Effect of terbium doping on the optical, electrical and magnetic properties of nanocrystalline nickel ferrite

The present study focuses on the preparation and the characterization of a series of rare-earth terbium (Tb3+) ion-doped nickel ferrite (NFO) nanoparticles [(NiTbxFe2-xO4, x = 0.10, 0.15, 0.20)]. These samples were synthesized using sol-gel method. Rare-earth Tb was doped to tune the structural, optical, dielectric and magnetic features of the spinel nickel ferrite nanoparticles. Therefore, the systematic impact of Tb3+ on the structural, optical, electrical and magnetic studies were carried out. X-ray diffraction (XRD) profile reveals the presence of a single spinel ferrite phase for small doping while in moderately doped NFO NPs, an additional orthorhombic phase along with the spinel phase exists. The strain is increased in Tb-doped NFO lattice. X-ray photoelectron spectroscopy (XPS) study also confirms the presence of Tb ions at the tetrahedral site of Tb-NFO nanoparticles. In absorption spectroscopy, the shift of absorption towards the visible region is significantly increased with the increase in doping amount of trivalent Tb ion. The empirical variable range hopping (VRH) model is introduced to evaluate the density of states and the hopping range, respectively. The electrical properties of Tb-doped NFO compounds exhibit high values of dielectric constant at room temperature with Tb doping. Electric modulus study confirms the presence of non-Debye type of relaxation behaviour in the samples. Two relaxation peaks are observed at higher doping concentration. Room temperature magnetization study confers hysteresis behaviour in Tb-doped nickel ferrite nanoparticle at high frequencies. Different magnetic parameters are evaluated from the magnetic hysteresis loops. There is a significant decrease in magnetization with Tb doping due to the lower magnetic ordering of rare-earth ions.