Electron spin resonance of the ferromagnetic Kondo lattice CeRuPO

The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated by electron spin resonance (ESR) at microwave frequencies of 1, 9.4 and 34 GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+ resonance in a metallic Ce compound and can be followed below the ferromagnetic transition temperature T-C = 14 K. At T > T-C the interplay between the RKKY exchange interaction and the crystal electric field anisotropy determines the ESR parameters. Near T-C the spin-relaxation rate is influenced by the critical fluctuations of the order parameter.