Electron spin resonance of Nd3+in CeRu2and ThRu2: a study of the superconducting and normal states

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Abstract
The authors have performed a careful ESR study of Nd3+ in the normal and superconducting states of CeRu2 and ThRu2. The superconducting transition temperature of the former compound was controlled by substituting Fe or Mn for Ru in CeRu2. This enabled a convenient temperature range to be chosen to study both the normal and superconducting states. The main features of the authors' experimental results are as follows: (a) The ESR thermal broadening is roughly the same in both the normal and superconducting states; (b) The hyperfine constant associated with the 143Nd isotope does not vary significantly upon going from the normal to the superconducting state. The feature (a) cannot be explained by theories developed for NMR in the mixed state. Although the authors cannot account for the first feature at present, it indicates a significant modification of the vortex state in the presence of magnetic impurities.