordered state to a modulated phase.

The transverse magnetoresistance, heat capacity, and magnetization of monodomain single crystals of dodecaboride Ho_0.5Lu_0.5B₁₂ with a cage-glass structure are investigated at helium temperatures. It is shown that the anisotropy of charge carrier scattering in the antiferromagnetic phase is due to dynamic charge stripes oriented along directions 〈110〉 in the fcc lattice.

Magnetization reversal is studied for Ta/Tb₂₉Co₇₁/Ta thin films with different types of nanostructure. The films are deposited onto structuring substrates of anodized aluminum with unpolished surfaces, polished surfaces, and barrier layers. Nanoholes are found to triple the coercivity, due likely to the pinning of domain walls. Continuous and antidot films reveal the strong effect nanoconvexities have on the slope of the hysteresis loops. Such surface features could be one of the main reasons for the attenuation of perpendicular anisotropy in films deposited onto porous substrates.

Dependences are studied for the parameters of the hysteresis loops of iron garnet monocrystalline films on film thickness as a result of their layered etching by ion-beam sputtering with an oxygen ion beam. The coercive force of the films in magnetic fields corresponding to the motion of domain walls does not exceed 0.6 Oe as a result of layered etching through as much as 90% of a film’s thickness. This is important when using films in devices based on domain walls and other nanoscale spin structures.

The magnetization of a film at different magnetic field strengths can be determined by measuring the torque to quantify the magnetization of different magnetic structures of thin films. Fulfillment of the condition of uniform rotation can thus be monitored.

The effect the variation in permeability in water-based magnetic emulsions is studied under the action of a pulsed magnetic field and a hydrodynamic field generated when the cuvette containing a sample is rotated. Considerable (400–500%) variation in the permeability of the emulsion samples in the magnetic field is observed. It is shown that the optical effect of the variation in permeability wanes in the rotating cuvette.

Spectral dependences of the transverse Kerr effect (TKE) are studied in (CoFeZr)_x(Al₂O₃)_{(1 − х)} magnetic nanocomposites. TKE spectra are modeled for an unannealed composite using the Maxwell–Garnett approximation (MGA) in an effective medium. TKE calculations are made by considering the particle sizes of the nanocomposite (the quasi-classical size effect). The experimental data are found to be consistent with the theoretical TKE spectra.

The possibility of controlling the characteristics of the low-frequency resonant magnetoelectric effect in composite structures using external effects is demonstrated. These composite structures contain ganged ferromagnetic and piezoelectric layers. The magnitude of the magnetoelectric effect in planar structures with layers of nickel and lead zirconate titanate changes by tens of percent, and the frequency of acoustic resonance is altered to ten percent under the action of a constant magnetic field or a constant electric field when the temperature changes or mechanical stresses are created in the structure.

An equation for the magnetization frozen into a continuous medium is derived in ferrohydrodynamics with equilibrium magnetization. It is shown that when the condition of magnetic equilibrium is violated, a magnetic fluid can be considered ideal if the magnetization is frozen into the medium.

A way of obtaining a biocompatible magnetic fluid and its parameters are described. It is proposed that depolarized dynamic light scattering be used to determine the size of nanoparticles in the fluid phase, and to estimate the aggregative and sedimentation stability of a magnetic fluid upon dilution. It is established that upon the dilution of the magnetic fluid, ellipsoidal aggregates consisting of 20 or more single nanoparticles form in it.

The phonon spectra of Ni₂MnGa and Ni₂MnAl Heusler alloys are investigated using first-principle methods. The effect the supercell elongation of the considered alloys has on the features of phonon dispersion curves is studied. It is shown that cell elongation affects the behavior of soft transverse acoustic mode ТА₂ in both Ni₂MnGa and Ni₂MnAl.

Flows of secondary electrons are studied using a medical electron accelerator with an energy of 20 MeV. The electrons are generated on the structural materials of the accelerator itself and in the treatment rooms. The experiments are based on means of activation based on (γ, n) and (n, γ) reactions on a detecting target of natural ¹⁸¹Ta tantalum. The irradiated tantalum targets are probed using a spectrometer with a large-volume ultrapure germanium detector. The energy distribution of neutrons is obtained using a spectrometer–dosimeter equipped with an organic scintillator. It is established that the flow of neutrons accounts for 7% of the flow of braking gamma-quanta.