A key challenge for manufacturers has been to reduce the requirement for rare earth metals such as neodymium, dysprosium, and terbium in the magnets used in electric vehicles, which are expensive and difficult to obtain. Working collaboratively with Toyota and a range of other partners in the EU and Japan, our group at the University of Exeter has played a crucial role in the development of magnetic materials which require significantly lower levels of rare earth metals. These materials have been employed in an estimated 6.5million hybrid vehicles produced by Toyota since 2016, reducing consumption of rare earth elements by 450 tonnes, with associated reductions in environmental damage. In addition, the use of the new magnetic materials has contributed to efficiency gains compared to standard hybrid vehicles, which have reduced carbon dioxide emissions from Toyota hybrid vehicles by 11 million tonnes worldwide since 2016. Professor Hrkac’s work also contributed to cost savings of $108M in production and maintenance for hybrid cars, enhancing job stability at Toyota and generating savings for consumers.
Our research group (Prof Hrkac, Dr Skelland) focuses on computational and theoretical magnetism, developing models to investigate complex interface effects on an atomistic scale in nano- and micro-scale materials. Magnetic materials are formed from grains with a distinct magnetic structure. For most applications it is the overall magnetic material properties that are important; these are determined by the interaction between grains, so interfaces and grain boundaries ultimately determine the useful magnetic properties such as the external magnetic field, magnetic flux, and magnetic energy density.
Supported by a Royal Society University Research Fellowship (2009-2014), Prof. Hrkac developed ab initio simulations of atomic structures and solid-state molecular dynamics to model the behaviour of amorphous and crystalline grain boundaries in neodymium (NdFeB) magnets. This early work showed that the coercivity of Nd2Fe14B magnets, containing neodymium (Nd) without the rare earth element dysprosium (Dy), was highly dependent upon local anisotropy profiles at grain boundaries. The significance of grain boundaries, highlighted by our work, was central to future magnet development. Further research highlighted the importance of Nd-oxides and the potential for using structured magnetic materials.
One of the key challenges in designing high-efficiency magnets for use in hybrid and electric vehicles is that they must be able to operate at high temperatures, whilst maintaining or improving the efficiency of the electric motors they are used to drive. When neodymium magnets are used at high temperatures, such as in automotive applications, other rare earth elements such as dysprosium or terbium (Tb) are generally added to increase high-temperature coercivity. However, these are rare and expensive metals found in locations with high geopolitical risks. Because of this, considerable efforts have been made to develop magnets that do not use these metals. Although production volumes of neodymium are relatively high amongst rare earth metals, there are concerns that shortages will develop as electric vehicles become increasingly popular in the future. To overcome the cost and availability issues of rare-earth metals, Toyota established its Magnetic Materials for High-Efficiency Motors (MagHEM) project in 2012, to develop technologies that would initially eliminate the use of terbium and dysprosium, and in the longer-term reduce the amount of neodymium used, whilst maintaining the high levels of heat resistance and minimizing loss of coercivity.
Due to our expertise, we played a leading role in the MagHEM project, providing all the interface materials modelling, with colleagues in Europe and Japan responsible for other elements such as fabrication and testing. The first phase of the research led to the development of magnets requiring very low levels of dysprosium/terbium, which were used by Toyota in their 4th generation Prius, released in December 2015.
