Size variation in nanocrystalline Zn0.2Ni0.8Gd0.05Fe1.95O4 ferrites: Exchange bias effect and its correlation with disordered surface spins

Abstract The article reports the influence of particle size variation on microstructural, optical and magnetic properties of nanocrystalline Gd doped Ni-Zn ferrites with a generic formula Zn0.2Ni0.8Gd0.05Fe1.95O4. The nanoparticles were synthesized using chemical co-precipitation technique and the average crystallite sizes were found in the range of 4 nm–29 nm as estimated from Scherrer’s relation. Raman spectra confirmed the lowering of symmetry of the octahedral sites of the cubic spinel structure with rare earth doping. A blue shift was observed in the absorption profile of the nanoparticles due to the size effect. The 7 T field cooled M-H plots recorded at 5 K exhibited exchange bias for the sample with the smallest particle size which was attributed to the high anisotropy of the canted surface spins compared to the core spins.