Structure Design And Physical Properties Of Two-Dimensional Magnetic Semiconductors

Since the discovery of graphene in 2004,many new two-dimensional materials have been synthesized by researchers in recent years.Among them,because of its magnetic and semiconductor properties,2D magnetic semiconductors have great application potential in low-dimensional spintronic devices and are expected to stand out in the field of spintronics.However,at present,most 2D intrinsic ferromagnets are limited to lower Curie temperature or Neel temperature,so they cannot work stably at room temperature.Therefore,finding magnetic materials with high critical temperatures is of great significance.In this paper,the magnetic and electronic properties of 2D materials T’-MoTeI,MnAsX(X=I,Br,Cl)and Mn2Cl8 are predicted by first-principles calculation.First,The present work finds the monolayer T’-MoTeI is an antiferromagnetic semiconductor with an indirect bandgap.The distorted T’-MoTeI exhibits dynamic stability.T’-MoTeI is an indirect-bandgap semiconductor with 1.35 eV.At biaxial strains of 6%to-6%,the minimum bandgap value is 0.6 eV and the maximum is 1.45 eV.Monte Carlo simulations predict that the TN of T’-MoTeI is 95 K,which can be improved to 210 K by the appropriate strains condition.The results suggest that the monolayer T’-MoTeI can be a potential candidate for spintronics applications.Second,we predict that the monolayer MnAsX(X=I,Br,Cl)is intrinsically a ferromagnetic semiconductor.It is found that due to the inversion symmetry breaking along the vertical direction,the out of plane piezoelectric coefficient and MAE of MnAsI are 6.11 pm/V and 314μeV,respectively.Further discussion was conducted on the spin-down energy band of MnAsX(X=I,Br,Cl),as the proportion of halide elements is very small.And the mechanism of superexchange interaction was used to explain that when the halogen atom changes from Cl to I,TC changes from 340 K to 542 K,which is an extremely fast reduction in direct exchange interaction,while the reduction in superexchange interaction is slower,leading to ferromagnetism being dominant and TC increasing.These excellent magnetic properties show the potential of using the 2D family in basic research on spintronic applications.At last,the present work finds the monolayer antiferromagnetic semiconductor Mn2Cl8.Monolayer Mn2Cl8 and Mn2Cl4X4(X=F,Br)are stable indirect bandgap semiconductors with 0.34 eV,0.95 eV and 0.55 eV,respectively.Under the strain action of-4%to 4%,the antiferromagnetic ground state is not affected,the bandgap increases from small to large,and the TN decreases from large to small.It is find that the compression strains can increase the TN by analyzing the exchange interaction.The Neel temperature can be increased from 245 K to 469 K by applying compressive strains,while the structure remained stable.In addition,hydrogen passivation can increase the band gap and TN of Mn2Cl8 to 2.08 eV and 817 K,respectively.This work find that element substitution,strains,and hydrogen passivation are efficient route to tune the electronic properties of monolayer Mn2Cl8.