双轴应变调控二维单层C2X2TM（X = O, H; TM=Fe, Cr） 的多铁性研究

基于密度泛函理论的第一性原理计算,系统地研究了过渡金属原子插层的单层氧化/氢化石墨烯的磁学性质和铁电性质.在考虑了电子在位库仑作用和自旋轨道耦合作用下,得到了过渡金属Fe、Cr插层形成的C₂X₂TM二维单层膜的稳定结构以及基态磁性结构,研究了不同应变作用下C₂X₂TM的磁性、能带、铁电极化以及电子结构的变化.结果发现,对于任何应变下的C₂X₂TM其基态磁性都为手性逆时针反铁磁结构.在无应变时体系存在一个较大的离子翻转势垒,通过外加双轴应变,可有效调控体系的势垒高度和能隙,发现25%应变下C₂O₂Cr和30%应变时C₂O₂Fe单层薄膜具有与GeS等二维铁电材料相近的铁电极化和翻转势垒,这些研究结果表明C₂O₂Fe(Cr)单层薄膜是一种新型二维多铁性材料.

Study on multiferroicity of two dimensional monolayer C2X2TM (X = O, H; TM=Fe, Cr) with biaxial strain control

Using first principles calculations based on the density functional theory, we systematically studied the magnetic and ferroelectric properties of two-dimensional monolayer C2X2TM (X=O, H; TM=Fe, Cr), where monolayer oxidized/hydrogenated graphene is intercalated by transition metal atoms Fe and Cr. Considering the electron in-situ Coulomb interaction and spin orbit coupling, the stable structure and ground state magnetic structure of two-dimensional monolayer C2X2TM are obtained. The changes of magnetism, energy band, ferroelectric polarization and electronic structure of C2X2TM under different strains are studied in detail. The results show that the barrier height and energy gap of the system can be effectively controlled by adding biaxial strain, but the chiral counterclockwise antiferromagnetic structure is remained. It is found that C2O2Cr at 25% strain and C2O2Fe at 30% strain monolayer films have ferroelectric polarization and reversal barriers similar to those of two-dimensional ferroelectric materials such as GeS. These results indicate that C2O2Fe(Cr) monolayer film is a new two-dimensional multiferroic material with coexisting FE and AFM order.