title: Self-assembled FePt nanocrystals with large coercivity: reduction of the fcc-to-L1(0) ordering temperature.
abstract: Herein we report the synthesis and properties of Fe(55)Pt(45) nanoparticles, both monodisperse and self-assembled into hexagonal close-packed and cubic arrays of 4.0 +/- 0.2 nm size in an L1(0) structure, obtained by a modified polyol process. The new synthetic route improved the control over the particle composition, thereby reducing the temperature required to convert from face-centered cubic (fcc) to face-centered tetragonal (fct) phase by some 30-50 degrees C without additives. Annealing at 550 degrees C for 30 min converts the self-assembled nanoparticles into ferromagnetic nanocrystals with large coercivity, H(C) = 11.1 kOe. Reducing the fcc-to-fct (L1(0)) ordering temperature avoided particle coalescence and decreased the loss in particle positional order without compromising the magnetic properties, as is generally observed when additives are used.
authors.affiliation: Laboratory of Magnetic Materials and Colloids, Department of Physical Chemistry, Institute of Chemistry, Universidade Estadual Paulista (UNESP), P.O. Box 355, 14801-970 Araraquara, São Paulo, Brazil.
authors.forename: Laudemir Carlos
authors.initials: LC
authors.lastname: Varanda
authors.forename: Miguel
authors.initials: M
authors.lastname: Jafelicci