Quantum imaging to aid magnetics design in power electronics
A research team led by Professor Mutsuko Hatano from the School of Engineering, Institute of Science Tokyo, Japan, has developed a novel method for analysing energy losses in soft magnetic materials by simultaneously imaging the amplitude and phase of AC stray fields.
These magnetic fields are key to understanding hysteresis losses. Energy losses at high frequencies are a key challenge in miniaturisation and achieving high efficiency in power electronics. The study was conducted in collaboration with Harvard University and Hitachi, Ltd.
The team utilised a diamond quantum sensor with nitrogen-vacancy (NV) centres and developed two protocols to provide wide-range AC magnetic field imaging. The protocols developed are Qubit Frequency Tracking (Qurack) for kHz and quantum heterodyne (Qdyne) imaging for MHz frequencies.
A proof-of-principle wide-frequency-range magnetic field imaging experiment was conducted by applying an alternating current to a 50-turn coil and sweeping the frequency from 100 Hz to 200 kHz for Qurack and 237 kHz to 2.34 MHz for Qdyne. In the experiment, the researchers used NV centres to validate both measurement protocols by visualising the amplitude and phase of the uniform AC Ampere magnetic field with a high spatial resolution (2–5 µm).
The imaging system enabled the team to simultaneously map the amplitude and phase of stray magnetic fields from CoFeB–SiO₂ thin films, which have been developed for high-frequency inductors. The findings showed that these films exhibit near-zero phase delay up to 2.3 MHz, indicating negligible energy losses along the hard axis. Moreover, they observed that energy loss depends on the material’s magnetic anisotropy—when magnetisation is driven along the easy axis, phase delay increases with frequency, signifying higher energy dissipation.
The results demonstrate how quantum sensing can be used to analyse soft magnetic materials operating at higher frequencies, a significant challenge in developing highly efficient electronics. In particular, the capacity to resolve domain wall motion, one of the magnetisation mechanisms strongly related to energy losses, is pivotal to achieving practical advances and optimisations in power electronics.
“Engineering improvements can enhance the Qurack and Qdyne techniques used in this study,” says Hatano. “Qurack’s performance can be enhanced by adopting high-performance signal generators to extend its amplitude range, whereas optimising spin coherence time and microwave control speed would broaden Qdyne’s frequency detection range.”
“Simultaneous imaging of the amplitude and phase of AC magnetic fields across a broad frequency range offers numerous potential applications in power electronics, electromagnets, non-volatile memory, and spintronics technologies,” says Hatano. “This success contributes to the acceleration of quantum technologies, particularly in sectors related to sustainable development goals and well-being.”
https://doi.org/10.1038/s43246-025-00812-4
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