Optimization of structure-property relationships in nickel ferrite nanoparticles annealed at different temperature

In this report, a detail analysis of the impact of annealing temperature on the structural, elastic, morphological, optical, and magnetic behavior of NiFe2O4 nanoparticles prepared by the citrate sol-gel method is presented. Analyzing the XRD patterns by the Rietveld method confirms that all the annealed samples have been crystallized to cubic spinel structure belonging to Fd3m space group with a single phase. Rietveld analysis demonstrates the change in structural and microstructural parameters and movement of cations from tetrahedral to octahedral sites and vice-versa upon annealing. The quantitative estimation of Ni2+ & Ni3+ and Fe2+ & Fe3+ has been carried out using XPS analysis. Decreases in peak broadening and shift of five Raman active peaks towards higher frequency upon annealing have been analyzed using the phonon confinement model. The variation in elastic parameters with annealing temperature has been assessed by FTIR analysis. The UV analysis reveals the increase of the optical energy band gap and the decrease of Urbach energy with annealing temperature enhancement. A noticeable sharp absorption band at 748 nm in UV spectra is attributed to 3A2g(3F)→3T1g(3F) electronic transition. Room temperature magnetic hysteresis loops exhibit an increase of saturation magnetization upon annealing which is discussed with reference to finite size effects and disorderly surface spins. The estimated value of magnetocrystalline anisotropy constant by Law of Approach to saturation (LAS) theory as well as coercivity value elucidates the annealing effect in changing the magnetic single domain state of the particle to a multidomain state. Analysis of ZFC and FC magnetization curve measured at 100 Oe in the temperature range 400 K–60 K reveals the significant impact of annealing temperature on magnetic anisotropy, inter-particle interaction, and blocking temperature. Exploring the magnetic hysteresis loop measured in the temperature range 60–400 K over field strength of ± 3 T demonstrates the significant role of annealing on magnetic exchange interaction. Temperature dependent behavior of saturation magnetization and coercivity has been analyzed using modified Bloch’s law and Kneller’s relation. The magnetic heating efficiency examined by the induction heating system reveals that the sample has enough potential for hyperthermia application.