Longitudinal relaxation time due to RKKY coupling in mixed-valence HgFeSe

The authors investigate the electron paramagnetic resonance (EPR) linewidth and amplitude of the Fe3+ ions in semimetallic HgSe:Fe. An effective spin relaxation mechanism caused by RKKY coupling between Fe3+ and Fe2+ ions is proposed to explain the experimental data. They conclude that the strongly nonuniform relaxation rate originating from the nonuniformity of the local environment of Fe3+, leads to a decrease of the EPR amplitude as observed in experiment.