As*

Antiferromagnetic Fe₂As attracts interest due to its tetragonal chemical structure with easy-plane magnetism and metallic electrical conductivity. To understand the electrically-activated switching process of the Néel vector in this material, anisotropy energy becomes an important parameter as an energy barrier. Anisotropy energy originates from spin-orbit interaction (SOI) and magnetic dipole-dipole interaction (MDD). We use density functional theory and classical modeling to investigate SOI and MDD, and find that in-plane anisotropy is dominated by SOI, which is two times larger than the MDD contribution to out-of-plane anisotropy. The in-plane anisotropy presents four-fold symmetry and is 276.5 J/m³ which is confirmed by torque magnetometry, and total out-of-plane anistoropy energy is 829772 J/m³ with two-folded symmetry. Based on anisotropy energy and magnetic susceptibility, the lowest frequency spin wave is predicted to have a frequency of 0.64 THz and out-of-plane anisotropy dominates. This suggests that easy-plane antiferromagnetic materials might exhibit fast dynamics and high speed of switching similar to uniaxial materials. However, these materials might suffer from low thermal stability, due to the extremely small in-plane anisotropy.