Magnetic, structural and magnetocaloric effect investigations on the substituted spinel Mg1-xZnxFe2O4 (0 ≤ x ≤ 1) prepared by sol-gel method

Abstract Polycrystalline Mg1-xZnxFe2O4 (0 ≤ x ≤ 1) ferrites were prepared with sol-gel method. The obtained samples were characterized by powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mossbauer spectrometry. The X-ray diffraction analysis combined with the Rietveld refinement confirmed that the samples crystallize in a single-phase cubic spinel structure with (SG: Fd¯3 m) and an average grain size in the range of 29.1 – 40 nm. Lattice parameter increases with increasing Zn concentration, due to the larger ionic radius of Zn2+ ions in regard of Mg2+ ions. The Curie temperature TC decreases linearly with substitution. Saturation magnetization (MS), magnetic moment of iron (µFe) and magnetic entropy change (-ΔSM) increase for x ≤ 0.5 and decrease for x ≥ 0.5, this behavior is attributed to the cationic distribution of the ions on tetrahedral [A] and octahedral [B] sites, where the structure turns from partially inverse spinel to normal spinel, affecting the remanent magnetization and the coercitive field. Moreover, a new empirical relation is acquired performing linear relation between magnetic moment and the inversion parameter δ. Mossbauer spectra show a transformation from sextuple to an only a doublet which indicates a transformation from ferrimagnetic to paramagnetic phase, this ferrimagnetism degradation is confirmed by the negative values of -ΔSM and the transition of the magnetocaloric effect from normal to inverse through substitution.