Collective ferromagnetism of artificial square spin ice

We have studied the temperature and magnetic field dependence of the total magnetic moment of large-area permalloy artificial square spin ice arrays. The temperature dependence and hysteresis behavior are consistent with the coherent magnetization reversal expected in the Stoner-Wohlfarth model, with clear deviations due to inter-island interactions at small lattice spacing. Through micromagnetic simulations, we explore this behavior and demonstrate that the deviations result from increasingly complex magnetization reversal at small lattice spacing, induced by inter-island interactions, and depending critically on details of the island shapes. These results establish new means to tune the physical properties of artificial spin ice structures and other interacting nanomagnet systems, such as patterned magnetic media.我们针对大面积坡莫合金人工方形自旋冰（artificial square spin ice）阵列的总磁矩，开展了温度与磁场依赖性的系统研究。该阵列的温度依赖特性与磁滞行为，与斯通纳-沃尔法思模型（Stoner-Wohlfarth model）所预测的相干磁化反转过程一致，但当晶格间距较小时，会因岛间相互作用出现显著偏差。借助微磁模拟（micromagnetic simulations），我们对该现象展开了深入探究，结果表明，这类偏差源自岛间相互作用在小晶格间距条件下诱发的愈发复杂的磁化反转过程，且该过程高度依赖纳米岛形状的具体细节。本研究成果为人工自旋冰结构及其他相互作用型纳米磁系统（如图案化磁介质）的物理特性调控提供了全新的可行路径。