Soft magnetic materials can be easily magnetized and demagnetized, which makes them a key component in electrical power devices, such as generators, transformers, and amplifiers. As power electronics advance toward high-frequency operation, demand is growing for low-loss soft magnetic materials. The efficiency of these materials is fundamentally limited by iron loss, where energy is lost as heat when a varying magnetic field passes through them, as is typical in transformers and generators. Iron loss mainly consists of hysteresis loss, classical eddy current loss, and excess eddy current loss. Among these, excess eddy current loss becomes increasingly dominant at high frequencies, but its mechanisms are not clearly understood.
When a varying magnetic field passes through a conductor, it generates eddy currents, resembling swirling eddies in water. These currents waste energy as heat, known as classical eddy current loss. Excess eddy current loss, however, arises due to localized eddy currents induced by irregular movement of magnetic domain walls (DWs) under a varying magnetic field. Magnetic DWs are boundaries separating tiny magnetic domains, separating uniformly magnetized regions.
Magnetic Barkhausen noise (MBN) serves as a key probe for DW dynamics. Yet, current MBN measurement systems do not possess the wide frequency coverage and high-sensitivity needed to capture the individual MBN events, making it difficult to understand the relationship between DW dynamics and eddy current losses.
To address this gap, a research team led by Assistant Professor Takahiro Yamazaki from the Department of Materials Science and Technology at Tokyo University of Science (TUS), Japan, developed a wide-band and high-sensitivity MBN measurement system. They used this system to investigate the magnetic DW dynamics in 25 μm-thick Fe–Si–B–P–Cu (NANOMET) ® ribbons, a class of soft magnetic alloys. Dr. Yamazaki explains, “The most fundamental understanding based on our previous studies is that ‘measure what was previously unmeasurable.’ With our wide-band, high-sensitivity MBN measurement system, we successfully obtained high-fidelity, single-shot capture of individual MBN pulses, providing direct experimental evidence of magnetic DW relaxation in metallic ribbons.”
The team also included Senior Researcher Shingo Tamaru from the National Institute of Advanced Industrial Science and Technology (AIST), Japan, and Professor Masato Kotsugu from TUS. The study, a collaboration between TUS and AIST, was published in Volume 13 of the journal IEEE Access on August 07, 2025.
The developed MBN measurement system integrates a dual-layer coil jig with full electromagnetic shielding, wiring, and a custom low-noise amplifier. Designed to minimize noise while maintaining a wide bandwidth, the system enables the capture of individual MBN pulses with the highest possible fidelity. This system enabled the team to effectively visualize the relaxation behavior and precise evaluation of DWs, focusing on the microstructural features associated with energy dissipation.
Using this setup, the team observed clear isolated MBN pulses, indicative of DW relaxation, in amorphous NANOMET® ribbons. These materials have exceptionally low coercivity and are well known for their soft magnetic properties. Statistical analysis of the captured pulses revealed a mean relaxation time constant of approximately 3.8 μs with a standard deviation of around 1.8 μs, much smaller than the values predicted by conventional models.
To explain this difference, they constructed a new physical model of DW relaxation. The model showed that the damping caused by eddy currents generated during DW motion is the main cause of excess eddy current loss, rather than the intrinsic magnetic viscosity of DWs themselves. This experimentally and theoretically clarifies the physical origin of excess eddy current losses, offering crucial insights for future material design.
The team further used their system to analyze heat-treated nanocrystalline NANOMET® ribbons, finding a significant decline in the amplitude of MBN pulses, indicating a substantial reduction in irregularity of the DW motion. This shows that it is possible to smoothen DW motion and therefore reduce energy loss through microstructural control. By collaborating with industries, NANOMET® could be translated into ultra-efficient components for renewable energy systems.
“Our method has the potential for wide application in the design of next-generation low-loss soft magnetic materials, especially in high-frequency transformers, electric vehicle motors, paving the way for smaller, lighter, and more efficient devices,” concludes Dr. Yamazaki. The insights gained from this study can aid in the designing of devices with improved driving performance and low power consumption.
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Reference
DOI: https://doi.org/10.1109/ACCESS.2025.3596507
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Assistant Professor Takahiro Yamazaki from Tokyo University of Science
Dr. Takahiro Yamazaki is currently working as an Assistant Professor at the Department of Materials Science and Technology at TUS, Japan. He specializes in magnetic analysis using machine learning and synchrotron radiation. In 2019, he received his Doctorate in Engineering from Yokohama National University.
His research focused on magnetic functional materials, analysis using magnetic Barkhausen noise, nano multi-phase materials, and radiation analysis. Before joining TUS, he worked as a JSPS Postdoctoral Researcher at Nagoya University, Japan, and the University of Maryland, US. He has refereed over 36 articles and has presented over 143 articles at various conferences.
Funding information
This work was supported in part by Japanese Government (MEXT)-Program for Creation of Innovative Core Technology for Power Electronics under Grant JPJ009777, in part by Japan Science and Technology Agency-JST/ACT-X under Grant JPMJAX22AL, and in part by Japan Society for the Promotion of Science-JSPS KAKENHI under Grant 23K13636.
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