Self-assembled Monolayer FePt Nanoparticle Film with High Coercivity and Easy Axis Orientation

Shishou Kang, Shifan Shi, David E. Nikles, and J.W. Harrell, Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, AL 35487

D. Li and J. Ping Liu, Dept of Physics, The University of Texas at Arlington, Arlington, TX 76019

The announcement by S. Sun in 2000 that highly monodisperse FePt nanoparticles could be produced by chemical synthesis generated great excitement because of the potential for storage densities orders of magnitude greater than current media [1]. This initial excitement has been tempered, however, by the difficulty of achieving monodisperse nanoparticle arrays with high coercivity and easy axis orientation. Recently, J. Ping Liu’s group has shown that high coercivities can be obtained while preventing sintered grain growth by annealing FePt nanoparticles in a salt matrix [2]. We have demonstrated that a self-assembled monolayer of these nanoparticles can be prepared with oriented magnetic easy axes. The TEM below shows a monolayer of 8-nm FePt nanoparticles with a room temperature coercivity of 15 kOe. The particle dispersion was dried in a magnetic field in the plane of the film. The angular variation of the intensity of the (200) diffraction ring suggests preferential orientation of the c-axes in the direction of the drying field. This is the first demonstration of a high coercivity monolayer FePt nanoparticle film with easy axis orientation.