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.我们研究了大面积坡莫合金（permalloy）人工方形自旋冰阵列的总磁矩对温度与磁场的依赖特性。该阵列的温度依赖行为与磁滞特征与斯通纳-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，会因纳米岛间相互作用出现明显偏差。通过微磁模拟，我们对该行为展开了系统探究，结果证实，这类偏差源于晶格间距较小时由纳米岛间相互作用引发的愈发复杂的磁化反转过程，且其强烈依赖于纳米岛的具体形貌细节。本研究结果为调控人工自旋冰结构及其他相互作用纳米磁系统（如图案化磁存储介质）的物理特性提供了全新途径。