Doubly Bottlenecked EPR in Cu:Cr,Mn

The temperature dependence of the EPR linewidth in Cu: Cr,Mn has been measured. A generalization of the Hasegawa theory for the case with two species of paramagnetic impurities is derived and found to exhibit two interconnected bottleneck conditions. Our data indicate that Cu: Cr,Mn is doubly bottlenecked, i.e., that both Cr and Mn participate dynamically in the EPR.