Dr Helen Walker has been presented with the European Synchrotron Radiation Facility's 2011 Young Scientist Award for her outstanding contributions to our understanding of multipolar ordered and multiferroic materials in her work using both non-resonant and resonant x-ray scattering techniques at the ESRF.
Helen's PhD thesis work, carried out at LCN under the supervision of Professor Keith McEwen, focused on studying the complex sequence of phase transitions exhibited by the uranium intermetallic compound UPd3. This material had been studied for many years, and a series of bulk property measurements had revealed four phase transitions at low temperatures between 8K and 4K. Neutron diffraction had shown that these transitions were not of magnetic, but of quadrupolar origin.
In a series of elegant experiments at ESRF on single crystals of UPd3 using the ID20 diffractometer, Helen was able to measure the azimuthal dependence of the superlattice reflections in the different phases below 8K. Extreme precision was necessary, in both sample orientation and temperature control, to minimize errors in the data. Helen calculated the azimuthal dependence of the possible order parameters and compared the calculations with the measured data. Whilst the primary order parameter could be clearly established for each antiferroquadrupolar ordered phase, the precision of the measurements allowed the presence of secondary order parameters to be deduced as well. This had important consequences for the subsequent development of the theory of UPd3.
After obtaining her PhD in 2007, Helen has worked as PostDoc with Professor Des McMorrow, on multiferroic systems, principally on TbMnO3 and related compounds. Together with the ID20 team, she pioneered a novel application of non-resonant magnetic scattering to study the electric field control of magnetism in TbMnO3.
Helen's research at ESRF has been extremely successful in advancing our understanding of new materials that display novel and exotic types of ordering at low temperatures. As well as carrying out experiments that require extreme precision of measurement, she has also been instrumental in the development of new experimental techniques. The 2011 Young Scientist Award recognises her achievements.