Observation of an Antiferromagnet in an Induced Staggered Magnetic Field: Dysprosium Aluminum Garnet near the Tricritical Point

We show that an external field in dysprosium aluminum garnet (DyAlG) couples not only to the magnetization, but also to the staggered magnetization, in a term linear in that order parameter. Neutron-scattering experiments are interpreted from this viewpoint. Reconsideration of the phase diagram of DyAlG leads to the conclusion that the previously reported tricritical point is, in fact, a wing critical point. Production of a staggered field should be possible in a class of compensated antiferromagnets.