Electron paramagnetic resonance for localized magnetic states in the superconducting La-Er system

Electron paramagnetic resonance for the localized Er magnetic moments in La in the normal and superconducting states is studied. A sharp narrowing of the resonance line on transition to the superconducting phase is observed. The contribution to the EPR line width is extracted which is due to the nonuniform distribution of the magnetic H field in a sample existing in the mixed state at Hsub(c1) (<=) H (<=) Hsub(c1). The results are interpreted by assuming that the ''electron bottle neck'' conditions and the efficiency of the indirect exchange interactions are increased on transition to the superconducting state