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Mössbauer study of iron-based superconductors A. Błachowski 1 , K. Ruebenbauer 1 , J. Żukrowski 2 1 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, Cracow, Poland 2 Department of Solid State Physics , Faculty of Physics and Applied Computer Science, - PowerPoint PPT Presentation
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Mössbauer study of iron-based superconductors
A. Błachowski1, K. Ruebenbauer1, J. Żukrowski2
1 Mössbauer Spectroscopy Division, Institute of Physics, Pedagogical University, Cracow, Poland
2 Department of Solid State Physics, Faculty of Physics and Applied Computer Science,AGH University of Science and Technology, Cracow, Poland
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ICAME 2013International Conference on the Applications of the Mössbauer Effect 1-6 September 2013, Opatija, Croatia
Contents
Introduction to the iron-based superconductors
Mössbauer spectroscopy results for:
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AFe2As2 (A = Ca, Ba, Eu) – “122” parent compounds A. Błachowski, K. Ruebenbauer, J. Żukrowski et al., Phys. Rev. B 83, 134410 (2011)
CaFe2-xCoxAs2 ; Ba1-xRbxFe2As2 ; EuFe2-xCoxAs2 – “122” superconductors A. Błachowski, K. Ruebenbauer, J. Żukrowski et al., Phys. Rev. B 84, 174503 (2011) A. Błachowski, K. Ruebenbauer, J. Żukrowski et al., Acta Phys. Pol. A 121, 726 (2012)
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Fe1+xTe – “11” parent compound A. Błachowski, K. Ruebenbauer et al., J. Phys.: Condens. Matter 24, 386006 (2012)
FeSe – “11” superconductor A. Błachowski, K. Ruebenbauer, J. Żukrowski et al., J. Alloys Comp. 494, 1 (2010)
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FeAs – grand-parent compound A. Błachowski, K. Ruebenbauer, J. Żukrowski et al., J. Alloys Comp. 582, 167 (2014)
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Conclusions
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
Journal of American Chemical SocietyReceived January 2008, Published online February 2008
Up to now the maximum superconducting critical temperature of iron-based superconductors
is 56 K
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Tsc max = 56 K 47 K 18 K 15 K
Fe-based Superconducting Familiespnictogens: P, As, Sb chalcogens: S, Se, Te
1111 122 111 11
LnO(F)FeAs AFe2As2 AFeAs FeTe(Se,S)
Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu, K A = Li , Na
Layered Structure of Fe-based Superconductors
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Parent Compounds
Doped Compounds
Superconductors
BaFe2As2
Ba1-xKxFe2As2
BaFe2-xCoxAs2
BaFe2As2-xPx
Phase DiagramHoles, electrons or isovalent doping
Spin density wave (SDW)
magnetic order
SDW
Spin density wave (SDW) – simple non-interlaced picture
] )12( sin[ )(1
12
N
nn qxnhqxB
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
perpendicular
longitudinal
commensurate or incommensurate
Spin density wave (SDW) seen by Mössbauer Spectroscopy
] )12( sin[ )(1
12
N
nn qxnhqxB
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 57Fe Mössbauer spectrum
”122” family of Fe-based superconductors
BaFe2As2 (parent)
TSDW = 136 K Ba0.7Rb0.3Fe2As2
(superconductor)
Tsc = 37 K
57Fe Mössbauer spectra
NM non-magnetic
Shape of SDW
SDW is suppressed by doping
CaFe2As2 (parent)
TSDW = 175 KCaFe1.92Co0.08As2
(superconductor)
Tsc = 20 KResistivity measurements:
It seems that
magnetism and superconductivity coexist (?).
Mössbauer measurements:
Superconductivity has filamentary character
and occurs
in the regions free of 3d magnetic moments.
EuFe2As2
critical exponent 0 ≈ 0.125 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
EuFe2-xCoxAs2
57Fe Mössbauer spectra
TSDW = 190 K
TSDW = 150 K
TSDW = 100 K
traces of SDW at 80 K
lack of SDW
TN (Eu) = 19 K
Eu2+ Transferred Field on 57Fe
filamentary superconductivity
superconductor
superconductor
superconductor
EuFe2-xCoxAs2
151Eu Mössbauer spectra
Eu(3+)
Eu(2+)
EuFe2As2
TSDW (Fe) = 190 KTN (Eu) = 19 K
Parent
Superconductor Tsc = 9.5 K
Over-doped
Eu2+ orders magnetically regardless of the Co-substitution level. Eu2+ moments rotate from a-axis to c-axis. Eu2+ magnetism and superconductivity coexist.
