In the relentless pursuit of energy efficiency and miniaturization in modern power electronics, soft magnetic materials stand as fundamental enablers inside the core of numerous electrical devices—from transformers and generators to amplifiers and electric motors. These materials, prized for their ability to be magnetized and demagnetized with ease, underpin the conversion and control of electrical energy. Yet, as power electronic systems progressively shift toward ultra-high frequency operation, the quest for magnetic materials that exhibit exceptionally low energy losses becomes both critical and challenging. Among the intrinsic limitations of soft magnetic materials lies the phenomenon of iron loss, an energy dissipation mechanism that converts useful electromagnetic energy into unwanted heat, fundamentally capping the efficiency of vital industrial and consumer technologies.
Iron loss in soft magnetic materials is traditionally dissected into three main components: hysteresis loss, classical eddy current loss, and excess eddy current loss. While the behavior of hysteresis and classical eddy current losses is relatively well-characterized, the elusive nature of excess eddy current loss, which intensifies markedly at high frequencies, has impeded strides toward next-generation low-loss materials. The scientific community has long suspected that this loss mechanism originates from localized eddy currents induced by the irregular, non-uniform motion of magnetic domain walls (DWs). These walls demarcate the microscopic magnetic domains—regions where atomic magnetic moments align uniformly—thus playing a cardinal role in magnetic behavior under the influence of time-varying magnetic fields.
Understanding the dynamics of DWs is no trivial task. The magnetic Barkhausen noise (MBN), a phenomenon that manifests as discrete bursts of noise during magnetization changes, holds the key to probing the subtle dance of DWs at the microscale. However, until now, existing MBN measurement technologies have been limited in their sensitivity and frequency bandwidth, preventing precise capture of individual Barkhausen pulses. This has left a gap in accurately correlating observed magnetic noise with the complex mechanisms driving excess eddy current loss, hindering theoretical and practical progress.
Filling this critical knowledge void, an innovative research team spearheaded by Assistant Professor Takahiro Yamazaki from Tokyo University of Science, Japan, has unveiled a groundbreaking wide-band and high-sensitivity MBN measurement system. Employing pioneering engineering design, this system features a dual-layer coil jig with comprehensive electromagnetic shielding and a bespoke low-noise amplifier architecture. The configuration minimizes extrinsic noise while preserving a broad frequency response, enabling the unprecedented capture of individual MBN pulses with exceptional fidelity.
Demonstrating the system’s prowess, the team focused their experimental investigations on 25-micrometer-thick Fe–Si–B–P–Cu (NANOMET®) amorphous alloy ribbons, a class of soft magnetic materials acclaimed for ultra-low coercivity and superior magnetic softness. Utilizing the state-of-the-art measurement setup, they obtained high-fidelity, single-shot MBN pulse recordings, providing direct experimental insight into magnetic DW relaxation phenomena previously out of reach. These measurements revealed isolated pulses whose characteristics embody the intrinsic relaxation behavior of domain walls subject to alternating magnetic fields.
Through rigorous statistical analyses of the accumulated MBN pulse data, the researchers identified a mean relaxation time constant averaging approximately 3.8 microseconds, with a remarkably narrow standard deviation around 1.8 microseconds. Intriguingly, these experimentally derived relaxation times starkly contrasted the longer times predicted by established theoretical models, prompting reconsideration of the fundamental damping mechanisms at play during DW motion.
In response, the team formulated an advanced physical model elucidating that it is the eddy current-induced damping—the resistance arising from currents generated within the material itself as the domain walls shift—that predominantly governs excess eddy current loss. This insight decisively shifts the paradigm away from intrinsic magnetic viscosity being the leading damping cause. The model achieves a unified explanation that couples microscopic DW kinetics with macroscopic energy dissipation, offering a robust framework to rationalize empirical observations and guide future material optimization.
The efficacy of the new MBN system was further validated through comparative studies on heat-treated nanocrystalline NANOMET® ribbons. The heat treatment induced microstructural refinement, attenuating irregularities in DW motion. This was evidenced by a marked decrease in MBN pulse amplitudes, signaling diminished localized eddy current activity and, consequentially, reduced energy loss. Such findings underscore the profound impact of microstructural engineering on magnetic performance and unlock pathways to tailor materials with finely controlled domain wall dynamics.
Importantly, these advancements herald transformative prospects for the engineering of ultra-efficient components integral to renewable energy applications, high-frequency transformers, and electric vehicle motors. By exploiting precise diagnostic capabilities and theoretical insights, material scientists and engineers can now envisage soft magnetic cores that operate with substantially suppressed excess eddy current losses at elevated frequencies, facilitating lighter, smaller, and more efficient electromagnetic devices.
Assistant Professor Yamazaki emphasizes the broader implications: “Our method equips the scientific community with unprecedented tools to visualize and quantify domain wall behavior at the microsecond scale. This capability is a vital step toward designing next-generation soft magnets optimized for the stringent demands of future power electronics, promising devices with superior performance and lower energy consumption.”
The collaboration also incorporated expertise from Senior Researcher Shingo Tamaru of Japan’s National Institute of Advanced Industrial Science and Technology (AIST) and Professor Masato Kotsugu from Tokyo University of Science. Their joint efforts reflect a synergistic marriage of experimental innovation and theoretical modeling, culminating in a comprehensive study published in the August 7, 2025 issue of the influential open-access journal IEEE Access.
Beyond academic novelty, this research is underpinned by substantial funding support from Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Science and Technology Agency (JST), and the Japan Society for the Promotion of Science (JSPS). This underscores the strategic importance a national agenda places on pioneering materials research that fuels technological innovation in sustainable energy and beyond.
Tokyo University of Science, the home institution of Assistant Professor Yamazaki, is Japan’s largest private science-focused university, known for cultivating a rich tradition of scientific excellence since 1881. The university’s multidisciplinary approach and steadfast commitment to creating knowledge that harmonizes nature, humanity, and society epitomize the spirit driving this cutting-edge investigation into magnetic materials.
As power devices continue to shrink in size yet grow in operational frequency, unlocking the mysteries of domain wall dynamics and associated energy losses will be instrumental in sustaining and advancing the global transition towards clean, efficient, and intelligent energy systems. This novel MBN measurement system and its revelatory findings mark a significant leap forward, furnishing the scientific community with both the tools and understanding needed to realize these ambitions.
Article Title: Analysis of Magnetic Barkhausen Noise to Reveal Domain Wall Dynamics in Amorphous/Nanocrystalline Ribbons
News Publication Date: 7-Aug-2025
References: DOI: 10.1109/ACCESS.2025.3596507
Image Credits: Credit: Dr. Takahiro Yamazaki, Tokyo University of Science, Japan
Keywords
Physical sciences, Physics, Electromagnetism, Electromagnetic fields, Energy, Electromagnetic induction, Magnetism, Electric charge, Electric current, Materials science, Materials engineering, Solid state physics, Material properties, Physical properties
