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

摘要: Jarosites are a family of minerals general formula ${\mathrm{AFe}}_{3}{(\mathrm{OH})}_{6}{(\mathrm{S}\mathrm{O}}_{4}{)}_{2}$ (where ${A}^{+}$ is typically univalent cation such as ${\mathrm{Na}}^{+},$ ${\mathrm{K}}^{+},$ ${\mathrm{Rb}}^{+},$ ${\mathrm{ND}}_{4}^{+},$ ${\mathrm{Ag}}^{+},$ ${\mathrm{Tl}}^{+},$ or ${\mathrm{D}}_{3}{\mathrm{O}}^{+}).$ They provide good model Heisenberg kagom\'e antiferromagnets with which to test suggestions that highly frustrated have unconventional magnetic ground states and excitations. In all cases ${\mathrm{Fe}}^{3+}$ ions $S=\frac{5}{2}$ moments, arranged on the vertices well-separated layers, coupled through strong antiferromagnetic exchange values Weiss constants \ensuremath{\theta} order -700 K. We report dc susceptibility $({\ensuremath{\chi}}_{\mathrm{dc}})$ powder neutron diffraction studies materials in ${A}^{+}={\mathrm{Na}}^{+},$ ${\mathrm{D}}_{3}{\mathrm{O}}^{+}$ show for except deuteronium ${(A}^{+}={\mathrm{D}}_{3}{\mathrm{O}}^{+})$ salt, long-range in-plane $q=0$ spin structure sets below temperature ${T}_{f}$ 50 $({\mathrm{D}}_{3}{\mathrm{O})\mathrm{F}\mathrm{e}}_{3}{(\mathrm{S}\mathrm{O}}_{4}{)}_{2}{(\mathrm{OD})}_{6}$ shows only spin-glass-like transition at ${T}_{f}\ensuremath{\cong}15\mathrm{K}.$ There no obvious difference structures salts order, salt coverage lattice, higher $(97\ifmmode\pm\else\textpm\fi{}3%)$ latter than rest (\ensuremath{\leqslant}95%, most \ensuremath{\cong} 90%). It proposed reduction lattice induces jarosites, material $({\mathrm{D}}_{3}{\mathrm{O})\mathrm{F}\mathrm{e}}_{3\ensuremath{-}x}{\mathrm{Al}}_{y}{(\mathrm{OD})}_{6}{(\mathrm{S}\mathrm{O}}_{4}{)}_{2},$ $89\ifmmode\pm\else\textpm\fi{}3%$ has been prepared characterized this hypothesis. ${\ensuremath{\chi}}_{\mathrm{dc}}$ cusp 25.5 K, reveals 1.4 K same ordering vector seen other materials.