FRUSTRATION IN THE PYROCHLORE ANTIFERROMAGNETS

In an antiferromagnet with the pyrochlore structure, the magnetic ions are situated on a framework of corner-sharing tetrahedra. This lattice results in a high degree of geometrical frustration, and theoretical studies predict that the magnetic ground state is continuously disordered. The majority of pyrochlore compounds are observed to remain disordered down to the lowest temperatures, and susceptibility measurements show that they often behave as conventional spin glasses. Neutron diffraction studies have discovered strong magnetic diffuse scattering at low temperatures. This reveals the presence of very short-ranged ferro- and antiferromagnetic correlations, similar in nature to the short-range correlations in a liquid. In this article, we review the current theoretical and experimental understanding of the pyrochlores, and present the results of recent experiments which have investigated the static and dynamic properties of this short-range order.