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MAGNETYZM NADPRZEWODNIKÓW NA BAZIE ŻELAZA Eu-122 BADANY METODĄ SPEKTROSKOPII MÖSSBAUEROWSKIEJ 57 Fe i 151 Eu K. Komędera 1 , L. M. Tran 2 , A. Błachowski 1 , K. Ruebenbauer 1 , J. Żukrowski 3,4 , Z. Bukowski 2

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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

4AGHAkademia Górniczo-Hutnicza, Wydział Fizyki i Informatyki Stosowanej, Katedra Fizyki Ciała Stałego, Kraków, Polska

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X Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2014

Wrocław, 15-18 czerwca 2014

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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

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Journal of American Chemical Society

Received January 2008, Published online February 2008

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Up to now

the maximum superconducting critical temperature of iron-based superconductors

is56 K

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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

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Layered Structure of Fe-based Superconductors

Spin density wave

(SDW)

magnetic order

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Phase Diagram

Holes, electrons or isovalent doping

BaFe2As2

Ba1-xKxFe2As2

BaFe2-xCoxAs2

BaFe2As2-xPx

‘122’ Parent Compounds

SDW

Doped Compounds

‘122’ Superconductors

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EuFe2As2

parent compound

EuFe2-xCoxAs2

TSDW (Fe) = 190 K

TN (Eu) = 19 K

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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)

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(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

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(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
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.