自旋转移纳米接触中稳定的磁液滴孤子
Stable Magnetic Droplet Solitons in Spin Transfer Nanocontacts
摘要：
具有垂直磁各向异性（PMA）的磁性薄膜具有对应于反向动态旋进磁矩的局部激发，称为磁滴孤子。基本上，这些激发与基本自旋激发之间的吸引相互作用相关联（即，磁振子），并预测在没有阻尼的情况下发生在PMA材料中[1，2]。虽然存在于所有磁性材料中的阻尼抑制了这些激励，但现在可以通过纳米级接触铁磁薄膜中的电流流动通过自旋转移扭矩来补偿阻尼[3，4]。一种理论预测了在纳米接触中的阈值电流下出现磁液滴孤子[5]，最近，已经报道了液滴成核的实验特征[6]。然而，到目前为止，已经观察到它们是几乎可逆的激发，仅具有部分反转的磁化，并且经受导致它们漂移远离纳米接触的不稳定性（即，漂移不稳定性）[6]。在这里，我们表明，磁液滴孤子可以稳定的自旋转移纳米接触。此外，它们表现出对场和电流的强滞后响应以及接触中几乎完全反转的磁化。这些观测结果，除了他们的基本利益，开辟了新的应用磁液滴孤子作为多态高频电流和场可调谐振荡器。
英文摘要：
Magnetic thin films with perpendicular magnetic anisotropy (PMA) have localized excitations that correspond to reversed dynamically precessing magnetic moments, known as magnetic droplet solitons. Fundamentally, these excitations are associated with an attractive interaction between elementary spin-excitations (i.e., magnons) and were predicted to occur in PMA materials in the absence of damping [1,2]. While damping, present in all magnetic materials, suppresses these excitations, it is now possible to compensate damping by spin transfer torques through electrical current flow in nanometer scale contacts to ferromagnetic thin films [3,4]. A theory predicts the appearance of magnetic droplet solitons at a threshold current in nanocontacts [5] and, recently, experimental signatures of droplet nucleation have been reported [6]. However, thus far, they have been observed to be nearly reversible excitations, with only partially reversed magnetization and to be subject to instabilities that cause them to drift away from the nanocontacts (i.e., drift instabilities) [6]. Here we show that magnetic droplet solitons can be stabilized in a spin transfer nanocontact. Further, they exhibit a strong hysteretic response to fields and currents and a nearly fully reversed magnetization in the contact. These observations, in addition to their fundamental interest, open up new applications for magnetic droplet solitons as multi-state high frequency current and field tunable oscillators.
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