论文标题：Determination of chirality and density control of Néel-type skyrmions with in-plane magnetic field

期刊：Communications Physics

作者：Senfu Zhang, Junwei Zhang, Yan Wen, Eugene M. Chudnovsky & Xixiang Zhang

发表时间：2018/07/17

数字识别码：10.1038/s42005-018-0040-5

原文链接：https://www.nature.com/articles/s42005-018-0040-5?utm_source=Other_website&utm_medium=Website_links&utm_content=RenLi-MixedBrand-multijournal-Multidisciplinary-China&utm_campaign=ORG_USG_JRCN_RL_article_promotion_sciencenet_Sep_3rd

近日《通讯-物理学》发表的一篇名为Determination of chirality and density control of Néel-type skyrmions with in-plane magnetic field的研究，描述了一种通过水平磁场的引入来分辨斯格明子的类型和手性，并提高斯格明子密度的方法。

磁性斯格明子是一种受拓扑保护的手性自旋结构，其主要存在于空间对称性破缺的磁性块体材料和多层膜样品中。根据自旋分布的方式，斯格明子可以分为奈尔型（Néel type）和布洛赫型（Bloch type）两种，而每种类型的斯格明子又有两种相反手性的自旋分布。布洛赫型斯格明子的手性可以通过洛伦兹透射电子显微镜（L-TEM）图像中心的亮斑或暗斑非常容易的分辨出来，然而奈尔型斯格明子的手性却很难分辨。

图1：不同类型和手性的斯格明子的偏好生长方向与水平磁场的关系。图源：Zhang等

沙特阿伯杜拉国王科技大学（KAUST）张西祥教授带领的科研团队利用L-TEM研究了 [Pt/Co/Ta]n 多层膜结构在倾斜磁场中的磁化反转过程。首先将样品饱和磁化，然后在缓慢降低外加磁场的过程中，一些斯格明子逐渐产生并生长为条状磁畴。有趣的是，该生长过程更倾向于沿着与水平磁场分量相反的方向进行。进一步的微磁学模拟研究表明，在斯格明子中心磁化方向确定的情况下，斯格明子偏好的生长方向与斯格明子的类型和手性直接相关。对于奈尔型的斯格明子，其偏好方向与水平磁场方向平行，然后通过是相同还是反向便可以判断出其手性。而布洛赫型斯格明子的生长方向则与水平磁场方向垂直。

此外，研究还发现，薄膜样品中产生的斯格明子的最大密度也可以通过增大水平磁场强度或降低薄膜的均匀度来提高。

图2：不同角度的倾斜磁场可以产生的斯格明子最大密度的洛伦兹电镜图。图源：Zhang 等

摘要：Magnetic skyrmions are topologically protected nanoscale spin textures exhibiting fascinating physical behaviors. Recent observations of room temperature Néel-type skyrmions in magnetic multilayer films are an important step towards their use in ultra-low power devices. Here, we investigate the magnetization reversal in [Pt/Co/Ta]n multilayer samples under a tilted magnetic field using in-situ Lorentz transmission electron microscopy. On decreasing the magnetic field, individual skyrmions appear to subsequently evolve into snake-like structures growing in the direction opposite to the in-plane magnetic field. We show that this unusual relation between the velocity vector and the magnetic field is dominated by the chirality of the Néel-type skyrmions. It allows one to extract the sign of the Dzyaloshinskii–Moriya constant. We also demonstrate that high concentration of skyrmions can be achieved on increasing the in-plane component of the field or increasing the disorder of the film. Our micromagnetic simulations agree with our experimental results.

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期刊介绍：Communications Physics (https://www.nature.com/commsphys/) is an open access journal from Nature Research publishing high-quality research, reviews and commentary in all areas of physics. Research papers published by the journal represent significant advances bringing new insight to a specialized area of research.

（来源：科学网）