Pure magnetic hard fct FePt nanoparticles: chemical synthesis, structural and magnetic properties correlations

FePt nanoparticles, containing a near-equal atomic percentage of Fe and Pt, with a face centered tetragonal structure (fct), are challenging for potential applications in high performance permanent magnets and high density data storage. In this study, we report on the chemical synthesis, carried out both solvothermally and hydrothermally in autoclave reacting iron (III) acetylacetonate and platinum (II) acetylacetonate with tri- or tetra-ethylene glycol, these employed as solvents, reducers and particle surface protecting agents as well. In both methods, a subsequent thermal treatment at high temperatures is necessary to transform the magnetic soft face centered cubic (fcc) phase to the hard fct one. Organic low-weight molecules, generally used to protect the nanoparticle surface and avoid particle aggregation, are decomposed by the thermal treatment resulting in particle aggregation and coalescence phenomena; on the contrary, in this case, a polymer matrix is formed as particle protecting agent and, by thermally treating the hydrotermally prepared nanoparticles up to 750 °C for 1h, the pure magnetic hard fct phase is obtained while preserving the nanostructure. A detailed study is carried out on FePt nanoparticle structure (fcc and fct phases) and correlated to the magnetic properties of the system.