Magnetic surface relaxation and reconstruction phenomena in frustrated magnetic systems

This thesis is concerned with magnetism at the surfaces of frustrated magnets, and in particular with magnetism on face-centred cubic (FCC) lattice systems. Normally, magnets do not react to a surface. Frustrated magnets do, however, and we consider two cases: Magnetic relaxation and the more unusual magnetic reconstruction phenomenon. Magnetic relaxation involves the extinction near the surface of a magnetic order that is present in the bulk and exists as a type of magnetic domain wall. Calculations of the ground state configuration of a semi-infinite system of uranium dioxide, an FCC triple-q magnet, show a solitonic solution corresponding to this relaxation. Fluctuations of this domain wall are considered in order to explain the unusual disordering observed experimentally in the near-surface region at a temperature below the bulk ordering transition temperature. The rarer case of reconstruction involves completely new magnetic order from the bulk appearing at the surface spontaneously and at a temperature below the bulk ordering transition temperature. Analysis of this phenomenon is undertaken via the construction of a phase diagram for a frustrated square lattice Heisenberg model. Regions of the phase diagram are found to exist in which the reconstruction is expected to occur, and furthermore the results can be mapped directly to type-1 FCC lattice systems.