Tuning magnetic order with geometry: Thermalization and defects in two-dimensional artificial spin ices
Tuning magnetic order with geometry: Thermalization and defects in two-dimensional artificial spin ices
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DOI：
10.1103/physrevb.101.144403
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发表时间：
2020-04
影响因子：
3.7
通讯作者：
Gavin M. Macauley;G. Paterson;Yue Li;R. Macêdo;S. McVitie;R. Stamps
中科院分区：
文献类型：
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作者：
Gavin M. Macauley;G. Paterson;Yue Li;R. Macêdo;S. McVitie;R. Stamps
人工自旋冰是相关的纳米级磁岛阵列，证明是研究拓扑结构在临界现象中的作用的绝佳场所。在这里，我们调查了一个连续的自旋冰的几何形状，参数化旋转的岛屿。在这样做的过程中，我们从经典的方形冰变形到最近研究的风车几何形状，旋转角度作为控制岛屿间相互作用的代理。我们实验观察到的过渡，从反铁磁有序方冰铁磁顶点的弱耦合风车冰热退火的钴阵列上使用洛伦兹透射电子显微镜略有偏好。旋转角度也会影响个别阵列的弛豫时间尺度，导致不同程度的热化，并支持的缺陷的性质的明显变化：从一维字符串在方形冰二维涡状结构的几何形状类似风车。这些量的数值标度与Kibble-Zurek机制预测的一致。我们的研究结果表明，人工自旋冰的磁序可以通过几何形状的变化来调整，并提出了在二维系统中实现真正受挫的冰规则相的可能性。此外，我们证明了这个系统作为一个测试平台，调查跨阶段的平衡动力学。
Artificial spin ices are arrays of correlated nano-scale magnetic islands that prove an excellent playground in which to study the role of topology in critical phenomena. Here, we investigate a continuum of spin ice geometries, parameterised by rotation of the islands. In doing so, we morph from the classic square ice to the recently studied pinwheel geometry, with the rotation angle acting as a proxy for controlling inter-island interactions. We experimentally observe a transition from antiferromagnetic ordering in square ice to a slight preference for ferromagnetic vertices in the weakly-coupled pinwheel ice using Lorentz transmission electron microscopy on thermally annealed cobalt arrays. The rotation angle also affects the relaxation timescales for individual arrays, leading to varying degrees of thermalisation, and an apparent change in the nature of the defects supported: from one-dimensional strings in square ice to two-dimensional vortex-like structures for geometries similar to pinwheel. The numerical scaling of these quantities is consistent with that predicted by the Kibble-Zurek mechanism. Our results show how magnetic order in artificial spin ices can be tuned by changes in geometry and suggest the possibility of realising a truly frustrated ice-rule phase in two-dimensional systems. Furthermore, we demonstrate this system as a testbed to investigate out-of-equilibrium dynamics across phases.