Transcript Slajd 1

Mössbauer spectroscopy of iron-based superconductors
A. Błachowski1, K. Ruebenbauer1, J. Żukrowski2, J. Przewoźnik2
11-family cooperation
K. Wojciechowski3, Z.M. Stadnik4
111-family cooperation
J. Marzec5
122-family cooperation
K. Rogacki6, J. Karpinski7, Z. Bukowski7
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, 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
LaFeAsO
1111
Tc max = 56K
BaFe2As2
122
LiFeAs
111
FeSe
11
38K
25K
15K
-FeSe
A tetragonal P4/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 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?
Fe1.05Se
P4/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
orthorhombic
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
orthorhombic
orthorhombic
and
superconducting
T (K)
S (mm/s)
Δ (mm/s)
 (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.
LiFeP
P4/nmm
a = 3.698(1) Å
c = 6.030(2) Å
Magnetization measured in ZFC mode
Mössbauer spectra of LiFeP
T (K)
S (mm/s)
Δ (mm/s)
 (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)
[FeP4]
tetrahedron coordination
122 family of Fe-based superconductors
BaFe2As2
100
100
95
98
133 K
RT
96
90
94
85
100
-2
-1
0
1
2
100
-2
-1
0
1
2
0
1
2
-1
0
1
2
-1
0
1
2
98
95
131 K
139 K
96
90
94
100
-2
-1
0
1
2
100
-2
-1
98
125 K
137 K
95
96
90
100
94
-2
-1
0
1
2
98
100
-2
98
80 K
135 K
96
96
94
94
-2
-1
0
1
Velocity (mm/s)
2
-2
Velocity (mm/s)
Ba0.7Rb0.3Fe2As2
Tc = 37K
100
95
RT
90
85
80
100
-2
-1
0
1
2
-1
0
1
2
-1
0
1
2
95
145 K
90
85
80
100
-2
95
80 K
90
85
80
-2
Velocity (mm/s)
EuFe2As2
100
100
96
210 K
92
96
100 -3
-2
-1
0
1
2
3
200 K
96
100 -3
-2
-1
0
1
2
3
-1
0
1
2
3
-1
0
1
2
3
-1
0
1
2
3
180 K
98
92
100
185 K
98
96
-3
-2
-1
0
1
2
3
100 -3
-2
98
195 K
96
170 K
98
94
96
92
100 -3
98
-2
-1
0
1
2
3
189 K
100 -3
-2
80 K
98
96
96
-3
-2
-1
0
1
Velocity (mm/s)
2
3
-3
-2
Velocity (mm/s)
100
96
210 K
92
88
100
-3
-2
-1
0
1
2
3
-1
0
1
2
3
-1
0
1
2
3
-1
0
1
2
3
-1
0
1
2
3
96
145 K
92
88
100
-3
96
-2
100 K
92
88
100
-3
-2
96
90 K
92
88
100
-3
96
-2
80 K
92
-3
-2
Velocity (mm/s)
EuFe2-xCoxAs2
Tc = 10K
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.