70年間測定できなかった磁石の「反転試行時間」を初めて決定 ― 次世代磁気デバイス設計に新指針 ―

2026-04-22 東北大学

図1. 磁石のS→Nの向き（磁化の向き）が熱的に反転する様子。

＜関連情報＞

• https://www.tohoku.ac.jp/japanese/2026/04/press20260422-01-magnet.html
• https://www.tohoku.ac.jp/japanese/newimg/pressimg/tohokuuniv-press20260422_01web_magnet.pdf
• https://www.nature.com/articles/s43246-026-01149-2

ナノ磁石における確率的スイッチング時定数と不安定性 Stochastic switching time constant and instability in nanomagnets

Shun Kanai,Keisuke Hayakawa,Mehrdad Elyasi,Keito Kobayashi,Junta Igarashi,Butsurin Jinnai,William A. Borders,Gerrit E. W. Bauer,Hideo Ohno & Shunsuke Fukami
Communications Materials  Published: 21 April 2026
DOI:https://doi.org/10.1038/s43246-026-01149-2

Abstract

The Arrhenius law governs thermally-activated phenomena with a pre-exponential factor, the attempt time τ₀, which defines the time constant of stochastic process. In nanomagnets, accessing τ₀ is a formidable task due to the temperature-dependent magnetic properties that preclude the use of a standard Arrhenius plot and lead to the questionable assumption that τ₀ = 1 ns for several decades. This is an untenable situation considering τ₀’s critical role in the performance of stochastic magnetic tunnel junctions (s-MTJs), particularly in the context of unconventional computing. Here we present a systematic measurement of τ₀ and reveal the governing physics. By analyzing the random telegraph noise as a function of applied magnetic fields along the hard axis, we derive a magnetic version of the Arrhenius plot, arriving at τ₀ = 3.7–12 ns depending on the perpendicular magnetic anisotropy. Furthermore, we reveal that the Suhl instability significantly increases τ₀ by the emission of spin waves. The results renew the understanding of stochastic dynamics in nanomagnets, offering a route to design high-performance s-MTJs.