1. Magnetism of the ‘11’ iron-based superconductors parent compound Fe1+xTe:
The Mössbauer study
A. Błachowski1, K. Ruebenbauer1, P. Zajdel2, E.E. Rodriguez3, M.A. Green3,4
1Mössbauer Spectroscopy Laboratory,
Pedagogical University, Kraków, Poland
2Division of Physics of Crystals, Institute of Physics,
Silesian University, Katowice, Poland
3NIST Center for Neutron Research, NIST, Gaithersburg, U.S.A.
4Department of Materials Science and Engineering, University of Maryland, U.S.A.
IX Ogólnopolskie Seminarium Spektroskopii Mössbauerowskiej OSSM’2012,
Lublin - Kazimierz Dolny, czerwca 2012

2. Fe-based Superconducting Families
pnictogens: P, As, Sb
chalcogens: S, Se, Te
LnFeAsO(F) AFe2As LiFeAs FeTe(Se,S)
Ln = La, Ce, Pr, Nd, Sm, Gd … A = Ca, Sr, Ba, Eu
Tc max = 56 K K K K

3. Fe1+xTe
x = 0.04 – 0.18
x = 0.06 , 0.10 , 0.14 , 0.18
E.E. Rodriguez et al.,
Phys. Rev. B (2011)

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

5. Alcoholic beverages induce superconductivity in FeTe1−xSx
K. Deguchi et al., Supercond. Sci. Technol (2011)

6. Magnetic-crystallographic phase diagram of the Fe1+xTe
E.E. Rodriguez et al., Phys. Rev. B (2011) S. Röler et al., Phys. Rev. B (2011)
G.F. Chen et al., Phys. Rev. B (R) (2009) 

7. Fe1.06Te

8. Fe1.10Te

9. Fe1.14Te

10. Fe1.18Te

11. Fe1+xTe
x=0.06
x=0.10
x=0.14
x=0.18
65 K K

12. Square root of the mean squared amplitude of SDW versus temperature

13. Conclusions
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 of the iron atoms on these sites. 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.
The critical exponent of the mean squared 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).
Interstitial iron has relatively large localized magnetic moment at least for the site with the highest hyperfine field. 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.

14. K. Deguchi et al., arXiv:1204.0190 (2012)
Clarification as to why alcoholic beverages have the ability to induce superconductivity
in Fe1+dTe1-xSx
K. Deguchi et al., arXiv: (2012)
”We found that the mechanism of inducement of superconductivity in Fe1+dTe1-xSx is the deintercalation of excess Fe from the interlayer sites.”
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