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通过自旋轨道转矩实现无外场确定性超快磁斯格明子的产生。

Field-free deterministic ultrafast creation of magnetic skyrmions by spin-orbit torques.

作者信息

Büttner Felix, Lemesh Ivan, Schneider Michael, Pfau Bastian, Günther Christian M, Hessing Piet, Geilhufe Jan, Caretta Lucas, Engel Dieter, Krüger Benjamin, Viefhaus Jens, Eisebitt Stefan, Beach Geoffrey S D

机构信息

Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Max-Born-Institut, Max-Born-Straße 2A, 12489 Berlin, Germany.

出版信息

Nat Nanotechnol. 2017 Nov;12(11):1040-1044. doi: 10.1038/nnano.2017.178. Epub 2017 Oct 2.

Abstract

Magnetic skyrmions are stabilized by a combination of external magnetic fields, stray field energies, higher-order exchange interactions and the Dzyaloshinskii-Moriya interaction (DMI). The last favours homochiral skyrmions, whose motion is driven by spin-orbit torques and is deterministic, which makes systems with a large DMI relevant for applications. Asymmetric multilayers of non-magnetic heavy metals with strong spin-orbit interactions and transition-metal ferromagnetic layers provide a large and tunable DMI. Also, the non-magnetic heavy metal layer can inject a vertical spin current with transverse spin polarization into the ferromagnetic layer via the spin Hall effect. This leads to torques that can be used to switch the magnetization completely in out-of-plane magnetized ferromagnetic elements, but the switching is deterministic only in the presence of a symmetry-breaking in-plane field. Although spin-orbit torques led to domain nucleation in continuous films and to stochastic nucleation of skyrmions in magnetic tracks, no practical means to create individual skyrmions controllably in an integrated device design at a selected position has been reported yet. Here we demonstrate that sub-nanosecond spin-orbit torque pulses can generate single skyrmions at custom-defined positions in a magnetic racetrack deterministically using the same current path as used for the shifting operation. The effect of the DMI implies that no external in-plane magnetic fields are needed for this aim. This implementation exploits a defect, such as a constriction in the magnetic track, that can serve as a skyrmion generator. The concept is applicable to any track geometry, including three-dimensional designs.

摘要

磁斯格明子通过外部磁场、杂散场能量、高阶交换相互作用以及Dzyaloshinskii-Moriya相互作用(DMI)的共同作用而得以稳定。后者有利于同手性斯格明子,其运动由自旋轨道转矩驱动且具有确定性,这使得具有大DMI的系统在应用中具有相关性。具有强自旋轨道相互作用的非磁性重金属与过渡金属铁磁层的不对称多层结构可提供大且可调的DMI。此外,非磁性重金属层可通过自旋霍尔效应将具有横向自旋极化的垂直自旋电流注入铁磁层。这会产生转矩,可用于在垂直磁化的铁磁元件中完全切换磁化方向,但仅在存在破坏对称性的面内磁场时,这种切换才具有确定性。尽管自旋轨道转矩在连续薄膜中导致畴成核,并在磁道中导致斯格明子的随机成核,但尚未报道在集成器件设计中在选定位置可控地创建单个斯格明子的实用方法。在此,我们证明亚纳秒级自旋轨道转矩脉冲可使用与移位操作相同的电流路径,在磁跑道中自定义位置确定性地生成单个斯格明子。DMI的作用意味着为此目的无需外部面内磁场。此实现利用了诸如磁道中的缩颈等缺陷,其可作为斯格明子发生器。该概念适用于任何轨道几何形状,包括三维设计。

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