Effect of spin relaxations on the spin mixing conductances for a bilayer structure

TL;DR

This paper investigates how spin relaxations, modeled via non-Hermitian Hamiltonians, influence the effective spin mixing conductance in bilayer structures, revealing potential for its enhancement through non-Hermitian effects.

Contribution

It introduces a non-Hermitian approach to model spin relaxations and derives the resulting effective spin-transfer torque and conductance, highlighting their dependence on system parameters and potential enhancement.

Findings

Effective spin mixing conductance can be enhanced in non-Hermitian systems.

The conductance depends on insulating gap, s-d coupling, and layer thickness.

Relations between real and imaginary parts of conductance are analyzed.

Abstract

The spin current can result in a spin-transfer torque in the normal-metal(NM)|ferromagnetic-insulator(FMI) or normal-metal(NM)|ferromagnetic-metal(FMM) bilayer. In the earlier study on this issue, the spin relaxations were ignored or introduced phenomenologically. In this paper, considering the FMM or FMI with spin relaxations described by a non-Hermitian Hamiltonian, we derive an effective spin-transfer torque and an effective spin mixing conductance in the non-Hermitian bilayer. The dependence of the effective spin mixing conductance on the system parameters (such as insulating gap, \textit{s-d} coupling, and layer thickness) as well as the relations between the real part and the imaginary part of the effective spin mixing conductance are given and discussed. We find that the effective spin mixing conductance can be enhanced in the non-Hermitian system. This provides us with the possibility to enhance the spin mixing conductance.