Exchange Narrowing Effects in the EPR Linewidth of Gd Diluted in Ce   Compounds
  Anomalous thermal behavior on the EPR linewidths of Gd impurities diluted in Ce compounds has been observed. In metals, the local magnetic moment EPR linewidth, \Delta H, is expected to increase linearly with the temperature. In contrast, in Ce_{x}La_{1-x}Os_{2} the Gd EPR spectra show a nonlinear increase. In this work, the mechanisms that are responsible for the thermal behavior of the EPR lines in Ce_{x}La_{1-x}Os_{2} are examined. We show that the exchange interaction between the local magnetic moments and the conduction electrons are responsible for the narrowing of the spectra at low temperatures. At high temperatures, the contribution to the linewidth of the exchange interaction between the local magnetic moments and the $Ce$ ions has an exponential dependence on the excitation energy of the intermediate valent ions. A complete fitting of the EPR spectra for powdered samples is obtained. 
Pablo A. Venegas and Paulo R. S. Netto