The magnetic susceptibilities of erbium and holmium ethylsulphates

Measurements of the principal magnetic susceptibilities of holmium and erbium ethylsulphates have been made in the temperature range 1.5-300 °K. The results are compared with calculations based on crystal field parameters A n m ⟨ r n ⟩ derived from the optical absorption spectra of these substances. At low temperatures, where the effects due to rare earth interactions become important, account is taken of both magnetic hyperfine, and first- and second-order magnetic dipole interactions, again using parameters derived from previous microwave resonance experiments. For both compounds, in both the principal crystallographic directions, the agreement is good, suggesting firstly that effects due to thermal expansion are surprisingly small over this wide temperature range, and secondly that rare earth electrostatic (exchange) interactions are quite negligible in these compounds at temperatures above 1 °K.