Magnetism and Alloy Theory
Professor JB Staunton
[Office: PS141, Physical Sciences; email: j.b.staunton at warwick.ac.uk]
ORCID: https://orcid.org/0000-0002-3578-8753
Google Scholar: Link here
Putting a spin on models of electrons in magnets. On the sub nanoscale, a material’s magnetic properties come from spin correlations of its septillions of interacting electrons. In many cases, this collective electron behaviour can be characterised in terms atomic-scale, relatively long-lived magnetic moments. The moments’ behaviour determines the overall magnetisation and its resilience and response to magnetic fields as well as affecting temperature dependent spin-polarised electronic structure. At high temperatures, the moments disorder so that there is no overall magnetisation in the paramagnetic state. As the temperature is lowered, they order into patterns describing magnetic phases whose structures and topologies depend on the nature of the local moment interactions. At T=0K, where magnetic order is complete, computational calculations using the first-principles spin-polarised Density Functional Theory (DFT) describe magnetic properties well and can be predictive. Julie Staunton and co-workers have shown how the disordered local moment (DLM) theory extends DFT to finite temperatures for magnetic materials and, together with experimental investigations, enables quantitative modelling of properties and input for further modelling and experimental analysis. Early DLM theory work described the electronic structure of ferromagnetic metals above their Curie temperatures [1] and now is instrumental in a range of applications: e.g. the magnetic anisotropy of FePt [2], magnetic order of the heavy rare earths [3], skyrmion lattices in centrosymmetric Gd intermetallics [4], caloric effects in La(Fe1-x Six)13 [5] and the hard magnetic properties of the ubiquitous permanent magnet Nd2Fe14B [6].
[1] B L Gyorffy et al. J. Phys. F: Met. Phys. 15 1337 (1985); [2] J B Staunton et al., Phys. Rev. Lett. 93, 257204 (2004); [3] I D Hughes et al. Nature, 446, 650, (2007); [4] J Bouaziz et al. Phys. Rev. Lett. 128, 157206 (2022); [5] E Mendive Tapia et al., J. of Phys.: Energy 5, 034004 (2023); [6] J. Bouaziz et al. Phys. Rev. B 10, L020401 (2023).
The Magnetism and Alloy Theory Group's research aims to describe the various properties of materials via a careful account of their electronic "glue" or structure which includes spin polarisation and relativistic effects such as spin-orbit coupling. This requires HPC techniques and resources such as those available at the Scientific Computing RTP (SCRTP) at the University of Warwick. The Group studies theoretical metallic magnetism in this way and also, with the same electronic basis, a theory for the types of alloys that can form when two or more metallic elements are combined. A strength of the work is that it is `first principled' so that many aspects can be tested in quantitative detail by a range of experimental measurements. The Group collaborates with several theoretical and experimental groups both nationally and internationally. Ongoing projects concern the development of ab-initio electronic structure theory beyond standard DFT to include the effects of strong electron correlations and finite temperatures to rare earth and transition metal material properties. Applications are being made to rare earth-free and rare earth-lean permanent magnets, multi-component alloy phase stability and properties, topological magnetic effects, spintronics, magnetic phase diagrams and caloric properties. A key motivation is to contribute to the design of new advanced functional materials.
PRETAMAG is a joint theory/experiment project exploring the physics of permanent magnets funded by EPSRC.
MARMOT is a software package designed to calculate Magnetism, Anisotropy, and more, using the Relativistic Disordered Local MOment picture at finite Temperature.
Julie Staunton is a founding member of the Centre for Doctoral Training in Modelling of Heterogeneous Systems (HetSys)