LOW-TEMPERATURE PROPERTIES OF CLASSICAL GEOMETRICALLY FRUSTRATED ANTIFERROMAGNETS

We study the ground-state and low-energy properties of classical vecto r spin models with nearest-neighbor antiferromagnetic interactions on a class of geometrically frustrated lattices, which includes the kagom e and pyrochlore lattices. We explore the behavior of these magnets th at results from their large ground-state degeneracies, emphasizing uni versal features and systematic differences between individual models. We investigate the circumstances under which thermal fluctuations sele ct a particular subset of the ground states, and find that this happen s only for the models with the smallest ground-state degeneracies; For the pyrochlore magnets, we give an explicit construction of all groun d states, and show that they are not separated by internal energy barr iers. We study the precessional spin dynamics of the Heisenberg pyroch lore antiferromagnet. There is no freezing transition or selection of preferred states. Instead, the relaxation time at low temperature T is of order (h) over bar/k(B)T. We argue that this behavior can also be expected in some other systems, including the Heisenberg model for the compound SrCr8Ga4O19. [S0163-1829(98)05441-1].