Structure of antiferromagnetic NiO/ferrimagnetic NiMn2O4 composite prepared by sorbitol-assisted sol-gel method

Polycrystalline powders of nickel manganite (NiMn2O4) and NiO/NiMn2O4 composite have been synthesized by simple sol-gel rout based on sorbitol as a chelating agent of metal ions. The samples are prepared in aqueous medium in the ratios of the nickel chloride to the manganese chloride namely 1:2 and 1:1 with 3 ml of sorbitol. The green gel is formed after solvent elimination and it is calcinated at temperature of 800 °C. The phase concentrations are determined by synchrotron X-ray powder diffraction and Rietveld method. The obtained NiMn2O4 sample is formed of single phase and produced NiO/NiMn2O4 composite is composed of NiO (49%) and NiMn2O4 (51%). Scanning electron microscopy and energy dispersive X-ray analysis are used to investigate the morphology and chemical composition of the produced samples. It includes strong evidences of interfaces between nickel oxide and nickel manganite particles, shading light on the mechanism of spin exchange coupling between these materials. Temperature and magnetic field dependence of magnetization are investigated for DC magnetization measurements. The magnetic transition for NiMn2O4 is observed at 98 K and for NiO/NiMn2O4 at 65 K and 109 K.