中文摘要：

运用全光学方法研究了具有较弱磁晶各向异性的FePt薄膜中的超快磁化进动行为。利用飞秒激光脉冲诱导产生磁化进动，基于时间分辨磁光克尔光谱方法测量其动力学过程，并通过拟合分析获得了进动频率与Gilbert阻尼因子的外场及激发能量依赖关系。基于微磁学理论和实验条件推导的磁化进动频率表达式能够很好地解释进动频率的非线性外场依赖关系，而频率随激发能量缓慢增大源于更高的平衡温度。分析表明本征磁阻尼因子比文献报道的L10-FePt薄膜的磁阻尼小得多，而有效磁阻尼随外场增大迅速减小源于磁不均匀性。实验还发现提高激发脉冲能量可以减缓一致性磁化进动的能量耗散。

英文摘要：

Ultrafast magnetization precession in the FePt film with weak magnetocrystalline anisotropy is studied using the all-optical method. The magnetization precession is induced by femtosecond laser pulses, and its dynamics is measured by time-resolved magneto-optical Kerr spectroscopy. After fitting and theoretical analyzing, field- dependent and excitation-energy-dependent precession frequency and Gilbert damping factor are obtained. Frequency equation deduced based on micromagnetics and the experimental condition can well explain the nonlinear field- dependence of precession frequency. Frequency is found to increase with the increasing excited energy, and can be attributed to the higher equilibrium temperature. In addition, intrinsic damping factor which is much smaller than that observed in L 10-FePt film reported in recent literature is obtained. The effective damping rapidly decreases with the increasing field, and that can be attributed to the magnetic inhomogeneity. Moreover, it is found that increase of excited energy can slow down energy dissipation of the uniform magnetization precession.