Experimental and theoretical studies of the dynamic magnetization in swept magnetic fields of the orthorhombic SrY_2O_4 single-crystals doped with the Dy^3+ Kramers ions (0.01 and 0.5 at. odd Dy isotopes are presented. Impurity ions substitute for Y^3+ ions at two nonequivalent crystallographic sites with the same local C_s symmetry but strongly different crystal fields. Well pronounced double-loop hysteresis is observed at temperatures 2, 4, 5 and 6 K for sweeping rates of 5 and 1 mT/s. The microscopic model of spectral, magnetic and kinetic properties of Dy^3+ ions is developed based on the results of EPR, site selective optical spectra and magnetic relaxation measurements. The derived approach to the dynamic magnetization in the sweeping field based on the numerical solution of generalized master equations with time-dependent transition probabilities induced by the electron-phonon interaction, quantum tunneling and cross-relaxation allowed us to reproduce successfully the evolution of the hysteresis loop shape with temperature, sweeping rate and concentration of paramagnetic ions.

Roman.Yusupov@kpfu.ru Abstract. A series of Pd 1- x Fe x alloy epitaxial films ( x = 0, 0.038, 0.062, and 0.080), a material promising for superconducting spintronics, was prepared and studied with ultrafast optical and magnetooptical laser spectroscopies in a wide 4 – 300 K temperature range. It was found that the transition to the ferromagnetic state causes the qualitative modification of both the reflectivity and the magnetooptical Kerr effect transients. Nanoscale magnetic inhomogeneity of the ferromagnet/paramagnet type inherent in the palladium-rich Pd 1- x Fe x alloys reveals itself in an occurrence of a relatively slow, 10-25 ps, photoinduced demagnetization component following a subpicosecond one; the former vanishes at low temperatures only in the x = 0.080 sample. We argue that the 10-ps timescale demagnetization originates most probably from the d -electron diffusive transport in the conditions of the nanometer-scale magnetic inhomogeneity. The low-temperature amount of the residual paramagnetic phase can be deduced from the magnitude of the slow reflectivity relaxation component, and is estimated as ~ 30% for x = 0.038 and ~ 15% for x = 0.062 films. The minimal iron content ensuring the magnetic homogeneity of the ferromagnetic state in Pd 1- x Fe x alloy at low temperatures is about 7 

A series of Pd1−xFex alloy epitaxial films (x = 0, 0.038, 0.062, and 0.080), a material promising for superconducting spintronics, was prepared and studied with ultrafast optical and magneto-optical laser spectroscopy in a wide temperature range of 4–300 K. It was found that the transition to the ferromagnetic state causes a qualitative change of both the reflectivity and the magneto-optical Kerr effect transients. A nanoscale magnetic inhomogeneity of the ferromagnet/paramagnet type inherent in the palladium-rich Pd1−xFex alloys reveals itself through the occurrence of a relatively slow, 10–25 ps, photoinduced demagnetization component following a subpicosecond one; the former vanishes at low temperatures only in the x = 0.080 sample. We argue that the 10 ps timescale demagnetization originates most probably from the diffusive transport of d electrons under the condition of nanoscale magnetic inhomogeneities. The low-temperature fraction of the residual paramagnetic phase can be deduced from the magnitude of the slow reflectivity relaxation component. It is estimated as ≈30% for x = 0.038 and ≈15% for x = 0.062 films. The minimal iron content ensuring the magnetic homogeneity of the ferromagnetic state in the Pd1−xFex alloy at low temperatures is about 7–8 atom %.

The paper presents an effect of mild annealing treatments on structural ordering and open edge morphology of graphite nanoflakes (GNF). Thin graphite flakes were obtained from the bulk highly oriented pyrolytic graphite by a prolonged grinding in a pure argon atmosphere and were annealed at T = 670 K for 24 h either in vacuum or in the air. Modification of GNF open edges was studied with high-resolution transmission electron microscopy (HRTEM) and 2D-Fourier analysis of the open edge area HRTEM-images. The morphology of the GNF edges evolve differently under annealing, revealing itself in the azimuthal width of the two-dimensional fast-Fourier transform (2D-FFT) maxima. After annealing in the air, the width decreased, while the vacuum treatment lead to its growth. We relate the former to the open edge flattening via removal of the edge defects by transformation to the gaseous carbon oxides, the latter - to the opposite process of defect accumulation in vacuum with the transformation of the near-edge structure to the less ordered one. The correlation is found between the intensity of the (101) powder X-ray diffraction maximum and the azimuthal width of the FFT-peaks indicating the direct relation of these quantities.

High-resolution spectroscopic studies of $\mathrm{LaAl}{\mathrm{O}}_{3}$ single crystal doped with holmium ions are reported. Polarized and unpolarized absorption and luminescence spectra were measured in the broad spectral range from 2000 to $23\phantom{\rule{0.16em}{0ex}}000\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--1}$ at temperatures of 4.5--5 K. Additional measurements were fulfilled using site-selective laser spectroscopy. Energies and symmetry properties of the corresponding wave functions of crystal-field levels of ${\mathrm{Ho}}^{3+}$ ions which substitute for ${\mathrm{La}}^{3+}$ ions in $\mathrm{LaAl}{\mathrm{O}}_{3}$ at sites with the ${D}_{3}$ symmetry were determined with high accuracy, and, on this basis, crystal-field calculations were performed. A thorough analysis of spectral line profiles with the fine doublet structure corresponding to singlet-doublet transitions in the trigonal crystal field was made, which showed the existence of the random deformation splitting phenomenon. The value of deformation splitting lies in the region $0.3--0.8\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{--1}$ that substantially exceeds the widths of the doublet hyperfine splitting. The observed line shapes were successfully modeled, assuming the interaction of the ${\mathrm{Ho}}^{3+}$ ions with random deformations of the crystal lattice induced by point defects and ferroelastic domain boundaries.

