Reid A H, Shen X, Maldonado P, Chase T, Jal E, Granitzka P W, Carva K, Li R K, Li J, Wu L, Vecchione T, Liu T, Chen Z, Higley D J, Hartmann N, Coffee R, Wu J, Dakovski G L, Schlotter W F, Ohldag H, Takahashi Y K, Mehta V, Hellwig O, Fry A, Zhu Y, Cao J, Fullerton E E, Stöhr J, Oppeneer P M, Wang X J, Dürr H A
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.
Nat Commun. 2018 Jan 26;9(1):388. doi: 10.1038/s41467-017-02730-7.
Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction-the underlying magnetoelastic stress-can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the sub-picosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.
磁致伸缩是指由磁化强度变化引起的应变，这是磁性材料中的一种普遍效应。由于难以揭示其微观起源，人们大多从唯象学角度对其进行处理。在此，我们展示了如何在时域中分离磁致伸缩的来源——潜在的磁弹性应力，从而为从原子层面理解磁致伸缩打开了大门。利用X射线和电子衍射来分离FePt纳米颗粒中亚皮秒级的自旋和晶格响应。在用50飞秒激光脉冲激发后，时间分辨X射线衍射表明纳米颗粒内的磁有序在146飞秒的时间常数内消失。超快电子衍射揭示，这种退磁之后是一种各向异性的三维晶格运动。对晶格运动的尺寸、速度和对称性进行分析，再结合考虑电子和声子引起的应力的从头算，使我们能够揭示退磁产生的磁弹性应力。
