Chemical synthesis of exchange-coupled nanocomposite magnets

Abstract

Nanocomposite magnets containing soft and hard magnetic phases have attracted immense attention for energy-related and biomedical applications. In particular, good control of the soft and hard phases at the nanoscale in the composites is of great importance for eective exchange coupling, allowing us to make the best of the strengths of soft and hard magnetic phases and to optimize the magnetic properties for targeted applications. Chemical methods offer an effective route to precisely control both phases at the nanoscale, and help understand magnetic interactions and develop advanced magnetic materials for various applications. In this talk, we will present recent progress on chemical synthesis of nanocomposite magnets. Firstly, a general protocol is reported to synthesize exchange-coupled nanoparticles with magnetically hard L1 0 -FePt as core and magnetically soft Co (or Ni, or Fe 2 C) as shell. These core/shell nanoparticles show shell thickness-dependent magnetic properties, providing an ideal model system for the study of exchange coupling at nanoscale, which will be essential for building superstrong magnets for various permanent magnet applications in the future. Secondly, we report a facile chemical route to prepare 200 nm single domain SmCo 5 @ Co core/shell magnets with coercivity of 20.7 kOe and saturation magnetization of 82 emu/g. We found that the incorporation of graphene oxide sheets are responsible for the generation of the unique structure. The single domain SmCo 5 core contributes to the large coercivity of the magnets and the exchange-coupled Co shell enhances the magnetization. This method can be further utilized in the synthesis other Sm-Co based exchange-coupled magnets. Thirdly, we developed chemical ways to prepare L1 0 -FePd/-Fe and Nd 2 Fe 14 B/-Fe nanocomposite magnets, providing a bottom-up approach using exchange-coupled nanocomposite magnets for engineering advanced permanent magnets with controllable magnetic properties.