报告人：季威

报告题目：Magnetic anisotropy dominated spiral to antiferromagnetic transition from bulk to monolayer NiI2

报告摘要：Mono- and few-layer NiI2 were recently evidenced to be two-dimensional type-II multiferroic materials. Such assessment is, however, based on an assumption that the spiral magnetic configuration of NiI2, experimentally found in its bulk counterpart, persists to the monolayer (1L) limit and it does not significantly contribute SHG signal. Here, we found that such hasty assumption is flawed at the monolayer limit where freestanding 1L NiI2 prefers to striped antiferromagnetism using density-functional-theory calculations. This configuration offers an intralayer antiferroelectricity. Thus, the NiI2 monolayer is, indeed, a type-I multiferroic material with both antiferromagnetism and antiferroelectricity. Such a magnetic groundstate variation from bulk to 1L NiI2 originates from the competition between in-plane single ion anisotropy of Ni atoms and out-of-plane contribution of interfacial I atoms to magnetic anisotropic energy (MAE). These theoretical results not only unveil the magnetic groundstate of 1L NiI2, but also enlighten us the role of layer-stacking induced change of magnetic anisotropy in thickness-dependent magnetic transitions of two-dimensional magnets.

报告简介：季威，中国人民大学物理学系教授。2008年从中国科学院物理研究所获得博士学位，随后在加拿大McGill大学从事博士后研究，2010年进入中国人民大学工作。研究兴趣主要为发展和应用独特的第一性原理计算方法，与实验紧密结合，模拟和预测低维量子系统和信息材料与器件的界面前沿问题。研究成果被选为2011年国际邮票素材、入选2013中国科学十大进展、2014年和2015年中国百篇最具影响国际学术论文。2014-2016年获得三个国家级青年人才计划或创新项目支持，2019年入选中科院青促会首批特邀会员，2021年入选国家高层次人次奖励计划。目前担任中国材料研究学会计算材料学委员会委员；ACS Applied Electronic Materials副主编，Science Bulletin、Chinese Physics B、《物理学报》、2D Materials和Frontiers of Physics编委。