Permanent Magnetic Materials: Past, Present and Future

Prof. Laura H. Lewis
Department of Chemical Engineering
Northeastern University
Boston, MA 02115

Abstract:
Magnetic materials play a key role in modern life and are present in advanced devices and motors of every kind.  Their unique ability to enable the conversion of electrical to mechanical energy, transmit and distribute electric power, facilitate microwave communications and provide the basis for data storage systems make them indispensable to modern life.  Advanced permanent magnets — which maintain a large magnetic flux in the absence of a magnetizing field — underlie the operation of generators, alternators, eddy current brakes, motors and relays.  Among many applications, permanent magnets are found in computers, automobiles, motor scooters, consumer electronic products, medical products and speakers/headphones.  They are of vital importance to military applications as they add functionality to jet fighter engines, electronic countermeasure systems, missile systems and satellite communication systems.  Finally, advanced permanent magnets are also integral parts of alternative energy technologies, such as those that harvest wind, wave and tidal power.

In this presentation, an overview of historic, current and future permanent magnets will be provided and presented in the 21st –century context of global strategic materials supply and world demand.  In particular, recent geopolitical events involving rare-earth metallic elements — essential ingredients for current “super magnets” — emphasize that new materials design paradigms for advanced rare-earth-free magnets must be developed. To this end, two new permanent magnetic design options that are free from rare-earth elements will be discussed.  The first option considers nanocomposites comprised of nanoscale antiferromagnetic and ferromagnetic phases with the potential to deliver simultaneous a high energy product via the interphase interaction known as “exchange bias”. The second option considers the development of materials with the tetragonal FeNi phase known as "tetrataenite". To date, tetrataenite has only been found in meteorites subjected to extremely slow cooling rates occurring over millions of years.  It is anticipated that a selection of metallurgical processing techniques and alloying additions can alter the kinetics of formation of this material to enable bulk laboratory synthesis.  In addition to other creative materials design concepts that are under current exploration , it is anticipated that the two concepts described above will contribute to the development of future permanent magnets.