Coexistence of spin glass behavior and long-range ferrimagnetic ordering in La- and Dy-doped Co ferrite

The structure, dc magnetization and ac susceptibility characteristics of the rare-earth (R = La,Dy) ion substituted cobalt-ferrites (CoO center dot Fe(1.925)La(0.075)O(3) and CoO center dot Fe(1.925)Dy(0.075)O(3)) are evaluated. R-substituted Co-ferrites crystallize in the cubic inverse spinel phase. The irreversible temperature (T(irr)) between zero field cooled (ZFC) and field cooled (FC) magnetization for CoO. Fe(1.925)La(0.075)O(3) and CoO center dot Fe(1.925)Dy(0.075)O(3) determined from the temperature variation of magnetization measurements are 283 and 292 K, respectively. The broadening of ZFC magnetization and more than one maximum indicates the coexistence of short-range ferrimagnetic clusters of different size with a long-range ferrimagnetic phase. Magnetization curves indicate no saturation up to 30 kOe suggesting the canted spin structure inside the clusters. The relaxation times of spin clusters calculated using the Vogel Fulcher law for the frequency-dependent ac susceptibility measurements are on the order of similar to 10(-6) s. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3562201]