FRUSTRATION DUE TO COMPETING CYCLIC RING EXCHANGES IN 2-DIMENSIONAL SOLID HE-3

A new insight is provided into ring-exchange processes occurring in two-dimensional solid He3 layers adsorbed on grafoil. Three-particle exchange dominates at high and moderate areal density leading to the ferromagnetic properties previously observed. At the low densities corresponding to the observation of commensurate phases, higher-order antiferromagnetic four- and six-spin exchanges are relatively more important and lead to a frustrated antiferromagnetic system. A variety of anomalies recently observed are explained in a unified way. © 1990 The American Physical Society.