Magnetic correlations in deuteronium jarosite, a model S = 5/2 Kagomé antiferromagnet

Deuteronium jarosite, $\rm (\kern-1ptD_3O\kern-1pt)Fe_3(\kern-1ptSO_4\kern-1pt)_2(\kern-1ptOD\kern-1pt)_6$, contains a Kagomé lattice of Heisenberg spins S=5/2 with a coverage of $97 \pm 1\%$. DC and AC susceptibility measurements show strong in-plane antiferromagnetic exchange ($\theta_{\rm CW} = -700 \pm 5\;{\rm K}$) and a spin-glass transition at $T_{\rm f} = 13.8\;{\rm K}$, while the magnetic contribution to the specific heat below Tf rises with T as T2, characteristic of two-dimensional propagating modes. Powder neutron diffraction reveals short-range magnetic correlations with a correlation length $\xi\approx 19\pm 2\;{\rm \AA}$ at 1.9 K.