Spatially resolved frequency jump in NV quantum sensing of domain wall movement in CoFeB magnetic thin films

Nitrogen-vacancy (NV) magnetometry has emerged as a powerful technique in condensed matter physics, particularly for investigating superconductivity and magnetism, owing to its exceptional spatial resolution and magnetic field sensitivity. Among various implementations, fluorescent nanodiamonds (FNDs) offer a cost-effective platform that minimizes the standoff distance between NV centers and the sample. When the FND size is reduced below the optical diffraction limit, spatial resolution is further enhanced. Here, we employ FND-based NV magnetometry to probe the domain-wall-induced magnetic field texture in a CoFeB strip. FNDs were drop-cast onto a patterned CoFeB structure, resulting in an approximate density of ten FNDs within a 35 × 35 µm² scanning area. By monitoring individual FNDs at different locations, we observe domain-wall motion induced by either an external magnetic field or a direct current. At specific field strengths, discrete jumps in the optically detected magnetic resonance frequency are observed, corresponding to domain walls moving past the FND.