Tunable Electronic and Magnetic Properties of Two-dimensional Janus Magnetic Materials

Abstract

Two-dimensional magnetic materials have attracted much attention since they provide new opportunities for the development of multifunctional devices.1-2 Half-metal materials with 100% spin polarization are highly desired in spin-based devices. Because they are not only the ideal electrode materials for the magnetic tunneling junctions (MTJ),3 but also can realize high efficient spin injection to the semiconductors.4 Janus magnetic materials have broken the time and space symmetries simultaneously, which may show novel physical properties comparing with their counterparts.5-6 However, the electronic and magnetic properties of Janus half-metal materials are still unclear, so we selected the half-metal, 1T-FeCl2 monolayer,7-8 as the prototype to study the electronic and magnetic properties of its Janus structures, and the stains are applied to tunable their properties in this work. The FeXY (X, Y = Cl, Br and I) monolayers are half-metals and their ferromagnetism stem from the super-exchange interaction according to the GKA theory. The Curie temperature (Tc) of Janus FeClBr, FeClI and FeBrI are 28, 21 and 29 K, respectively (Figure 1 (a)). In the meantime, the Tc under biaxial strains is investigated and the Tc are 54, 42 and 61 K at e = -6%, increasing about 100% comparing with the unstrained FeXY monolayer. Besides, the MAE of FeXY strongly relies on the angle of magnetization and increases considerably under compressive strain. The MAE of FeBrI as an example is shown in Fig. 1 (c), the unstrained FeBrI is IMA, but translating from IMA to PMA when e < 0 and e > 2%, this will help to increase the density of storage. And the absolute value of MAE enhances one order magnitude when the e = -6%. It is demonstrated that the compressive strains effectively enhance the ferromagnetism of FeXY. The atom-resolved MAE shows that the main contributions of MAE come from Fe and I atoms. Additionally, the MAE of I atom translates from IMA to PAM when e < -2% which induce the translation of total MAE. To further explicate the change of MAE, the orbital-resolved MAE of FeBrI is calculated and the results plotted in Figure 2. The I atom is IMA at e = 0%, because the matrix element differences between px and py orbitals are negative and the absolute value is larger than the py and pz orbitals. However, the px and py orbitals hybridization translate to the positive at e = -6%, which make the magnetic anisotropy translate from IMA to PMA. Our studies provide an example of the 2D Janus half-metal materials and enrich the 2D magnetic material library.This work is supported by National Natural Science Foundation of China (51871161 and 52071233). **