Imaging AC magnetization response of soft magnetic thin films using diamond quantum sensors

The energy loss in inductor core is a significant limitation in high-frequency power electronics. For evaluating and optimizing soft magnets, simultaneous imaging of both amplitude and phase of AC stray fields beyond 10 kHz is crucial. Here, we develop an imaging technique for analyzing AC magnetization response using diamond quantum sensors. For frequencies up to 200 kHz, we propose a measurement protocol, Qubit Frequency Track (Qurack), where microwave frequency modulation tracks qubit frequency oscillations. For higher frequencies above MHz, quantum heterodyne (Qdyne) imaging is employed. The soft magnetic CoFeB–SiO2 thin films, developed for high-frequency inductors, exhibit near-zero phase delay up to 2.3 MHz, indicating negligible energy loss. Moreover, the energy loss depends on the anisotropy: when the magnetization is driven along the easy axis, phase delay increases with frequency, signifying higher energy dissipation. These results suggest potential applications in analyzing soft magnets and improving the performance of power electronics. To efficiently optimize soft magnets for high-frequency applications, simultaneous imaging of both amplitude and phase of AC stray fields is essential. Here, an imaging technique for analyzing AC magnetization response from DC to 2.3 MHz is developed using diamond quantum sensors with nitrogen-vacancy centers.