Shock Compression of FePt and FePt/Fe3Pt Nanoparticles: Exchange-Coupled Nanocomposite Magnets

The shock‐compression response of partially‐ordered 10–20 nm size FePt and FePt/Fe3Pt nanocomposite particles has been studied in this work. The chemically synthesized and annealed nanoparticle powders were packed into three‐capsule plate‐impact fixtures at ∼45% density and shock consolidated using a gas‐gun at impact velocities of 500 and 750 m/s. The compacts were recovered as disc‐shaped bulk magnets, with up to ∼90% higher density than the initial packing density. Transmission electron microscopy analysis revealed plastic deformation and flow of nanoparticles in the process of void annihilation and densification. High‐resolution imaging revealed complete retention of nano‐size of particles in the dense magnets. Shock compression of the FePt nanoparticles also resulted in an order‐to‐disorder phase transition from fct‐to‐fcc structure. However, annealing at temperatures around 700°C caused complete reversal and formation of ordered fct structure. The resulting magnetic property measurements showed energy product (BH)max up to 14 MGOe and coercivity Hc up to 14.6 kOe, which are higher than the values measured for the starting nanoparticles.