Current-induced spin wave excitation in Pt|YIG bilayer

TL;DR

This paper presents a comprehensive theory for current-induced spin wave excitation in Pt|YIG bilayers, accounting for complex interactions and surface effects, and explains experimental observations through mode-specific dynamics.

Contribution

It introduces a self-consistent model that incorporates dipolar interactions, surface anisotropy, and spin pumping, revealing mode-dependent excitation and spectral shifts.

Findings

Spin transfer torque can excite multiple modes simultaneously.

Spin pumping influences surface modes more than bulk modes.

Surface anisotropy modes are essential to match experimental results.

Abstract

We develop a self-consistent theory for current-induced spin wave excitations in normal metal-magnetic insulator bilayer systems, thereby establishing the relation between spin wave excitation and the experimentally controlled parameters. We fully take into account the complex spin wave spectrum including dipolar interactions and surface anisotropy as well as the spin-pumping at the interface. Our results focus on the mode-dependent power close to the critical currents for spin wave excitation. The major findings are (a) the spin transfer torque can excite different spin-wave modes simultaneously; (b) spin pumping counterbalances spin-transfer torque and affects the surface modes more than the bulk modes; (c) spin pumping inhibits high frequency spin-wave modes, thereby redshifting the excitation spectrum. We can get agreement with experiments on yttrium iron garnet|platinum bilayers by postulating the existence of surface anisotropy modes.