Theoretical Study On The Electronic Structure And Magnetic Coupling Mechanism Of Two Dimensional Intrinsic Magnets

Two-dimensional?2D?intrinsic magnets are platform to utilize spintronics and topological materials.Nonetheless,the practical application is hindered by the low magnetic ordering temperature.In this dissertation,electronic and magnetic properties have been studied for 2D intrinsic magnet based on density functional theory.The stable magnetic mechanism is proposed,according to which rational modifications has been applied to improve the magnetic ordering temperature.The main conclusion is as following:?1?The calculation of exfoliation energy indicates the that the 2D CrBr₃ lattice is available from its bulk,and the ground state is ferromagnetic semiconducting.Carrier?hole and electron?doping,Cr/Br vacancy and in-plane strain are used to improve magnetic ordering temperature.,among which carrier doping and tensile strain are positive strategies.Further,an insulator to half metal character transition could be actualized via carrier doping and Cr vacancy.With coexisting Cr and Br vacancies,the half metallic character is sensitive to the distance between defects.?2?The insulating character of 2D VI₃ lattice is well rationalized by the extra V atom in the hollow site.Moreover,the ferromagnetic interaction is found to be originated from d_x2y2-p_x,p_y-d_x2y2,a strong pd?hybridization,based on a model of hole resident on I 5p texture.I defect can raise the Curie temperature to above room temperature?419K?,a powerful tool via triggering additional itinerant ferromagnetic path via d_x2y2-p_x-d_x2y2.with desirable half metal behavior.?3?Ni doped CrCl₃(Cr_0.5Ni_0.5Cl)monolayer is studied to disclose some tips for electronic and magnetic coupling manner.The calculated cleavage energy?0.34J/m² and0.32J/m² for C2/m and R-3?underlines the Cr_0.5Ni_0.5Cl monolayer is available from its bulk counterpart.In the ideal half doped Cr_0.5Ni_0.5Cl₃ monolayer,the magnetic ground state is sensitive to the Cr 3d electron correlation(U_Cr)and with U_Cr=4eV or larger,a half metallic ferrimagnetism is established.Ni vacancy and Cl vacancy would trigger a FIM-ferromagnetic transition with the HM character survived.In contrast,Cl vacancy and Cr-rich non-stoichiometry should be exclusive as they would lead to zigzag antiferromagnetic?z AFM?normal metal.Moreover,Ni-rich non-stoichiometry would be positive to stablize the HM-FIM,which brings the critical temperature above room temperature,holding great promise for real application.