X Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2014 MAGNETYZM NADPRZEWODNIKÓW NA BAZIE ŻELAZA Eu-122 BADANY METODĄ SPEKTROSKOPII MÖSSBAUEROWSKIEJ 57Fe i 151Eu   K. Komędera1, L. M. Tran2, A. Błachowski1, K. Ruebenbauer1, J. Żukrowski3,4, Z. Bukowski2 1Zakład Spektroskopii Mössbauerowskiej, Instytut Fizyki, Uniwersytet Pedagogiczny, Kraków, Polska 2Instytut Niskich Temperatur i Badań Strukturalnych, Polska Akademia Nauk, Wrocław, Polska 3AGH Akademia Górniczo-Hutnicza, Akademickie Centrum Materiałów i Nanotechnologii, Kraków, Polska 4AGH Akademia Górniczo-Hutnicza, Wydział Fizyki i Informatyki Stosowanej, Katedra Fizyki Ciała Stałego, Kraków, Polska ------------------------------------------------------------------------------------------------------ X Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2014 Wrocław, 15-18 czerwca 2014

Superconducting Materials

Superconductivity in the non-magnetic state of iron under pressure K Superconductivity in the non-magnetic state of iron under pressure K. Shimizu et al. Nature 412, 316 (2001) hcp Fe becomes superconductor at temperatures below 2 K and at pressures between 15 and 30 GPa

Journal of American Chemical Society Received January 2008, Published online February 2008 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Up to now the maximum superconducting critical temperature of iron-based superconductors is 56 K

Fe-based Superconducting Families pnictogens: P, As, Sb chalcogens: S, Se, Te 1111 122 111 11 LnO(F)FeAs AFe2As2 AFeAs FeTe(Se,S) Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu, K A = Li , Na Tsc max = 56 K 47 K 18 K 15 K

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 Compound Tc [K] Ca0.6Na0.4Fe2As2 26 CaFe1.94Co0.06As2 17 CaFe2As1.925P0.075 13 Ba0.6K0.4Fe2As2 38 BaFe1.8Co0.2As2 23 BaFe2As1.3P0.7 30 Eu0.5K0.5Fe2As2 32 EuFe1.63Co0.37As2 9.5 EuFe2As1.7P0.3 5 ‘122’ Parent Compounds Compound TSDW(Fe) / TN(R) [K] CaFe2As2 170 SrFe2As2 205 BaFe2As2 140 EuFe2As2 190 / 19 SDW Doped Compounds  ‘122’ Superconductors

”122” family of Fe-based superconductors Parent compounds Superconductors Overdoped EuFe2As2 EuFe1.63Co0.37As2 EuFe1.42Co0.58As2 (Eu0.72Ca0.28)(Fe1.64Co0.36)As2  

EuFe2As2 EuFe2-xCoxAs2 parent compound TSDW (Fe) = 190 K TN (Eu) = 19 K

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)

(Eu1-yCay)(Fe2-xCox)As2 57Fe Mössbauer spectra TN (Eu) = 19 K TSDW = 192 K TSDW  100 K TSDW  80 K lack of SDW filamentary superconductivity Eu2+ Transferred Field on 57Fe

151Eu Mössbauer spectroscopy

(Eu1-yCay)(Fe2-xCox)As2 151Eu Mössbauer spectra EuFe2As2 TSDW (Fe) = 190 K TN (Eu) = 19 K  Parent  Superconductor Tsc = 9.5 K Superconductor Tsc = 11 K  Over-doped Eu(2+)   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.

Conclusions The SDW order diminishes in (Eu1-yCay)(Fe2-xCox)As2 with addition of Co and Ca, i.e., a transition temperature is lowered together with the SDW amplitude. SDW survives across the region of superconductivity and it vanishes in the overdoped region. However, in the region of superconductivity one has some non-magnetic component with the intensity increasing with the Co and Ca substitution. It seems that superconductivity has some filamentary character. Eu2+ orders magnetically regardless of the Co and Ca substitution . Europium moments rotate from the a-axis in the direction of the c-axis (within a-c plane). Europium magnetic order and superconductivity coexist in the same volume.

Thank you very much for your attention!