Crystallographic structures and magnetic properties of L1₀-type FePt nanoparticle monolayered films stabilized on functionalized surfaces

Crystallographic structures and magnetic properties of chemically synthesized FePt nanoparticles, which were firmly stabilized into a monolayer on thermally oxidized Si substrate using 3-amino propyldimethylethoxysilene, were studied. The two-dimensional structure of FePt nanoparticles was confirmed by plan-view high-resolution scanning microscopy observation. The particles transformed from fcc to highly ordered L1₀ structure by annealing at 800°C under high vacuum with minimal coalescence. From rotational hysteresis loss analysis, a large magnetic anisotropy field of over 80kOe for the 800°C-annealed film was estimated. The coercivity of the annealed sample was very small and of the order of 10²Oe at room temperature, meanwhile, the remanence coercivity obtained from DC demagnetization measurement was over 11kOe. This large difference was resulted from the co-existence of Fe-poor particles with different low anisotropy fields in the monolayered film.