Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor

TL;DR

This paper demonstrates the use of a single NV center in diamond to locally probe and characterize spin-torque oscillations in a magnetic insulator, revealing detailed spin-wave mode behavior and auto-oscillation phenomena.

Contribution

It introduces a novel method for nanoscale magnetic field measurement using NV centers to study spin-torque oscillators in insulators, enabling detailed mode analysis and damping control.

Findings

Resolved multiple spin-wave modes with NV sensing

Observed auto-oscillation with reduced linewidth

Achieved synchronization of STO to external microwave

Abstract

Coherent, self-sustained oscillation of magnetization in spin-torque oscillators (STOs) is a promising source for on-chip, nanoscale generation of microwave magnetic fields. Such fields could be used for local excitation of spin-wave resonances, control of spin qubits, and studies of paramagnetic resonance. However, local characterization of fields emitted by an STO has remained an outstanding challenge. Here, we use the spin of a single nitrogen-vacancy (NV) defect in diamond to probe the magnetic fields generated by an STO in a microbar of ferromagnetic insulator yttrium-iron-garnet (YIG). The combined spectral resolution and sensitivity of the NV sensor allows us to resolve multiple spin-wave modes and characterize their damping. When damping is decreased sufficiently via spin injection, the modes auto-oscillate, as indicated by a strongly reduced linewidth, a diverging magnetic power spectral density, and synchronization of the STO frequency to an external microwave source. These results open the way for quantitative, nanoscale mapping of the microwave signals generated by STOs, as well as harnessing STOs as local probes of mesoscopic spin systems.