Optical excitation of spin-ordered rare earth metals triggers a complex response of the crystal lattice since expansive stresses from electron and phonon excitations compete with a contractive stress induced by spin disorder. Using ultrafast x-ray diffraction experiments, we study the layer specific strain response of a dysprosium film within a metallic heterostructure upon femtosecond laser-excitation. The elastic and diffusive transport of energy to an adjacent, non-excited detection layer clearly separates the contributions of strain pulses and thermal excitations in the time domain. We find that energy transfer processes to magnetic excitations significantly modify the observed conventional bipolar strain wave into a unipolar pulse. By modeling the spin system as a saturable energy reservoir that generates substantial contractive stress on ultrafast timescales, we can reproduce the observed strain response and estimate the time- and space dependent magnetic stress. The saturation of the magnetic stress contribution yields a non-monotonous total stress within the nanolayer, which leads to unconventional picosecond strain pulses.

中文翻译：

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由光激发稀土层内的磁应力饱和导致的非常规皮秒应变脉冲

自旋有序稀土金属的光激发触发了晶格的复杂响应，因为来自电子和声子激发的膨胀应力与自旋无序引起的收缩应力竞争。使用超快X射线衍射实验，我们研究了飞秒激光激发后金属异质结构中a膜的层比应变响应。能量向相邻的非激​​发检测层的弹性和扩散传输清楚地将时域中的应变脉冲和热激励的作用分开。我们发现，磁激发的能量转移过程将观察到的常规双极应变波显着改变为单极脉冲。通过将自旋系统建模为可饱和的储能器，该储能器会在超快的时间尺度上产生大量的收缩应力，我们可以重现观察到的应变响应，并估计与时间和空间有关的磁应力。磁应力贡献的饱和在纳米层内产生非单调的总应力，这导致非常规的皮秒应变脉冲。