Spin Seebeck effect and phonon energy transfer in heterostructures containing layers of a normal metal and a ferromagnetic insulator

This is the final version. Available from the American Physical Society via the DOI in this recordIn the framework of the kinetic approach based on the Boltzmann equation for the phonon distribution function, we analyze phonon heat transfer in a heterostructure containing a layer of a normal metal (N) and a layer of a ferromagnetic insulator (F). Two realistic methods for creating a temperature gradient in such a heterostructure are considered: by heating the N layer by an electric current and by placing the N/F bilayer between massive dielectrics with different temperatures. The electron temperature Te in the N layer and the magnon temperature Tm in the F layer are calculated. The difference in these temperatures determines the voltage VISHE on the N layer in the Seebeck spin effect regime. The dependence of VISHE on the bath temperature and on the thickness of the N and F layers is compared with the available experimental data.European Union Horizon 202

Role of magnons and the size effect in heat transport through an insulating ferromagnet/insulator interface

This is the final version. Available from the American Physical Society via the DOI in this recordWhile recent experiments on the spin Seebeck effect have revealed the decisive role of the magnon contribution to the heat current Q in hybrid systems containing thin ferromagnetic layers, the available acoustic mismatch theory does not account for their magnetic properties. Here, we analyze theoretically the heat transfer through an insulating ferromagnet (F) sandwiched between two insulators (I). Depending on the relation between the F thickness d, and the mean free path of phonons generated by magnons lls, we reveal two qualitatively different regimes in the nonlinear heat transport through the F/I interfaces. Namely, in thick F layers the regime of conventional "Joule" heating with Q-Ts4 is realized, in which the detailed structure of the F/I interfaces is inessential. Here Ts is the magnon temperature. By contrast, in thin F layers with dlls, most of the phonons emitted by magnons can leave F without being absorbed in its interior, giving rise to the magnon overheating regime with Q-Tsm and m-7. Conditions for the examination of both regimes and the determination of Ts from experiments are discussed. The reported results are relevant for the theoretical analysis of the spin Seebeck effect and the development of magnon-based spin caloritronic devices.European Union Horizon 202

Temperature dependence of the magnon-phonon energy relaxation time in a ferromagnetic insulator

This is the final version. Available from the American Physical Society via the DOI in this recordWe have used the Boltzmann kinetic equation for the phonon distribution function to analyze the relaxation kinetics of the spin system of a ferromagnetic insulator (F) lying on a massive dielectric substrate with high thermal conductivity. Under periodic heating of the spin system, the relaxation depends on the thickness of the F layer and on the frequency of the thermal source ω. When the thickness of the F layer is much greater than the phonon-magnon scattering length, the magnon temperature dependence on the frequency has two features related to specific characteristic times of the system. One of them determines the dependence in the low-frequency regime and is related to the average phonon escape time from the F layer to the substrate τes. In turn, the high-frequency behavior is determined by the magnon-phonon collisions time τmp. From the latter, the time of phonon-magnon collisions τpm can be found. In contrast, the response of effectively thin F layers is characterized by just one feature, which is determined by the time τmp. Thus, based on the obtained theoretical results, the times τes,τmp, and τpm can be deduced from experiments on the parametric excitation of spin waves by electromagnetic radiation modulated at frequency ω.European Union Horizon 202

Peculiarities of pseudogap in Y0.95Pr0.05Ba2Cu3O7−δ single crystals under pressure up to 1.7 GPa

The effect of hydrostatic pressure up to P = 1.7 GPa on the fluctuation conductivity σ′(T) and pseudogap ∆*(T) in Y0.95Pr0.05Ba2Cu3O7-δ single crystal with critical temperature Тс = 85.2 K (at P=0) was investigated. The application of pressure leads to the increase in Tc with dTc/dP = +1.82 K∙GPa-1 while the resistance decreases as dlnρ(100K)/dP = - (10.5±0.2) %∙GPa-1. Regardless of the pressure, in the temperature interval from Tc to T0 (~ 88 K at P = 0) the behaviour of σ′(T) is well described by the Aslamazov – Larkin (AL – 3D) fluctuation theory, and above the T0 by the Lawrence – Doniach theory (LD). The Maki-Thompson (MT – 2D) fluctuation contribution is not observed. This indicates the presence of structural defects in the sample induced by Pr. Here it is determined for the first time that when the pressure is applied to the Y1-xPrxBa2Cu3O7-δ single crystal, the pseudogap increases as dlnΔ*/dP = 0.17 GPa–1