Neutron scattering studies of frustrated magnets.

Here is presented an experimental study of the low-temperature magnetic behaviour of the spin ice holmium titanate, Ho_2Ti_2O_7; stuffed spin ice, Ho_{2+x}Ti_{2-x}O_{7-x/2}; and neodymium zirconate, Nd_2Zr_2O_7. The main techniques utilised here are based on neutron scattering which gives information on the static and dynamic behaviour of materials. Stuffed spin ice represents the addition of holmium magnetic moments into holmium titanate. This addition of the Ho^3^+ affects the oxygen lattice which is responsible for the considerable magnetocrystalline anisotropy in these materials. Inelastic scattering measurements reveal that a crystal of Ho_{2.3}Ti_{1.7}O_{6.85} is a static magnetic system at the lowest energies. Elastic neutron scattering on the same crystal reveals short-range order that distinguishes it from spin ice. Neodymium zirconate, Nd_2Zr_2O_7, is a stoichiometric pyrochlore material isomorphous to holmium titanate in structure. Here a single crystal and a powder sample have been investigated by both elastic and inelastic scattering. The powder and crystals exhibit low temperature intensity in the same temperature range indicating a low temperature transition which has been shown to be second order. A field induced transition has also been studied, but its origin has not been established. Holmium titanate is a stoichiometric material unlike stuffed spin ice. Here a study has been conducted into scattering in the hhl plane under application of a magnetic field at a temperature of 60 mK. The results indicate a breaking of the ordered \alpha-chain structure within the material as the field is removed.