Analog to the ⁴He melting curve in a model geometrically frustrated magnet

Gadolinium gallium garnet, Gd₃Ga₅O₁₂ (GGG) has an extraordinary low-temperature phase diagram. Although the Curie-Weiss temperature of GGG is ∼-2 K, GGG shows no long-range order down to T ∼ 0.4 K. At low temperatures GGG has a spin-glass phase at low fields (≲0.08 T), a field-induced long-range-ordered anti-ferromagnetic (AFM) phase at fields of between 0.7 and 1.3 T, and, at intermediate fields, an apparent spin-liquid (SL) phase without long-range order. We have performed specific heat, magnetocaloric, and static magnetization measurements near the SL/AFM phase boundary. Our results show that the lower field boundary of the AFM phase has a distinct minimum at T ∼ 0.2 K, in analogy to the minimum in the melting curve of ⁴He.