Microwave resonant and zero-field absorption study of pure and doped ferrite nanoparticles

► Microwave absorption was studied for Fe3O4 MNP's prepared by coprecipitation. ► NiCuZnFe2O4 MNP's prepared by the sol-gel combustion method. ► In all cases only one ferromagnetic resonance line was observed. ► Fe3O4 MNP's showed no absorption at zero field. ► NiCuZnFe2O4 MNP's exhibited a sizable zero-field loss.