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!