Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model
Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model
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DOI：
10.1103/physrevb.84.144414
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发表时间：
2011-10-10
影响因子：
3.7
通讯作者：
Chubykalo-Fesenko, O.
中科院分区：
文献类型：
--
作者：
Atxitia, U.;Chubykalo-Fesenko, O.
根据不同自旋s值的Landau-Lifshitz-Bloch （LLB）方程分析了超快激光诱导磁化动力学。在LLB模型中，超快退磁时间（tau(M)）和横向阻尼（alpha（垂直））由微观自旋翻转速率定义的本征耦合参数λ来参数化。我们证明了LLB模型等价于最近引入的M3TM模型[B]。Koopmans et al., Nature Mat. 9, 259(2010)]在假设本然散射机制是声子介导的Elliott-Yafet散射的情况下，S = 1/2。因此，在这个过程中，lambda与非平衡声子和电子温度之间的比例成正比，而不是与lambda = const的先前模型。研究了有限自旋数和散射速率参数λ对超快磁化动力学的影响。过渡金属和Gd中退磁时间尺度的差异是由于后一种情况下该参数几乎小了两个数量级。利用已有的实验数据，验证了飞秒退磁率与垂直皮秒-纳秒阻尼之间的关系。对Ni、Co和Gd的分析结果吻合较好，验证了LLB模型的正确性。
Ultrafast laser-induced magnetization dynamics is analyzed in terms of the Landau-Lifshitz-Bloch (LLB) equation for different values of spin S. Within the LLB model the ultrafast demagnetization time (tau(M)) and the transverse damping (alpha(perpendicular to)) are parametrized by the intrinsic coupling-to-the-bath parameter lambda, defined by the microscopic spin-flip rate. We show that the LLB model is equivalent to a recently introduced M3TM model [B. Koopmans et al., Nature Mat. 9, 259 (2010)] with S = 1/2 within the assumption that the intrinsic scattering mechanism is the phonon-mediated Elliott-Yafet scattering. As a result, for this process lambda is proportional to the ratio between the nonequilibrium phonon and electron temperatures, in contrast to previous models with lambda = const. We investigate the influence of the finite spin number and the scattering rate parameter lambda on the ultrafast magnetization dynamics. The differences in the demagnetization time scale in transition metals and Gd are attributed to the fact that this parameter is almost two orders of magnitude smaller in the latter case. The relation between the femtosecond demagnetization rate and the perpendicular picosecond-nanosecond damping, provided by the LLB theory, is checked based on the available experimental data. A good agreement is obtained for Ni, Co, and Gd, providing validation of the LLB model.