Evidence is presented for the existence of exchange interactions between the ${\mathrm{Eu}}^{2+}$ impurities and the $J=1\mathrm{}$ excited states of ${\mathrm{Sm}}^{2+}$ ions in SmS and SmSe. The temperature dependences of the ${\mathrm{Eu}}^{2+}$ $g$ shifts are found to be well explained by the addition of these interactions to those arising from the $J=0\mathrm{}$ ground states. Some peculiarities in the EPR behavior of the mixed-valence compound ${\mathrm{Sm}}_3$${\mathrm{S}}_4$(Eu) are also reported.

• Received 10 November 1977

DOI:https://doi.org/10.1103/PhysRevB.17.3707