铁磁薄膜中圆偏振光感应的瞬态磁光Kerr峰的物理起源

Physical origin of transient Kerr peak induced by circularly polarized laser in ferromagnetic films

使用飞秒时间分辨抽运-探测磁光Kerr光谱技术,实验研究了圆偏振光抽运面内磁化FePt和垂直磁化GdFeCo薄膜的磁化演化动力学,发现在时间延迟零点处均出现瞬态Kerr峰.分析了此Kerr峰的起源,指出此瞬态Kerr峰与铁磁性无关,可能起源于自由电子的顺磁磁化,而顺磁磁化的外磁场来自圆偏振抽运光的逆Faraday效应.基于顺磁磁化模型的计算结果支持此观点.基于此观点,逆Faraday效应感应的磁场脉冲宽度应该与激光脉冲宽度一致。

The magnetization dynamics of in-plane anisotropic FePt and perpendicularly anisotropic GdFeCo films induced by circularly polarized laser excitation is investigated using femtosecond time-resolved pump-probe Kerr spectroscopy.It is found that a transient Kerr peak occurs near zero-time delay,respectively for each sample.The origin of the peaks is analyzed.It is pointed out that the transient Kerr peaks are not related to ferromagnetism and may originate from paramagnetic magnetization of free electrons in the samples,while the magnetic field that magnetizes the free electrons comes from inverse Faraday effect of the circularly polarized pump laser.The calculation results based on the paramagnetic magnetization model support such a viewpoint.Based on our points,the duration of magnetic pulses induced by inverse Faraday effect should be the same as that of the pump laser pulses.