Simulation of the paramagnetic susceptibility in rare earth oxychlorides

The average magnetic susceptibilities of polycrystalline rare earth oxychlorides (REOCl; RE=Ce, Pr, Nd, Sm, Tb, Dy and Ho) were measured between 2 and 300 K. The susceptibility of most REOCl samples follows the paramagnetic Curie–Weiss behaviour down to low temperatures (<20 K). However, TbOCl, SmOCl, and DyOCl show additional antiferromagnetic ordering at 4, 8, and 11 K, respectively. The experimental paramagnetic susceptibilities were simulated with the aid of the van Vleck formalism based on the wave functions and energy level values obtained from a previous phenomenological simulations of spectroscopic data. The deviation of the magnetic susceptibilities of several REOCl from the Curie–Weiss behaviour at low temperatures can be explained by the gradual population of the crystal field (c.f.) components of the ground 2S+1LJ level. At high temperatures the difference between the calculated and experimental data is due to the modification of the c.f. effect as a result of the lattice expansion. The strong preferred orientation of the REOCl crystallites may affect the experimental data because of the strong anisotropy of the paramagnetic susceptibility.