Magnetic and hyperfine properties of Fe sub(2)P nanoparticles dispersed in a porous carbon matrix

Structural and magnetic properties of nanocomposite, consisting of Fe sub(2)P particles dispersed in a porous carbon matrix, have fully been investigated using X-ray diffraction, Mossbauer and ac and dc magnetization measurements. Besides production of the nanocomposite, using an activated carbon (prepared by chemical activation of a char with H sub(3)PO sub(4)), impregnation with a Fe super(3+) salt in aqueous medium and subsequent heat treatments under N sub(2) flow, we found a formation of hexagonal Fe sub(2-x)P and orthorhombic FeP in a mass ratio of 4:1, respectively. Low temperature Mossbauer spectra revealed that a large fraction (ca. 28%) of the material is in the paramagnetic state, suggesting that part of the Fe sub(2-x)P phase appears in the form of very small particles. A metamagnetic phase transition was also observed for non-stoichiometric Fe sub(2-x)P nanoparticles. It is observed at about 150 K, well below the ordering temperature of the Fe sub(2)P phase (230 K), and is dependent on the dc-probe fields. Also, the Fe sub(2-x)P nanoparticles were found to have a hard-like magnetic character at low temperatures, with coercive field H sub(C) 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.