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A neutron scattering study of the under-doped Ba1-xKxFe2As2, x=0.09 and 0.17 self-flux grown single crystals and the universality of the tricritical point

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Autori: C. R. Rotundu , W. Tian, K. C. Rule, T. R. Forrest, J. Zhao, J. L. Zarestky, and R. J. Birgeneau

Editorial: APS, Physical Review B, 85, p.144506, 2012.


We present a combination of elastic neutron scattering measurements in zero and 14.5 T and magnetization
measurements in zero and 14 T on underdoped superconducting Ba1−xKxFe2As2 (x = 0.17), and the same
measurements in zero field on a nonsuperconducting crystal with x = 0.09. The data suggest that the underdoped
materials may not be electronic phase separated but rather have slightly inhomogeneous potassium doping. The
temperature dependence of the magnetic order parameter below the transition of the sample with x = 0.09 is
more gradual than that for the case of the undoped BaFe2As2, suggesting that this doping may be in the vicinity
of a tricritical point. We advance therefore the hypothesis that the tricritical point is a common feature of all
superconducting 122s. For the x = 0.17 sample, while Tc is suppressed from 17 to 8 K by a magnetic field
of 14 T, the intensity of the magnetic Bragg peaks (1 0 3) at 1.2 K is enhanced by 10%, showing competition
of superconductivity and antiferromagnetism. The intensity of the magnetic Bragg peaks (1 0 3) in the (Tc, TN)
temperature interval remain practically unchanged in 14.5 T within a 10% statistical error. The present results
are discussed in the context of the existing literature.

Cuvinte cheie: iron-arsenide high temperature superconductors, phase transitions, tricritical point