[1] Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England
[2] Paul Scherrer Inst, Lab Sci Dev & Novel Mat, CH-5232 Villigen, Switzerland
[3] Paul Scherrer Inst, Lab Synchrotron Radiat Condensed Matter, CH-5232 Villigen, Switzerland
[4] Paul Scherrer Inst, Lab Neutron Scattering & Imaging, CH-5232 Villigen, Switzerland