Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal.
Disparate ultrafast dynamics of itinerant and localized magnetic moments in gadolinium metal.
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gadolinium金属中巡回和局部磁矩的不同超快动力学。
DOI：
10.1038/ncomms9262
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发表时间：
2015-09-10
影响因子：
16.6
通讯作者：
Weinelt M
中科院分区：
文献类型：
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作者：
Frietsch B;Bowlan J;Carley R;Teichmann M;Wienholdt S;Hinzke D;Nowak U;Carva K;Oppeneer PM;Weinelt M
海森伯-狄拉克原子内交换耦合是形成原子自旋矩的原因，因此是磁性中最强的相互作用。因此，一般认为，原子内交换导致在单独的原子轨道中自旋的磁矩动力学中的准瞬时对准过程。在金属钆的超短光激发下，我们同时记录了光电子发射的4f磁性线性二向色性和5d交换分裂。它们的动力学相差一个数量级，衰减常数分别为14和0.8 ps。基于轨道分辨海森堡哈密顿量的自旋动力学模拟结合第一性原理计算很好地解释了5d和4f自旋矩的特殊动力学，并证实了5d交换分裂密切跟踪5d自旋矩动力学。因此，钆显示出不同的动力学的本地化4f和巡回5d的自旋时刻，展示了一个崩溃的原子内交换排列在皮秒的时间尺度。 由于原子内交换相互作用的强度，通常假设原子内轨道中自旋矩的对准是准瞬时的。在这里，作者证明了在超短光激发后钆中4f和5d电子之间的这种关系的崩溃。
The Heisenberg–Dirac intra-atomic exchange coupling is responsible for the formation of the atomic spin moment and thus the strongest interaction in magnetism. Therefore, it is generally assumed that intra-atomic exchange leads to a quasi-instantaneous aligning process in the magnetic moment dynamics of spins in separate, on-site atomic orbitals. Following ultrashort optical excitation of gadolinium metal, we concurrently record in photoemission the 4f magnetic linear dichroism and 5d exchange splitting. Their dynamics differ by one order of magnitude, with decay constants of 14 versus 0.8 ps, respectively. Spin dynamics simulations based on an orbital-resolved Heisenberg Hamiltonian combined with first-principles calculations explain the particular dynamics of 5d and 4f spin moments well, and corroborate that the 5d exchange splitting traces closely the 5d spin-moment dynamics. Thus gadolinium shows disparate dynamics of the localized 4f and the itinerant 5d spin moments, demonstrating a breakdown of their intra-atomic exchange alignment on a picosecond timescale. Due the strength of the intra-atomic exchange interaction, it is generally assumed that alignment of spin moments in intra-atomic orbitals is quasi-instantaneous. Here, the authors demonstrate the breakdown of this relation between the 4f and 5d electrons in gadolinium following ultrashort optical excitation.