Evolution of domain structure in Fe_3GeTe_2

Two-dimensional(2D)magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices.The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism.Here,we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe₃GeTe₂(FGT)with a thickness range of 11.2-112 nm.Three types of domain structures and their corresponding hysteresis loops can be obtained.The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness,which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields.These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness.Our finding not only enriches the fundamental magnetism,but also paves a way towards spintronics based on 2D magnet.     

砂土统一模型的显式计算及加载速度影响研究

以砂土体渐进破坏问题为背景，采用显式方法进行高、低压下砂土统一模型的二次开发以克服隐式算法在软化计算中的强非线性不收敛问题，实现具有剪胀软化、剪缩硬化特性材料的模拟计算．在此基础上开展三个压力等级、不同位移加载速度条件下的平面应变压缩试验，分析位移加载速度对显式计算结果的影响效应．通过分析得到结论：(1)采用动力学显式算法对常压至高压范围的砂土统一模型进行计算是可行的，受荷响应随加载速度的降低逐渐趋于稳定并最终得到静力学计算结果，能够反映砂土在低压下的剪胀软化以及高压下的剪缩硬化特性；(2)砂土统一模型的显式计算结果受加载速度的影响呈双折线趋势，并存在加载速度界限值，试样在加载速度界限值前后呈现不同的受荷变形破坏形态；(3)采用显式计算方法开展砂土统一模型的准静态模拟过程中，须结合计算结果偏差面积比随加载速度的关系曲线，来确定满足一定偏差面积比并且小于界限值的准静态位移加载速度．