Structural Chemistry and Metamagnetism of an Homologous Series of Layered Manganese Oxysulfides Zolta´Na.Ga´L,† Oliver J

Published on Web 06/10/2006 Structural Chemistry and Metamagnetism of an Homologous Series of Layered Manganese Oxysulfides Zolta´nA.Ga´l,† Oliver J. Rutt,† Catherine F. Smura,† Timothy P. Overton,† Nicolas Barrier,† Simon J. Clarke,*,† and Joke Hadermann‡ Contribution from the Department of Chemistry, UniVersity of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, U.K., and Electron Microscopy for Materials Science (EMAT), UniVersity of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium Received February 7, 2006; E-mail: [email protected] Abstract: An homologous series of layered oxysulfides Sr2MnO2Cu2m-δSm+1 with metamagnetic properties is described. Sr2MnO2Cu2-δS2 (m ) 1), Sr2MnO2Cu4-δS3 (m ) 2) and Sr2MnO2Cu6-δS4 (m ) 3), consist of 2+ MnO2 sheets separated from antifluorite-type copper sulfide layers of variable thickness by Sr ions. All three compounds show substantial and similar copper deficiencies (δ ≈ 0.5) in the copper sulfide layers, and single-crystal X-ray and powder neutron diffraction measurements show that the copper ions in the m ) 2 and m ) 3 compounds are crystallographically disordered, consistent with the possibility of high two-dimensional copper ion mobility. Magnetic susceptibility measurements show high-temperature Curie- Weiss behavior with magnetic moments consistent with high spin manganese ions which have been oxidized to the (2+δ)+ state in order to maintain a full Cu-3d/S-3p valence band, and the compounds are correspondingly p-type semiconductors with resistivities around 25 Ω cm at 295 K. Positive Weiss temperatures indicate net ferromagnetic interactions between moments. Accordingly, magnetic susceptibility measurements and low-temperature powder neutron diffraction measurements show that the moments within a MnO2 sheet couple ferromagnetically and that weaker antiferromagnetic coupling between sheets leads to A-type antiferromagnets in zero applied magnetic field. Sr2MnO2Cu5.5S4 and Sr2MnO2Cu3.5S3 are metamagnets which may be driven into the fully ordered ferromagnetic state below 25 K by the application of fields of 0.06 and 1.3 T respectively. The relationships between the compositions, structures, and physical properties of these compounds, and the prospects for chemical control of the properties, are discussed. Introduction with complex crystal structures composed of distinct oxide and chalcogenide or pnictide layers which may form an homologous The chemistry and physics of solid-state compounds with series.6 layered structures is often quite different from that of compounds Layered oxychalcogenides of current interest include the with isotropic structures.1-3 Low-dimensional structures are LnOCuS7,8 series (Ln ) lanthanide) composed of alternating 4 often favored when the anions are polarizable, and there are Ln2O2 fluorite layers and Cu2S2 antifluorite layers: La1-xSrxOCuS more examples of layered sulfides than there are of layered is a rare example of a transparent p-type semiconductor9 in oxides. The layered nature of sulfides can be reinforced if two which the Cu-3d/S-3p valence band is doped with holes. Related different metal cations are incorporated which have different copper sulfide antifluorite layers are found in the more complex chemical requirements.5 A more extreme way of enforcing a homologous series of compounds described in this paper which layered crystal structure is to choose compounds in which the also contain strontium manganese oxide layers. Figure 1 shows - chemical preferences and/or coordination requirements of both the idealized crystal structures of a series of such compounds.10 13 the cation- and anion-forming elements are different. While this To emphasize the layered nature of these compounds we will approach is not guaranteed to lead to a single-phase compound, write the formulas so as to reflect the compositions of the distinct there are many examples of, for example, oxychalcogenides and oxide and sulfide layers. oxypnictides where it is successful. The results are compounds (6) Cava, R. J.; Zandbergen, H. W.; Krajewski, J. J.; Siegrist, T.; Hwang, H. Y.; Batlogg, B. J. Solid State Chem. 1997, 129, 250. (7) Ueda, K.; Inoue, S.; Hirose, S.; Kawazoe, H.; Hosono, H. Appl. Phys. Lett. † University of Oxford. 2000, 77, 2701. ‡ University of Antwerp. (8) Hiramatsu, H.; Kamioka, H.; Ueda, K.; Hirano, M.; Hosono, H. J. Ceram. (1) Canadell, E.; Whangbo, M. H. Chem. ReV. 1991, 91, 965. Soc. Jpn. 2005, 113, 10. (2) Rouxel, J.; Brec, R. Annu. ReV. Mater. Sci. 1986, 16, 137. (9) Takano, Y.; Yahagi, K.; Sekizawa, K. Physica B 1995, 206-207, 764. (3) deJongh, L. J. Magnetic Properties of Layered Transition Metal Compounds; (10) Barrier, N.; Clarke, S. J. Chem. Commun. 