On the Magnetic Susceptibility of FeF₂

Abstract

Adopting the effective Hamiltonian by Pryce and the molecular field approximation, the parallel and perpendicular susceptibilities of FeF₂ are calculated. According to the experiments by Stout and Matarrese, the perpendicular susceptibility below the Néel point decreases with decreasing temperature. Denoting the components of the D-tensor in Pryce’s effective Hamiltonian by D_i (i=x, y, z) where the z-axis is taken as the c-axis and the x-axis as the direction of the line connecting two nearest neighbouring F ions, this behaviour of the perpendicular susceptibility can be explained if Dx, Dy>Dz. The parallel susceptibility at absolute zero has a non-zero value proportional to (Dx–Dy)². However this term is of the same or small order compared with the temperature-independent part of the magnetic susceptibility. Comparisons with experiments are made by using the values of the D-tensor and the g-factor obtained by Tinkham. If the reasonable values of exchange integrals are adopted, the calculated susceptibilities are in good agreement with the experimental results by Stout and Matarrese.