1. 151Eu AND 57Fe MÖSSBAUER STUDY OF Eu1-xCaxFe2As2
SUPERCONDUCTOR AND PARENT COMPOUNDS
K. Komędera1, A. Błachowski1, K. Ruebenbauer1, J. Żukrowski2, S. M. Dubiel3, L. M. Tran4, M. Babij4, Z. Bukowski4 
1Mössbauer Spectroscopy Laboratory, Institute of Physics, Pedagogical University, Kraków, Poland
2Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, Kraków, Poland
3AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Kraków, Poland
4Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wrocław, Poland
XII Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2018
Goniądz, czerwca 2018

2. Fe-based Superconductors pnictogens: P, As, Sb
chalcogens: S, Se, Te
BaFe2As2
SrFe2As2
CaFe2As2
EuFe2As2
KFe2As2
RbFe2As2
CsFe2As2
low Tc superconductors
Nonsuperconducting parent compounds

3. Magnetic structure of EuFe2As2
Two magnetic sublattices
Fe2+ 3d itinerant electrons
Spin Density Wave
Fe saturation moment of µB aligned along the long a axis.
TSDW=190 K
localised Eu2+ 4f electrons,
spin S=7/ µeff= 7.94 µB
A-type Antiferromagnet TN=19 K
Xiao et al. PRB 80,

4. Spin density wave (SDW)
perpendicular
longitudinal
commensurate
or incommensurate
h2n-1 – amplitudes of subsequent harmonics
q – wave number of SDW
x – relative position of the resonant nucleus along propagation direction of the stationary SDW 4

5. Spin density wave (SDW) seen by Mössbauer Spectroscopy
h2n-1 – amplitudes of subsequent harmonics
q – wave number of SDW
x – relative position of the resonant nucleus along propagation direction of SDW
SDW hyperfine field distribution Fe Mössbauer spectrum

6. Effect of pressure Pressure-suppressed SDW order
Pressure-induced superconductivity
Persistent Eu2+ magnetic order
Kurita et al. PRB 83, (2011)
Kumar et al. Appl. Phys. Lett. 104, (2014)

7. Effect of dilution of Eu sublattice with nonmagnetic ions
Disappearance of Eu2+ magnetic order
SDW order remains intact ?
Zapf and Dressel, Rep. Prog. Phys. 80 (2017)

8. Phase diagram of Eu magnetic ordering in Sn-flux-grown Eu(Fe1−xCox)2As2 single crystals
suppression of SDW order
superconductivity coexists with Eu ferromagnetism
superconductivity competes with Fe SDW antiferromagnetic order
W. T. Jin et al., PRB 94, (2016)

9. Effect of Co-doping on Eu2+ magnetic ordering in Eu(Fe1−xCox)2As2 single crystals
ferromagnetic Eu2+ moment of 6.2μB purely along the c direction
Fe2+ moment is estimated to be 0.63(4) μB
Neutron diffraction
Co concentration x AF
CAF F
W. T. Jin et al., PRB 94, (2016)

10. Electric Field Gradient + Hyperfine field on 151Eu Mössbauer spectroscopy

11. ”122” family of Fe-based superconductors
Parent compounds
EuFe2As2
Eu0.57Ca0.43Fe2As2
CaFe2As2
Superconductors
Eu(Fe0.81Co0.19)2As2
Eu0.73Ca0.27(Fe0.87Co0.13)2As2

12. Relative Resistivity Parent compounds TSDW (Fe) TN (Eu) EuFe2As2 192 K
Eu0.57Ca0.43Fe2As2
195 K
≈10 K
CaFe2As2
175 K
Superconductor
TSC
Tre-SC
Eu0.73Ca0.27(Fe0.87Co0.13)2As2
12 K
10 K
Eu0.73 (Fe0.81Co0.19)2As2
9.5 K

13. 57Fe Mössbauer spectra of parent compound
TN (Eu) = 19 K
TSDW = 192 K
TSDW = 195 K
TSDW = 175 K

14. Spin density wave (SDW)
TSDW = 192 K
TSDW = 195 K
TSDW = 175 K

15. hyperfine field distribution
57Fe Mӧssbauer spectra
hyperfine field distribution
shape of SDW
Spin density wave (SDW)
Eu0.57Ca0.43Fe2As2
TSDW = 195 K

16. Mean squared amplitudes of SDW versus temperature
Total spectral shift versus temperature

17. 57Fe Mössbauer spectra of EuFe2As2-based superconductors
Hyperfine transferred field from Eu to Fe about 1T

18. 151Eu Mössbauer spectroscopy

19. 151Eu Mössbauer spectroscopy
151Eu Mӧssbauer effect shift scale
Nuclear energy levels of 151Eu in the presence of quadrupol interaction
Nuclear energy levels for 151Eu in the presence of a magnetic hyperfine interaction
G. J. Long et al. (eds.), Mössbauer Spectroscopy Applied to Inorganic Chemistry
© Springer Science+Business Media New York 1989

20. 151Eu Mössbauer spectroscopy

21. 151Eu Mössbauer spectra Parent compounds TSDW = 192 K Superconductor
TSC = 9.5 K
Parent compounds
TSDW = 195 K
Superconductor
TSC = 12 K

22. Conclusions
The SDW develops in a similar fashion for the compound Eu0.57Ca0.43Fe2As2 as for parent EuFe2As2.
In superconductors Eu(Fe0.81Co0.19)2As2, Eu0.73Ca0.27(Fe0.87Co0.13)2As2 hyperfine transferred field from Eu to Fe is about 1T.
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.