Coexistence of spin ordering on ladders and spin dimer formation in a new-structure-type compound Sr2Co3S2O3

Kwing To Lai,Martin Valldor

doi:10.1038/srep43767

Abstract

We report on the syntheses and characterizations of single crystalline and polycrystalline Sr2Co3S2O3 with a novel crystal structure type. It contains Co–O 2-leg rectangular ladders and necklace ladders. The two ladders share common legs and construct a hybrid spin ladder. A rare meridional heteroleptic octahedral coordination is found for the Co2+ ions in the 2-leg ladder. Within the necklace ladders, the Co2+ ions are in trans-octahedral coordination. An antiferromagnetic order is observed at TN ~ 267 K, while a broad maximum in magnetic susceptibility is found below TN. This relatively high ordering temperature among Co-based ladder compounds is related to the highly anisotropic mer-coordination of the Co2+ ions. The trans-octahedrally coordinated Co2+ ions, on the other hand, corresponds to the possible short-range magnetic correlations through dimers with an effective . This results in a rare situation that spin ordering and spin dimers coexist down to 2 K.

Highlights

The Bragg peaks according to the crystal structure model obtained from the single crystal x-ray diffraction can be well assigned in the powder x-ray diffraction pattern except the peaks from a small amount of CoO impurity (~1%)
Mer-octahedral coordinations can be found in some metal organic complexes, with either homoleptic coordination by N in e.g. mer-[Co(dien)(NO2)3]19, [Co(dien)2]X3 · 2H2O (X =Cl, Br)[20] and mer-[Ni(dien)2][SCN]221 or heteroleptic coordination by N and O in [Cr(HP2O7)(NH3)3(H2O)] · 2H2O22
For non-complex inorganic materials, the mer-heteroleptic coordination exists in M2[Nb3O5X7] (M = NH4, K, Rb, Cs; X =Cl, Br) and in La6Ti2S8O5, where the octahedra are composed by a Nb5+(Ti4+) ion surrounding by three O2− and three X−(S2−) ions[23,24,25]

Summary

Introduction

With the cooperation of octahedral crystal field and spin-orbital coupling, the lowest-lying orbital level of Co2+ splits into a Kramers doublet, a quartet and a sextet. Its magnetic properties can be realized by a S = Regarding spin-ladder. Necklace ladders (see Fig. 1b), which can be regarded as 3-leg zigzag ladders, are so far not found in Co-based compounds but in some Cu-based materials like ferrimagnets A3Cu3(PO4)[4] (A =Ca, Sr, Pb)[15]. The novel ladder-type compound Sr2Co3S2O3 is investigated. It demonstrates a new orthorhombic crystal structure type. With the measurements of magnetic properties and specific heat, an antiferromagnetic transition is found close to room temperature www.nature.com/scientificreports/. (TN ~ 267 K) along with a broad maximum in magnetic susceptibility below TN. The broad maximum hints at the possible coexistence of spin ordering and short-range ordering below TN, where the short-range ordering may be formed from dimers with an effective S

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Conclusion