Wessels Philipp, Vogel Andreas, Tödt Jan-Niklas, Wieland Marek, Meier Guido, Drescher Markus
The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany.
Center for Optical Quantum Technologies (ZOQ), University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany.
Sci Rep. 2016 Feb 24;6:22117. doi: 10.1038/srep22117.
The analysis of isolated spin-wave packets is crucial for the understanding of magnetic transport phenomena and is particularly interesting for applications in spintronic and magnonic devices, where isolated spin-wave packets implement an information processing scheme with negligible residual heat loss. We have captured microscale magnetization dynamics of single spin-wave packets in metallic ferromagnets in space and time. Using an optically driven high-current picosecond pulse source in combination with time-resolved scanning Kerr microscopy probed by femtosecond laser pulses, we demonstrate phase-sensitive real-space observation of spin-wave packets in confined permalloy (Ni80Fe20) microstripes. Impulsive excitation permits extraction of the dynamical parameters, i.e. phase- and group velocities, frequencies and wave vectors. In addition to well-established Damon-Eshbach modes our study reveals waves with counterpropagating group- and phase-velocities. Such unusual spin-wave motion is expected for backward volume modes where the phase fronts approach the excitation volume rather than emerging out of it due to the negative slope of the dispersion relation. These modes are difficult to excite and observe directly but feature analogies to negative refractive index materials, thus enabling model studies of wave propagation inside metamaterials.
对孤立自旋波包的分析对于理解磁输运现象至关重要，并且在自旋电子学和磁子学器件的应用中特别有趣，在这些器件中，孤立自旋波包实现了一种残余热损耗可忽略不计的信息处理方案。我们已经在时空上捕捉到了金属铁磁体中单个自旋波包的微观磁化动力学。通过使用光驱动的高电流皮秒脉冲源，并结合飞秒激光脉冲探测的时间分辨扫描克尔显微镜，我们展示了在受限坡莫合金（Ni80Fe20）微带中对自旋波包的相敏实空间观测。脉冲激发允许提取动力学参数，即相速度和群速度、频率和波矢。除了已确立的达蒙 - 埃什巴赫模式外，我们的研究还揭示了具有反向传播的群速度和相速度的波。对于反向体模，预计会出现这种不寻常的自旋波运动，其中相面前往激发体积而不是由于色散关系的负斜率而从激发体积中出现。这些模式难以直接激发和观测，但具有与负折射率材料的相似性，从而能够对超材料内部的波传播进行模型研究。
