Broadband optomechanical transduction of nanomagnetic spin modes

Abstract

The stable vortex state that occurs in micron-scale magnetic disks is one of the most interesting and potentially useful phenomena in nanomagnetism. A variety of tools have been applied to study the vortex state and collective spin excitations corresponding to harmonic motion of the vortex, but to-date, these tools either have measured strongly driven vortex resonances or have been unable to simultaneously measure static properties such as the magnetization. Here, we show that by combining the sensitivity of cavity optomechanics with the technique of torque-mixing magnetic resonance spectroscopy, we are able to measure the magnetization, in-plane susceptibility, and spin resonances of individual vortices in the low-drive limit. These measurements demonstrate the complex behavior of the vortex as it moves through the pinning landscape of the disk. Furthermore, we observe gyrotropic resonances as high as 1.1 GHz, suggesting the use of engineered defects for applications such as microwave-to-optical wavelength conversion.