Study of the low temperature thermal properties of the geometrically frustrated magnet: Gadolinium gallium garnet

Gadolinium gallium garnet, Gd₃Ga₅O₁₂ (GGG) has an extraordinary low temperature phase diagram. Although the Curie-Weiss temperature of GGG is about -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 (≤0.1 T) and a field-induced long-range order antiferromagnetic state at fields of between 0.7 and 1.3 T [P. Schiffer et al., Phys. Rev. Lett. 73, 2500 (1994), S. Hov, H. Bratsberg, and A. T. Skjeltorp, J. Magn. Magn. Mater. 15-18, 455 (1980); S. Hov, Ph.D. thesis, University of Oslo, 1979 (unpublished), A. P. Ramirez and R. N. Kleiman, J. Appl. Phys. 69, 5252 (1991)]. However, the nature of the ground state at intermediate fields is still unknown, and has been hypothesized to be a three-dimensional spin liquid. We have measured the thermal conductivity (κ) and heat capacity (C) of a high-quality single crystal of GGG in the low temperature regime in order to study the nature of this state. The field dependence of κ shows that phonons are the predominant heat carriers and are scattered by spin fluctuations. We observe indications in κ(H) and C(H) of both the field induced ordering and the spin glass phase at low temperatures (T≤200 mK).