First Principles Study On The Electronic Structure And Magnetic Properties Of Mo/W-doped CrBr₃

The two-dimensional（2D）intrinsic magnetic material Cr Br₃is widely used in spintronics devices and magnetic memory devices because of its efficient magnetic cooling technology,green environment,large magnetothermal effect and low cost.As the miniaturization of electronic devices continues to approach the physical limit,the traditional charge-based devices are bottlenecked by quantum effects and can no longer meet the technical needs.Researchers have fused the two endogenous properties of electrons to design spintronic devices with magnetic properties possessing superior properties including small power loss,rapid speed of functioning and large density of storage.However,the research on 2D intrinsic magnetic materials is still in the early stage,and most of them have weak magnetic anisotropy energy（MAE）and Curie temperature（T_C）far below room temperature,which is not conducive to the stability of magnetic storage units and is difficult to measure experimentally,which significantly hampers their proper use at room temperature.The design of 2D intrinsic magnetic materials with high T_Cand strong MAE is an urgent research problem in the field of spintronics.In this work,the 4d transition metal（TM）element Mo and the 5d TM element W are chosen to replace the Cr atoms in the monolayer Cr Br₃to construct the alloy compounds Cr_8-xMo_xBr₂₄,Cr_8-xW_xBr₂₄and Cr₆Mo WBr₂₄,respectively,and their electronic structures and magnetic properties were systematically investigated by first-principles calculations based on density generalization theory,and the main research contents are as follows:1.The electronic structure and magnetic properties of intrinsic Cr Br₃were investigated.The monolayer intrinsic Cr Br₃is an indirect bandgap semiconductor having a bandgap value of1.31 e V.Its magnetic ground state is a ferromagnetic（FM）state with FM superexchange interactions dominating the total exchange interactions.The exchange energy value is 65 me V,MAE is 202μe V/Cr,the easy magnetization axis is oriented perpendicular to the Cr Br₃system plane,and the T_Cis 33.2 K.2.The electronic structure and magnetic properties of Cr_8-xMo_xBr₂₄were investigated.Cr_8-xMo_xBr₂₄are thermally stable in the room temperature range,they maintain their semiconductor properties,the forbidden band widths all decrease,and the energy band structure of Cr_8-xMo_xBr₂₄（x=2-4）changes from the indirect band gap to the direct band gap.The doping does not undergo a magnetic phase transition and Cr_8-xMo_xBr₂₄are all in the FM state with enhanced FM coupling,T_Cvalues compared to the intrinsic Cr Br₃.Their MAE increases linearly with increasing doping concentration.The magnetic properties of Cr₄Mo₄Br₂₄can be further modulated by the application of biaxial tensile strain.3.The electronic structure and magnetic properties of Cr_8-xW_xBr₂₄were studied.Cr_8-xW_xBr₂₄are thermally stable in the room temperature range.They maintain the semiconductor properties and the bandgap values are more reduced compared to Cr_8-xMo_xBr₂₄.The doping does not undergo a magnetic phase transition,and Cr_8-xW_xBr₂₄are all in the FM state,and their FM coupling was stronger than that of Cr_8-xMo_xBr₂₄.The MAE increases linearly with increasing doping concentration,and the T_Cvalue is significantly higher than that of Cr Br₃.The MAE of Cr₄W₄Br₂₄is 11.6 times higher than that of Cr Br₃,and the applied biaxial tensile strain regulates the magnetic properties of Cr₄W₄Br₂₄better.It was found that W doping of Cr Br₃was better than Mo doping.4.The electronic structure and magnetic properties of Cr₆WMo Br₂₄were investigated.Cr₆WMo Br₂₄maintains semiconductor properties with reduced band width,stability,FM coupling,and MAE between Cr₆Mo₂Br₂₄and Cr₆W₂Br₂₄.MAE between them is due to the larger SOC intensity of W and the smaller SOC intensity of Mo than W.The SOC contribution of W contribution is larger than that of Mo.The results of this work show that the doping of Cr Br₃with different concentrations of homologous Mo and W elements and the application of biaxial strain can obtain intrinsic magnetic semiconductors with high T_Cand strong MAE,and W is more effective than Mo doping.The work has expanded the family of 2D magnetic semiconductor materials,providing a theoretical basis for the preparation of high-temperature ferromagnetic semiconductors and a direction for optimising the performance of Cr Br₃-based optoelectronic devices,promoting the use of Cr Br₃in high-density magnetic memory and spintronics.