Nanoscale Mapping of Magnetic Auto-oscillations with a single Spin Sensor

TL;DR

This study uses a single spin quantum sensor to nanoscale image magnetic auto-oscillations in spin Hall nano-oscillators, revealing that auto-oscillation spots are determined by magnetic field minima, which act as potential wells for spin-waves.

Contribution

It introduces a novel quantum sensing method to directly image auto-oscillation sources and demonstrates the role of magnetic field minima in mode formation in SHNOs.

Findings

Auto-oscillation spots are located at magnetic field minima.

Magnetic stray field magnitude correlates with auto-oscillation mode frequencies.

Single spin sensors enable rapid, nanoscale imaging of auto-oscillations.

Abstract

Magnetic auto-oscillations are damping-compensated magnetization precessions. They can be generated in spin Hall nano-oscillators (SHNO) among others. Current research on these devices is dedicated to create next generation energy-efficient hardware for communication technologies. However, the underlying physics governing the formation of auto-oscillation modes, their output power and line width in a single SHNO device have remained elusive so far. We image the sources of magnetic auto-oscillations in a metallic SHNO using a single spin quantum sensor. We directly measure the microwave field generated by an auto-oscillation spot at the nanoscale by driving the electron spin resonance transition of the sensor spin, enabling faster acquisition speed (100 ms/pixel). Instead of being defined by the points of the largest antidamping only, we experimentally demonstrate for the first time with quantitative magnetometry that the auto-oscillation spots are determined by the positions of the magnetic field minima. The latter act as local potential wells for confining spin-waves, thus supporting large amplitude auto-oscillations. By comparing the magnitude of the magnetic stray field at these spots, we decipher the different frequencies of the auto-oscillation modes. The insights gained regarding the interaction between auto-oscillation modes and spin-wave potential wells enable advanced engineering of real devices.