V. A. Seredkin

Polarized absorption spectra and spectroscopic parameters of Tm3+ in the TmAl3(BO3)4 single crystal

High-optical-quality single crystals of the TmAl3(BO3)4 compound were synthesized from a solution in the melt. The absorption spectra in the σ and π polarizations for the 3H6 → 3F4, 3H6 → 3H5, 3H6 → 3H4, 3H6 → 3F3, 3H6 → 3F2, 3H6 → 1G4, and 3H6 → 1D2 transitions in the Tm3+ ion were recorded at room temperature. The transition intensities were analyzed in the framework of the Judd-Ofelt theory generalized to the case of anisotropic crystals, and the following parameters of the theory were obtained: Ω2 = 6.14 × 10−20 cm2, Ω4 = 3.09 × 10−20 cm2, and Ω6 = 2.04 × 10−20 cm2. The lifetimes and the branching ratios were determined for all possible transitions.

Scale invariance of the structure upon explosive crystallization of amorphous films

Experimental results that are obtained in the process of the explosive crystallization of x-ray amorphous films Fe2Tb and CoPd with magnetic anisotropy perpendicular to the film plane are reported. The internal bending of thus obtained “single crystals” reaches 100 deg/μm. An explanation of the mechanism and kinetics of explosive crystallization in the Fe2Tb and CoPd films is proposed in the framework of the shear transformation zone theory.

Structure and magnetic properties of Co-P films of nanometer thickness

The main features of the formation of chemically deposited thin polycrystalline Co-P films of nanometer thickness have been determined experimentally. Changes in the surface structure of films with different thicknesses have been determined using an atomic force microscope. It has been established that at thicknesses smaller than 10 nm the films represent a set of weakly connected nuclei of crystallites with random orientations of easy axes. The subsequent increase in the thickness of films leads to the formation of a uniform polycrystalline layer. Estimates are given, which make it possible to determine the magnetic state of crystallites for the case of their weak magnetic interaction.

Magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in silicon oxide

The magnetic and magneto-optical properties of ion-synthesized cobalt nanoparticles in the amorphous silicon oxide matrix are investigated as a function of the implantation dose. The analysis of the field dependences of the magnetization and the magneto-optical Faraday and Kerr effects demonstrates that, as the ion implantation dose increases, the superparamagnetic behavior of an ensemble of cobalt nanoparticles at room temperature gives way to a ferromagnetic response with the anisotropy characteristic of a thin magnetic film. The magnetization curves for the superparamagnetic and ferromagnetic ensembles of cobalt nanoparticles are simulated to determine their average sizes and the filling density in the irradiated layer of the silicon dioxide matrix. It is revealed that the spectral dependences of the Faraday and Kerr effects for ion-synthesized cobalt nanoparticles differ substantially from those for continuous cobalt films due to the localized excitations of free electrons in the nanoparticles.

Magneto-optical properties of polycrystalline CoCrFeO4 films

A methods of obtaining polycrystalline CoCrFeO4 films based on solid-phase reactions in Cr2O3/Co/Fe layer structures in the regimes of isothermal annealing and self-propagating high-temperature synthesis (SHS) is described. The magneto-optical properties of the obtained films have been studied. It is established that the spectra of magneto-optical characteristics depend on the solid-phase reaction regime and synthesis temperature. The Faraday rotation angle exhibits a local maximum (2θF = 5 deg/μm) at a wave-length of 630 nm.

Structural and magnetic features of solid-phase transformations in Mn/Bi and Bi/Mn films

Solid-phase transformations at different annealing temperatures in Mn/Bi (Mn on Bi) and Bi/Mn (Bi on Mn) films have been studied using X-ray diffraction, electron microscopy, and magnetic measurements. It has been shown that the synthesis of the α-MnBi phase in polycrystalline Mn/Bi films begins at a temperature of ~120°C and the Mn and Bi layers react completely at 300°C. The resulting α-MnBi(001) samples have a large perpendicular magnetic anisotropy (Ku ≃ 1.5 × 107 erg/cm3) and a coercive force H > HC ~ 3 kOe. In contrast to Mn/Bi, the ferromagnetic α-MnBi phase in Bi/Mn films is not formed even at annealing processes up to 400°C and Mn clusters are formed in a Bi melt. This asymmetry in phase transformations occurs because chemosorbed oxygen existing on the surface of the Mn film in Bi/Mn films suppresses a solid-phase reaction between Mn and Bi. The analysis of the results obtained implies the existence of new low-temperature (~120°C) structural transformation in the Mn–Bi system.

Studying the mechanism of exchange coupling in ferro/ferrimagnet NiFe/DyCo film structures

Dependence of the magnetic and magnetooptical properties of an exchange-coupled NiFe/DyCo bilayer system on the thickness (tDyCo) of a magnetically hard layer has been studied. It is established that the unidirectional anisotropy vanishes at tDyCo ∼ 400 Å, while the coercive field in the magnetically soft layer becomes comparable to the exchange-induced field shift. In this case, the DyCo layer magnetization is almost parallel to the film plane, whereas a reference DyCo film exhibits a perpendicular anisotropy. A model of the magnetic state of layers in the ferro/ferrimagnetic layer structure under consideration is proposed, which assumes that a 180° domain wall is formed at the interface upon magnetization reversal in the magnetically soft layer.

Unidirectional anisotropy in ferromagnetic-ferrimagnetic film structures

A mechanism of unidirectional anisotropy formation in an exchange-coupled ferromagnetic-ferrimagnetic film structure with orthogonal effective magnetizations in the layers is investigated. The reason for unidirectional anisotropy is the magnetic heterogeneity of the ferrimagnetic layer in the compensation range. Magnetization reversal in the magnetically soft layer of an (REE–transition metal)/NiFe film structure is discussed based on a model of uniform rotation of magnetization. It is found that unidirectional anisotropy sharply decreases the magnetic noise level in the magnetically soft layer. The field of application of these materials is outlined.

Effect of alkali reagents on the crystal structure of chemically deposited CoP films

The effect alkali reagents have on the crystal structure of CoP films prepared via chemical deposition is investigated. It is shown that the use of sodium hydrogen carbonate and ammonium hydroxide in low concentrations leads to growth of the hexagonal phase in the films. As the concentration of alkali reagents is increased, the formation of a cubic or amorphous phase is observed.

Magneto-optical properties of nanogranulated Co-Ti-O films

The results from studies of the magneto-optical properties of Co-Ti-O nanogranulated films obtained under conditions of solid-state reaction with oxygen exchange in CoO/Ti layered structures are presented. The magneto-optical spectra of the polar Kerr effect in films with a relative volume of the magnetic fraction of 0.38 to 0.64 has a resonance character in the wavelength range of 450–650 nm. The Kerr rotation angle of the films increases by a factor of 3–5, relative to conventional Co films.