Spin excitations in frustrated Kagom\'{e} lattice systems

We present experimental results on the behavior of interacting spins on the two-dimensional frustrated Kagom\'{e} lattice. Basic concepts of geometrical frustration will be reviewed, and measurements on single crystal and powder samples of ideal Kagom\'{e} systems (both classical and quantum) will be described. For a system with S=5/2, our inelastic neutron scattering measurements of the spin wave excitations reveal a novel ``flat mode'' which is a direct consequence of the high degree of frustration. We observe interesting behavior related to spin chirality (both vector and scalar). Recently, we have performed measurements on a material with spin-1/2 ions in an ideal Kagom\'{e} lattice arrangement. We discuss our results in relation to the excitations proposed for novel quantum spin liquid states.