| With the rapid development of science and technology,traditional semiconductor electronics technology based on electronic charge is gradually approaching the physical limit.Spintronics,which uses the charge and spin as the information carrier,can greatly improve the device information processing speed and storage density,and are thus attracted a lot of attention recently.In recent years,two-dimensional materials represented by graphene have become a hot topic of condensed matter physics.These two-dimensional materials have great potential applications in the field of electronic and optoelectronic devices due their rich and.novel physical and chemical properties.However,most of the existing two-dimensional materials are not magnetic.It can not be directly applied to the spintronics devices.Finding a new two-dimensional magnetic materials has been concerned by a lot of researchers.Two-dimensional layered transition metal compounds are considered to a candidate for future spintronics,because it has the partially filled d-shell and the monolayers are very easy to be exfoliated mechanically.Fe3GeTe2,which is studied in this paper,is a kind of layered ferromagnetic transition metal compound which has been successfully prepared by experiments.It has high Curie temperature and has great potential application.However,the magnetic coupling mechanism of the material is still unclear,and it is necessarily to be studied.In this paper,the first-principles calculation based on density functional theory is used to study the layered transition metal compound Fe3GeTe2 and its monolayer deeply.The electronic structure and magnetic properties are obtained,and the magnetic exchange is calculated based on the Ising model.The magnetic field transition temperature was then obtained by using the mean field theory and Monte Carlo simulation.The main contents include:The structure and electronic structure of Fe3GeTe2 were studied.It is found that the ground state of Fe3GeTe2 is ferromagnetism by PBE method,and the calculated lattice constant and the ground state of Fe3GeTe2 are in good agreement with the experimental results.The electronic states in the range of-6-leV are found to be contributed mainly by the d-orbit of the Fe.And the states near the Fermi level are mainly contributed by the d-orbit of the Fe and the p-orbit of Te.Then,the spin-orbit coupling effect is also considered to calculate the magnetic anisotropy energy of few-layer Fe3GeTe2.It is found that the system is typically Ising Ferro-magnetism and the easy-direction is c-axis.The magnetic anisotropy is layer-insensitive and the value is about 1100 ? eV/atomFinally,the magnetic exchange interaction of single-layer Fe3GeTe2 is obtained by combing DFT and Ising model,and Curie temperature was also studied comparably by mean field approximation(MFA)and Monte Carlo simulation(MC).The response magnetic exchange interaction and Curie temperature with strain are also considered in the calculation.The results obtained by MFA and MC are 261K and 240K,in good agreement with the experiment.In addition,the calculation also found Curie temperatures in the considered strain range remained essentially unchanged.The analysis shows that J ?and J?show the opposite change and the contribution of system energy kept almost invariant under strain,which leads to strain-independent Curie temperature. |
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