Interaction-Induced Spin Coplanarity in a Kagomé Magnet: SrCr ${}_{9\mathit{p}}$Ga ${}_{12-9\mathit{p}}$${\mathrm{O}}_{19}$

We report the first detailed magnetic measurements on single crystals of the frustrated kagomé magnet $\mathrm{SrCr}{}_{9p}\mathrm{Ga}{}_{12-9p}{\mathrm{O}}_{19}$. Significant anisotropy develops in the linear susceptibility at low temperatures, providing experimental evidence for coplanar spin states. In a magnetic field, the anisotropy is suppressed and displays a peak (unreported in other spin-glass-like materials) at temperatures well above the spin-glass-like transition. The signatures of the spin-glass-like transition also show strong anisotropy, suggesting that the component of the system's magnetization which is normal to the kagomé planes freezes completely, while the component parallel to the planes does not.