2010 Holweck medal and prize
Professor Steven T Bramwell
University College London
For pioneering new concepts in the experimental and theoretical study of spin systems
Professor Bramwell is recognised for his concept of “spin ice”, his calculation of a key critical exponent, and a probability distribution named after him. These innovative ideas have made a substantial impact in both materials magnetism and statistical mechanics, and have influenced diverse fields of research from nanotechnology to turbulence and geophysics.
Bramwell started his research career at Oxford and Harwell, conducting careful neutron scattering experiments on magnetic materials. Before joining UCL in 1994, he spent 5 years at the Institut Laue-Langevin, Grenoble, where he started two long running research themes involving both experiment and theory on ‘model magnets’. These are materials that, through their collective spin interactions, represent the generic physics of complex interacting systems.
The first theme involves so-called ‘frustrated’ magnets. These model the competing interactions that govern many complex phenomena from high Tc superconductivity to protein folding. Bramwell developed the concept of spin ice (with M J Harris), a class of magnetic material that effectively disobeys the Third Law of thermodynamics. His research on these and related materials has underpinned a new theoretical understanding of the principles of frustration, and has influenced the design of magnetic arrays in nanotechnology (‘artificial spin ice’).
The second research theme is the experimental importance of finite size corrections to thermodynamic properties. Bramwell (with P C W Holdsworth) illustrated how these are crucial to understanding experiments on two-dimensional systems. They predicted the universal exponent β = 0.23, that has been ubiquitously observed in many experiments on ultrathin magnetic films. This work further suggested an analogy between the ‘critical’ fluctuations of magnetisation and power fluctuations in turbulent flow, which implied a universal probability distribution (sometimes called the BHP distribution after Bramwell, Holdsworth and Pinton) and led to a deep insight into stochastic behaviour in condensed matter and beyond.