First-principles Investigations On Electronic Structure And Spin-orbit Coupling In Antiferromagnetic Materials

Antiferromagnetic materials have various advantages in spintronic device applications including their robustness against external magnetic field perturbation,exhibiting ultrafast dynamics and holding zero average magnetic moment.They are promising candidates for next generation high speed,low power consumption,high density non-volatile magnetic memory.It may be used to solve some issues in memory device based on ferromagnetic material,such as the slow speed of reading and writing,high power consumption,limited recording density.At present,manipulation the Néel vector of antiferromagnetic materials are based on Spin-Orbit Torque effect（SOT）generated by current pulse which need current densities of?10⁷A/cm².And using the anisotropic magnetoresistance measurements reads out the Néel vector orientation.However,switching ratio is too low.Thus,we need an effective means to manipulate the Néel vector.Besides,high switching ratio antiferromagnetic materials are necessary.In this paper,we investigate three typical antiferromagnetic materials with great potential spintronics applications:NiO,Cu₃TeO₆,Mn₂Au.First-principles calculations were used to study their electronic band structure,density of states,exchange coupling constants,magnon spectra,magnetocrystalline anisotropy energy（MAE）and magnetocrystalline anisotropy constants.Further make a detailed discussion on the response of the magnetocrystalline anisotropy under strain.Based on these,we have done the following works:1.Strain dependence of magnetic properties of NiO:The MAE of the tetragonal NiO changes drastically compared with cubic NiO.The easy axis changes from[-110]to[110].Moreover,the maximum of MAE in the（010）and（110）plane of the tetragonal NiO increases nearly 10 times compared to cubic NiO,and the angular dependence becomes stronger.The magnon spectra of NiO is consistent with the experimental data,but we get a slightly lower maximum frequency than the experiment.2.For Cu₃TeO₆,we obtain a band gap of approximately 1.68 eV.Considering the sixth nearest neighbours exchange coupling in the Heisenberg Hamiltonian,the linear-spin-wave theory is applied to obtain the magnon spectra of Cu₃TeO₆.At the high symmetry point,there are band crossing with topological properties,which is consistent with the experimental data.3.For Mn₂Au,the Mn spin moment is approximately 3.68μ_B.The easy axis is[010]or[100]in plane of（001）.When strain is applied,Mn₂Au exhibits two tetragonal structures.The easy axis is[100]and the MAE increases by approximate 60 times compared with the cubic Mn₂Au.The Heisenberg exchange coupling constant is approximately-62.76 meV.On the high symmetric path X-（38）,the magnon spectra is degenerate,and it is impossible to split by choice of further Heisenberg exchange coupling constants.