Nanoparticles and nanocomposites for new permanent magnets

Since the declaration of rare earths as “critical materials” by the U.S. Department of Energy in 2011, the design of rare earth-free permanent magnets has been an actively focused area of research. Nanomaterial synthesis techniques have allowed rational engineering of magnetic composite materials which approach the requirements for maximized magnetic energy. Here, recent significant advances in chemical and physical syntheses of nanostructured permanent magnets are described, for both single-phase hard magnetic materials and for hard/soft exchange-coupled nanocomposites. This chapter focuses on the engineering of nanocrystalline rare earth and rare earth-free magnets. New discoveries which will guide the design of future materials are also detailed, including the importance of dipolar interactions between magnetic components, techniques in bottom-up nanocomposite engineering, and tolerance of materials to higher operating temperatures. A brief outlook for the next stage of magnetic nanomaterials research is given in the concluding section.