A research team consisting of Postdoctoral Researcher Ravi Gautam, Chief Researcher Hiroaki Mamiya, Deputy Center Director Tadakatsu Ohkubo, and Group Leader Hossein Sepehri Amin from NIMS Center for Magnetic and Spintronic Materials; Research Fellow Nikita Kulesh from NIMS ICYS; Researcher Shozo Hiramoto, Professor Satoshi Okamoto, and Doctoral Student Nobuhisa Ono from Tohoku University Institute of Multidisciplinary Research for Advanced Materials; and Senior Researcher Takeshi Ogasawara from the AIST Core Electronics Technology Research Institute has developed a new method for precisely controlling the nanostructure and magnetic domain structure inside iron-based soft magnetic amorphous ribbons. This breakthrough has achieved the world's first success in reducing power loss in soft magnetic materials by more than 50% compared with the initial amorphous ribbons, particularly in the high-frequency range up to several tens of kilohertz where applications in transformers and electric vehicle power circuits are anticipated. This achievement brings new prospects for the design of high-performance soft magnetic materials while expanding options for low-loss materials suitable for next-generation power electronics, accelerating the global transition toward cleaner and more efficient energy conversion technologies. The research was published in Nature Communications.
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With the rapid expansion of power demand from AI data centers and electric vehicles, highly efficient power utilization has become a critical challenge. In power electronics technology, which is fundamental to this, the performance of soft magnetic materials used in transformers and inductors for power conversion and supply holds the key to efficiency improvements. Soft magnetic materials are metallic materials with an excellent magnetization response that react quickly to external magnetic fields and can suppress power loss. However, with the increasing frequency of power electronics technology, the growing energy loss occurring in soft magnetic materials has become a serious problem.
The research team conducted detailed microstructural analysis of samples with partially crystallized iron-based amorphous ribbons fabricated by the melt-spinning technique using transmission electron microscopy and atom probe tomography, confirming the dispersion of nanoscale iron crystals. Furthermore, magnetic domain observations using magneto-optical Kerr effect microscopy confirmed the development of fine stripe-shaped magnetic domain structures.
Based on these observations, micromagnetic simulations revealed that the emergence of this stripe-shaped magnetic domain structure was caused by the development of weak perpendicular magnetic anisotropy. As a result, it was found that excess loss, which accounts for more than 80% of power loss in soft magnetic materials in the high-frequency range of several tens of kilohertz, could be significantly suppressed.
The newly developed ribbons consist of more than 94% iron by weight along with other low-cost elements (boron, phosphorus, carbon, copper, silicon) and were fabricated using conventional rapid cooling processes. Ribbons with 60-millimeter width and 25-micrometer thickness can be manufactured, confirming sufficient scalability for industrial use. This achievement is exceptional in that it leads to extremely high-efficiency power conversion without dependence on rare and expensive constituent elements.
In conventional soft magnetic materials, reducing magnetostriction was considered common sense, and the compositional range available to achieve low magnetostriction was limited. In contrast, in the materials developed in this research, moderate magnetostriction (approximately 30 ppm) serves as a factor for the development of weak perpendicular magnetic anisotropy, demonstrating that even materials with high magnetostriction can become excellent soft magnetic materials by combining nanostructure control with magnetic domain structure control. This has opened up new areas to be explored for soft magnetic materials.
Journal Information
Publication: Nature Communications
Title: Ultra-low core loss in Fe-enriched soft magnetic ribbons enabled by nanostructure and high-frequency domain engineering
DOI: 10.1038/s41467-025-63139-1
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