Abstract
Lanthanum (La)-substituted cobalt ferrites CoFe2-x La x O4 (x = 0.00-0.09) were successfully prepared using the sucrose sol-gel auto-combustion route. La-substitution effects on the structural, magnetic, and electrical/dielectric characteristics were investigated using different techniques. X-ray diffraction (XRD) results displayed a deviation from the single-phase structure at La-content >= 0.04 because of the formation of orthorhombic LaFeO3 at the boundaries of the grains. Both XRD and Fourier transform infrared (FT-IR) measurements showed that the crystal structure had not been significantly affected by La-substitution attributed to the crystallization out of this LaFeO3. Vibrating sample magnetometry (VSM) measurements revealed gradual decreases in the magnetization as the La-content increases, which could be referred to as the decrease in the super-exchange interaction in the octahedral sites because of the preferential substitution of large ionic radius La3+ ions in the octahedral positions. As the antiferromagnetic LaFeO3 formed, a severe reduction in the magnetization appeared. The increase in the magnetization at 0.09 was attributed to the cationic redistribution among sublattices. On the other hand, the coercivity data indicated the hard magnetic characteristics of all the samples. The electrical conductivity results showed the semiconducting character of all samples with obvious decreases with increasing La-content. According to Verwey's hopping mechanism, these decreases were attributed to the preferential occupation of La3+ by octahedral positions. Dielectric results versus temperature indicated anomalies relaxations around 460 K with the successive addition of lanthanum attributed to the electrical inhomogeneity that occurred due to oxygen vacancy created or the Maxwell-Wagner mechanism.