Mssbauer spectroscopy of ironbased superconductors A Bachowski 1
Mössbauer spectroscopy of iron-based superconductors A. Błachowski 1, K. Ruebenbauer 1, J. Żukrowski 2, J. Przewoźnik 2 11 -family cooperation K. Wojciechowski 3, Z. M. Stadnik 4 111 -family cooperation J. Marzec 5 122 -family cooperation K. Rogacki 6, J. Karpinski 7, Z. Bukowski 7 1 2 Solid State Physics Department, Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Cracow, Poland 3 6 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, Cracow, Poland Department of Inorganic Chemistry, Faculty of Material Science and Ceramics, AGH University of Science and Technology, Cracow, Poland 4 Department of Physics, University of Ottawa, Canada 5 Department of Hydrogen Energy, Faculty of Energy and Fuels, AGH University of Science and Technology, Cracow, Poland Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław, Poland 7 Laboratory for Solid State Physics, ETH Zürich, CH-8093 Zürich, Switzerland
Superconducting Materials
Fe-based Superconducting Families La. Fe. As. O 1111 Tc max = 56 K Ba. Fe 2 As 2 122 Li. Fe. As 111 Fe. Se 11 38 K 25 K 15 K
-Fe. Se A tetragonal P 4/nmm phase transforms into Cmma orthorhombic phase at about 100 K, and this phase is superconducting with Tc ≈ 8 K. There are two questions concerned with tetragonal/orthorhombic Fe. Se: 1) is there electron spin density (magnetic moment) on Fe? 2) is there change of electron density on Fe nucleus during transition from P 4/nmm to Cmma structure?
Fe 1. 05 Se P 4/nmm a = 3. 7720(1) Å c = 5. 5248(1) Å
Magnetic susceptibility measured upon cooling and subsequent warming in field of 5 Oe - point A - spin rotation in hexagonal phase - region B - magnetic anomaly correlated with transition between orthorhombic and tetragonal phases - point C - transition to the superconducting state
tetragonal phase transition orthorhombic and superconducting Change in isomer shift S ↓ Change in electron density on Fe nucleus S = +0. 006 mm/s ↓ ρ = – 0. 02 electron/a. u. 3
tetragonal phase transition orthorhombic and superconducting T (K) S (mm/s) Δ (mm/s) 120 0. 5476(3) 0. 287(1) 0. 206(1) 105 0. 5529(3) 0. 287(1) 0. 203(1) 90 0. 5594(3) 0. 286(1) 0. 198(1) 75 0. 5622(3) 0. 287(1) 0. 211(1) 4. 2 0. 5640(4) 0. 295(1) 0. 222(1) Quadrupole splitting Δ does not change - it means that local arrangement of Se atoms around Fe atom does not change during phase transition
Mössbauer spectra obtained in external magnetic field aligned with γ-ray beam Hyperfine magnetic field is equal to applied external magnetic field. Principal component of the electric field gradient (EFG) on Fe nucleus was found as negative.
Li. Fe. P P 4/nmm a = 3. 698(1) Å c = 6. 030(2) Å
Magnetization measured in ZFC mode
Mössbauer spectra of Li. Fe. P T (K) S (mm/s) Δ (mm/s) RT 0. 247(1) 0. 101(1) 0. 172(1) 77 0. 356(1) 0. 112(2) 0. 224(1) 4. 2 0. 364(1) 0. 119(3) 0. 227(2) [Fe. P 4] tetrahedron coordination
122 family of Fe-based superconductors
Ba. Fe 2 As 2 Velocity (mm/s)
Ba 0. 7 Rb 0. 3 Fe 2 As 2 Tc = 37 K Velocity (mm/s)
Eu. Fe 2 As 2 Velocity (mm/s)
Eu. Fe 2 -x. Cox. As 2 Tc = 10 K Velocity (mm/s)
Conclusions Fe. Se 1. There is no magnetic moment on iron atoms in the P 4/nmm and Cmma phases. 2. The electron density on iron nucleus is lowered by 0. 02 electron/a. u. 3 at 105 K during transition from P 4/nmm to Cmma phase. Li. Fe. P 3. There is no magnetic order in the superconducting Li. Fe. P.
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