NiFe₂O₄nanorod: porosity effect on spin canting, quadrupole splitting and hyperfine magnetic properties

Abstract

Porous nickel ferrite nanorods having diameter ∼200 nm and length ∼2.5 to 3.0 μm were synthesized by microemulsion method followed by calcination at 450 °C. The morphology and structure of the final as well as intermediate materials, formed during this method, were characterized by x-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope and Fourier transform infrared spectroscopy. Positron annihilation spectroscopy was used to identify the structural defects such as vacancies and surface disorder, and to find out the porosity of the synthesized nanorods. Mössbauer spectroscopy was used to determine the cation distribution and magnetic hyperfine property of the nanorods. Detailed magnetic characterization by measuring magnetization as a function of magnetic field and temperature were examined by physical property measurement system and SQUID magnetometer, respectively. The reduced saturation magnetization (Ms = 20.3 emu gm−1) and enhanced coercive (Hc = 37 Oe) field of our synthesized samples was explained on the basis of surface electron effect. Moreover, formation mechanism and effect of precursor materials were also discussed.