Frustrated Magnetic Pyrochlores - a Rich Playground for the Study of Exotic Collective Phenomena

Frustration is a ubiquitous phenomenon in condensed matter physics, and in science in general. One can even read about it on Wikipedia: In simple terms, frustration arises when a system cannot minimize its total classical ground state energy by minimizing the energy between interacting degrees of freedom, pair by pair. There has been in recent years an explosion of experimental and theoretical activities directed at the study of geometrically frustrated magnetic systems. The motivation stems from the hope that highly frustrated magnetic systems may give rise to exotic quantum and classical phenomena. Experimentally, materials where magnetic moments (spins) reside on a three-dimensional pyrochlore lattice of corner-sharing tetrahedra have proven to be the host of unusual and intriguing behaviours. Examples include the spin ice phenomenology, collective paramagnetic (spin liquid) state, persistent spin dynamics down to absolute zero temperature and, most recently, topological excitations akin to magnetic monopoles connected by effective “Dirac strings”. In this talk, I will review the motivation for the search of exotic phenomena in highly frustrated magnetic systems, and discuss some of the interesting ones that are being explored in the magnetic pyrochlore oxide materials.