Spin Seebeck effect and magnon-magnon drag in Pt/YIG/Pt structures

The formation of the two: injected ("coherent") and "thermally" excited, different in energies magnon subsystems and the influence of its interaction with phonons and between on drag effect under spin Seebeck effect conditions in the magnetic insulator part of the metal/ferromagnetic insulator/metal structure is studied. An approximation of the effective parameters, when each of the interacting subsystems ("injected", "thermal" magnons, and phonons) is characterized by its own effective temperature and drift velocities have been considered. The analysis of the macroscopic momentum balance equations of the systems of interest conducted for different ratios of the drift velocities of the magnon and phonon currents show that the "injected" magnons relaxation on the "thermal" ones is possible to be dominant over its relaxation on phonons. This interaction will be the defining in the forming of the temperature dependence of the spin-wave current under spin Seebeck effect conditions, and inelastic part of the magnon-magnon interaction is the dominant spin relaxation mechanism.