Effect of Ni2+ substitution on magnetic, optical and electrical properties of SrFe2O4

Abstract

Citrate gel combustion method is used for the synthesis of Ni2+ substituted strontium ferrite Sr1-xNixFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8). The characterization of synthesized material is done by different techniques. Fourier transform Infra-red (FT-IR) spectra revealed the inverse spinel structure and showed slight shift in spectrum. X-ray diffraction (XRD) patterns demonstrated the orthorhombic phase of spinel formation with trace of secondary phase impurity of SrCO3. Scanning electron microscopy (SEM) images showed agglomeration of particles. The effect of Ni2+ substitution in SrFe2O4 on structural, magnetic, optical and direct current (DC) electrical resistivity properties are investigated. Room temperature vibrating sample magnetometer (VSM) studies indicated increase in trend of saturation magnetization (Ms) and remanence magnetization (Mr) with increase in content of Ni2+ ion. The squareness ratio (SQR) Mr/Ms for SrFe2O4 is found to be 0.5752, while for remaining samples it is found to be less than 0.5 which demonstrated multi domain to single domain transition. Variation of band gap energy with Ni2+ substitution is reported with the help of ultra-violet diffuse reflectance spectra (UV-DRS). Temperature dependent DC electrical resistivity by two probe method measurement obeyed Arrhenius equation and revealed the typical semiconducting behavior of the samples. The change in slope of line observed in resistivity due to ferrimagnetic to paramagnetic transition in all samples attributed strong exchange interaction between the outer and inner electrons. Activation energy (Ea) for ferri and paramagnetic region is calculated. For ferrimagnetic region the Ea is found to increase with increasing Ni2+ content while, in paramagnetic region for Ni2+ substituted samples the Ea is found to be greater than 0.2 eV which inferred the hopping motion of small polarons are responsible for conductivity. The complex impedance spectra revealed the information about conduction mechanism.