Enhanced ferromagnetic order in Sr 4 Mn 3 O 3 (GeO 4 ) 3 featuring canted [MnO 4 ] 1 spin chains of mixed-valent Mn(III)/Mn(IV). Aliovalent substitution of the Sr 4  x Ln x Mn III 2+x Mn IV 1  x O 3 (GeO 4 ) 3 solid-solution J. Palmer West a , Dino Sulejmanovic a , Gregory Becht b , Jian He c , Dale Hitchcock c , Yonggao Yan d , Shiou-Jyh Hwu a,n a Department of Chemistry, Clemson University, Clemson, SC 29634, USA b E. I. du Pont, Wilmington, DE 19880-0500, USA c Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA d Wuhan University of Technology, Wuhan 430070, PR China article info Article history: Received 23 May 2013 Received in revised form 16 July 2013 Accepted 28 July 2013 Available online 3 August 2013 Keywords: Chain structures Double aliovalent substitution Ferromagnetism Kagomé Mixed-valent compounds abstract Crystals of Sr 4 x Ln x Mn 3 O 3 (GeO 4 ) 3 (x ¼0; x 0.15 for Ln ¼La, Pr, Nd, Sm. Eu, Gd, Dy; x 0.3 for Ln ¼Gd) were isolated upon using high-temperature, solid-state methods in molten-salt media. These compounds are isostructural with the previously reported Na 3 LnMn 3 O 3 (AsO 4 ) 3 (Ln ¼La, Sm, Gd) series that contains the same [MnO 4 ] 1 spin chains. The synthesis of the Sr 4 Mn 3 O 3 (GeO 4 ) 3 (x ¼0) phase was carried out by a double aliovalent substitution with respect to the Sr 2+ and Ge 4+ ions that replace Na + /Ln 3+ and As 5+ in Na 3 LnMn 3 O 3 (AsO 4 ) 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 Na 3 LnMn 3 O 3 (AsO 4 ) 3 series. To form the Sr 4 x Ln x Mn 3 O 3 (GeO 4 ) 3 solid solution, one of the Sr 2+ sites, i.e., the original Ln-site in Na 3 LnMn 3 O 3 (AsO 4 ) 3 , is partially substituted by Ln 3+ in a statistical disorder of Sr 1x /Ln x . Initial magnetic investigations of selected derivatives reveal higher ferromagnetic ordering temperatures than those reported for the Na 3 LnMn 3 O 3 (AsO 4 ) 3 series, presumably attributed to a lesser degree of canting as a result of introducing non-Jahn–Teller Mn 4+ ions. Also intriguing is the observation of multiple anomalies at low temperatures which appear to be of electronic origins. & 2013 Elsevier Inc. All rights reserved. 1. Introduction 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. Fascinating cooperative phenomena, such as metal–insulator tran- sitions [1,2], charge–density waves [3,4], superconductivity [5,6], thermoelectricity [7–10], and recently, slow relaxation of magne- tization [11–14], have received considerable attention. In the pursuit of quantum magnetic solids, nanostructures featuring quasi-one-dimensional (quasi-1D) spin chains are of interest because of their confined and highly anisotropic nature [15,16]. Prior to this study, some simple, pseudo-binary compounds showing notable stepped magnetization have drawn considerable attention. Compounds relevant to the present studies of quasi-1D systems include the Co-based Ising-chain compounds CsCoX 3 (X ¼ Cl, Br) [17] and Ca 3 Co 2 O 6 [11–14], as well as the non-3d Sr 5 Rh 4 O 12 phase [18]. It is noted that, upon investigating these novel phenomena in quasi-low-dimensional systems, complications arise due in part to multiple spin states of low, intermediate, and high spin configura- tions and mixed-valence states inherent to the TM cations. Unfortunately, there are a limited number of reports where structure/property correlations have been carried out for quasi- 1D systems containing mixed-valence states as a result of aliova- lent cation substitution. One notable exception comes from the study of the Ca 3 x Y x Co 2 O 6 series [19]. The lack of apparent systems is possibly attributed in part to the rigid monoanion (halide and oxide) structures that these systems possess. It is known, however, that polyanion-based (PO 4 3  , AsO 4 3  , SiO 4 4  and, in this case, GeO 4 4  ) mixed-metal oxides have shown a propensity to adopt greater structural flexibility where aliovalent cation substitution is intuitively more prominent. The title com- pound series demonstrates how facile aliovalent cation substitu- tions can occur within such a polyanion-based chemical system, and in turn, the feasibility for correlation studies of electronic/ structural parameters of magnetic importance. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jssc Journal of Solid State Chemistry 0022-4596/$ - see front matter & 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2013.07.033 n Corresponding author. Fax: +1 864 656 6613. E-mail address: shwu@clemson.edu (S.-J. Hwu). Journal of Solid State Chemistry 206 (2013) 51–59