Magnetic and electronic properties of layered Sr_2NiO_2Cl_2 with square planar coordination

摘要

Local coordination geometry is crucial in determining the physical properties of transition metal compounds. In this work, we report a detailed density functional theory study on the magnetic and electronic properties of layered Sr_2NiO_2Cl_2, which possesses an unusual square planar coordination. Due to the crystal field and spin splitting, Ni 3d electrons fully occupy the d_(xz), d_(yz), and d_(xy) orbitals, while partially occupy the d_(z~2) and d_(x~2-y~2) states, leading to the high spin state of Ni~(2+) ions and strong antiferromagnetic in-plane nearest-neighbor exchange interaction J_1, Thus, Sr_2NiO_2Cl_2 is predicted to exhibit a G-type magnetic ground state, which all nearest-neighbor magnetic moments are antiparallel to each other in the NiO_2 plane. A band gap is opened irrespective of the specific magnetic state since the unique square planar crystal field splitting. Finally, large orbital moments and giant easy-plane magnetocrystalline anisotropy energy are obtained, which is again related to the unique coordination environment.