Nanocomposites for Permanent Magnets

Permanent magnets are exploited in a variety of devices (e.g. motors, generators, sensors, actuators) used in various fields of applications including transportation (e.g. (hybrid)electric vehicles), energy management (wind turbines…) and information technology (e.g. hard disc drives). Permanent magnet research today is concerned with improving the performance of magnets based on various hard magnetic phases while reducing dependence on any critical materials used. Nanocomposite magnets which combine a high coercivity hard magnetic phase with a high magnetisation soft magnetic phase hold great potential to rise to this challenge. In this chapter, we briefly outline the history of permanent magnets and explain the basic physical concepts behind nanocomposite permanent magnets. We recall the metallurgical and physical vapour deposition synthesis routes used to fabricate bulk and thin film nanocomposites, respectively. We then focus on chemical synthesis methods which offer the possibility to produce hard and soft magnetic nanoparticles or core-shell nanoparticles that can be used as building blocks to fabricate bulk hard-soft nanocomposites. We present three case studies concerning the fabrication and structural and magnetic characterisation of FePt-Fe3Pt, FePd-Fe and SmCo5-Fe nanocomposites. We wrap up the chapter with an outline of the challenges faced in producing hard-soft nanocomposite magnets using chemically synthesised nanoparticles, and an overview of the advanced magnetic characterisation tools being used to study the complex magnetisation reversal processes at play in hard-soft nanocomposites.