Frustration Induced Spin Freezing in a Site-Ordered Magnet: Gadolinium Gallium Garnet

We measured the low-temperature ac magnetic susceptibilities ( ${\chi }^{\prime }$, ${\chi }^{\prime \prime }$, and ${\chi }_3$), static magnetization, and the specific heat of a high-quality single crystal of gadolinium gallium garnet (GGG), which is a geometrically frustrated Heisenberg magnet. We find a spin glass transition at low temperatures, in addition to unusual behavior in ${\chi }^{\prime \prime }$ and ${\chi }_3$. Comparison to nonmagnetic isomorphs and the low levels of structural and chemical disorder in GGG suggests that the transition is due to the highly frustrated geometry of the magnetic lattice.