4 research outputs found
Possible re-entrant superconductivity in EuFe2As2 under pressure
We studied the temperature-pressure phase diagram of EuFe2As2 by measurements
of the electrical resistivity. The antiferromagnetic spin-density-wave
transition at T_0 associated with the FeAs-layers is continuously suppressed
with increasing pressure, while the antiferromagnetic ordering temperature of
the Eu 2+ moments seems to be nearly pressure independent up to 2.6 GPa. Above
2 GPa a sharp drop of the resistivity, \rho(T), indicates the onset of
superconductivity at T_c \approx 29.5 K. Surprisingly, on further reducing the
temperature \rho(T) is increasing again and exhibiting a maximum caused by the
ordering of the Eu 2+ moments, a behavior which is reminiscent of re-entrant
superconductivity as it is observed in the ternary Chevrel phases or in the
rare-earth nickel borocarbides
Interplay between superconductivity and magnetism in K-doped EuFe2As2
Superconductivity is found in 50% K-doped EuFe2As2 sample below 33 K. Our
results of electrical resistivity, magnetic susceptibility and 57Fe and 151Eu
Mossbauer spectroscopy provide clear evidence that the ordering of the Fe
moments observed at 190 K in undoped EuFe2As2 is completely suppressed in our
50% K doped sample, thus there is no coexistence between the Fe magnetic order
and the superconducting state. However, short range ordering of the Eu moments
is coexisting with the superconducting state below 15 K. A bump in the
susceptibility well below Tc as well as a slight broadening of the Fe Mossbauer
line below 15 K evidence an interplay between the Eu magnetism and the
superconducting state.Comment: 7 pages, 6 figure
AFe2As2 (A = Ca, Sr, Ba, Eu) and SrFe_(2-x)TM_(x)As2 (TM = Mn, Co, Ni): crystal structure, charge doping, magnetism and superconductivity
The electronic structure and physical properties of the pnictide compound
families OFeAs ( = La, Ce, Pr, Nd, Sm), FeAs ( = Ca,
Sr, Ba, Eu), LiFeAs and FeSe are quite similar. Here, we focus on the members
of the FeAs family whose sample composition, quality and single
crystal growth are better controllable compared to the other systems. Using
first principles band structure calculations we focus on understanding the
relationship between the crystal structure, charge doping and magnetism in
FeAs systems. We will elaborate on the tetragonal to
orthorhombic structural distortion along with the associated magnetic order and
anisotropy, influence of doping on the site as well as on the Fe site, and
the changes in the electronic structure as a function of pressure.
Experimentally, we investigate the substitution of Fe in
SrFeAs by other 3 transition metals, = Mn, Co, Ni.
In contrast to a partial substitution of Fe by Co or Ni (electron doping) a
corresponding Mn partial substitution does not lead to the supression of the
antiferromagnetic order or the appearance of superconductivity. Most calculated
properties agree well with the measured properties, but several of them are
sensitive to the As position. For a microscopic understanding of the
electronic structure of this new family of superconductors this structural
feature related to the Fe-As interplay is crucial, but its correct ab initio
treatment still remains an open question.Comment: 27 pages, single colum