Magnetyzm i nadprzewodnictwo w EuFe2-xCoxAs2 – badania metodą spektroskopii mössbauerowskiej 57Fe i 151Eu

A. Błachowski1, K. Ruebenbauer1, J. Żukrowski2,

Z. Bukowski3, K. Rogacki3, P.J.W. Moll4, J. Karpinski4, M. Matusiak3

1Laboratorium Spektroskopii Mössbauerowskiej, Uniwersytet Pedagogiczny, Kraków, Polska

2Katedra Fizyki Ciała Stałego, Wydział Fizyki i Informatyki Stosowanej, Akademia Górniczo-Hutnicza, Kraków, Polska

3Instytut Niskich Temperatur i Badań Strukturalnych PAN, Wrocław, Polska

4Laboratory for Solid State Physics, ETH Zurich, Switzerland

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IX Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2012, Lublin - Kazimierz Dolny, 10-13 czerwca 2012

Tc max = 56 K 38 K 18 K 15 K

Fe-based Superconducting Families pnictogens: P, As, Sb chalcogens: S, Se, Te

1111 122 111 11

LnFeAsO(F) AFe2As2 LiFeAs FeTe(Se,S)

Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu

Layered Structure of Fe-based Superconductors

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Parent Compounds

Doped Compounds ↓

Superconductors

Ba1-xKxFe2As2

BaFe2-xCoxAs2

BaFe2As2-xPx

Phase Diagram

”122” family of Fe-based superconductors

CaFe2As2

TSDW = 175 K CaFe1.92Co0.08As2

Tsc = 20 K

57Fe Mössbauer spectra

Relative resistivity (normalized to the resistivity at 300 K)

versus temperature

A.Błachowski, K.Ruebenbauer, J.Żukrowski, Z.Bukowski, M.Matusiak, J.Karpinski, Acta Physica Polonica A 121, 726 (2012)

BaFe2As2

TSDW = 136 K

Ba0.7Rb0.3Fe2As2

Tsc = 37 K

57Fe Mössbauer spectra

NM non-magnetic

Shape of SDW for various temperatures

Square root from the mean squared amplitude of SDW versus temperature

EuFe2As2

TSDW = 192 K0 = 0.124

A.Błachowski, K.Ruebenbauer, J.Żukrowski, K.Rogacki, Z.Bukowski, J.Karpinski,Phys. Rev. B 83, 134410 (2011)

Square root from the mean squared amplitude of SDW versus temperature

EuFe2-xCoxAs2

TN (Eu) = 19 K

A.Błachowski, K.Ruebenbauer, J.Żukrowski, Z.Bukowski, K.Rogacki, P.J.W.Moll, J.Karpinski,Phys. Rev. B 84, 174503 (2011)

EuFe2-xCoxAs2

57Fe Mössbauer spectra

TSDW = 190 K

TSDW = 150 K

TSDW = 100 K

traces of SDW at 80 K

lack of SDW

TN (Eu) = 19 K

Eu2+ Transferred Field on 57Fe

EuFe2-xCoxAs2

57Fe Mössbauer spectra Shape of SDW

EuFe1.66Co0.34As2

EuFe2-xCoxAs2

Square root from the mean squared amplitude of SDW versus temperature

151Eu Mössbauer spectroscopy

EuFe2-xCoxAs2

151Eu Mössbauer spectra

Conclusions 1. The SDW order diminishes in EuFe2-xCoxAs2 with addition of Co, i.e., a transition

temperature is lowered together with the SDW amplitude. Substitution has similar effect on the SDW shape like temperature, albeit fluctuations are enhanced in comparison with the temperature effect.

2. 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-substitution. It seems that superconductivity has some filamentary character.

3. Eu2+ orders magnetically regardless of the Co-substitution level. Europium moments rotate from the a-axis in the direction of the c-axis (within a-c plane) with increasing substitution. Some Eu3+ appears upon substitution with the amount increasing with the increasing Co concentration. Europium magnetic order and superconductivity coexist in the same volume.

4. Iron experiences a transferred magnetic field from europium for the substituted material – in the SDW and non-magnetic state both.