Rational Design of Two-Dimensional Magnetic Chromium Borides Based on First-Principles Calculation

Two-dimensional (2D) magnetic materials have been experimentally recognized recently, however, the Curie temperatures (T_\rm C) of known 2D systems are quite low. Generally, magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements. Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high T_\rm C. Based on this, we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems. Using our self-developed software package IM^2ODE, we design a series of chromium-boride based 2D magnetic materials. Nine stable magnetic systems are identified. Among them, we find that CrB_4-I, CrB_4-II and CrB_5-I with common structural units CrB_8 are ferromagnetic metals with estimated T_\rm C of 270 K, 120 K and 110 K, respectively. On the other hand, five CrB_3 phases with structural units Cr_2B_12 are antiferromagnetic metals. Additionally, we also find one antiferromagnetic semiconductor CrB_2-I. Our work may open new directions for identifying 2D magnetic systems with high T_\rm C.