Nanodiamond Sensing of Stray Fields during Domain Reversal
Quantitative measurement of nanoscale stray magnetic fields during domain reversal is important for understanding and optimizing magnetic memory and logic devices. Yet, achieving high spatial resolution with minimally invasive probes remains challenging. Here we demonstrate nanodiamonds (NDs) hosting an ensemble nitrogen vacancy (NV) centers as local quantum sensors of domain-reversal stray fields in a CoFeB strip. During magnetic-field-driven reversal, the ND sensors resolve three distinct local responses depending on their positions relative to the strip: a positive frequency jump at the edge, an unexpected negative jump just outside the strip, and a negligible change near the center. These contrasting signals are quantitatively explained by magnetostatic boundary fields from micromagnetic simulations. We further implement a fully constrained fitting procedure for optically detected magnetic resonance spectra, enabling robust field extraction even when resonances are partially resolved. Together, these results establish NV-ND magnetometry as a simple, transferable, and quantitative approach for characterizing spatially heterogeneous magnetic fields in thin-films and spintronic devices.