Superconductivity in Pt- and La-Doped BaFe₂As₂ Compounds Prepared by Solid-State Reaction

Abstract

We report magnetization, resistivity and heat capacity measurements on samples of BaFe2As2, BaFe1.9Pt0.1As2 and Ba0.7La0.3Fe1.9Pt0.1As2 having been prepared by solid state reaction. Standard four-probe transport measurements in the temperature range 4.2-300 K showed that the substitution of nonisoelectronic Pt for Fe produced an electron-doped situation resulting a superconductive phase transition at Tc = 24 K. Furthermore, we observe that the coupled Spin-Density-Wave (SDW/AFM) transition which occurs for the BaFe2As2 sample at 140K as expected, occurs also in the Pt doped BaFe1.9Pt0.1As2 sample with only a small decrease in critical temperature to 138 K. We have also investigated in detail the superconducting state with magnetization measurements in the temperature range 5-400 K, up to a field of 9 T. From the magnetization data for BaFe1.9Pt0.1As2 we observe that Tc = 21.7 K, in good agreement with the resistivity measurement. The zero-field cooled (ZFC) results correspond to a large Meissner fraction. In Ba0.7La0.3Fe1.9Pt0.1As2 we also see a large diamagnetic response, with a reduction in Tc to 19.6 K. In addition, we analyzed heat capacity measurements for the electronic and phonon behavior of these materials. The analysis shows an excess entropy associated with the change in electronic behavior consistent with what is expected for Fe local moments, pointing to an electronic density of states that is based on a spin-fluctuation mechanism. We discuss the results in relation to a varying electronic density of states present in the samples, and a possible pseudogap induced by addition of Pt.Index Terms-DC magnetic susceptibility, Superconductivity, Spin density wave, Meissner effect.

Critical current density and flux pinning in BaFe1.9Pt0.1As2 and La doped Ba0.95La0.05Fe1.9Pt0.1As2 polycrystals

“…As it is seen, the calculated value of H fj is very close to the observed first flux jump field values. We used C ~ γT 3 [50] the value of γ to be 0.011 J (mol K) −1 for BaFe 1.9 Pt 0.1 As 2 ) and the molecular weight of the sample to be 0.413 kg mol −1 . It is not coincidental to obtain such a close value to the corresponding experimental results; we believe that the occurrence of the first flux jumps at these fields confirms in some way the correctness of the model suggested (mentioned above) for the switching from the isothermal critical state to an adiabatic critical state.…”

“…This is the most important reason to motivate us to study on La doped BaFe 2 As 2 . Concerning the question why Pt impurity is used in this study, the reason is obvious, Pt atoms induces the superconductivity due to strong spin-orbit effects [48][49][50][51][52]. As a result, we believe that electron correlation effects are important for the mechanism of high-T c superconductivity in these Fe pnictides.…”