Magnetic and hyperfine properties of Fe2P nanoparticles dispersed in a porous carbon matrix

Structural and magnetic properties of nanocomposite, consisting of Fe2P particles dispersed in a porous carbon matrix, have fully been investigated using X-ray diffraction, Mössbauer and ac and dc magnetization measurements. Besides production of the nanocomposite, using an activated carbon (prepared by chemical activation of a char with H3PO4), impregnation with a Fe3+ salt in aqueous medium and subsequent heat treatments under N2 flow, we found a formation of hexagonal Fe2−xP and orthorhombic FeP in a mass ratio of 4:1, respectively. Low temperature Mössbauer spectra revealed that a large fraction (ca. 28%) of the material is in the paramagnetic state, suggesting that part of the Fe2−xP phase appears in the form of very small particles. A metamagnetic phase transition was also observed for non-stoichiometric Fe2−xP nanoparticles. It is observed at about 150 K, well below the ordering temperature of the Fe2P phase (230 K), and is dependent on the dc-probe fields. Also, the Fe2−xP nanoparticles were found to have a hard-like magnetic character at low temperatures, with coercive field HC of 1.3 KOe. Considering these interesting magnetic and hyperfine properties and also the large specific surface area of the porous carbon matrix, which is not severely reduced after impregnation with the Fe-containing compounds, one may point to promising technological applications of the produced nanocomposite.