Mössbauer and electrical studies of NixCo1-xFe2O4 nanoparticles

Nanocrystalline nickel substituted cobalt spinel ferrites with chemical formula NixCo1-xFe2O4 (0 ≤ x ≤ 1.0) have been synthesized by the glycol-thermal technique under low reaction temperature of 200 °C. The crystallite size ranges from about 8 nm to 14 nm across the composition range. Strong correlation between particle size and sample reaction pressure has been observed. This shows dependence of the magnetic properties on the synthesis conditions. 57Fe Mössbauer spectra recorded at room temperature (∼300 K) show ferrimagnetic behaviour of the compounds and have been explained on the bases of composition and crystallite size. MÓ§ssbauer data recorded at 80 K are indicative of enhanced hyperfine fields and isomer shifts due to increased magnetic order. Magnetization results reveal superparamagnetic nature of the compounds investigated. Resistivity measurements on the pellet samples annealed at 1100 °C show evidence of semiconducting behaviour. The current results also show significant differences in the resistivity determined from each face of a pellet.