First Principles Study On The Magnetic Properties Of Single And Double Layers Of M₂As（M=Fe,Mn）

Since the discovery of graphene in 2004,two-dimensional materials have received widespread attention and developed rapidly due to their many unique properties.However,due to the early theory that the magnetic phase transition does not appear in a strict two-dimensional system,the research on two-dimensional intrinsic magnetic materials has not made a breakthrough until recent years,which is marked by the experimental development of single-layer Cr I₃ and Fe₃Ge Te₂.With the deepening of research,people began to discover that some physical properties of the existing van der Waals（vd W）type two-dimensional magnetic materials,such as low Curie temperature（T_C）and poor stability,have restricted their wide application.Therefore,researchers are constantly striving to explore more two-dimensional magnetic materials.In this paper,a new type of two-dimensional magnetic material M₂As（M=Fe,Mn）is predicted based on first-principles calculations.Aiming at the problems of low Curie temperature and low conductivity of existing two-dimensional magnetic materials,the layered non-vd W type is used.The material has the characteristics of weak interlayer metal bond.It is predicted that single-layer M₂As has higher stability,good conductivity and higher Curie temperature.On this basis,the magnetic properties of double-layer M₂As are studied.The specific conclusions are as follows:For single-layer M₂As,the phonon spectrum and molecular dynamics calculations show that the single-layer M₂As structure is stable both in dynamics and thermodynamics.Through careful calculation,it is found that the ground state of single-layer Mn₂As is ferrimagnetic state,while the single-layer Fe₂As is ferromagnetic state.They all have obvious out-of-plane magnetic anisotropy and large magnetic anisotropy（Mn₂As is 101μe V/Mn,Fe₂As is 84μe V/Fe）,combined with the calculation results and the average field approximation study,it is found that their Curie temperatures are relatively high（single-layer Mn₂As is 450 K,single-layer Fe₂As is251 K）.In addition,we have also studied the effect of strain on its magnetic properties,and found that a single layer of Mn₂As will undergo a ferromagnetic-antiferromagnetic transition under a certain biaxial strain,while a single layer of Fe₂As maintains a higher T_C ferromagnetic state.These results indicate that single-layer M₂As has stable ferromagnetism and may be applied at room temperature.For the double-layer M₂As,by calculating and comparing the energy of different magnetic configurations,it is found that the ground state of the two double-layer materials is an antiferromagnetic state;the calculation of the density of states and energy band shows that the double-layer M₂As is metallic.The calculated results of the magnetic anisotropy show that the easy magnetization axis of the double-layer Mn₂As is in the XY plane,while the easy magnetization axis of the double-layer Fe₂As is still in the out-of-plane Z-axis.In addition,the practicability of the double-layer M₂As was investigated by calculating the influence of the applied strain.It was found that the double-layer Fe₂As is prone to antiferromagnetic-ferromagnetic transition when the strain is applied,while the double-layer Mn₂As can maintain the anti-iron in a larger strain range.Magnetic state.These properties indicate that the double-layer Mn₂As may be more suitable for antiferromagnetic spintronic devices,and the controllable magnetism of the double-layer Fe₂As is more worthy of further theoretical research.Our research shows that the few-layer M₂As（M=Fe,Mn）thin films are expected to be potential candidates for spintronics,providing new ideas for exploring new non-van der Waals two-dimensional magnetic systems based on arsenic materials.