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Mössbauer study of iron-based superconductors A. Błachowski 1 , K. Ruebenbauer 1 , J. Żukrowski 2

Mössbauer study of iron-based superconductors A. Błachowski 1 , K. Ruebenbauer 1 , J. Żukrowski 2 1 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, Cracow, Poland 2 Department of Solid State Physics , Faculty of Physics and Applied Computer Science,

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Mössbauer study of iron-based superconductors A. Błachowski 1 , K. Ruebenbauer 1 , J. Żukrowski 2

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  1. Mössbauer study of iron-based superconductors A. Błachowski1, K. Ruebenbauer1, J. Żukrowski2 1 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, Cracow, Poland 2Department of Solid State Physics, Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Cracow, Poland --------------------------------------------------------------------------------------------------------------------------------------------------------- ICAME 2013 International Conference on the Applications of the Mössbauer Effect 1-6 September 2013, Opatija, Croatia

  2. Superconductivity in the non-magnetic state of iron under pressureK. Shimizu et al. Nature 412, 316 (2001)hcp Febecomes superconductorat temperatures below 2 Kand at pressures between 15 and 30 GPa

  3. Journal of American Chemical Society Received January 2008, Published online February 2008 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Up to now the maximum superconducting critical temperature of iron-based superconductors is56 K

  4. Fe-based Superconducting Families pnictogens:P, As, Sb chalcogens:S, Se, Te 111112211111 LnO(F)FeAsAFe2As2AFeAs FeTe(Se,S) Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu, K A = Li , Na Tscmax = 56 K 47 K 18 K 15 K

  5. Layered Structure of Fe-based Superconductors Spin density wave (SDW) magnetic order --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Phase Diagram Holes, electrons or isovalent doping BaFe2As2 Ba1-xKxFe2As2 BaFe2-xCoxAs2 BaFe2As2-xPx Parent Compounds SDW Doped Compounds  Superconductors

  6. Spin density wave (SDW) – simple non-interlaced picture perpendicular longitudinal commensurate or incommensurate h2n-1–amplitudes of subsequent harmonics q – wave number of SDW x – relative position of the resonant nucleus along propagation direction of the stationary SDW

  7. Spin density wave (SDW) seen by Mössbauer Spectroscopy h2n-1–amplitudes of subsequent harmonics q – wave number of SDW x – relative position of the resonant nucleus along propagation direction of SDW SDWhyperfine field distribution57Fe Mössbauer spectrum

  8. ”122” family of Fe-based superconductors

  9. 57Fe Mössbauer spectra BaFe2As2 (parent) TSDW = 136 K Ba0.7Rb0.3Fe2As2 (superconductor) Tsc = 37 K Shape of SDW NM non-magnetic SDW is suppressed by doping

  10. CaFe2As2 (parent) TSDW = 175 K CaFe1.92Co0.08As2 (superconductor) Tsc = 20 K Resistivity measurements: It seems that magnetism and superconductivity coexist (?). Mössbauer measurements: Superconductivity has filamentary character and occurs in the regions free of 3d magnetic moments.

  11. EuFe2As2 Root mean square amplitude of SDW critical exponent 0≈ 0.125universality class (1, 2) ↓ one dimension in the spin space (Ising model) and two dimensions in the real space (magnetic planes)

  12. EuFe2-xCoxAs2 57Fe Mössbauer spectra TN (Eu) = 19 K TSDW = 190 K TSDW = 150 K TSDW = 100 K traces of SDW at 80 K lack of SDW superconductor superconductor superconductor filamentary superconductivity Eu2+ Transferred Field on 57Fe

  13. EuFe2-xCoxAs2 151Eu Mössbauer spectra Eu(2+)  • EuFe2As2 • TSDW (Fe) = 190 K • TN (Eu) = 19 K • Parent • Superconductor Tsc = 9.5 K • Over-doped  Eu(3+) Eu2+ orders magnetically regardless of the Co-substitution level. Eu2+ moments rotate from a-axis to c-axis. Eu2+magnetism and superconductivity coexist.

