Internal structure of hexagonal skyrmion lattices in cubic helimagnets
Internal structure of hexagonal skyrmion lattices in cubic helimagnets
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DOI：
10.1088/1367-2630/18/9/095004
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发表时间：
2016-09-29
影响因子：
3.3
通讯作者：
Togawa, Y.
中科院分区：
文献类型：
--
作者：
McGrouther, D.;Lamb, R. J.;Togawa, Y.
我们报告了迄今为止最精确的观测结果，关于磁skyrmions的自旋结构的立方B20结构的FeGe的边缘标本。通过我们先进的微分相衬（DPC）成像（在扫描透射电子显微镜（STEM））的发展，我们已经获得了高空间分辨率的定量测量skyrmion内部自旋轮廓。对于六角skyrmion晶格细胞，稳定的面外施加磁场，映射的面内分量的磁感应强度揭示了精确的自旋分布和内部结构具有内在的六重对称性。随着场强的增加，Skyrmion核的直径减小，并伴随着晶格周期的非线性变化。还研究了利用新的增加灵敏度的DPC检测方案和各种对称性降低扭曲的晶格区域的单个skyrmions的结构变化。为了深入了解基本的能量学，我们已经构建了一个唯象模型，我们的实验观察的自旋分布和场诱导的核心直径的变化是在良好的协议与预测的结构中的中间的边缘晶体。在附近的晶体表面，我们的模型预测存在的面内扭曲变形，我们目前的实验观察不敏感。作为一种替代的磁各向异性的尚未确定的来源的要求，我们证明，表面状态可以提供所需的能量稳定的锥形磁相位占主导地位。
We report the most precise observations to date concerning the spin structure of magnetic skyrmions in a nanowedge specimen of cubic B20 structured FeGe. Enabled by our development of advanced differential phase contrast (DPC) imaging (in a scanning transmission electron microscope (STEM)) we have obtained high spatial resolution quantitative measurements of skyrmion internal spin profile. For hexagonal skyrmion lattice cells, stabilised by an out-plane applied magnetic field, mapping of the in-plane component of magnetic induction has revealed precise spin profiles and that the internal structure possesses intrinsic six-fold symmetry. With increasing field strength, the diameter of skyrmion cores was measured to decrease and accompanied by a nonlinear variation of the lattice periodicity. Variations in structure for individual skyrmions across an area of the lattice were also studied utilising a new increased sensitivity DPC detection scheme and a variety of symmetry lowering distortions were observed. To provide insight into fundamental energetics we have constructed a phenomenological model, with which our experimental observations of spin profiles and field induced core diameter variation are in good agreement with predicted structure in the middle of the nanowedge crystal. In the vicinity of the crystal surfaces, our model predicts the existence of in-plane twisting distortions which our current experimental observations were not sensitive to. As an alternative to the requirement for as yet unidentified sources of magnetic anisotropy, we demonstrate that surface states could provide the energetic stabilisation needed for predomination over the conical magnetic phase.