Spin-transfer torque based damping control of parametrically excited spin waves in a magnetic insulator

TL;DR

This study demonstrates control over spin-wave damping in a YIG/Pt bilayer using spin transfer torque induced by a dc current, achieving significant damping variation through the spin Hall effect.

Contribution

It introduces a method to modulate spin-wave damping in magnetic insulators via spin transfer torque driven by a dc current in an adjacent metal.

Findings

Damping variation of ±7.5% achieved at 5×10^10 A/m^2 current density.

Damping can be increased or decreased depending on current polarity.

Spin Hall effect induces spin currents that exert torque on YIG spin waves.

Abstract

The damping of spin waves parametrically excited in the magnetic insulator Yttrium Iron Garnet (YIG) is controlled by a dc current passed through an adjacent normal-metal film. The experiment is performed on a macroscopically sized YIG(100nm)/Pt(10nm) bilayer of 4x2 mm^2 lateral dimensions. The spin-wave relaxation frequency is determined via the threshold of the parametric instability measured by Brillouin light scattering (BLS) spectroscopy. The application of a dc current to the Pt film leads to the formation of a spin-polarized electron current normal to the film plane due to the spin Hall effect (SHE). This spin current exerts a spin transfer torque (STT) in the YIG film and, thus, changes the spin-wave damping. Depending on the polarity of the applied dc current with respect to the magnetization direction, the damping can be increased or decreased. The magnitude of its variation is proportional to the applied current. A variation in the relaxation frequency of +/-7.5% is achieved for an applied dc current density of 5*10^10 A/m^2.