New measurements of EPR spectra in single crystals CsCdBr3:Yb3+ are presented. The lines due to pairs of Yb3+ ions and single Yb3+ ions are observed. The spectra indicate the existence of several types of single Yb3+ paramagnetic centers. Resolved superhyperfine structure of some lines of these centers is observed for the first time.

Among different magnetic thin films, L10 FePt due to high magnetocrystalline anisotropy is attracting much attention for applications in new generation of magnetic recording media. In this work, switching time and switching mechanism of magnetization as essential properties of L10 FePt film was studied by magneto-optical Kerr effect (MOKE) and time-resolved magneto-optical Kerr effect (TR-MOKE). For this purpose, static in plane and out of plane magnetic hysteresis loop of the 20-nm thick L10 FePt film on (1 0 0) MgO was measured and modeled using polar and longitudinal MOKE and mumax code, respectively. Furthermore, the switching time of magnetization was studied using laser-induced ultrafast demagnetization and relaxation of the sample by TR-MOKE, in which for the first time, the magnetic field was applied in the plane of the sample for this measurement.

In the paper we report on the synthesis, structural and magnetic characterization and time-resolved polar magnetooptical Kerr effect studies of thin epitaxial films of the ordered L1(0)-phase of FePt and FePd compounds. Time scales of the photoinduced demagnetization and magnetization recovery are found. It is shown that demagnetization of FePt and FePd films occurs on different time scales, similar to 0.2 ps and similar to 3 ps, respectively. This difference makes these films promising for artificial multilayer ferrimagnets with high perpendicular anisotropy suitable for all-optical fast high-capacity information storage devices.

Exchange-coupled BiFeO3/ferromagnet thin film heterostructures are promising for a fast and power efficient control of magnetization of the ferromagnetic layer. In the paper, the results of the study of magnetic properties of the epitaxial Fe2B/BiFeO3 heterostructure on (001)-SrTiO3 substrate with ferromagnetic resonance (FMR) spectroscopy are presented. The hierarchy of magnetic anisotropies that determine the angular variation of the resonance field in-plane and in-/out-of the plane of the system include the tetragonal four-fold and uniaxial terms for the Fe2B layer, uniaxial term for antiferromagnetic BiFeO3 layer and the exchange coupling at the interface. We find out that the exchange bias direction can be switched by a strong enough applied magnetic field. Both the exchange bias and an in-plane FMR resonance field of the heterostructure are strongly affected by the illumination with lambda = 405 nm light. An optical tunability of the exchange bias and ferromagnetic resonance fields of the heterostructure has been demonstrated. (C) 2018 Elsevier B.V. All rights reserved.

A study of high-quality SrTiO3 single crystals doped with the Mn4+ ions in the cubic phase (T > 105 K) with X-band electron paramagnetic resonance reveals direct correspondence between a shape of a sample and magnetic anisotropy of the impurity Mn4+ centers. In particular, for a sample with the shape of a square base rectangular prism, a size of (a x a x h) and faces perpendicular to the < 100 > crystallographic directions, zero-field splitting parameter D is approximately proportional to (a/h - 1) quantity. Temperature dependence of D indicates that this peculiar symmetry lowering is a feature characteristic for the cubic Fm3m phase of the strontium titanate. Diminishing of the D value with the decrease of the surface roughness for a thin (001)-oriented SrTiO3:Mn platelet shows that the observed effect originates from the sample surface.

Electron paramagnetic resonance (EPR) study of the impurity Gd3+ ions in the multi-site SrY2O4 crystal iso-structural to the magnetically-frustrated SrGd2O4 compound is reported. Analysis of the angular dependences of the EPR spectra at room temperature allowed us to establish the spin-level energy patterns in the ground states of the Gd3+ ions at the Y(1) and Y(2) sites. Parameters of the spin-Hamiltonian in the frames related to the crystal axes and to the principal center axes are determined.

The paper deals with the processes of producing materials with new electrochemical properties by ion implantation method. Both the positive and negative processes accompanied implantation are considered. The paper generalizes the promising examples of the use of ion implantation method for improving the corrosion resistance and activity of electrocatalysts.

The methods of calculating the parameters of the thermodynamic model sander obtained by electrical analogies. The presented model allows to study the interaction of elastic and thermal dynamic processes during grinding. Process, and thermal subsystem process abrading internal thermal barrier coatings are presented in the form of electrical circuits. Calculation of temperature and power parameters of the grinding process is carried out numerically using nodal analysis used in electrical engineering. The paper presents the dependences for determining equivalent circuit parameters that reflect the processes of heat transfer in the cutting zone during grinding. Considered parameters electrothermal models describe the distribution of heat flow between the chip, the workpiece and the grinding wheel grain.

The problem of calculating the values of the thermal resistance of the element in the cutting zone electrothermal replacement scheme for the analysis of thermal processes for grinding internal thermal barrier coatings was study. Electrothermal model includes thermal resistance, heat capacity and voltage sources, which provide an adequate modeling of thermal processes in the zone of contact interaction of grain grinding wheel with machined surface thermal barrier coating. The potentials at the nodal points of the equivalent system reflect the average temperature characteristic elements of the original system, including the workpiece, chips and grains of the grinding wheel. On the basis of the replacement scheme electrothermal established between the heat flow in the area of the abrasion. Examples of calculation of temperature and cutting forces during grinding rubber heat-resistant coating. This mathematical model is designed for the management of technological regimes of the grinding process in order to improve the quality of the machined surface