On the anisotropy in the exchange field experienced by Er ions in the metallic cubic compounds PrSb and TmSb

The electron spin resonance spectra of Er in PrSb and TmSb single crystals exhibit two lines with appreciable angular dependent resonance fields. The data is analysed in terms of a Lambda ₈⁽¹⁾ crystalline field ground state together with a generalized exchange interaction between the Er ions and the host Pr (or Tm) rare earth ions. Using the crystalline field parameters as determined for the analogue compounds YSb:Er and LaSb:Er, the exchange parameters for PrSb:Er were found. Unlike previous predictions, no evidence for a significant orbital anisotropy in the exchange was observed.