We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO₃ thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Grüneisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime.

中文翻译：

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激光激发 SrRuO3 中与温度和注量相关的磁应力分析

我们使用超快 X 射线衍射来研究飞秒激光激发下膨胀声子和收缩磁应力驱动金属钙钛矿 SrRuO ₃薄膜皮秒应变响应的影响。我们举例说明了如何使用各向异性体平衡热膨胀来预测薄膜对超快能量沉积的响应。与近平衡热膨胀相比，考虑横向均匀激光激发会改变应变响应是关键，因为平衡的面内应力会抑制皮秒时间尺度上的泊松应力。我们发现一个非常大的负格鲁奈森常数描述了自旋系统中少量能量所施加的大收缩应力。双脉冲激励方案的应变响应的温度和注量依赖性证明了高注量区域中磁应力的饱和。