We investigate the spin dynamics driven by terahertz magnetic fields in epitaxial thin films of cobalt in its three crystalline phases. The terahertz magnetic field generates a torque on the magnetization which causes it to precess for about 1 ps, with a subpicosecond temporal lag from the driving force. Then, the magnetization undergoes natural damped THz oscillations at a frequency characteristic of the crystalline phase. We describe the experimental observations solving the inertial Landau-Lifshitz-Gilbert equation. Using the results from the relativistic theory of magnetic inertia, we find that the angular momentum relaxation time $\eta$ is the only material parameter needed to describe all the experimental evidence. Our experiments suggest a proportionality between $\eta$ and the strength of the magnetocrystalline anisotropy.

中文翻译：

---

外延钴薄膜中的惯性自旋动力学

我们研究了在钴的三个晶相外延薄膜中由太赫兹磁场驱动的自旋动力学。太赫兹磁场在磁化上产生扭矩，使其进动约 1 ps，驱动力具有亚皮秒级的时间滞后。然后，磁化以结晶相的频率特征经历自然阻尼太赫兹振荡。我们描述了求解惯性 Landau-Lifshitz-Gilbert 方程的实验观察结果。利用磁惯性相对论的结果，我们发现角动量弛豫时间$\eta$是描述所有实验证据所需的唯一材料参数。我们的实验表明之间存在比例关系$\eta$和磁晶各向异性的强度。