On the Magnetic Anisotropy of FeF₂and CoF₂

The magnetic anisotropies of FeF 2 and CoF 2 are studied in detail by calculating the crystalline field acting on their magnetic ions and considering the effect of the spin-orbit coupling. The electronic energy level splittings of the ions Fe ++ and Co ++ in the crystalline field are calculated assuming first that all the surrounding ions are point charges and then taking account of the overlapping of their 3 d electrons with the electron clouds of the surrounding fluorine ions. The spin-orbit coupling is then introduced and the g -values are calculated. Further, introducing the exchange coupling in the approximation of molecular field, the parallel and perpendicular susceptibilities of FeF 2 are calculated and a reasonable agreement with experiment is found. For CoF 2 , however, the calculated level splitting is not successful in explaining the observed susceptibilities. Discussions are given on the possible sources of this disagreement and the nature of the approximations made in this study.