2025-10-28 京都大学
図1：スピン歳差運動とTHzファラデー回転測定の概念とサンプル構造
（A）磁性体における異常ホール効果（AHE）とTHz偏光回転の概念図。スピンが歳差運動しており、y軸方向の電流とTHz光の偏光が変調される。太矢印（白色）は上向きスピン（↑）と下向きスピン（↓）の電子がそれぞれ異なる方向に流れる様子を示す。（B）SiO₂基板上に成膜された強磁性多層膜構造。M：磁性体内部の磁化ベクトル。
＜関連情報＞
- https://www.kuicr.kyoto-u.ac.jp/sites/topics/251028/
- https://www.kuicr.kyoto-u.ac.jp/sites/wp-content/uploads/hirori_20251028.pdf
- https://journals.aps.org/prapplied/abstract/10.1103/4p39-gyrd
コヒーレント磁化歳差運動による異常ホール伝導度の超高速変調Co-Pt薄膜 Ultrafast modulation of the anomalous Hall conductivity by coherent magnetization precession in Co-Pt thin films
Zhenya Zhang, Yoichi Shiota, Shutaro Karube, Yuichi Watanabe, Teruo Ono, and Hideki Hirori
Physical Review Applied Published: 24 October, 2025
DOI: https://doi.org/10.1103/4p39-gyrd
Abstract
Ultrafast dynamics of magnetic properties in the high gigahertz (GHz) or even terahertz (THz) frequency range may be exploited in next-generation data storage and processing devices, and therefore suitable methods for detecting ultrafast dynamics of magnetization need to be developed. In this work, we investigate the impact of optically induced ultrafast precession of magnetization on the anomalous Hall conductivity in a ferromagnetic Co−Pt multilayer structure using THz-based pump-probe measurements. From the measured Faraday rotation, the time-dependent anomalous Hall conductivity is extracted, and our data reveals an initial ultrafast quench due to laser-induced demagnetization and a subsequent oscillation with a frequency that increases with the strength of the applied external magnetic field Hext. for ext= 30 kOe, the oscillation frequency reaches approximately 100 GHz. The magnetic-field dependence of the oscillation frequency is in good agreement with the prediction from the ferromagnetic resonance model, confirming that the observed oscillation is caused by coherent magnetization precession. These findings are considered to be useful for studies that aim to integrate spintronics and THz electronics.
