First-principles Studies On Magnetic Properties Of Two-dimensional Layered Compound Fe₃GeTe₂

With rapid development of spintronics and improving demand for device miniaturization,the search for two-dimensional magnetic materials that can be applied to spintronics devices has become a hot topic.Among the two-dimensional magnetic materials that have been discovered,Fe₃Ge Te₂ stands out because of its relatively high Curie temperature(T_C),which is closest to room temperature,making it most potential for application.In this paper,first-principles calculations are used to conduct theoretical research on the magnetic ground state,T_C,and magnetic anisotropy energy(MAE)of Fe₃Ge Te₂ using strain and atomic substitution methods.The main results are as follows:(1)By calculating the static energy of different magnetic configurations,the magnetic ground state of the antiferromagnetic(AFM)coupling between inter-layers of Fe₃Ge Te₂ is determined,that is,the magnetic moments of Fe atoms are parallel when located in a van der Waals layer and antiparallel when located in different layers.The AFM ground state will change to ferromagnetic coupling(FM)under a smaller strain range(-2%?4%)of a-axis and isotropic strain on the lattice.However,when the c-axis strain is applied,the AFM ground state can be maintained in a larger strain range.(2)By calculating the inter-atom exchange in Fe₃Ge Te₂,the change of T_C dominated by the Fe-Fe atomic exchange in the same layer is obtained.When uniaxial strain is applied along the a-axis or c-axis,the T_C can be increased to 302 K and 313 K,respectively;when isotropic strain is applied,the T_C fluctuates,with a small overall increase.In addition,in the research of different types of atomic doping,it is found that when Cr atoms are doped at the Fe site,the T_Cwill be reduced.And when Mn and Si atoms are doped at the Fe and Ge site,respectively,the T_C of Fe₃Ge Te₂ will increase.Among them,the change of T_C induced by atomic substitution of Mn is largest.The T_C can be boosted to 667 K at 60%doping concentration.(3)The MAE calculation of Fe₃Ge Te₂ shows that it has a relatively large magnetic anisotropy in the FM state,the easy axis is along the c-axis direction,and a larger MAE can be obtained in the AFM state.When strain is applied,the MAE value of the FM ground state only increases slightly in the range of-1%to 1%,and the overall trend is downward;the MAE value of the AFM ground state has a substantial increase in the range of-5%to 1%,and the maximum can be increased from 12.69 me V/f.u.to 25.34 me V/f.u.The local density of states analysis shows that this is mainly related to the change of the(9and(92_-2 orbitals of Fe atom at the Fermi level.