Quasi-low-dimensional compounds containing transition-metal (TM) cations with partially filled d orbitals have long been studied for their distinct electrical and magnetic properties. Systems relevant to the current study include the previously reported quasi-1D 3133 and 2112 manganese(III) arsenate compounds, e.g., Na3LnMn3O3(AsO4)3 (Ln = La, Sm, Gd) [Inorg. Chem. 2009 , 48, 8439] and Na2LnMnO(AsO4)2 (Ln = Sm, Gd, Dy) [Angew. Chem. Int. Ed. 2011 , 50, 3780], respectively. The title compounds are isostructural with 3133 and, like the 2112 series, exhibit [MnO4]� spin chains interlinked by arsenate anions. Interesting phenomena concerning stepped magnetization and multiple spin dynamics at temperatures below Tc (~20K) have been reported in the 2112 series. This low-dimensional magnetic behavior was attributed theoretically to the electronic encapsulation of magnetic spin chains by closed-shell, nonmagnetic oxyanions. Crystals of Sr4?xLnxMn3O3(GeO4)3 (x = 0; x ~ 0.15 for Ln = La, Pr, Nd, Sm. Eu, Gd, Dy; x ~ 0.3 for Ln = Gd) were isolated upon using high-temperature, solid-state methods in molten-salt media. The synthesis of the Sr4Mn3O3(GeO4)3 (x = 0) phase was carried out by a double aliovalent substitution with respect to the Sr2+ and Ge4+ ions that replace Na+/Ln3+ and As5+ in Na3LnMn3O3(AsO4)3, respectively. The title series contains mixed-valent Mn(III)/Mn(IV) and shows a limited range of solid solution, both of which were not observed in the previously reported Na3LnMn3O3(AsO4)3 series. To form the Sr4?xLnxMn3O3(GeO4)3 solid solution, one of the Sr2+ sites, i.e., the original Ln-site in Na3LnMn3O3(AsO4)3, is partially substituted by Ln3+ in a statistical disorder of Sr1?x/Lnx. Initial magnetic investigations reveal higher ferromagnetic ordering temperatures than those reported for the Na3LnMn3O3(AsO4)3 series, presumably attributed to a lesser degree of canting as a result of introducing non-Jahn-Teller Mn4+ ions. Also intriguing is the observation of multiple anomalies at low temperatures which appear to be of electronic origins.

Enhanced ferromagnetic order in Sr4Mn3O3(GeO4)3 featuring canted [MnO4]� spin chains of mixed-valent Mn(III)/Mn(IV): Aliovalent substitution of the Sr4?xLnxMnIII2+xMnIV1?xO3(GeO4)3 solid-solution

248th National Meeting (2014)

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