Single-ion anisotropy in compounds of rare earths other than Sm: Importance of J-mixing in the room-temperature range

Abstract

Contrary to the established view, J-mixing is found to strongly affect the magnetic anisotropy of compounds of all light rare earths and also of terbium. The fractional contribution of J-mixing to second-order anisotropy constants in the room-temperature range is proportional to absolute temperature and depends on the rare earth element involved but not on the characteristics of the specific solid. For the light rare earths this contribution is given by 12(2J−1)−1kT/Δso, where Δso is the spin-orbit splitting between the centers of gravity of the ground and first excited multiplets, and amounts to 22% for Pr and Nd and to as much as 83% for Sm at T=400 K. For the heavy rare earths the corresponding expression is 12(2J+3)−1kT/Δso, which is 11% for Tb at T=400 K and significantly less for the rest of the rare earth series. Analytical expressions are obtained which allow for the J-mixing and are accurate in the room-temperature range for all rare earths with the possible exception of Sm.