Murakami Mitsuko, Zhang G P
Department of Physics, Indiana State University, Terre Haute, IN 47809, United States of America.
J Phys Condens Matter. 2023 Sep 13;35(49). doi: 10.1088/1361-648X/acf6a2.
Demagnetization in ferromagnetic transition metals driven by a femtosecond laser pulse is a fundamental problem in solid state physics, and its understanding is essential to the development of spintronic devices.calculation of time-dependent magnetic moment in the velocity gauge so far has not been successful in reproducing the large amount of demagnetization observed in experiments. In this work, we propose a method to incorporate intraband transitions within the velocity gauge through a convective derivative in the crystal momentum space. Our results for transition-element bulk crystals (bcc Fe, hcp Co and fcc Ni) based on the time-dependent quantum Liouville equation show a dramatic enhancement in the amount of demagnetization after the inclusion of an intraband term, in agreement with experiments. We also find that the effect of intraband transitions on each ferromagnetic material is distinctly different because of their band structure and spin property differences. Our finding has a far-reaching impact on understanding of ultrafast demagnetization.
飞秒激光脉冲驱动的铁磁过渡金属中的退磁是固态物理学中的一个基本问题，对其理解对于自旋电子器件的发展至关重要。到目前为止，在速度规范下计算随时间变化的磁矩尚未成功再现实验中观察到的大量退磁现象。在这项工作中，我们提出了一种方法，通过在晶体动量空间中的对流导数将带内跃迁纳入速度规范。我们基于含时量子刘维尔方程对过渡元素体晶体（体心立方铁、六方密堆积钴和面心立方镍）的计算结果表明，在包含带内项后，退磁量显著增加，这与实验结果一致。我们还发现，由于它们的能带结构和自旋特性不同，带内跃迁对每种铁磁材料的影响明显不同。我们的发现对超快退磁的理解具有深远影响。
