Surface effect in PVP coated Sm doped magnetite nanoparticles prepared by the polyol method

Abstract

We report the synthesis of Sm doped magnetite (Fe2.68Sm0.32O4) nanoparticles by using the polyol method. To protect the particles from oxidation we have used poly (N-vinilpyrrolidone) (PVP) polymer. The structural and magnetic properties were studied by X-ray diffraction, transmission electron microscopy (TEM), Mössbauer spectroscopy and DC magnetometry. The sample has a narrow distribution of particle sizes with a mean diameter of 5.2 nm. The nanoparticles have superparamagnetic behavior at room temperature with a mean blocking temperature at TB = 9.9 K and effective magnetocrystalline constant of 4 × 105 J/m3 at 5 K. At room temperature, the M-H curve show anhysteretic behavior (Hc=0) and the Mössbauer spectrum has a single paramagnetic component, while at 5 K the saturation magnetization is of 18.9 emu/g and the field cooling M-H loop shows an exchange bias of − 110 Oe. The magnetic results are discussed in terms of the cation distribution in the inverse spinel lattice, as determined by Mössbauer spectroscopy, and from the lower magnetic contribution of a thin layer at the nanoparticles surface with enhanced magnetocrystalline anisotropy.