UCL-RI researchers have made a series of unprecedented discoveries in the field of new magnetic phenomena and magnetic materials. Professor Bramwell's studies of new "spin ice" and other magnetically disordered phases and chaotic phenomena studied by Dr. A. Wills have been enabled by targeted solid state syntheses, coupled with advanced measurements of magnetic properties in the laboratory and at large-scale neutron scattering and muon spin relaxation facilities. The resulting new materials and their field-, temperature and strain-dependent magnetic transitions between states will result in new information storage and transfer capabilities. Part of this work is now being carried out in collaboration with Professor Gabriel Aeppli, from the Department of Physics and Astronomy, and Director of the London Centre for Nanotechnology. Magnetoresistance effects (MR), in which materials show unexpectedly large changes in their electrical resistivity upon application of an external magnetic field, is of immense technological importance in the manufacture of magnetic storage and sensing devices, including computer hard disks and random access memories (RAM). Materials based on existing magnetic/non-magnetic multilayer technology exhibit MR values of 20-40%. "Giant" and "Colossal" MagnetoResistance (GMR, CMR) values that exceed 50-60% have now been demonstrated in newly-developed manganate perovskites and related materials, opening up a wide range of potential new devices. Research within Dr. M. Green's group at UCL and at the DFRL is targeted at exploring new families of CMR/GMR materials with improved performance at high magnetic fields and low temperatures. Recently-prepared classes of spinel chalcogenides have far superior properties to any compounds yet reported, with ~70-80% T-independent CMR effects at low applied fields. We are exploring such new GMR/CMR materials within the MCC. Research within the DFRL group of Professor Peter Day (FRS) has resulted in creation of new families of "molecular magnets", that are being developed for use in display technologies, magnetic recording, and nanotechnology applications. The new "Magnetism" laboratory within the MCC is equipped with MagLab and AC-SQUID facilities, as well as impedance analysis over a wide frequency range, for studies of electronic and ionic conductivity and dielectric phenomena, and magnetism, magnetic relaxation, and frustration. New studies are being extended to magnetism, conductivity and superconductivity at extremely high densities.
This work is both fundamental and highly exploratory in nature, and it is resulting in a deeper understanding of magnetic phenomena within materials. The results will permit design of new materials and meta-materials, and processes based on chaotic responses to applied stress that we must master as we enter nanoscale regimes. The "Chemical Magnetism" group has begun a fruitful collaboration with Professors G. Aeppli and D. McMorrow in this area. The establishment of the new facilities within the MCC in close proximity to the London Centre for Nanotechnology is now permitting solid-state and chemical/organometallic syntheses of new magnetic materials to be carried out in close proximity to characterisation studies of their magnetic properties, in bulk and at the nanoscale.
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