A new approach has been developed to understand the “rare-earth transition-metal” family of magnets – the most widely-used magnets in industrial and commercial settings – at the quantum mechanical level. The approach is based on density-functional theory (DFT). DFT is the method of choice for many computational materials scientists studying a wide range of systems, but special care is needed (a) when dealing with magnets at room temperature and above, and (b) with materials containing “rare earths”, that is, the group of elements including those sitting at the bottom of the periodic table, from lanthanum to lutetium. The new approach combines two already established theories – the so-called disordered local-moment picture of magnetism and the self-interaction correction - to tackle (a) and (b) on an equal footing. The new theory has been used to calculate the magnetic critical temperatures of the family of magnets which combine the rare earths with cobalt. The most prominent member of this magnet class, SmCo5, is well known for performing very well at high temperature. The calculations have uncovered a mechanism which offers, for the first time, to provide a fundamental physical explanation of why this is the case.

Journal reference: Phys. Rev. B 97, 224415 (2018)