Entropy-driven order in an array of nanomagnets
Entropy-driven order in an array of nanomagnets
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DOI：
10.1038/s41567-022-01555-6
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发表时间：
2022-04-07
期刊：
影响因子：
19.6
通讯作者：
Schiffer, Peter
中科院分区：
文献类型：
--
作者：
Saglam, Hilal;Duzgun, Ayhan;Schiffer, Peter
长程有序通常与熵的减少有关。然而，在某些特殊情况下，它也可以由熵增加驱动。在这里，我们证明了人工自旋冰阵列的单域纳米磁体可以设计产生这样的熵驱动的顺序。我们专注于俄罗斯方块人工自旋冰结构，一个高度沮丧的阵列几何与零点鲍林熵，这是通过选择性地创建正则空位上的规范方形冰晶格。我们探测热活性俄罗斯方块人工自旋冰实验和模拟，测量单个纳米磁体的磁矩。我们发现在这些时刻的一个子集，我们证明是由无序（即熵增加）在另一个子集的时刻引起的二维磁序。与其他熵驱动的系统相比，俄罗斯方块人工自旋冰的离散自由度是二元的，并且在微观尺度上既可设计又可直接观察，并且系统的熵可以在模拟中精确计算。这个例子中，系统的相互作用和基态熵得到了很好的定义，扩展了熵驱动有序研究的实验范围。
Long-range ordering is typically associated with a decrease in entropy. Yet, it can also be driven by increasing entropy in certain special cases. Here we demonstrate that artificial spin-ice arrays of single-domain nanomagnets can be designed to produce such entropy-driven order. We focus on the tetris artificial spin-ice structure, a highly frustrated array geometry with a zero-point Pauling entropy, which is formed by selectively creating regular vacancies on the canonical square ice lattice. We probe thermally active tetris artificial spin ice both experimentally and through simulations, measuring the magnetic moments of the individual nanomagnets. We find two-dimensional magnetic ordering in one subset of these moments, which we demonstrate to be induced by disorder (that is, increased entropy) in another subset of the moments. In contrast with other entropy-driven systems, the discrete degrees of freedom in tetris artificial spin ice are binary and are both designable and directly observable at the microscale, and the entropy of the system is precisely calculable in simulations. This example, in which the system's interactions and ground-state entropy are well defined, expands the experimental landscape for the study of entropy-driven ordering.