Events in Physics
Bruce Gaulin, McMaster University, Canada
Frustrated and Satisfied Ground States in Pyrochlore Magnets
Geometrical frustration arises quite generally when pairwise interactions in magnetic materials are incompatable with their local geometry. This often involves magnetic materials made up of assemblies of triangles or tetrahedra. The frustration is manifest by disordered low temperature states for the magnetic material - some of which are described by spin liquids, spin glasses, and spin ice. I will discuss (mostly) neutron scattering work on two magnetic pyrochlores Tb2Ti2O7 and Er2Ti2O7, which can be thought of in terms of Ising and XY moments, respectively, decorating a network of corner-sharing tetrahedra. Tb2Ti2O7 displays a spin liquid ground state, but can be brought to order in an applied magnetic field. Er2Ti2O7 displays a long range ordered state at low temperatures which can be driven into a quantum disordered state by application of a magnetic field.