Effect of Er doping on the structural and magnetic properties of cobalt-ferrite

Nanocrystalline particulates of Er doped cobalt-ferrites CoFe(2–x)ErxO4 (0 ≤ x ≤ 0.04), were synthesized, using sol-gel assisted autocombustion method. Co-, Fe-, and Er- nitrates were the oxidizers, and malic acid served as a fuel and chelating agent. Calcination (400–600 °C for 4h) of the precursor powders was followed by sintering (1000 °C for 4 h) and structural and magnetic characterization. X-ray diffraction confirmed the formation of single phase of spinel for the compositions x = 0, 0.01, and 0.02; and for higher compositions an additional orthoferrite phase formed along with the spinel phase. Lattice parameter of the doped cobalt-ferrites was higher than that of pure cobalt-ferrite. The observed red shift in the doped cobalt-ferrites indicates the presence of induced strain in the cobalt-ferrite matrix due to large size of the Er+3 compared to Fe+3. Greater than two-fold increase in coercivity (~66 kA/m for x = 0.02) was observed in doped cobalt-ferrites compared to CoFe2O4 (~29 kA/m)