MSSBAUER STUDY OF NONARSENIC IRONBASED SUPERCONDUCTORS AND THEIR
MÖSSBAUER STUDY OF NON-ARSENIC IRON-BASED SUPERCONDUCTORS AND THEIR PARENT COMPOUNDS K. Komędera 1, A. K. Jasek 1, A. Błachowski 1, K. Ruebenbauer 1, J. Żukrowski 2, A. Krztoń-Maziopa 3, Z. Bukowski 4 1 Mössbauer 2 AGH Spectroscopy Laboratory, Pedagogical University Kraków, Poland University of Science and Technology, Academic Center for Materials and Nanotechnology Kraków, Poland 3 Warsaw 4 Institute University of Technology, Faculty of Chemistry Warsaw, Poland of Low Temperature and Structure Research, Polish Academy of Sciences Wrocław, Poland --------------------------------------------------- XI Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’ 2016 Radom-Turno, 19 -22 czerwca 2016
Laboratorium Spektroskopii Mössbauerowskiej Uniwersytet Pedagogiczny w Krakowie Maria Podgórna Aleksandra Jasek Kamila Komędera doktorantka, I rok doktorantka, IV rok doktorantka, III rok
Fe-based Superconductors pnictogens: P, As chalcogens: S, Se, Te Ax. Fe 2 -y. Se 2 A = K, Cs, Rb, … , Lix(C 5 H 5 N)
Fe-based Superconductors pnictogens: P, As chalcogens: S, Se, Te Ax. Fe 2 -y. Se 2 A = K, Cs, Rb, … , Lix(C 5 H 5 N) T. Noji et al. , Physica C 504, 8 (2014)
Ba. Fe 2 Se 3 XRF Ba 0. 992 Fe 1. 998 Se 3 Orthorhombic structure (space group Pnma) a = 11. 947 Å , b = 5. 431 Å , c = 9. 171 Å M. Mourigal et al. , Phys. Rev. Lett. 115, 047401 (2015)
57 Fe Mössbauer spectra of Ba. Fe 2 Se 3 · mixed-valence state of Fe · two spin ladders with rotation of Fe. Se 4 in different ways · twist between Fe. Se 4 along the ladder · superconducting Fe. Se (3%)
57 Fe Mössbauer spectra of Ba. Fe 2 Se 3
Superconductors Ax. Fe 2 -y. Se 2 A = Cs, Lix(C 5 H 5 N) W. Bao et al. , Chin. Phys. Lett. 28 (2011) 086104
Csx. Fe 2 -z. Se 2 XRF XRD Cs 0. 77 Fe 1. 59 Se 2 I 4/mmm a = 3. 960 Å, c = 15. 285 Å I 4/mmm 1 Oe DSC heating 20 K/min (redline), cooling (blue) Tp – nano-scale phase separation Ts – vacancy order-disorder annealing 60 h / 210 °C TSC 25 K
57 Fe Mössbauer spectra of Csx. Fe 2 -z. Se 2
Lix(C 5 H 5 N)y. Fe 2 -z. Se 2 1 Oe TSC 40 K tetragonal structure P 4/mmm as-prepared a = 3. 591 Å , c = 16. 398 Å annealed 60 h / 215 °C a = 9. 905 Å , c = 23. 112 Å
57 Fe Mössbauer spectra of Lix(C 5 H 5 N)y. Fe 2 -z. Se 2
Conclusions Superconducting Ax. Fe 2 -y. Se 2 samples despite showing almost single phase X-ray patterns are in fact multi-phase systems on the microscopic scale. One has superconducting and magnetic regions within the same material – spatially separated. Larger separation of the Fe–Se layers as provided by lithium/pyridine in comparison with cesium leads to increase of the critical temperature and superconducting volume fraction in agreement with the hypothesis of the two-dimensional superfluid density.
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