Structural, electrical and magnetic properties of Zr–Mg cobalt ferrite

Spinel cobalt ferrite, CoFe2−xMxO4 has been synthesized by substitution of the combination of metallic elements M=Zr–Mg by the microemulsion method using polyethylene glycol as a surfactant. Powder X-ray diffraction analysis reveals that the substitution results in shrinkage of the unit cell of cobalt ferrite due to higher binding energy of the synthesized samples. The energy-dispersive X-ray fluorescence analysis confirms the stoichiometric ratios of the elements present. The thermogravimetric analysis shows that the minimum temperature required for the synthesis of these substituted compounds is 700 °C. A two-point probe method was employed for the measurement of the electrical resistivity in a temperature range of 293±5 to 673±5 K. It appears that there is a decrease in the number of Fe2+/Fe3+ pairs at the octahedral sites due to the substitution and corresponding migration of some of the Fe3+ ions to tetrahedral sites, consequently increasing the resistivity and the activation energy of hopping of electron at the octahedral sites. The susceptibility data also suggest migration of Fe3+ to tetrahedral site in the initial stage, which results in an increase in A–B interactions leading to large increase in the blocking temperature (TB) as observed in samples having dopant content x=0.1.