Nanodiamond Sensing of Stray Fields during Domain Reversal

Quantitative measurement of nanoscale stray magnetic fields during domain reversal is important for optimizing magnetic memory and logic devices. Yet, achieving high spatial resolution with minimally invasive probes remains challenging. Here we demonstrate nitrogen vacancy centers in nanodiamonds (NDs) as local sensors 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 extend ND magnetometry to quantitatively characterize heterogeneous stray fields during magnetic domain reversal in thin films and spintronic devices.