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 spinglass 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.