Fe1+xTe
x = 0.04 – 0.18x = 0.06 , 0.10 , 0.14 , 0.18
Magnetic-crystallographic phase diagram
S. Röler et al., Phys. Rev. B 84 174506 (2011)
x in Fe1+xTe
Parent CompoundFe1+yTe
Doped Compound → Superconductory ≈ 0
Fe1+yTe1-xSex Fe1+yTe1-xSx
K. Katayama et al., J. Phys. Soc. Japan 79 113702 (2010)
Fe1.06Te 57Fe Mössbauer spectrum SDW field distribution shape of SDW
regular (tetrahedral) Fe excess (interstitial) Fe SDW
Fe1.14Te
57Fe Mössbauer spectrum SDW field distribution shape of SDW
Three different kinds (surroundings) of excess (interstitial) Fe. Magnetism of the excess Fe and SDW disappear at the same transition temperature.
regular Fe - SDW
Fe1+xTe
x=0.06
x=0.10
x=0.14
x=0.18
65 K 4.2 Kshape of SDW
at 4.2 K
SDW is very sensitive to concentration of interstitial iron with relatively large localized magnetic moments.
Localized iron moments prevent superconductivity, so interstitial iron must be removed by doping and/or deintercalation to get superconducting material.
regular Fe (SDW) excess Fe
Fe1.01Se Tsc = 8 K
High (external) magnetic field Mössbauer spectroscopy
Hyperfine magnetic field is equal to applied external magnetic field- it means that there is no magnetic moment on the Fe atoms
tetragonal
orthorhombic
orthorhombicandsuperconductor
orthorhombic
structuraldistortion
sharp magnetic transition paramagnetic
region magnetic
region
SPIN SPIRAL
FeAs
Crystal structurePnma or Pna21 ?
Arrows show Pna21 – like distortion E.E. Rodriguez et al., PRB 8383, 134438 (2011)
Anisotropy of the hyperfine magnetic fields (spiral projections onto a-b plane) in FeAsLeft column shows [0 k+1/2 0] iron, right column shows [0 k 0] iron.
Ba and Bb - iron hyperfine field components along the a-axis and b-axis, respectively.
Orientation of the EFG and
hyperfine magnetic field in the main crystal axes
Average hyperfine fields <B> for
[0 k+1/2 0] and [0 k 0] irons.
Tc - transition temperature - static critical exponent
A. Błachowski et al., JALCOM 582, 167 (2014)
FeAs
Spectral shift S and
quadrupole coupling constant AQ versus temperature
for [0 k+1/2 0] iron and [0 k 0] iron.
Line at 72 K separate magnetically ordered region from paramagnetic region.
Relative recoilless fraction <f>/<f0> versus temperature
Green points correspond to magnetically ordered region. Red point is the normalization point.
Inset shows relative spectral area RSA plotted versus temperature.
. 1
RSA1 0
0
C
n
n
N
NN
C
Conclusions
Thank you very much for your attention!
AFe2As2 - parentsThe SDW magnetic order with universality class (1, 2) and with almost rectangular shape at saturation.
Ba1-xRbxFe2As2
The SDW vanishes upon doping leading to superconductivity.
CaFe2-xCoxAs2
Superconductivity has filamentary character and occurs in the regions free of 3d magnetic moments.
EuFe2-xCoxAs2
Localized 4f magnetic moments could order within the superconducting phase.
Fe1+xTeExcess (interstitial) iron with relatively large localized magnetic moment strongly influence on the ordering temperature, shape and amplitude of the SDW.
FeSeThere is no magnetic moment on iron in superconducting FeSe and it is PRESUMABLY the feature of all iron-based superconductors.
FeAsSpin spiral leads to the complex variation of the hyperfine field amplitude with the spin orientation (local magnetic moment) varying in the a-b plane. Pattern express symmetry of 3d electrons in the a-b plane with the significant distortion caused by the arsenic bonding p electrons.Strong coupling between magnetism and lattice dynamics i.e. strong phonon-magnon interaction.