Quantitative determination of surface spins contribution of magnetization, anisotropy constant, and cation distribution of manganese ferrite-silica nanocomposite
Résumé
We investigate the impact of silica concentration on the morphology, structure and and magnetic properties of xMnFe2O4-(100-x)SiO2, x=100, 15, and 10, nanocomposites synthesized by a rapid, one-step auto-combustion method. XRD patterns show formation of single-phase cubic spinel structure of MnFe2O4 in all samples without any evidence of secondary phase crystallization. According to TEM analysis, the maximum crystallite size was found for 100MnFe/Si, while 15MnFe/Si has the lowest mean size, being 7.2 nm.
Cation distributions were determined using Mossbauer spectroscopy measuremnts and it was confrimed that the iron species are exclusively in Fe3+ valence state for xMnFe/Si nanocomposites. The impact of disordered surface spins on the total magnetization was systematically investigated by defining a modified Langevin function. Extensive morphological, magnetic and Mossbauer studies depicted that the MnFe2O4/Silica ratio, cations arrangement, interparticle interactions, particle volume distribution and, also, volume/surface ratio, largely impact on the magnetic characteristics of MnFe/Si nanocomposites.