利用超短、兆高斯磁脉冲在YIG薄膜中产生宏观、层状洋葱壳状磁畴结构
Macroscopic, layered onion shell like magnetic domain structure generated in YIG film using ultrashort, megagauss magnetic pulses
摘要：
研究大尺度有序结构的形成和演化是科学中一个永恒的主题。大尺寸磁畴的产生、演化和控制是一项有趣且具有挑战性的任务，因为在任何磁系统中存在复杂的竞争相互作用。在这里，我们展示了大规模的非共面有序的自旋，驱动皮秒，兆高斯磁脉冲来自高强度，飞秒激光。我们对一种特殊设计的钇铁石榴石（YIG）/电介质/金属膜夹层靶的研究表明，该靶产生了复杂的、大的、同心的、椭圆形的磁畴，类似于洋葱的层状壳结构。最大的壳具有超过数百微米的长轴，与在磁性材料中发现的常规亚微米尺度多边形、条纹状或气泡状磁畴或在用基于加速器的相对论性电子束照射的磁性膜中产生的大哑铃状磁畴形成鲜明对比。通过微磁学模拟，我们发现，巨大的磁场脉冲产生超快太赫兹（THz）自旋波。这些快速传播的自旋波的快照被存储为YIG膜中的分层洋葱壳形域。通常，在兆子器件中通过自旋波的信息传输发生在千兆赫（GHz）范围内，其中器件在室温下容易受到热干扰。我们的强激光脉冲- YIG夹层靶组合为室温桌面THz自旋波器件铺平了道路，该器件的工作温度刚好高于或在热噪声基底范围内。这种无耗散的设备提供了在几百微米的距离上对自旋信息的超快控制。
英文摘要：
Study of the formation and evolution of large scale, ordered structures is an enduring theme in science. The generation, evolution and control of large sized magnetic domains are intriguing and challenging tasks, given the complex nature of competing interactions present in any magnetic system. Here, we demonstrate large scale non-coplanar ordering of spins, driven by picosecond, megagauss magnetic pulses derived from a high intensity, femtosecond laser. Our studies on a specially designed Yttrium Iron Garnet (YIG)/dielectric/metal film sandwich target, show the creation of complex, large, concentric, elliptical shaped magnetic domains which resemble the layered shell structure of an onion. The largest shell has a major axis of over hundreds of micrometers, in stark contrast to conventional sub micrometer scale polygonal, striped or bubble shaped magnetic domains found in magnetic materials, or the large dumbbell shaped domains produced in magnetic films irradiated with accelerator based relativistic electron beams. Through micromagnetic simulations, we show that the giant magnetic field pulses create ultrafast terahertz (THz) spin waves. A snapshot of these fast propagating spin waves is stored as the layered onion shell shaped domains in the YIG film. Typically, information transport via spin waves in magnonic devices occurs in the gigahertz (GHz) regime, where the devices are susceptible to thermal disturbances at room temperature. Our intense laser light pulse - YIG sandwich target combination, paves the way for room temperature table-top THz spin wave devices, which operate just above or in the range of the thermal noise floor. This dissipation-less device offers ultrafast control of spin information over distances of few hundreds of microns.
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