  14. Fe1+xTe x = 0.04 – 0.18 x = 0.06 , 0.10 , 0.14 , 0.18 Magnetic-crystallographic phase diagram x in Fe1+xTe S. Röler et al., Phys. Rev. B 84 174506 (2011)

  15. Parent Compound Fe1+yTe Doped Compound→Superconductor y ≈ 0 Fe1+yTe1-xSexFe1+yTe1-xSx K. Katayama et al., J. Phys. Soc. Japan 79 113702 (2010)

  16. 57Fe Mössbauer spectrum SDW field distribution shape of SDW Fe1.06Te  regular (tetrahedral) Feexcess (interstitial) Fe SDW

  17. 57Fe Mössbauer spectrum SDW field distribution shape of SDW Fe1.14Te regular Fe - SDW   Three different kinds (surroundings) of excess (interstitial) Fe. Magnetism of the excess Fe and SDW disappear at the same transition temperature.

  18. 65 K 4.2 K regular Fe (SDW)excess Fe  Fe1+xTe x=0.06 x=0.10 x=0.14 x=0.18 shape of SDW at 4.2 K SDW is very sensitive to concentration of interstitial iron with relatively large localized magnetic moments. Localized iron moments prevent superconductivity, so interstitial iron must be removed by doping and/or deintercalation to get superconducting material.

  19. Fe1.01SeTsc = 8 K High (external) magnetic field Mössbauer spectroscopy tetragonal structural distortion orthorhombic orthorhombic • Hyperfine magnetic field is equal to applied external magnetic field • it means that there is no magnetic moment on the Fe atoms orthorhombic and superconductor

  20. paramagnetic region magnetic region sharp magnetic transition FeAs Crystal structure Pnma or Pna21? SPIN SPIRAL Arrows show Pna21 – likedistortion E.E. Rodriguez et al., PRB 83, 134438 (2011)

  21. Anisotropy of the hyperfine magnetic fields (spiral projections onto a-b plane) in FeAs Left column shows[0 k+1/2 0] iron,right column shows[0 k 0] iron. Baand Bb- iron hyperfine field components along the a-axis and b-axis, respectively. Orientation of the EFG and hyperfine magnetic field in the main crystal axes Average hyperfine fields <B> for [0 k+1/2 0] and [0 k 0] irons. Tc - transition temperature  - static critical exponent A. Błachowski et al., JALCOM 582, 167 (2014)

  22. FeAs Spectral shift S and quadrupole coupling constant AQ versus temperature for [0 k+1/2 0] iron and[0 k 0] iron. Line at 72 K separate magnetically ordered region from paramagnetic region. Relative recoilless fraction <f>/<f0> versus temperature Green points correspond tomagnetically ordered region. Red point is the normalization point. Inset shows relative spectral area RSA plotted versus temperature.

  23. Conclusions AFe2As2 - parents The SDW magnetic order with universality class (1, 2) and with almost rectangular shape at saturation. Ba1-xRbxFe2As2 The SDW vanishes upon doping leading to superconductivity. CaFe2-xCoxAs2 Superconductivity has filamentary character and occurs in the regions free of 3d magnetic moments. EuFe2-xCoxAs2 Localized 4f magnetic moments could order within the superconducting phase. Fe1+xTe Excess (interstitial) iron with relatively large localized magnetic moment strongly influence on the ordering temperature, shape and amplitude of the SDW. FeSe There is no magnetic moment on iron in superconducting FeSe and it is PRESUMABLY the feature of all iron-based superconductors. FeAs Spin spiral leads to the complex variation of the hyperfine field amplitude with the spin orientation (local magnetic moment) varying in the a-b plane. Pattern express symmetry of 3d electrons in the a-b plane with the significant distortion caused by the arsenic bonding p electrons. Strong coupling between magnetism and lattice dynamics i.e. strong phonon-magnon interaction. Thank you very much for your attention!

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