2003, 164. Kluwer Academic Publishers: Dordrecht, 1990. (11) Zhu, W. J.; Hor, P. H. J. Solid State Chem. 1997, 130, 319. (4) Madden, P. A.; Wilson, M. Chem. Soc. ReV. 1996, 339. (12) Zhu, W. J.; Hor, P. H. J. Solid State Chem. 2000, 153, 26. (5) Meerschaut, A. Curr. Opin. Solid State Mater. Sci. 1996, 1, 250. (13) Zhu, W. J.; Hor, P. H. J. Solid State Chem. 1997, 134, 128. 8530 9 J. AM. CHEM. SOC. 2006, 128, 8530-8540 10.1021/ja060892o CCC: $33.50 © 2006 American Chemical Society An Homologous Series of Layered Manganese Oxysulfides ARTICLES glasses with no long-range magnetic order. Investigations of the n ) 2; m ) 1 and n ) 3; m ) 1 representatives of the 13 Srn+1MnO3n-1Cu2mSm+1 homologous series, Sr3Fe2O5Cu2S2, 12 and Sr4Mn3O7.5Cu2Ch2 (Ch ) S, Se) reveal that these Mott- Hubbard insulators show low dimensional antiferromagnetic ordering. The properties of the analogous band gap insulators 11 such as Sr2ZnO2Cu2S2 are, like those of LaOCuS, dominated by the ease of depletion of the antibonding states at the top of the Cu-3d/S-3p valence band. Hole doping, achieved by + 2+ substituting 5% Na for Sr in Sr2ZnO2Cu2S2, has been shown to enhance the conductivity by 7 orders of magnitude.19 The layered oxychalcogenides and oxypnictides of the 1st row transition metals exhibit a range of properties and present numerous, as yet largely unexploited, opportunities for control Figure 1. Idealized structures of the homologous series of compounds of the magnetic and electronic transport properties via ionic Srn+1MnO3n-1Cu2mSm+1, mostly represented by compounds in which M ) Mn. Compounds D and E are described here for the first time together substitutions on many of the crystallographic sites. 11 10 with new measurements on compound C. (Color key: Sr: blue; Mn/Fe: Although Sr4Mn2O4Cu5S5, is the first of these oxysulfide gray; O: red; Cu: green; S: yellow). 2- intergrowths to be reported containing [Cu2mChm+1] layers with m > 1, several ternary chalcogenides contain these The homologous series Srn+1MnO3n-1Cu2mSm+1 (where M is ) 25 26 27 ) ) structural fragments, notably TlCu2mSm+1 (m 1, 2, 3 ), a transition metal) is represented by the n 1, 2, 3; m 1 28 26 29 30 31 TlCu2mSem+1 (m ) 1, 2 ), ACu4S3 (A ) K, Rb, Cs ) and members in which Cu2S2 antifluorite layers (which we refer to 26,32 ACu4Se3 (A ) K, Rb, Cs ). These all formally contain as “single” copper sulfide layers) are separated either by Sr2MO2 - [Cu S + ] monoanionic layers, and this implies the existence layers containing MO sheets (n ) 1), as in numerous examples 2m m 1 2 of one hole per formula unit in the Cu-3d/S-3p valence band. of compounds Sr MO Cu S (M ) Mn,11 Co,14-16 Ni,17 Cu,17 2 2 2 2 Conductivity measurements show these compounds to be Zn11,18,19)(C in Figure 1), or by thicker oxide layers which metallic29 and calculations on these layers33 suggest that such resemble fragments of the perovskite structure: Sr3M2O5Cu2S2 - holes should be mobile in the [Cu S + ] layers due to large (B)(n ) 2; M ) Fe,13 Sc17) and Sr Mn O Cu S (A)(n ) 2m m 1 4 3 7.5 2 2 Cu-3d/S-3p overlap. In the oxysulfide intergrowth compounds 3).12 Here we introduce the new n ) 1; m ) 2, 3 manganese- reported here, the structural, magnetic and electronic properties containing members of the series (D and E) containing “double”- will be determined by the geometry of the transition metal cation and “triple”-thickness copper sulfide layers respectively, and in the oxide layer, the structural demands of both the oxide and provide further analysis of the n ) 1, m ) 1 member sulfide layers, and the electronic communication between the Sr MnO Cu - S (C).11 These n ) 1 members of the homolo- 2 2 2 δ 2 oxide and sulfide layers. Here we discuss the correlation between gous series Sr + M O - Cu S + will be referred to by their n 1 n 3n 1 2m m 1 the compositions, crystal structures and properties of the m ) m indices. Sr Mn O Cu S ,10 a 1:1 intergrowth of the m ) 1 4 2 4 5 5 1, m ) 2, and m ) 3 members of the homologous series Sr Mn- and m ) 2 members, hints that a more complex series of 2 O Cu - S + . intergrowth phases of this type may be attainable. 2 2m δ m 1 11 ) ) Property measurements on Sr2MnO2Cu2S2 (n 1; m 1) Experimental Section and isostructural relatives reveal complex chemistry and physics. 11 - + ) The reported susceptibility measurements of Sr2MnO2Cu2S2 Synthesis of Sr2MnO2Cu2m δSm 1 (m 1, 2, 3). The products of suggest three-dimensional antiferromagnetic ordering of man- these reactions are air stable, however moisture-sensitive reactants < ganese moments. The semiconducting cobalt-containing ana- required a drybox (combined O2 and H2O content 1 ppm) for manipulations of solids. Starting materials were: MnO powder (ALFA logue Sr CoO Cu S 14-16 also shows long-range antiferromag- 2 2 2 2 2 99.999%), Cu powder (ALFA 99.9995%), Mn flake (Aldrich 99.99%) netic ordering, but also more complex electronic behavior ground into powder, CuO powder (ALFA 99.99%).

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