Structural, magnetic and magnetocaloric study of Ni 0.5 Zn 0.5 Fe 2 O 4 spinel

The objective of this work was to study the influence of annealing temperature on the structural changes and magnetic properties of the Ni0.5Zn0.5Fe2O4 spinel-type nanoparticles. The nanomaterial was prepared by the chemical co-precipitation method and studied by thermal analysis (TG–DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic measurements and 57Fe Mossbauer spectrometry. XRD has revealed that the as-prepared sample shows poor crystallization with less defined diffraction lines. As the annealing temperature increases, the diffraction peaks become intense and well defined, reflecting perfect crystallization of the sample. The estimated crystallite size varies from 25 to 83 nm. TEM observations give information on the morphology and confirm the XRD results. To quantify the proportions of the iron atoms in the tetrahedral and octahedral sites, in-field Mossbauer spectrometry measurements were carried out at low temperature. Saturation magnetization (Ms) and the average hyperfine magnetic field $$ \left( {\left\langle {B_{\text{hf}} } \right\rangle } \right) $$ increase gradually with annealing temperature. For the sample annealed at 1000 °C, the magnetic entropy change $$ \left| {\Delta S_{\text{M}}^{\hbox{max} } } \right| $$ and relative cooling power, measured under field change of 2T, are 0.67 J kg−1 K−1 and 112.5 J kg−1, respectively.