Abstract：

　　Anisotropic magnetic exchange interactions lead to a surprisingly rich variety of the magnetic properties. Considering the spin orbit coupling (SOC) as perturbation, we extract the general expression of a bilinear spin Hamiltonian, including isotropic exchange interaction, antisymmetric Dzyaloshinskii-Moriya (DM) interaction and symmetric Γ term. Though it is commonly believed that the magnitude of the DM and Γ interaction correspond to the first and second order of SOC strength respectively, we clarify that the term proportional to λ² also has contribution to DM interaction. Based on combining magnetic force theorem and linear-response approach, we have presented the method of calculating anisotropic magnetic interactions, which now has been implemented in the open source software WienJ. Furthermore, we introduce another method which could calculate the first and second order SOC contribution to the DM interaction separately, and overcome some shortcomings of previous methods. Our methods are successfully applied to several typical weak ferromagnets for 3d, 4d and 5d transition metal oxides. We also predict the conditions where the DM interactions proportional to λ are symmetrically forbidden while the DM interactions proportional to λ² are nonzero, and believe that it is widespread in certain magnetic materials.

报告人简介：

　　万贤纲，南京大学物理学院教授，1990年至2000年在南京大学学习，获得学士、硕士、博士学位。2001起在南京大学历任讲师，副教授，2010年任教授。主要学术成绩为：提出了新型拓扑量子态—Weyl半金属, 该工作被评为“2011年中国百篇最具影响国际学术论文”，该工作也入选美国物理学会PRB期刊创刊50年“里程碑”(MILESTONE)文章，评语是：提出了一种新的量子物质状态外尔半金属(The Weyl semimetal, a new state of quantum matter, is proposed.)；发展了一套计算磁性相互作用的方法并确定多个复杂体系的基态磁构型；基于原子绝缘体基组发展了高效判断拓扑性能的理论方法，并用其对无机材料数据库里面所有非磁材料的拓扑特性进行了分类，构造了拓扑材料数据库。该工作被评为“2019年中国百篇最具影响国际学术论文”，该工作也入选“2019中国十大科技进展新闻”。获中国物理学会2018-2019年度叶企孙物理奖。2019年获首届腾讯基金会“科学探索奖”。 2020年获第二届全国创新争先奖。