Physics of rare earth - transition metal permanent magnets: theory of their magnetostriction

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Permanent magnets are pervasive in both established and developing technologies. Found in motors and generators, transducers, magnetomechanical devices and magnetic field and imaging systems, there is a multi-billion pound worldwide market for them. They are also both fascinating and challenging in terms of their fundamental materials physics. At the Universities of Warwick and Birmingham an integrated EPSRC-funded theory-experiment programme - the PRETAMAG project (Investigations of the Physics underlying the principles of design of Rare Earth Transition metAl permanent MAGnets) - is uncovering key design principles. This PhD project is part of this effort and will be directed at developing the theory for important magneto-structural and magnetoelastic effects. The project will involve condensed matter physics theory and high performance computing.Most strong magnets are comprised of rare earth (RE) and transition metal (TM) atoms arranged in specific crystal structures. The TM element, such as iron or cobalt, helps the ferromagnetism to persist to high temperatures and the RE component, such as samarium or neodymium, is there to generate a large magnetisation which is hard to reorientate away from an easy' direction specified by the crystal structure. There is now a concerted effort worldwide to come up with new permanent magnetic materials with improved magnetic characteristics and reduced dependence on critical elements. Each RE atom in the magnet has a magnetic moment which is set up by its nearly localised f-electrons. These moments are immersed in a glue of septillions of valence electrons coming from all the RE and TM atoms. Local magnetic moments associated with the TM atoms can also emerge from this complex electron fluid. We will establish and apply a theory (see 1) which provides a parameter-free accurate account of this physics and enables predictive modelling of the temperature, compositional and structural dependence of the magnetic hardness of the RE-TM magnets. At each stage, we will test and improve the theory by comparison with detailed experimental measurements.