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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 - PowerPoint PPT Presentation
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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, Polska3AGH 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
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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. 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 SocietyReceived January 2008, Published online February 2008
Up to now the maximum superconducting critical temperature of iron-based superconductors
is 56 K
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Tsc max = 56 K 47 K 18 K 15 K
Fe-based Superconducting Familiespnictogens: 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
Layered Structure of Fe-based Superconductors
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‘122’ Parent Compounds
Doped Compounds
‘122’ Superconductors
BaFe2As2
Ba1-xKxFe2As2
BaFe2-xCoxAs2
BaFe2As2-xPx
Phase DiagramHoles, electrons or isovalent doping
Spin density wave (SDW)
magnetic order
SDWCompound TSDW(Fe) / TN(R) [K]
CaFe2As2 170
SrFe2As2 205
BaFe2As2 140
EuFe2As2 190 / 19
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” family of Fe-based superconductors
Parent compounds Superconductors Overdoped
EuFe2As2
EuFe1.63Co0.37As2 EuFe1.42Co0.58As2
(Eu0.72Ca0.28)(Fe1.64Co0.36)As2
EuFe2-xCoxAs2
TSDW (Fe) = 190 KTN (Eu) = 19 K
EuFe2As2
parent compound
EuFe2As2
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)
Root mean square amplitude of SDW
(Eu1-yCay)(Fe2-xCox)As2
57Fe Mössbauer spectra
TSDW = 192 K
TSDW 100 K
TSDW 80 K
lack of SDW
TN (Eu) = 19 K
Eu2+ Transferred Field on 57Fe
filamentary superconductivity
151Eu Mössbauer spectroscopy
(Eu1-yCay)(Fe2-xCox)As2
151Eu Mössbauer spectra
Eu2+ orders magnetically regardless of the Co-substitution level. Eu2+ moments rotate from a-axis to c-axis. Eu2+ magnetism and superconductivity coexist.
Eu(3+)
Eu(2+)
EuFe2As2TSDW (Fe) = 190 KTN (Eu) = 19 K
Parent
Superconductor Tsc = 9.5 K
Superconductor Tsc = 11 K
Over-doped
Conclusions
1. 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.
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 and Ca substitution. It seems that superconductivity has some filamentary character.
3. 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!