Pobieranie prezentacji. Proszę czekać

Pobieranie prezentacji. Proszę czekać

Nadprzewodniki na bazie żelaza FeSe i LiFeP – badania metodą spektroskopii mössbauerowskiej oraz pomiary magnetyczne A. Błachowski 1, K. Ruebenbauer 1,

Podobne prezentacje


Prezentacja na temat: "Nadprzewodniki na bazie żelaza FeSe i LiFeP – badania metodą spektroskopii mössbauerowskiej oraz pomiary magnetyczne A. Błachowski 1, K. Ruebenbauer 1,"— Zapis prezentacji:

1 Nadprzewodniki na bazie żelaza FeSe i LiFeP – badania metodą spektroskopii mössbauerowskiej oraz pomiary magnetyczne A. Błachowski 1, K. Ruebenbauer 1, J. Żukrowski 2, J. Przewoźnik 2, J. Marzec 3, K. Wojciechowski 4, Z.M. Stadnik 5, U.D. Wdowik 6 1 Zakład Spektroskopii Mössbauerowskiej, Instytut Fizyki, Uniwersytet Pedagogiczny, Kraków 2 Katedra Fizyki Ciała Stałego, Wydział Fizyki i Informatyki Stosowanej, Akademia Górniczo-Hutnicza, Kraków 3 Katedra Energetyki Wodorowej, Wydział Energetyki i Paliw, Akademia Górniczo-Hutnicza, Kraków 4 Katedra Chemii Nieorganicznej, Wydział Inżynierii Materiałowej i Ceramiki, Akademia Górniczo-Hutnicza, Kraków 5 Department of Physics, University of Ottawa, Ottawa, Canada 6 Zakład Zastosowań Informatyki, Instytut Techniki, Uniwersytet Pedagogiczny, Kraków

2 Superconducting Materials

3 T C max = 56K 38K 25K 15K Fe-based Superconducting Families LaFeAsOF BaFe 2 As 2 LiFeAs FeSe

4 Fe-Se phase diagram The following phases form close to the FeSe stoichiometry: 1) tetragonal P4/nmm structure similar to PbO, called β-FeSe (or α-FeSe) 2) hexagonal P6 3 /mmc structure similar to NiAs, called δ-FeSe 3) hexagonal phase Fe 7 Se 8 with two different kinds of order, i.e., 3c (α-Fe 7 Se 8 ) or 4c (β-Fe 7 Se 8 ) A tetragonal P4/nmm phase transforms into Cmma orthorhombic phase at about 100 K, and this phase is superconducting with T c 8 K.

5 Aim of this contribution is to answer two questions concerned with tetragonal/orthorhombic FeSe: 1) is there electron spin density (magnetic moment) on Fe ? 2) is there change of electron density on Fe nucleus during transition from P4/nmm to Cmma structure ? Crystal structure of -FeSe

6 Fe 1.05 Se

7 P4/nmm a = (1) Å c = (1) Å

8 - 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 Magnetic susceptibility measured upon cooling and subsequent warming in field of 5 Oe

9 Change in isomer shift S Change in electron density on Fe nucleus S = mm/s ρ = –0.02 electron/a.u. 3 tetragonal orthorhombic and superconducting orthorhombic phase transition

10 tetragonal orthorhombic and superconducting orthorhombic phase transition Quadrupole splitting Δ does not change - it means that local arrangement of Se atoms around Fe atom does not change during phase transition T (K)S (mm/s)Δ (mm/s) (mm/s) (3)0.287(1)0.206(1) (3)0.287(1)0.203(1) (3)0.286(1)0.198(1) (3)0.287(1)0.211(1) (4)0.295(1)0.222(1)

11 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.

12 Total electron spin density versus energy for the Cmma phase at null pressure Spin-up and spin-down states are plotted separately in red and green colors, respectively. Fermi level is marked by the vertical line. This is obviously non-magnetic metallic system.

13 Phonon dispersion relations at null pressure and for the ground state

14 PHONON DYNAMICS IN TETRAGONAL/ORTHORHOMBIC PHASE Total density of the phonon states versus pressure for the orthorhombic phase (DOS) V. Ksenofontov, G. Wortmann, A.I. Chumakov et al., Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure, arXiv:

15 Electron spin density versus energy for the hexagonal phase A transition from the ferromagnetic insulating state to the metallic state with very small magnetic moment at high hydrostatic pressure Energy gap and magnetic moment in the hexagonal phase

16 LiFeP P4/nmm a = 3.698(1) Å c = 6.030(2) Å

17 Magnetization measured in ZFC mode

18 Magnetic hysteresis obtained at 2 K and 20 K

19 Magnetization measured in sweep mode

20 Mössbauer spectra of LiFeP T (K)S (mm/s)Δ (mm/s) (mm/s) RT0.247(1)0.101(1)0.172(1) (1)0.112(2)0.224(1) (1)0.119(3)0.227(2) [FeP 4 ] tetrahedron coordination

21 Conclusions FeSe 1. There is no magnetic moment on iron atoms in the P4/nmm and Cmma phases. 2. The electron density on iron nucleus is lowered by 0.02 electron/a.u. 3 at 105K during transition from P4/nmm to Cmma phase. LiFeP 3. There is no magnetic order in the superconducting LiFeP.


Pobierz ppt "Nadprzewodniki na bazie żelaza FeSe i LiFeP – badania metodą spektroskopii mössbauerowskiej oraz pomiary magnetyczne A. Błachowski 1, K. Ruebenbauer 1,"

Podobne prezentacje


Reklamy Google