Streubel Robert, Kent Noah, Dhuey Scott, Scholl Andreas, Kevan Steve, Fischer Peter
Materials Sciences Division , Lawrence Berkeley National Laboratory , Berkeley California 94720 , United States.
Physics Department , UC Santa Cruz , Santa Cruz California 95064 , United States.
Nano Lett. 2018 Dec 12;18(12):7428-7434. doi: 10.1021/acs.nanolett.8b01789. Epub 2018 Sep 26.
We use nano disk arrays with square and honeycomb symmetry to investigate magnetic phases and spin correlations of XY dipolar systems at the micro scale. Utilizing magnetization sensitive X-ray photoemission electron microscopy, we probe magnetic ground states and the "order-by-disorder" phenomenon predicted 30 years ago. We observe the antiferromagnetic striped ground state in square lattices, and 6-fold symmetric structures, including trigonal vortex lattices and disordered floating vortices, in the honeycomb lattice. The spin frustration in the honeycomb lattice causes a phase transition from a long-range ordered locked phase over a floating phase with quasi long-range order and indications of a Berezinskii-Thouless-Kosterlitz-like character, to the thermally excited paramagnetic state. Absent spatial correlation and quasi periodic switching of isolated vortices in the quasi long-range ordered phase suggest a degeneracy of the vortex circulation.
我们使用具有方形和蜂窝对称性的纳米盘阵列，在微观尺度上研究XY偶极系统的磁相和自旋相关性。利用磁化敏感的X射线光电子发射电子显微镜，我们探测了磁基态以及30年前预测的“无序致序”现象。我们在方形晶格中观察到反铁磁条纹基态，在蜂窝晶格中观察到6重对称结构，包括三角涡旋晶格和无序的浮动涡旋。蜂窝晶格中的自旋阻挫导致了一个相变，从具有准长程序和类似Berezinskii-Thouless-Kosterlitz特征的浮动相的长程有序锁定相，到热激发顺磁态。在准长程序相中，孤立涡旋缺乏空间相关性和准周期性切换，这表明涡旋环流存在简并性。
