Mechanical alloyed Ho3+ doping in CoFe2O4 spinel ferrite and understanding of magnetic nanodomains

We doped Ho3+ in CoFe1.95Ho0.05O4 spinel ferrite by mechanical alloying and subsequent annealing at different temperatures (600-1200 degrees C). We understood the structural and magnetic properties of the samples using X-ray diffraction, SEM, Thermal analysis (TGA and DTA), and VSM measurement. The samples have shown structural stabilization within cubic spinel phase for the annealing temperature (T-AN) >= 800 degrees C. Thermal activated grain growth kinetics has been accompanied with the substantial decrease in lattice strain. The gain size dependent magnetism is evident from the variation of magnetic moment, remanent magnetization and coercivity of the material. The paramagnetic to ferrimagnetic transition temperature T-C(similar to 805 K) seems to be grain size independent in the present material. The magnetic nanograins, either single domain/pseudo-single domain (50-64nm) or multidomain (above 64 nm) regime, showed superparamagnetic blocking below T-m, which is below T-C (805 K) and also well above the room temperature. (C) 2009 Elsevier B.V. All rights reserved.