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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.

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Prezentacja na temat: "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."— Zapis prezentacji:

1 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 1 Zakład Spektroskopii Mössbauerowskiej, Instytut Fizyki, Uniwersytet Pedagogiczny, Kraków, Polska 2 Instytut Niskich Temperatur i Badań Strukturalnych, Polska Akademia Nauk, Wrocław, Polska 3 AGH Akademia Górniczo-Hutnicza, Akademickie Centrum Materiałów i Nanotechnologii, Kraków, Polska 4 AGH Akademia Górniczo-Hutnicza, Wydział Fizyki i Informatyki Stosowanej, Katedra Fizyki Ciała Stałego, Kraków, Polska X Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2014 Wrocław, czerwca 2014

2 Superconducting Materials

3 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

4 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

5 T sc max = 56 K 47 K 18 K 15 K Fe-based Superconducting Families pnictogens: P, As, Sb chalcogens: S, Se, Te LnO(F)FeAs AFe 2 As 2 AFeAs FeTe(Se,S) Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu, K A = Li, Na

6 Layered Structure of Fe-based Superconductors ‘122’ Parent Compounds Doped Compounds  ‘122’ Superconductors BaFe 2 As 2 Ba 1-x K x Fe 2 As 2 BaFe 2-x Co x As 2 BaFe 2 As 2-x P x Phase Diagram Holes, electrons or isovalent doping Spin density wave (SDW) magnetic order SDW CompoundT SDW (Fe) / T N (R) [K] CaFe 2 As SrFe 2 As BaFe 2 As EuFe 2 As / 19 CompoundT c [K] Ca 0.6 Na 0.4 Fe 2 As 2 26 CaFe 1.94 Co 0.06 As 2 17 CaFe 2 As P Ba 0.6 K 0.4 Fe 2 As 2 38 BaFe 1.8 Co 0.2 As 2 23 BaFe 2 As 1.3 P Eu 0.5 K 0.5 Fe 2 As 2 32 EuFe 1.63 Co 0.37 As EuFe 2 As 1.7 P 0.3 5

7 ”122” family of Fe-based superconductors Parent compoundsSuperconductorsOverdoped EuFe 2 As 2 EuFe 1.63 Co 0.37 As 2 EuFe 1.42 Co 0.58 As 2 (Eu 0.72 Ca 0.28 )(Fe 1.64 Co 0.36 )As 2

8 EuFe 2-x Co x As 2 T SDW (Fe) = 190 K T N (Eu) = 19 K EuFe 2 As 2 parent compound

9 EuFe 2 As 2 critical exponent  0 ≈  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

10 (Eu 1-y Ca y )(Fe 2-x Co x )As 2 57 Fe Mössbauer spectra T SDW = 192 K T SDW  100 K T SDW  80 K lack of SDW T N (Eu) = 19 K Eu 2+ Transferred Field on 57 Fe filamentary superconductivity

11 151 Eu Mössbauer spectroscopy

12 (Eu 1-y Ca y )(Fe 2-x Co x )As Eu Mössbauer spectra Eu 2+ orders magnetically regardless of the Co-substitution level. Eu 2+ moments rotate from a-axis to c-axis. Eu 2+ magnetism and superconductivity coexist.  Eu(3+) Eu(2+)  EuFe 2 As 2 T SDW (Fe) = 190 K T N (Eu) = 19 K  Parent  Superconductor T sc = 9.5 K  Superconductor T sc = 11 K  Over-doped

13 Conclusions 1.The SDW order diminishes in (Eu 1-y Ca y )(Fe 2-x Co x )As 2 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.Eu 2+ 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.

14 Thank you very much for your attention!


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