Role of pH value during chemical reaction, and site occupancy of Ni2+ and Fe3+ ions in spinel structure for tuning room temperature magnetic properties in Ni1.5Fe1.5O4 ferrite

Abstract

The magnetic properties of Ni1.5Fe1.5O4 ferrite have been investigated using the techniques of dc magnetometry and Mӧssbauer spectroscopy. The material has been prepared by chemical reaction of metal nitrates at different pH values and subsequently, annealed at different temperatures to improve the microstructure. The samples with single-phased cubic spinel structure have been used for magnetic study. The material showed a variety of magnetic features, including superparamagnetic and soft ferromagnetic properties. At room temperature, changes of the ferromagnetic parameters of the material have been found in the range 0–47emu/g for spontaneous magnetization, 0–0.37 for squareness, and 0–195Oe for coercivity. Variation of the pH value during chemical reaction and changes of the grain size by thermal treatment played an important role in tuning the coexisting superparamagnetic and ferromagnetic components in the material. Samples prepared at high pH value showed small grain size and superparamagnetic features, whereas the samples prepared at low pH value produced large grain size and better ferromagnetic features. The ferromagnetic properties of the material have been enhanced by lowering the pH value and increasing the annealing temperature. Mössbauer spectra provided insight of the local magnetic order, site occupancy of Ni and Fe ions and oxidation state of Fe ions in the spinel structure of Ni1.5Fe1.5O4 ferrite.