Magnets with strong geometric frustration

A nontechnical introduction to the theory of magnets with strong geometric frustration is given, concentrating on magnets on corner-sharing (Kagome, pyrochlore, SCGO, and GGG) lattices. Their rich behaviour is traced back to a large ground-state degeneracy in model systems, which renders them highly unstable towards perturbations. A systematic classification according to properties of their ground states is discussed. Other topics addressed in this overview article include a general theoretical framework for thermal order-by-disorder, the dynamics of how the vast regions of phase space accessible at low temperature are explored, the origin of the featureless magnetic susceptibility fingerprint of geometric frustration, the role of perturbations, and spin ice. The rich field of quantum frustrated magnets is also touched on.