Oriented exchange-coupled L1₀-FePt/Co core-shell nanoparticles with variable Co thickness

Exchange-coupled core-shell nanoparticles are expected to be the new generation of permanent magnets, where the orientation of the hard magnetic phase is supposed to play a key role in improving their magnetic performance. In this work, L1₀-FePt/Co core-shell nanoparticles with Co thickness ranging from 0.6 to 2.2 nm have been synthesized by a seed-mediated growth method. The exchange coupling effect between the hard core and soft shell led to a 60% improvement of the maximum magnetic energy product ((BH)_max), compared with the pure L1₀-FePt core. By tuning the amount of precursor, nanoparticles with different Co shell thicknesses were synthesized. Furthermore, the L1₀-FePt/Co core-shell nanoparticles were dispersed in epoxy resin and oriented under an external magnetic field. The (BH)_max of the anisotropic nanocomposite magnet with a Co thickness of 1 nm is 7.1 MGOe, enhanced by 117% compared with the isotropic L1₀-FePt magnet, which paves the way for the development of high-performance permanent magnets for energy conversion applications.