Interplay between magnetism and superconductivity in EuFe 2-x Co x As 2 studied by 57 Fe and 151 Eu Mössbauer spectroscopy A. Błachowski 1, K. Ruebenbauer 1, J. Żukrowski 2, Z. Bukowski 3, K. Rogacki 3, J. Karpinski 4 1 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, Cracow, Poland 2 Solid State Physics Department, Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Cracow, Poland 3 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław, Poland 4 Laboratory for Solid State Physics, ETH Zürich, Switzerland XV Krajowa Szkoła Nadprzewodnictwa, Kazimierz Dolny, października 2011

T c max = 56 K 38 K 18 K 15 K Fe-based Superconducting Families pnictogens: P, As, Sb chalcogens: S, Se, Te LnFeAsO(F) AFe 2 As 2 LiFeAs FeTe(Se,S) Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu

Layered Structure of Fe-based Superconductors Parent Compounds Doped Compounds Superconductors Ba 1-x K x Fe 2 As 2 BaFe 2-x Co x As 2 BaFe 2 As 2-x P x Phase Diagram

Mössbauer Spectroscopy 1 mm/s 48 neV -ray energy is modulated by the Doppler effect due to the source motion vs. absorber

Hyperfine Interactions Isomer Shift Quadrupole Splitting Magnetic Splitting Electron Density Electric Field Gradient Magnetic Hyperfine Field B = 10 T

Electric Field Gradient + Magnetic Hyperfine Field = 0° = 90° B = 10 T

122 family of Fe-based superconductors

BaFe 2 As 2 T SDW = 136 K Ba 0.7 Rb 0.3 Fe 2 As 2 T sc = 37 K 57 Fe Mössbauer spectra NM non-magnetic

CaFe 2 As 2 T SDW = 175 K CaFe 1.92 Co 0.08 As 2 T sc = 20 K 57 Fe Mössbauer spectra Relative resistivity (normalized to the resistivity at 300 K) versus temperature

Shape of SDW for various temperatures Square root from the mean squared amplitude of SDW versus temperature

EuFe 2 As 2 T SDW = 192 K 0 = A.Błachowski, K.Ruebenbauer, J.Żukrowski, K.Rogacki, Z.Bukowski, J.Karpinski, PRB (2011) Square root from the mean squared amplitude of SDW versus temperature

EuFe 2-x Co x As 2 T N (Eu) = 19 K A.Błachowski, K.Ruebenbauer, J.Żukrowski, Z.Bukowski, K.Rogacki, P.J.W.Moll, J.Karpinski, arXiv:

EuFe 2-x Co x As 2 57 Fe Mössbauer spectra T SDW = 190 K T SDW = 150 K T SDW = 100 K traces of SDW at 80 K lack of SDW T N (Eu) = 19 K Eu 2+ Transferred Field on 57 Fe

EuFe 2-x Co x As 2 57 Fe Mössbauer spectra Shape of SDW

EuFe 1.66 Co 0.34 As 2 EuFe 2-x Co x As 2 Square root from the mean squared amplitude of SDW versus temperature

EuFe 2-x Co x As Eu Mössbauer spectra

Zakład Spektroskopii Mössbauerowskiej Instytut Fizyki Uniwersytet Pedagogiczny ul. Podchorążych 2, Kraków