Crystal fields in ErCu, ErAg, and ErZn

Abstract

The splitting of the crystal-field levels in the intermetallic compounds $\mathrm{Er}M$ ($M=\mathrm{A}\mathrm{g},\mathrm{C}\mathrm{u},\mathrm{Z}\mathrm{n}$) has been determined by inelastic neutron scattering experiments. In all three cases, the crystal-field parameters $A_4^0 〈 r^4 〉$ and $A_6^0 〈 r^6 〉$ are negative and of the same order of magnitude. The ground state is always a ${\Gamma }_8^{\mathrm{}\left(3\right)\mathrm{}}$ quadruplet. The point-charge model fails to explain the large values of the sixth-order terms. The crystal-field Hamiltonian interprets well the magnetic properties of these compounds.