Dr Andrew Wills

Biography

• Exploration of new magnetic ground states that result from magnetic frustration
• Characterisation of the coupling between lattice and magnetism in multiferroic materials
• Development of corepresentation/representation theory for determining magnetic structures and aiding the analysis of neutron diffraction data (author of the SARAh programs)
• Development of neutron scattering techniques to measure magnetisation densities in powder samples

Research Interest

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.

Other activities

Committees:

• Member of the Structural Condensed Matter Group of the IOP (2004-)
• Member of the Magnetism Group of the IOP (2006-)
• Member of the ILL Scientific Council (2006-)

Teaching:

• 1st year Maths for chemists
• 1st year Physical lab organiser
• 2nd year Inorganic tutorials
• 4th year Course organiser for Physical Materials Chemistry

Publications

• “Magnetic ordering in Gd2S2O7:  the archetypal pyrochlore Heisenberg antiferromagnet”, A.S. Wills, M.E. Zhitomirsky, B. Canals, J.P. Sanchez, P. Bonville P. Dalmas de Reotier and A. Yaouanc, J. Phys.:Condens. Matter. 18, L37 (2006). (Letter)
•  “Symmetry in the solid state- working beyond the space group”, A.S. Wills, J. Mater. Chem. 15, 245-252 (2005). (Feature Article +Front Cover)
•  “Magnetisation distribution measurements from powders using a 3He spin filter: a test experiment”, A.S. Wills, E. Lelièvre-Berna, F. Tasset, J. Schweizer, R. Ballou, Physica B 356, 254-258 (2004) (10.1016/j.physb.2004.10.086)

Biography

• 2006-    Reader, University College London
• 2002-    Royal Society University Research Fellow, University College London
• 2001-02 Instrument Scientist, Institute Laue Langevin (ILL), France
• 1998-01 Marie Curie Individual Fellowship, CEA-Grenoble, France
• 1997-98 Research Fellow, McMaster University, Canada
• 1993-97 Ph.D., University of Edinburgh
• 1989-93 BA, University of Oxford

 
Research

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.