Abstract
Hematite iron oxide (alpha-Fe2O3) and spinel ferrite nanopowders were synthesized by hydrothermal technique. The spinel ferrite MFe2O4 is prepared using three divalent metals M = Cu, Zn and Co. In order to investigate the spinel phase formation mechanism, we have used two atomic ratios (M/Fe) between Fe and divalent metal (above and below the stoichiometric ratio) and two preparation times (6 and 10 h). The nanopowder structure and morphology were characterized by mean of X-ray diffraction, scanning and transmission electron microscopies observation. The magnetic properties of the powder were archived using vibrating sample magnetometer. The results reveal that using low divalent metallic concentration yields to a powder composed of hematite and spinel phases. However, increasing the divalent metal concentration leads to the formation of monophasic spinel powder with a metallic oxide secondary phase. The spinel phase formation enthalpy controls the powder crystallite size and the secondary phase formation. The magnetic properties of the powder are altered by the presence of secondary phase. The magnetic exchange between the phase causes the surface spin canting resulting in the magnetic properties deterioration.