An Erratum to this paper has been published: https://doi.org/10.1134/S0031918X2355001X

This work describes experimental study by a direct and indirect method of magnetocaloric properties of Ni-based alloys: Ni 93.8 V 6.2 , Ni 89.5 Al 10.5 , Ni 72.5 Cu 27.8 , which are promising materials for self adjusting magnetic hyperthermia. It has been demonstrated that the temperature of the maximum magnetocaloric effect determined by these methods can differ significantly, which is of critical importance for self-adjusting hyperthermia.

Magnetooptical spectroscopy is an effective method for studying the magnetic microstructure of homogeneous and heterogeneous magnets. This review is devoted to analysis of numerous factors affecting the intensity and spectral dependence of a magnetooptical signal of the equatorial Kerr effect in nanocomposites “ferromagnetic metal–dielectric” in the visible and near infrared spectral regions. Examples of the influence of the metal concentration, nanoparticle size and shape, the substrate, the material of the dielectric, the amorphization of grains, the deposition method, and other factors on the magnetooptical spectrum are considered. The differences in the magnetooptical spectra for the superparamagnetic, superferromagnetic, and ferromagnetic states are demonstrated. It is noted that in the presence of fractions with different field dependences of the magnetization in a nanocomposite, the magnetooptical signal is not proportional to the total magnetization. Examples of enhancement and sign inversion of the magnetooptical signal in nanocomposites are considered. The possibility of the description of magnetooptical spectra using the methods of the effective medium (the Bruggeman method and the Maxwell–Garnett symmetrized approximation) is discussed.

Nanocomposites (CoFeB)x(LiNbO3)100 – x with x = 17–48 at % have been synthesized by ion beam sputtering of a composite target comprised of Co40Fe40B20 and LiNbO3 onto silicon substrates, and the tran-sitions from the superparamagnetic state to the superferromagnetic and ferromagnetic states with an increase in the concentration of the magnetic component are studied by magneto-optical methods. The magneto-optical properties have been investigated in the geometry of the equatorial (transverse) Kerr effect (TKE). Magneto-optical spectra are recorded in the range of 0.5–4.0 eV in fields up to 2.5 kOe at 20–300 K, field and temperature dependences of the TKE at certain wavelengths are obtained, and the domain structure during magnetization reversal is visualized using a magneto-optical Kerr microscope. It is shown that the sample with x = 17 at % is superparamagnetic at temperatures above the blocking temperature (about 30 K). The interaction between the granules is considerable already at x = 20 at %, the transition to the superferro-magnetic state occurs at x ≈ 32–36 at %, and the transition to the ferromagnetic state occurs at x ≈ 44 at %near the metal–dielectric transition, i.e., at a concentration below the percolation transport threshold.

Magnetic Heusler alloys X 2 BZ (where X and B are 3 d elements and Z belongs to the sp group) exhibit diverse magnetic and structural properties, which are important for designing multifunctional smart materials. Electronic band structure calculations demonstrate that, if the valence of element B is higher than that of element X, such alloys (so-called inverse Heusler alloys) can behave differently as compared to traditional Heusler alloys. The growth, the crystal structure, and the magnetic properties of thin films of a new Mn 2 FeSi Heusler alloy deposited under various conditions (including various substrates and annealing temperatures) are studied in this work. A temperature-induced structural transition into a low-magnetization martensitic phase and a thermally stable austenitic phase are detected. A magnetic field of 500 Oe applied to some samples at a temperature of 380 K is found to cause a large exchange bias (about 1 kOe) at T = 10 K. The influence of the type of substrate and the annealing temperature on the magnetic and structural properties of the films is discussed.

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.

Abstract—The magnetostatic and magnetodynamic properties of laminated materials based on glass-reinforced plastic laminate coated with magnetic (Co40Fe40B20)60(SiO2)40 nanocomposite are studied. The modified magnetic composite structural materials based on glass fiber are characterized by hysteresis with a low coercivity and magnetic shape anisotropy related to fiber geometry. No significant absorption of electromagnetic radiation was observed in the range of frequencies of natural ferromagnetic resonance, except for the bulk composite sample, where minor peaks at 3 and 5 GHz were detected. In the variation in the coefficient of electromagnetic radiation transfer versus frequency curves, the signal intensity is substantially attenuated at 6–12 GHz owing to dielectric loss in the composite film.

The transport properties of film nanocomposites (Co 40 Fe 40 B 20 ) x (AlO y ) 100 − x and (Co 84 Nb 14 Ta 2 ) x (AlO y ) 100 − x based on AlO y oxide ( y ~ 1), containing a ferromagnetic metal, are studied in the region of the metal–insulator transition (57 > x > 47 at %). It is found that at x > 49 at %, the conductivity of nanocomposites is well described by a logarithmic law of σ( T ) = a + b ln T , which can be explained by the peculiarities of the Coulomb interaction in nanogranular systems with metallic conductivity near the metal—insulator transition. It is shown that parameter b is determined by the characteristic size of the percolation cluster cell, which in nanocomposites of both types happen to be the same (~8 nm) and correlates well with the results of electron microscopy studies. The temperature dependence of the anomalous Hall effect at the logarithmic dependence of conductivity is studied for the first time. In the immediate vicinity of the transition, a power-law scaling between the anomalous Hall resistance and longitudinal resistance ρ H a ∝ ρ 0.4 , is detected, which can be explained by the suppression of its own mechanism of the anomalous Hall effect under the strong scattering of charge carriers.

Thin films of (Co 41 Fe 39 B 20 ) x (SiO 2 ) 100 – x nanocomposites and hybrid nanocomposite–semiconductor [(Co 41 Fe 39 B 20 ) x (SiO 2 ) 100 – x /C] 50 multilayers are synthesized by ion-beam deposition at various contents x of ferromagnetic metallic Co 41 Fe 39 B 2O nanogranules in an SiO 2 matrix and at various carbon layer thicknesses h < 2 nm. Their magnetic and electrical properties, high-frequency magnetic permeability, magnetooptical spectra, and FMR spectra are studied. It is found that both the single-layer nanocomposites and the multilayers with carbon interlayers are superparamagnetic at x < x per , where x per is the electric conduction percolation threshold: a hysteresis at room temperature is absent, and the blocking temperature determined in quasi-static measurements does not exceed 20–30 K and weakly depends on the carbon layer thickness. At a carbon layer thickness h = 1.2–1.8 nm, the real and imaginary parts of complex magnetic permeability at 50 MHz and room temperature are substantially higher than those of the nanocomposites without carbon layers: their values are typical of ferromagnets. This dependence points to an exchange interaction between nanogranules in layers through a carbon interlayer. The influence of a conducting layer on the static and dynamic magnetic properties of a system of interacting superparamagnetic particles is discussed.