New Theory Illuminates Mechanisms Behind Tunnel Magnetoresistance Oscillations

On June 9, 2025, a research team from the National Institute for Materials Science (NIMS) in Japan unveiled a groundbreaking theory elucidating the oscillatory behavior of tunnel magnetoresistance (TMR) in magnetic tunnel junctions (MTJs). This phenomenon, which is pivotal for advancements in magnetic memory technologies, was explored in a letter published in the *Physical Review B*, a journal of the American Physical Society.

Tunnel magnetoresistance is characterized by variations in electrical resistance depending on the orientation of magnetizations in two magnetic layers separated by an insulating barrier. An enhanced understanding of TMR oscillations could lead to improved magnetic sensors and expanded magnetic memory capacities. The international research community has long been aware of the importance of maximizing TMR ratios, yet the underlying mechanisms for their oscillation had remained elusive despite extensive inquiries over two decades.

Keisuke Masuda, a Senior Researcher at the Spin Theory Group of NIMS, led the team responsible for this innovative theory. Masuda stated, "The new theory takes into account the superposition of wave functions between majority- and minority-spin states at the interface of the magnetic layers and the insulating barrier. This aspect had previously been overlooked in theoretical considerations."

The researchers' findings demonstrate that TMR ratios calculated through their model align closely with experimentally observed values, underscoring the theory's validity. Masuda emphasized, "Understanding the physical origins of TMR oscillation is vital for achieving even higher TMR ratios, which can significantly enhance the performance of devices utilizing MTJs."

Yoshio Miura, an Invited Researcher at NIMS, noted that earlier experiments regarding TMR oscillations predominantly utilized a limited selection of magnetic materials, primarily iron. Going forward, the team plans to broaden their experimental scope to include various magnetic materials, facilitating a comparative analysis that could yield deeper insights into TMR behavior. Miura remarked, "We expect that experimenting with a wider array of magnetic materials will provide critical data to further refine our theoretical model."

Hiroaki Sukegawa, Leader of the Spintronics Group at NIMS, added, "This research could contribute significantly to the design of MTJs with superior TMR ratios, which is essential for the next generation of memory devices and sensors."

The implications of this work extend beyond mere academic interest; advancements in TMR technology could drive innovations across multiple sectors, including electronics, data storage, and information technology. As the demand for more efficient and compact memory solutions grows, this research stands to play a crucial role in shaping the future of magnetic memory technologies.

The study was funded by the Japan Society for the Promotion of Science (JSPS) and the Ministry of Education, Culture, Sports, Science and Technology (MEXT) under various grant numbers. The collaborative effort involved researchers from NIMS, including Thomas Scheike, Seiji Mitani, and Yusuke Kozuka, highlighting the interdisciplinary nature of this vital field of research.

In conclusion, the newly proposed theory not only clarifies existing uncertainties surrounding TMR oscillations but also lays a foundation for future explorations aimed at optimizing magnetic tunnel junctions. As researchers pursue further experimental validations, the potential for developing high-performance magnetic memory devices appears promising, paving the way for more advanced technological applications in the coming years.