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 deg. 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