Exchange-coupled FePt nanoparticle assembly

We have produced exchange-coupled FePt nanoparticle assemblies by chemical synthesis and subsequent thermal annealing. As the interparticle distances decrease by tuning the annealing conditions, interparticle interactions change from dipolar type to exchange type, and the magnetization reversal mechanism switches from rotation controlled to domain-nucleation controlled. With increasing annealing temperature, the coercivity first increases due to improved chemical ordering, and then drops significantly, resulting from excessive interparticle exchange coupling. For the samples exhibiting exchange coupling, both the remanence ratio and coercive squareness increase.