Extensive experimental investigations of the magnetic structures and excitations in the XY pyrochlores have been carried out over the past decade. Three families of XY pyrochlores have emerged: Yb₂B₂O₇, Er₂B₂O₇, and, most recently, Co₂F₇. In each case, the magnetic cation (either Yb, Er, or Co) exhibits XY anisotropy within the local pyrochlore coordinates, a consequence of crystal field effects. Materials in these families display rich phase behavior and are candidates for exotic ground states, such as quantum spin ice, and exotic ground-state selection via order-by-disorder mechanisms. In this review, we present an experimental summary of the ground-state properties of the XY pyrochlores, including evidence that they are strongly influenced by phase competition. We empirically demonstrate the signatures for phase competition in a frustrated magnet: multiple heat capacity anomalies, suppressed T_N or T_C, sample- and pressure-dependent ground states, and unconventional spin dynamics.

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