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The alternating current (a.c.) susceptibility versus temperature and magnetization measurements are reported for the disordered spinel ferrite system Znx COl_x Fe2 04 prepared by a wet chemical method before and after high temperature annealing. The low field a.c. susceptibility measurements indicate that the low temperature synthesis of wet prepared Co-Zn ferrites aids the formation of spin-clusters and thereby increases the magnetic inhomogeneity. The X-ray analysis shows that the samples are single phase spinels and the variation of lattice constant with zinc concentration deviates from Vegard's law i-1 ]. The high temperature annealing changes the wet prepared ferrites into the ordered magnetic structure of the ceramic ferrites.

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The alternating current (&c.) low field susceptibility vs temperature, magnetization and STFe M6ssbauer effect measurements are reported for the spinel solid solution series MgxCol_xFe204 synthesized by a wet-chemical method before and after high temperature annealing. The observed features for the wet samples, such as the coexistence of paramagnetic doublet and magnetic sextets in M6ssbauer spectra and lower saturation magnetization values confirm small particle ferrite behaviour. Especially, M6ssbauer spectra of wet samples reveal the presence of superparamagnetic particles which exist simultaneously with ferrimagnetic regions in the materials well supported by a.c. susceptibility data. The high temperature annealing changes the wet-prepared ferrites into the ordered magnetic structure of ceramic ferrites.

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