近场laser增强促进的FePt颗粒层的磁开关
Magnetic switching in granular FePt layers promoted by near-field laser enhancement
摘要：
鉴于在下一代高密度磁纪录中的潜在应用，磁性材料中纳米尺度下的光-物质相互作用是一个热门的研究课题。激光辅助开关提供了一种克服高各向异性和高堆积密度介质的材料限制的途径，尽管关于开关过程的动力学仍然没有被探索。我们使用超快小角度X射线散射在X射线自由电子激光探测嵌入在碳基体的FePt纳米颗粒的磁开关动力学的光飞秒激光脉冲激发。我们观察到，激光激发和施加的静态磁场，一个数量级小于矫顽场的组合，可以克服“向上”和“向下”磁化之间的磁各向异性障碍，使磁化切换。这种磁开关被发现是不均匀的整个材料，与一些个别的FePt纳米粒子既不开关也不退磁。这种行为的起源被确定为近场修改周围的FePt纳米粒子的入射激光辐射。非开关纳米粒子的分数的影响，由FePt和散热层之间的热流。
英文摘要：
Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle x-ray scattering at an x-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, one order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between "up" and "down" magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material, with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. The fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.
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