The resonance spin rectification (RSR) and resonance magnetoresistance (RMR) have been studied on La_2/3Sr_1/3MnO₃ epitaxial thin films in the temperature range of 300-365 K, including the Curie point (T_C). The RSR effect is found to be caused by anisotropic magnetoresistance under conditions of the magnetic-resonance microwave pumping; it decreases upon heating and disappears at T_C. Unlike that, the RMR is maximal at T_C and shows clear correlation with the colossal magnetoresistance (CMR) of the material under study. The interpretation implies decreasing of the sample magnetization due to resonance saturation, thus leading to an increase in electric resistivity in terms of the CMR mechanism. Quantitative agreement is demonstrated between the experimental RMR data and theory accounting for Bloch-type relaxation in the vicinity of the phase transition.

The process of self-diffusion of particles confined to porous solids is studied for time intervals corresponding to particle displacements shorter than the characteristic pore size. The solid matrix is modeled as a (random) potential field with an infinitely large potential within the solid which decays to zero at distances of the order of a few particle sizes from the pore walls. Diffusion of particles in the thus created potential field is described by the Smoluchowski diffusion equation. It is shown that, for short diffusion times, the resulting equation for the time-depended diffusivity reproduces that earlier obtained in the literature [Mitra et al., Phys. Rev. Lett. 68, 3555 (1992)], but with the numerical constant differing by factor 2. The conditions under which this discrepancy arises are highlighted and discussed.

Is it possible to suggest a general theory for consideration of reproducible data that are measured in many experiments? One can prove that successive measurements have a memory and this important fact allows separate all data on two large classes: ideal experiments without memory and experiments with a memory. We introduce the concept of an intermediate model (IM) that helps to describe quantitatively a wide class of reproducible data. Experiments with memory require for their description the Prony's decomposition while experiments without memory are needed for their presentation the Fourier decomposition only. In other words, it means that a measured function extracted from reproducible data can have a universal description in the form of the amplitude-frequency response (AFR) that belongs to the generalized Prony's spectrum (GPS). It is shown also how real data distorted by the experimental equipment and how to eliminate these uncontrollable factors in order to reproduce approximately the conditions corresponding to ideal experiment. New and elegant solution of elimination of the apparatus (instrument) function is suggested. In an ideal case the decomposition coefficients belong to the Fourier transform and presentation of reproducible data in this form leads to the IM for this case. The suggested general algorithm allows considering many experiments from the unified point of view. The real example based on available electron paramagnetic resonance (EPR) data confirms this general concept. The unified “bridge” between the treated experimental data and a set of competitive hypothesis that pretend for their description is discussed. The results obtained in this paper help to put forward a new paradigm in data/signal processing.

Within the framework of the London model the distribution of local magnetic field near the surface of plate of anisotropic type-II superconductor is found when the external magnetic field is perpendicular to the axis of symmetry of the crystal. There is obtained the distribution of the local magnetic field depending on the distance to the surface of the superconducting plate. It is shown that the lineshape of distribution of local magnetic field near the surface changes considerably as compared with the distribution in the depth of massive superconductor. This change should be taken into account when interpreting experimental data on the observation of the local magnetic field in the near-surface region of massive superconductor and in thin superconducting films (thickness is less than the depth of penetration of the magnetic field in the superconductor).

The relaxation of Yb³⁺ in YBa₂Cu₃O_x (x = 6.1 and 6.4) was studied using Electron Paramagnetic Resonance (EPR). In these samples the Yb³⁺ relaxation is dominated by a phonon mechanism. It was shown that the conventional Raman two-phonon process involving acoustic phonons can not describe the temperature dependence of the Yb³⁺ relaxation. Instead, the Raman process involving optical phonons or an Orbach-like process via the excited vibronic levels of Cu²⁺ ions with energy Ω = 500(50) K is responsible for the phononic part of the Yb³⁺ relaxation in YBa₂Cu₃O_x. The present results provide clear experimental evidence that optical phonons or local vibrations are the dominant source of spin-lattice relaxation at sufficiently high temperatures, which cannot be described by the traditional approach using the Debye approximation.

We derive the dynamical spin susceptibility in the t-J-G model combining the random phase approximation (RPA) and projection operator method, which allows describing the mutual interplay between the local and the itinerant components of susceptibility. Near the antiferromagnetic wave vector the calculated dispersion of the spin excitations reproduces well the so-called hour-glass dispersion, characteristic for several layered cuprates. It is formed as a result of competition between the original spin-gap in magnon-like excitations spectrum and the superconducting gap, which affects the itinerant component of the susceptibility. Furthermore, the calculated collective spin excitations along (0,0)-(0,π) are in agreement with the positions of the absorption peaks in the inelastic X-ray scattering spectra. They refer to the paramagnon-like modes, characteristic to the itinerant spin system, rather than magnon-like excitations that originate from short range order effect in the system of local spins at Cu sites.

Role of bottlenecked spin relaxation and proportionality between small polaron hopping conductivity and electron paramagnetic resonance (EPR) linewidth (intensity) was emphasized. This idea gave a background for several experimental and theoretical investigations and it was starting point for its further generalization on variable range hopping conductivity and its influence on EPR linewidth in rare earth manganites.

Review of our recent results concerning the spin valve effect are presented. Using the spin switch design F1/F2/S proposed theoretically that comprises a ferromagnetic bilayer (F1/F2) as a ferromagnetic component, and an ordinary superconductor (S) as the second interface component, we have realized for the first time a full spin switch effect for the superconducting current. For CoO_x/Fe1/Cu/Fe2/In multilayered systems with varying Fe2-layer thickness we observed the sign-changing oscillating behavior of the spin valve effect ΔT_c = T_c^AP - T_c^P  (here T_c^AP and T_c^P are the superconducting transition temperatures for antiparallel and parallel orientations of magnetizations of the F1 and F2 layers, respectively). We have also studied the angular dependence of T_c for the spin valve system CoO_x/Fe1/Cu/Fe2/Pb. We found that this dependence is nonmonotonic when passing from the parallel to the antiparallel case of mutual orientation of magnetizations of the Fe1 and Fe2 layers and reveals a distinct minimum near the orthogonal configuration. The analysis of the data in the framework of the superconducting triplet spin valve theory gives direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the two magnetizations.

This paper is a brief review of investigations, which were carried out during last years by team of magnetic nanostructures and spintronics laboratory, and is dedicated to the 80th anniversary of our Teacher - professor B.I. Kochelaev.

LaCu₃Ru_xTi_4-xO₁₂ undergoes a metal-to-insulator transition (MIT) from a heavy-fermion metal (x = 4) with moderately enhanced electronic masses to an antiferromagnetic insulator (x = 0) with colossal dielectric constants. So far, the exact value x_c of the MIT could not be obtained from electrical resistivity or specific-heat data, which are governed by local-moment scattering and Schottky anomalies, respectively. To investigate the MIT by electron spin resonance (ESR) technique, polycrystalline samples of the solid-solution series La_1-yGd_yCu₃Ru_xTi_4-xO₁₂ were synthesized for the substitution range 1 ≤ x ≤ 4 and 0.05 ≤ y ≤ 0.15, where Gd³⁺ (⁸S_7/2 ground state) serves as ESR probe. For x = 4 the Gd³⁺ ESR linewidth exhibits an enhanced Korringa relaxation at low temperatures (T<50 K) as typically expected for heavy-fermion metals. This metallic contribution gradually diminishes on decreasing Ru content x and vanishes for x = 2.25 localizing the MIT close to the onset of spin-glass behavior arising for x ≤ 2.