Synthesis and Self-Assembly of Films Containing FeCoPt Nanoparticles
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Synthesis and Self-Assembly of Films Containing FeCoPt Nanoparticles
Min Chen and David E. Nikles* The University of Alabama, Tuscaloosa, Center for Materials for Information Technology, Box 870209, Tuscaloosa, Alabama, 35487-0209, US *dnikles@mint.ua.edu ABSTRACT Fe49Co7Pt44 and Fe40Co17Pt43 nanoparticles were synthesized by simultaneous chemical reduction of platinum acetylacetonate and cobalt acetylacetonate and thermal decomposition of iron pentacarbonyl. As-prepared the particles had a disordered face-centered cubic lattice with an average diameter of 3.2 nm and were superparamagnetic. These particles were well dispersed in a 50/50 mixture of hexane and octane. The particles self-assembled into ordered superlattices when deposited onto carbon coated Cu TEM grids or onto single crystal Si (100) substrates. After vacuum annealing (from 500°C to 700 oC), the particles transformed to the tetragonal phase. The coercivity of the film strongly depended on the composition and annealing temperature. For the Fe49Co7Pt44 film, coercivity of 8700 Oe and a squareness of 0.75 after annealing at 700 oC for 30 minutes. XPS shows existance of oxidized iron and cobalt on the surface of film. INTRODUCTION Ordered superlattices of nanosize particles have received considerable attention in recent years, as they present an interest both for fundamental and potential applications. Some of methods used for preparing ordered superlattices from the liquid phase are Langmuir-Blodgett technique, [1] self-assembly by slowing evaporation of solvent [2-5], and electrophoretic deposition [6]. It has been found that formation of ordered closed-packing nanoparticle array requires the monodispersed particles and proper stabilization by surfactants. The synthesis of nanoparticles, characterized by a low size distribution, is a new challenge in solid-state chemistry. Due to their small size, nanoparticles exhibit novel material properties that differ considerably from those of the bulk solid state. Up to date, ordered self-assembly of nanocrystals has been successfully fabricated for several materials, such as Ag [2], Au [3], Fe2O3 [4], CoO [5]. Equatomic FePt and CoPt nanocrystals attracted high interest for the ultrahigh density magnetic hard media because they have large uniaxial magnetocrystalline anisotropies (Ku) due to their tetragonal L10 crystal structure. Recently, (Co100-xFex)50Pt50 thin films, with 20
