Structural and magnetic model of self-assembled FePt nanoparticle arrays

X-ray diffraction, small angle neutron scattering, and magnetometry were used to investigate chemically ordered, self-assembled FePt nanoparticle arrays with high magnetic anisotropy. Thin assemblies of polyethylenimine (PEI) and 4 nm Fe 58Pt 42 nanoparticles were analyzed. A metallic magnetic core surrounded by a weakly magnetic or nonmagnetic shell resulted from annealing FePt nanoparticles in the PEI-FePt assembly. The L1 0 chemical ordering and FePt nanoparticles having high coercivity were derived from high temperature annealing.