Magnetic properties of pure and diamagnetically doped jarosites: Modelkagoméantiferromagnets with variable coverage of the magnetic lattice

Jarosites are a family of minerals of general formula ${\mathrm{AFe}}_3{\mathrm{}\left(\mathrm{OH}\right)\mathrm{}}_6{(\mathrm{S}\mathrm{O}}_4{)}_2$ (where $A^{+}$ is typically a univalent cation such as ${\mathrm{Na}}^{+},$ ${\mathrm{K}}^{+},$ ${\mathrm{Rb}}^{+},$ ${\mathrm{ND}}_4^{+},$ ${\mathrm{Ag}}^{+},$ ${\mathrm{Tl}}^{+},$ or ${\mathrm{D}}_3{\mathrm{O}}^{+}).\mathrm{}$ They provide good model Heisenberg kagomé antiferromagnets with which to test suggestions that highly frustrated antiferromagnets have unconventional magnetic ground states and excitations. In all cases ${\mathrm{Fe}}^{3+}$ ions provide $S=\frac{5}{2}$ moments, arranged on the vertices of well-separated kagomé layers, and are coupled through strong antiferromagnetic exchange with values of the Weiss constants θ of the order of -700 K. We report dc magnetic susceptibility $\left({\chi }_{\mathrm{dc}}\right)$ and powder neutron diffraction studies of materials in which $A^{+}={\mathrm{Na}}^{+},$ ${\mathrm{Rb}}^{+},$ ${\mathrm{ND}}_4^{+},$ ${\mathrm{Ag}}^{+},$ or ${\mathrm{D}}_3{\mathrm{O}}^{+}$ and show that for all materials except the deuteronium ${(A}^{+}={\mathrm{D}}_3{\mathrm{O}}^{+})$ salt, long-range magnetic order with the in-plane $q=0\mathrm{}$ spin structure sets in below a temperature $T_f$ of the order of 50 K. $({\mathrm{D}}_3{\mathrm{O})\mathrm{F}\mathrm{e}}_3{(\mathrm{S}\mathrm{O}}_4{)}_2{\mathrm{}\left(\mathrm{OD}\right)\mathrm{}}_6$ shows only a spin-glass-like transition at