This note is dedicated to Professor B.I. Kochelaev on the occasion of his 85th anniversary.

In this article I present a short review on the intense and fruitful collaboration of Boris Kochelaev with our group around K. Alex Müller at the Physics Institute of the University of Zurich. I will not only focus on the scientific part of this collaboration, but also rather on the human and social side of Boris as a friend and scientist.

Pure spin current induced by ferromagnetic resonance (FMR) excitation in thin-film heterostructures consisting of ferromagnetic (FM) and normal metal (NM) layers is studied as a function of FMR line shape and width. Experiments were carried out with thin films of ferromagnetic La_2/3Sr_1/3MnO₃ (LSMO) grown epitaxially on NdGaO₃ substrate and covered with Pt. The spin current injected into the NM layer was measured using the inverse spin Hall effect (ISHE) in the temperature range of 100-350 K. The samples under study revealed different width of the FMR line, which was attributed to inhomogeneous broadening with a specific Voigt shape of the ISHE signal. To take this effect into account, substantial corrections are proposed to the existing theory of spin pumping.

The analytical expressions for the energy coupling of exchange coupled spins with electric field, induced by odd crystal field has been derived in the third order perturbation theory, combining the action of electric field, spin-orbit and exchange interactions. The magnetoelectric coupling due to the partial replacement of the Cu²⁺ positions by Li⁺ in LiCuVO₄ has been discussed.

A brief review of investigations carried out in recent years by teams of the Laboratory of Physics of Magnetic Nanostructures and Spintronics and the Laboratory of the Synthesis and Analysis of Thin-Film Systems is presented.

Fluctuations of various order parameters are considered as the significant components of understanding the mechanism of high-T_c superconductivity. To study these fluctuations in the cuprate and Fe-based superconductors we use the joint measurements of direct current resistivity and non-resonant microwave absorption. Comparing data obtained with both methods allowed us to extract the contribution of dynamic charge density waves in La_2−xSr_xCuO₄, superconducting fluctuations in Bi₂Sr₂Ca_1−xY_xCu₂O₈ and nematic fluctuations in FeTe_1−xSe_x.

We report on ESR measurements in polycrystalline LaFeAsO and PrFeSbO and in single crystalline Mn-doped Ba(Fe_0.975Mn_0.025)₂As₂. The absorption spectrum can be described by a broad resonance line with Lorentzian lineshape. The intensity of the resonance absorption follows the temperature dependence of the dc-susceptibility and mirrors the spin-density wave anomaly, while the linewidth roughly agrees with the electrical resistivity.

Magnetoelectric materials with coupled and microscopically coexisting magnetic and electric polarizations have attracted great interest. The motivation behind this interest stems from the novel and interesting physical phenomena involved, but also from possible applications for novel electronic devices. Here we demonstrate the existence of magnetoelectric coupling at room temperature in ferrimagnetic Y-type hexaferrite Ba_0.6Sr_1.4Zn₂Fe₁₂O₂₂ single crystal. By using a recently developed electrically modulated magnetic resonance spectroscopy, we determined quantitatively the magnetoelectric coupling strength in this compound. Obtained results show that Y-type hexaferrites belong to the rare class of materials with significant magnetoelectric coupling and large magnetic moment at room temperature.

In this paper, a new method for restoration of the desired correlations is proposed. It allows to evaluate the "content" of the external factors (l = 1, 2,..., L) setting in the form of data arrays y_m^(l)(x) (m = 1, 2,..., M) inside the given Y_m(x) function that is supposed to be subjected by the influence of these factors. As contrasted to the conventional correlation analysis, the proposed method allows finding the "influence" functions b_l(x) (l = 1, 2,..., L) and evaluating the "remnant" array G_m(x) that is remained as a "quasi-independent" part from the influence of the factors y_m^(l)(x). The general expression works as a specific "balance" and reproduces the wellknows cases, when b_l(x) = C_l (it is reduced to the linear least square method with G_m(x) ≅ 0) and coincides with the remnant function Y_m(x) ≅ G_m(x), when the influence functions becomes negligible (b_l(x) ≅ 0). The available data show that the proposed method allows to extract a small signal from the "pattern" background and it conserves its stability/robustness in the presence of a random fluctuations/noise. The method is rather flexible and allows to consider the cases of strong correlations, when the external factors act successively, forming the causeand-effect chains. It can be generalized for expressions containing the bonds expressed in the form of memory functions. The proposed method adds new quantitative ties expressed in the form of the desired functions to the conventional correlation relationships expressed in the form of the correlation coefficients forming, in turn, the correlation matrices. New relationships allow to understand deeper the existing correlations and make them more informative, especially in detection of the desired deterministic and stable bonds/laws that can be hidden inside.

In the framework of a density functional theory, an ab initio calculation of a band structure of single-layer graphene doped by nitrogen atoms was carried out. It is established that structural and electronic properties of such systems are strongly influenced by a dopant concentration and its location in a crystal lattice of graphene. Effects of doping of the graphene monolayer on its electronic spectrum are studied. These results indicate a possibility to regulate a band gap width by an appropriate choice of the dopant concentration and its location in the crystal lattice of graphene.

Resonant tunneling is studied theoretically for the asymmetric double-barrier antiferromagnetic tunnel junction (DAMTJ) with a bias voltage is applied. In this nanostructure, the direction of magnetization of the middle ferromagnetic layer is parallel (antiparallel) to the direction of magnetization of the top layer and antiparallel (parallel) to the direction of magnetization of the bottom ferromagnetic layer. Analytical expression for the transmission coefficient of the double-barrier nanostructure is received, which is expressed through single-barrier transmission coefficients taking into account the voltage drop on each barrier and spin degrees of freedom of the electron conductivity. The theoretical model of spin-polarized conductance and tunnel magnetoresistance in asymmetric DAMTJ in the quasi-classical approximation is developed. The dependences of the transmission coefficient and tunnel magnetoresistance on the applied voltage under resonant conditions are shown.

Resonant tunneling is studied theoretically for the asymmetric double-barrier antiferromagnetic tunnel junction (DAMTJ) with a bias voltage is applied. In this nanostructure, the direction of magnetization of the middle ferromagnetic layer is parallel (antiparallel) to the direction of magnetization of the top layer and antiparallel (parallel) to the direction of magnetization of the bottom ferromagnetic layer. Analytical expression for the transmission coefficient of the double-barrier nanostructure is received, which is expressed through single-barrier transmission coefficients taking into account the voltage drop on each barrier and spin degrees of freedom of the electron conductivity. The theoretical model of spin-polarized conductance and tunnel magnetoresistance in asymmetric DAMTJ in the quasi-classical approximation is developed. The dependences of the transmission coefficient and tunnel magnetoresistance on the applied voltage under resonant conditions are shown.