Entropy driven order in an array of nanomagnets

Long-range ordering, while typically understood as a decrease in entropy, can also be driven by increasing system entropy in certain special cases. We demonstrate that artificial spin ice arrays of single-domain nanomagnets can be designed to produce entropy-driven order. We probe thermally active tetris artificial spin ice, known to have a zero point Pauli entropy, both experimentally and through simulations. We find two-dimensional magnetic ordering in one subset of the nanomagnet moments, which we demonstrate to be induced by disorder (i.e., increased entropy) in another subset of moments. Contrasting with other entropy-driven systems, the degrees of freedom in artificial spin ice are both designable and directly observable at the microscale, and the entropy of the system is precisely calculable in simulations. This robust example, in which the system’s interactions and ground state entropy are well-defined, significantly expands the experimental landscape for the study of entropy-dr...长程有序通常被认为是熵减过程，但在某些特殊情况下，也可由系统熵增驱动。我们证明，可通过设计单畴纳米磁体（single-domain nanomagnets）构成的人工自旋冰（artificial spin ice）阵列，实现熵驱动的有序结构。我们通过实验与模拟两种手段，对已知具有零点泡利熵（zero point Pauli entropy）的热激活俄罗斯方块型人工自旋冰开展研究。我们观察到，部分纳米磁体磁矩呈现二维磁有序结构，且该有序结构由另一部分磁矩的无序状态（即熵增）诱导产生。与其他熵驱动系统不同，人工自旋冰的自由度既可以精准设计，又可在微观尺度下直接观测，且其系统熵可通过模拟精确计算。该鲁棒性实例中，系统的相互作用与基态熵均已明确，极大拓展了熵驱动相关研究的实验场景。