Quantum sensing reveals energy loss patterns in soft magnetic materials

Led by Professor Mutsuko Hatano, the team demonstrated how nitrogen-vacancy (NV) center-based quantum sensors in diamonds can image both the amplitude and phase of alternating current (AC) stray magnetic fields. This dual-mode imaging capability is essential for studying hysteresis losses in soft magnetic components.

The team developed two quantum sensing protocols: Qubit Frequency Tracking (Qurack) for frequencies in the kilohertz range and quantum heterodyne (Qdyne) imaging for the megahertz range. Together, these tools enabled the researchers to conduct wide-range AC magnetic field imaging with high spatial resolution.

Their experimental setup involved applying AC current to a 50-turn coil while sweeping frequencies from 100 Hz to 2.34 MHz. Both Qurack and Qdyne protocols successfully captured uniform AC magnetic field behavior using NV centers, confirming the system's capability across a broad frequency spectrum.

Focusing on CoFeB-SiO2 thin films, the researchers mapped stray magnetic fields and discovered near-zero phase delay up to 2.3 MHz along the hard axis, indicating minimal energy loss. However, higher energy dissipation was noted when magnetization aligned with the easy axis, demonstrating the importance of magnetic anisotropy in material performance.

This quantum imaging technique also allowed the observation of domain wall motion, a crucial mechanism in magnetization and energy loss. The insights gathered provide a promising path for improving soft magnetic materials used in high-frequency electronics, particularly inductors.

Professor Hatano emphasized future enhancements: "Qurack's performance can be enhanced by adopting high-performance signal generators to extend its amplitude range, whereas optimizing spin coherence time and microwave control speed would broaden Qdyne's frequency detection range."

She added, "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 well-being."

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