Large easy-plane magnetic anisotropy in square planar coordinate Sr2CoO2X2 (X = Cl, Br)

Abstract Large magnetocrystalline anisotropy energy (MAE) is an important requirement for applications in spintronic devices. Here, we focus on layered cobalt oxyhalides Sr2CoO2X2 (X = Cl, Br) with unusual square planar coordination, which are naturally expected to possess a strong MAE. Based on density functional calculations, we find Co ions adopt a high spin state due to the large spin-exchange splitting and exhibit a sizable orbital moment of about 0.6 μB for both compounds. The in-plane nearest-neighbor exchange interaction J1 is antiferromagnetic coupling, and at least one order of magnitude stronger than other exchange interactions, which results in the observed G-type magnetic ground state. As expected, Sr2CoO2X2 have a giant MAE of about 13 meV per Co atom, and the magnetic moments prefer to lie in the ab plane, which is largely originated from the unique crystal field environment and could be explained by perturbation theory.