Andrade L H F, Laraoui A, Vomir M, Muller D, Stoquert J-P, Estournès C, Beaurepaire E, Bigot J-Y
Institut de Physique et Chimie des Matériaux de Strasbourg, (UMR 7504 CNRS-ULP), Strasbourg 67034, France.
Phys Rev Lett. 2006 Sep 22;97(12):127401. doi: 10.1103/PhysRevLett.97.127401.
The ultrafast magnetization and electron dynamics of superparamagnetic cobalt nanoparticles, embedded in a dielectric matrix, have been investigated using femtosecond optical pulses. Our experimental approach allows us to bypass the superparamagnetic thermal fluctuations and to observe the trajectory of the magnetization vector which exhibits a strongly damped precession motion. The magnetization precession is damped faster in the superparamagnetic particles than in cobalt films or when the particle size decreases, suggesting that the damping is enhanced at the metal dielectric interface. Our observations question the gyroscopic nature of the magnetization pathway when superparamagnetic fluctuations take place as we discuss in the context of Brown's model.
利用飞秒光脉冲研究了嵌入介电基质中的超顺磁性钴纳米颗粒的超快磁化和电子动力学。我们的实验方法使我们能够绕过超顺磁性热涨落，观察到磁化矢量的轨迹呈现出强烈阻尼的进动运动。超顺磁性颗粒中的磁化进动比钴薄膜中或颗粒尺寸减小时的进动衰减得更快，这表明在金属-介电界面处阻尼增强。正如我们在布朗模型的背景下所讨论的，当发生超顺磁性涨落时，我们的观察结果对磁化路径的陀螺性质提出了质疑。
