LAUSR

This is a detailed study of the local magnetic anisotropy of rare-earth ions in RFeAsO (R = Ce, Nd, Sm) compounds. A modified crystal field theory method is used to calculate the energy levels of the rare-earth ions and the g-factors. The temperature dependences of the components of the magnetic susceptibility are constructed, along with the fourth order anisotropy constants. A method is proposed for determining the “easy” direction of the magnetic moment. The calculations show that the “easy” directions of the magnetic moments of Ce3+ and Nd3+ ions in the orthophase are the [100] and [010] axes, respectively, and in the tetraphase the [110] axis is the “easy” axis for both ions. In the case of Sm3+ the “easy” direction is the [001] axis regardless of the symmetry of the phase.