Spin Arrangements in Magnetic Compounds of the Rocksalt Crystal Structure

Abstract

The ground state spin arrangements in magnetic compounds of the NaCl type structure are studied by consideration of exchange interactions between nearest neighbors (J₁) and between next-nearest neighbors (J₂). Ferromagnetic arrangement as well as antiferromagnetic arrangements of the first kind, second kind, and improved first kind are obtained in different intervals of the parameter γ=J₂⁄J₁. Each of the three antiferromagnetic arrangements is degenerate due to the cubic symmetry of the crystal and the spin arrangement indefinite. Since the monoxides of the iron group elements are slightly distorted below the Néel point, the relevant small changes in J₁ and J₂ are taken into account to see if the degeneracy is removed. It turns out that the degeneracy is removed partially or completely. Helical spin arrangements appear in certain intervals of γ. Finally, anisotropy energy of the form DS_z² is taken into account, but the degeneracy still remains unlifted in some cases.