Max Planck Institute for Intelligent Systems (formerly Max Planck Institute for Metals Research), Heisenbergstrasse 3, 70569 Stuttgart, Germany.
J Phys Condens Matter. 2011 Dec 14;23(49):493201. doi: 10.1088/0953-8984/23/49/493201. Epub 2011 Nov 17.
For metallic magnets we review the experimental and electron-theoretical investigations of fast magnetization dynamics (on a timescale of ns to 100 ps) and of laser-pulse-induced ultrafast dynamics (few hundred fs). It is argued that for both situations the dominant contributions to the dissipative part of the dynamics arise from the excitation of electron-hole pairs and from the subsequent relaxation of these pairs by spin-dependent scattering processes, which transfer angular momentum to the lattice. By effective field theories (generalized breathing and bubbling Fermi-surface models) it is shown that the Gilbert equation of motion, which is often used to describe the fast dissipative magnetization dynamics, must be extended in several aspects. The basic assumptions of the Elliott-Yafet theory, which is often used to describe the ultrafast spin relaxation after laser-pulse irradiation, are discussed very critically. However, it is shown that for Ni this theory probably yields a value for the spin-relaxation time T(1) in good agreement with the experimental value. A relation between the quantity α characterizing the damping of the fast dynamics in simple situations and the time T(1) is derived.
对于金属磁体，我们回顾了关于快速磁化动力学（在纳秒到 100 皮秒的时间尺度上）和激光脉冲诱导的超快动力学（几百飞秒）的实验和电子理论研究。我们认为，对于这两种情况，动力学耗散部分的主要贡献来自电子-空穴对的激发以及随后通过自旋相关散射过程对这些电子对的弛豫，自旋相关散射过程将角动量转移到晶格。通过有效场理论（广义呼吸和冒泡费米面模型），我们表明，通常用于描述快速耗散磁化动力学的吉尔伯特运动方程必须在几个方面进行扩展。对常用来描述激光脉冲辐照后超快自旋弛豫的 Elliott-Yafet 理论的基本假设进行了非常严格的讨论。然而，我们表明，对于 Ni，该理论可能会给出与实验值非常吻合的自旋弛豫时间 T(1)的数值。导出了一个量 α，它描述了简单情况下快速动力学的阻尼，与时间 T(1)之间的关系。
