Exchange narrowing of the dipolar fields in EuX (X = O,S, Se,Te, B6) from ESR at 70 GHz

The exchange narrowed ESR linewidth is expected to become frequency dependent if the resonance frequency and the reciprocal correlation time of the local dipolar fields are in the same order of magnitude. We report on a corresponding ESR linewidth investigation of the four Eu-monochalcogenides and of EuB₆ which were performed up to 70 GHz.