Antiferromagnetic fluctuations and short-range order in a Kagomé lattice.

Abstract

We report neutron-scattering measurements on ${\mathrm{SrCr}}_{8\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{4+\mathit{x}}$${\mathrm{O}}_{19}$, a layered compound containing Kagom\'e planes of S=3/2 ${\mathrm{Cr}}^{3+}$ ions. From magnetic-susceptibility data, the Curie-Weiss constant is large and negative; ${\mathrm{\ensuremath{\theta}}}_{\mathrm{CW}}$\ensuremath{\simeq}-500 K. Even so, our measurements for a sample with x=0.87 reveal only short-range antiferromagnetic order with a correlation length \ensuremath{\xi}=7\ifmmode\pm\else\textpm\fi{}2 \AA{}\ensuremath{\approxeq}2a, where a is the inter-Cr spacing. Below 8 K, there is a spin-freezing transition to a state where the magnetic fluctuations have large amplitude and a spectrum (averaged over reciprocal space) characteristic of two-dimensional antiferromagnets with \ensuremath{\xi}\ensuremath{\gg}a.