Effects of microstructure on the magnetic properties of polycrystalline NiMn2O4 spinel oxides

Polycrystalline NiMn₂O₄ samples were synthesized by sol-gel method at 500 °C (S500), 700 °C (S700), and 800 °C (S800). The three samples were then structurally characterized by X-ray diffraction and Rietveld refinement. Results indicate that samples are single phase and crystallize in the $\mathrm{Fd}\overline{3}m$ space group with spinel structure. Williamson-Hall analysis shows that samples present different lattice strains. NiMn₂O₄ compounds show the magnetic transition from ferrimagnetic to paramagnetic at nearly 100 K. Hysteresis loops measured at T = 1.7 K after cooling the samples under magnetic field are asymmetric along the field axis.