Diamond quantum sensors offer breakthrough in power electronics

Scientists from the Institute of Science Tokyo, working with Harvard University and Hitachi, Ltd., used a novel imaging technique to visualise both the amplitude and phase of alternating current (AC) stray magnetic fields – an advancement poised to support the development of more efficient electronic systems.

The team, led by Professor Mutsuko Hatano from the School of Engineering at the Institute of Science Tokyo, developed quantum protocols that enabled simultaneous imaging of AC stray fields across a wide frequency range, extending up to 2.3MHz. These findings demonstrated that quantum sensing technology, specifically based on diamond sensors with nitrogen-vacancy (NV) centres, could be instrumental in advancing soft magnetic materials for high-frequency applications.

Improving energy conversion efficiency in power electronics is essential for achieving long-term sustainability, with wide-bandgap semiconductors such as GaN and SiC already offering benefits due to their high-frequency performance. However, energy losses in passive magnetic components remain a bottleneck to further efficiency gains and miniaturisation – highlighting the importance of better magnetic materials.

To address this challenge, the team introduced two key protocols: Qubit Frequency Tracking (Qurack) for kilohertz (kHz) frequencies, and quantum heterodyne (Qdyne) imaging for megahertz (MHz) frequencies. In a proof-of-principle experiment, they applied an AC current to a 50-turn coil and swept the frequency from 100Hz to 200kHz using Qurack, and from 237kHz to 2.34MHz using Qdyne. The NV centres imaged both the amplitude and phase of the resulting magnetic field with spatial resolutions between 2-5µm.

Using this quantum imaging approach, the researchers studied CoFeB–SiO₂ thin films – materials engineered for high-frequency inductors. Their analysis revealed a near-zero phase delay in magnetic response up to 2.3MHz when the field was aligned along the hard axis, indicating minimal energy loss. Conversely, along the easy axis, the phase delay increased with frequency, suggesting higher energy dissipation due to magnetic anisotropy.

Crucially, the imaging system also resolved domain wall motion, a key mechanism behind energy loss in soft magnetic materials. This capability offers a new pathway to optimise materials for high-frequency electronics, addressing a long-standing technical obstacle.

Looking ahead, Professor Hatano outlined areas for further enhancement of the techniques: “The Qurack and Qdyne techniques used in this study can be enhanced by engineering improvements,” said 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.”

She also noted the broader implications for the technology: “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.

“This success contributes to the acceleration of quantum technologies, particularly in sectors related to sustainable development goals and wellbeing.”