High resolution microstructural analysis of phase separation phenomena in Fe-based superconductors

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• Dr. Susannah Speller, Department of Materials, University of Oxford
• Friday 03 May 2013, 14:00-15:00
• Physics East 217.

If you have a question about this talk, please contact Elizabeth Blackburn.

Understanding the interplay between superconductivity and magnetism in iron-based superconductors is likely to provide significant insights into the elusive mechanisms responsible for high temperature superconductivity. The co-existence of magnetic order and superconductivity is a common feature of the iron-based superconductors, raising the question of whether these phases are spatially distinct or whether the same electrons are responsible for both phenomena. To investigate the nature of the phase separation in Fe-based single crystals, we have employed a combination of microanalytic techniques to assess the chemical and structural uniformity of single crystalline samples used for fundamental property measurements. In particular I will discuss the use of the high resolution Electron Backscatter Diffraction (EBSD) technique, pioneered for strain mapping in aerospace alloys [1], to map local variations in lattice parameter with exceptional precision and sub-micron spatial resolution for a range of different iron-based compounds including Fe(Se,Te) [2] and AFe2Se2 (A=Cs,Rb) [3]. In AFe2Se2, the intrinsic phase separation is very extreme, with significant chemical and structural differences associated with the spatially distinct electronic phases. Here we will present recent results on the microstructural development of AFe2Se2 single crystals upon annealing, and how this influences the superconducting/magnetic properties. In addition I will present recent work on how the microstructural changes which occur in CaFe2As2 upon annealing affect its low temperature structural transitions, comparing the results to the effects of applying external pressure [4].

[1] A. Wilkinson, G. Meaden and D. Dingley, Ultramicroscopy, vol. 106, p. 307, 2006.

[2] S.C. Speller, T.B. Britton, G. Hughes, S. Lozano-Perez, A.T. Boothroyd, E. Pomjakushina, K. Conder, C.R.M. Grovenor, App. Phys. Lett., (2011), 99, 192504.

[3] S.C. Speller, T.B. Britton, G.M. Hughes, A. Krzton-Maziopa, E. Pomjakushina, K. Conder, A.T. Boothroyd, C.R.M. Grovenor, Supercond. Sci. Technol., (2012), 25(8), 084023.

[4] S. Ran, S.L. Bud’ko, D.K. Pratt, A. Kreyssig, M.G. Kim, M.J. Kramer, D.H. Ryan, W.N. Rowan-Weetaluktuk, Y. Furukawa, B. Roy, A.I. Goldman, and P.C. Canfield, Phys. Rev. B (2011) 83, 144517.

This talk is part of the Condensed Matter Physics Seminars series.

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