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

Gadolinium gallium garnet, Gd3Ga5O12 (GGG) has an extraordinary low tempera ture phase diagram. Although the Curie-Weiss temperature of GGG is about -2 K, GGG shows no long-range order down to T similar to 0.4 K. At low temper atures GGG has a spin glass phase at low fields (less than or equal to 0.1 T) and a field-induced long-range order antiferromagnetic state at fields o f between 0.7 and 1.3 T [P. Schiffer et al., Phys. Rev. Lett. 73, 2500 (199 4), 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 D. thesis, University of Oslo, 1979 (unpublished), A. P. Ramirez and R. N. Kleiman, J. Appl.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, an d has been hypothesized to be a three-dimensional spin liquid. We have meas ured the thermal conductivity (kappa) and heat capacity (C) of a high-quali ty single crystal of GGG in the low temperature regime in order to study th e nature of this state. The field dependence of kappa shows that phonons ar e the predominant heat carriers and are scattered by spin fluctuations. We observe indications in k( H) and C( H) of both the field induced ordering a nd the spin glass phase at low temperatures (T less than or equal to 200 mK ). (C) 1999 American Institute of Physics. [S0021-8979(99)27008-9].