Optically Detected Ferromagnetic Resonance in Metallic Ferromagnets via Nitrogen Vacancy Centers in Diamond

TL;DR

This paper demonstrates a method to detect ferromagnetic resonance in thin films using nitrogen-vacancy centers in diamond, revealing a new way to perform nanoscale magnetic microscopy without direct frequency matching.

Contribution

It introduces a novel optically detected FMR technique utilizing NV centers, expanding the capabilities of magnetic sensing and microscopy at the nanoscale.

Findings

ODFMR signals depend on NV-ferromagnet separation

Spinwave-induced dipolar fields cause NV relaxation during FMR

Method enables nanoscale ferromagnetic resonance sensing

Abstract

We report quantitative measurements of optically detected ferromagnetic resonance (ODFMR) of ferromagnetic thin films that use nitrogen-vacancy (NV) centers in diamonds to transduce FMR into a fluorescence intensity variation. To uncover the mechanism responsible for these signals, we study ODFMR as we 1) vary the separation of the NV centers from the ferromagnet (FM), 2) record the NV center longitudinal relaxation time $T_1$ during FMR, and 3) vary the material properties of the FM. Based on the results, we propose the following mechanism for ODFMR. Decay and scattering of the driven, uniform FMR mode results in spinwaves that produce fluctuating dipolar fields in a spectrum of frequencies. When the spinwave spectrum overlaps the NV center ground-state spin resonance frequencies, the dipolar fields from these resonant spinwaves relax the NV center spins, resulting in an ODFMR signal. These results lay the foundation for an approach to NV center spin relaxometry to study FM dynamics without the constraint of directly matching the NV center spin-transition frequency to the magnetic system of interest, thus enabling an alternate modality for scanned-probe magnetic microscopy that can sense ferromagnetic resonance with nanoscale resolution.