Conduction-electron enhancement of exchange interactions in SmS

La doping of SmS is found to greatly increase both the Sm2+-Sm2+ exchange interaction (as measured by the Van Vleck susceptibility) and the Sm2+-Eu2+ (impurity) exchange interaction (as measured by the EPR g shift). It is shown that this enhancement is primarly due to the indirect exchange caused by the conduction electrons donated by the La. Furthermore, these two exchange interactions have different dependences on La doping. © 1973 The American Physical Society.