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

• Ni 2+ substituted strontium ferrite Sr 1-x Ni x Fe 2 O 4 (x = 0.0 0.2, 0.4, 0.6, 0.8) • Decrease in squareness ratio is due to substitution of Ni 2+ in SrFe 2 O 4 lattice. • Squareness ratio revealed the transition of multi domain to single domain particles. • Resistivity values demonstrated semiconductor behavior of all synthesized material. • The conduction mechanism at higher temperature is dependent on hopping of polarons. Citrate gel combustion method is used for the synthesis of Ni 2+ substituted strontium ferrite Sr 1-x Ni x Fe 2 O 4 (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 SrCO 3 . Scanning electron microscopy (SEM) images showed agglomeration of particles. The effect of Ni 2+ substitution in SrFe 2 O 4 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 Ni 2+ ion. The squareness ratio (SQR) Mr/Ms for SrFe 2 O 4 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 Ni 2+ 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 (E a ) for ferri and paramagnetic region is calculated. For ferrimagnetic region the E a is found to increase with increasing Ni 2+ content while, in paramagnetic region for Ni 2+ substituted samples the E a 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.