ASW is specialist in magnetism, magnetic structures, and neutron scattering. His achievements we recently acknowledged by the awards of the 2004 B.T.M. Willis Prize (Institute of Physics) and the 2004 PANalytical prize (British Crystallography Association). As well as developing neutron scattering techniques for magnetism, he has worked on many geometrically frustrated magnets including jarosites, lithium manganate spinels, pyrochlores, delafossites, and atacamites. On a more theoretical side, he has developed group theoretical methods for the study of their often complex magnetic structures and wrote the widely used computer package SARAh that allows the unspecialised user to perform group theory analysis based on representational theory, and then to refine structures using reverse-Monte Carlo methods.
Highly frustrated systems have degenerate ground states that lead to novel properties. In magnetism its consequences underpin exotic and technologically important effects, such as, high temperature superconductivity, colossal magnetoresistence, and the anomalous Hall effect. One of the enduring mysteries of highly frustrated magnetism is why certain experimental systems have a spin glass transition that it is not determined by the strength of the dominant magnetic interactions. We have shown that the spin glass transition in the model kagomé antiferromagnet hydronium jarosite arises from a spin anisotropy and unusual collective zero energy excitations termed ‘spin folds’ (highlighted in yellow): a) shows a `closed spin fold' based upon a magnetic lattice with staggered chirality (the √3´√3 structure) ; b) shows an `open spin fold', which traverses a lattice if based upon the uniform chirality (the q=0 structure). This finding simplifies hugely treatment of the complex spin glass dynamics and has implications far beyond magnetism, as spin glasses provide important models for the out-of-equilibrium dynamics in other frustrated systems, including proteins and neural networks.