1. Magnetism of the regular and excess iron in Fe1+xTe
studied by Mössbauer spectroscopy
A. Błachowski1, K. Ruebenbauer1, P. Zajdel2, E.E. Rodriguez3, M.A. Green3, 4
1Mössbauer Spectroscopy Division, Institute of Physics,
Pedagogical University, Kraków, Poland
2Division of Physics of Crystals, Institute of Physics,
Silesian University, Katowice, Poland
3National Institute of Standards and Technology,
Center for Neutron Research, Gaithersburg, U.S.A.
4Department of Materials Science and Engineering, University of Maryland, U.S.A.
XVI National Conference on Superconductivity, 7-12 October 2013, Zakopane, Poland

2. Fe-based Superconducting Families
pnictogens: P, As, Sb
chalcogens: S, Se, Te
LnO(F)FeAs AFe2As AFeAs FeTe(Se,S)
Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu, K A = Li , Na
Tsc max = 56 K K K K
37 K at 9 GPa

3. Layered Structure of Fe-based Superconductors
Spin density wave
(SDW)
magnetic order
Fe1+xTe BaFe2As2
perpendicular
longitudinal
COMMENSURATE
or INCOMMENSURATE

4. 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

5. Magnetic-crystallographic phase diagram
Fe1+xTe
x = 0.04 – 0.18
x = 0.06 , 0.10 , 0.14 , 0.18
S. Röler et al., Phys. Rev. B (2011)
x in Fe1+xTe
G.F. Chen et al.,
Phys. Rev. B (R) (2009)

6. Fe1+yTe1-xSex Fe1+yTe1-xSx
Parent Compound
Fe1+yTe
Doped Compound → Superconductor
y ≈ 0
Fe1+yTe1-xSex Fe1+yTe1-xSx
K. Katayama et al.,
J. Phys. Soc. Japan 79, (2010)
Y. Mizuguchi et al.,
J. Appl. Phys. 109, (2011)

7. Alcoholic beverages induce superconductivity in FeTe1−xSx
K. Deguchi et al., Supercond. Sci. Technol. 24, (2011)
”Some components present in alcoholic beverages, other than water and ethanol,
have the ability to induce superconductivity in FeTe0.8S0.2 compound.”

8. Fe1.06Te regular (tetrahedral) Fe excess (interstitial) Fe
57Fe Mössbauer spectra SDW field distribution shape of SDW
Fe1.06Te
   
regular (tetrahedral) Fe excess (interstitial) Fe
SDW higher magnetic fields than SDW

9. Three different kinds (surroundings) of excess (interstitial) Fe.
57Fe Mössbauer spectra SDW field distribution shape of SDW
Fe1.14Te
SDW
regular Fe
  
Three different kinds (surroundings) of excess (interstitial) Fe.
Magnetism of the excess Fe and SDW disappear at the same transition temperature.

10. Fe1+xTe 65 K 4.2 K x=0.06 x=0.10 x=0.14 x=0.18 shape of SDW at 4.2 K
regular Fe (SDW) excess Fe
   
Fe1+xTe
x=0.06
x=0.10
x=0.14
x=0.18
shape of SDW
at 4.2 K
SDW is very sensitive to concentration of interstitial iron
with relatively large localized magnetic moments.

11. Root mean square amplitude of SDW versus temperature
The critical exponent of the mean square amplitude of SDW versus temperature indicates that
the universality class is close to the (1, 2) class,
i.e. the one dimension of the spin space (Ising model) and two spatial dimensions (Fe-Te layers).

12. Conclusions
Excess (interstitial) iron with relatively large localized magnetic moment
strongly influences ordering temperature, shape and amplitude of the regular iron SDW order.
Despite existence of the single crystallographic site for the excess iron one sees at least three different kinds of these atoms. Such situation could occur due to the partial filling of the available interstitial sites by iron and due to some ordering (or clustering). The site with the highest magnetic hyperfine field is likely to contain almost isolated ions, i.e., surrounded by the vacancies on the interstitial sites.
The magnetism of the excess iron and SDW are coupled one with another. Both kinds of magnetism disappear at the same transition temperature.
Interstitial iron has relatively large localized magnetic moment. These moments interact strongly with the electrons having ability to form Cooper pairs and prevent appearance of the superconductivity. One has to remove interstitial iron to have a chance to get superconducting material.
A. Błachowski, K. Ruebenbauer, P. Zajdel, E.E. Rodriguez, M.A. Green,
Mössbauer study of the ‘11’ iron-based superconductors parent compound Fe1+xTe,
J. Phys.: Condens. Matter 24, (2012)

13. K. Deguchi et al., Supercond. Sci. Technol. 25, 084025 (2012)
Clarification as to why alcoholic beverages have the ability to induce superconductivity
in Fe1+dTe1-xSx
K. Deguchi et al., Supercond. Sci. Technol. 25, (2012)

14. K. Deguchi et al., Supercond. Sci. Technol. 25, 084025 (2012)
Clarification as to why alcoholic beverages have the ability to induce superconductivity
in Fe1+dTe1-xSx
K. Deguchi et al., Supercond. Sci. Technol. 25, (2012)
”We found that the mechanism of inducement of superconductivity in Fe1+dTe1-xSx
is the deintercalation of excess Fe from the interlayer sites.”