Effect of Ti4+ ions doping on microstructure and dc resistivity of nickel ferrites

Abstract Nanostructured nickel ferrites (NiFe 2 O 4 ) were prepared by doping with Ti 4+ ions using solid-state reaction route. Lowest grain size of 55 nm was achieved in the specimens with 20 mole% TiO 2 doping. Magnetization in the specimens decreases with decreasing grain sizes. Lower volume fractions of ferrite phase due to dissociation of the magnetic phase into smaller particles by the disruption of super exchange interaction by the titanium substitution results a decrease in magnetizations. Coercivity showed an increasing trend. This was explained as arising due to multidomain/monodomain magnetic behavior of magnetic nanoparticles. Small polaron hopping conduction between Fe 2+ and Fe 3+ sites controls the dc electrical properties of the specimens. The presence of an interfacial amorphous phase between the sites is evident from Mott's analysis. Specimens containing 10 mole or more TiO 2 and sintered at 1350 °C contain NiTiO 3 as a secondary phase and show unusual dc conductivity.