18 research outputs found
Hall-plot of the phase diagram for Ba(Fe1-xCox)2As2
The Hall effect is a powerful tool for investigating carrier type and
density. For single-band materials, the Hall coefficient is traditionally
expressed simply by , where is the charge of the carrier,
and is the concentration. However, it is well known that in the critical
region near a quantum phase transition, as it was demonstrated for cuprates and
heavy fermions, the Hall coefficient exhibits strong temperature and doping
dependencies, which can not be described by such a simple expression, and the
interpretation of the Hall coefficient for Fe-based superconductors is also
problematic. Here, we investigate thin films of Ba(FeCo)As
with compressive and tensile in-plane strain in a wide range of Co doping. Such
in-plane strain changes the band structure of the compounds, resulting in
various shifts of the whole phase diagram as a function of Co doping. We show
that the resultant phase diagrams for different strain states can be mapped
onto a single phase diagram with the Hall number. This universal plot is
attributed to the critical fluctuations in multiband systems near the
antiferromagnetic transition, which may suggest a direct link between magnetic
and superconducting properties in the BaFeAs system.Comment: Accepted for publication in Scientific Reports, 6 main figures plus
Supplemental Information (8 figures
The influence of the in-plane lattice constant on the superconducting transition temperature of FeSe0.7Te0.3 thin films
Epitaxial Fe(Se,Te) thin films were prepared by pulsed laser deposition on
(La0.18Sr0.82)(Al0.59Ta0.41)O3 (LSAT), CaF2-buffered LSAT and bare CaF2
substrates, which exhibit an almost identical in-plane lattice parameter. The
composition of all Fe(Se,Te) films were determined to be FeSe0.7Te0.3 by energy
dispersive X-ray spectroscopy, irrespective of the substrate. Albeit the
lattice parameters of all templates have comparable values, the in-plane
lattice parameter of the FeSe0.7Te0.3 films varies significantly. We found that
the superconducting transition temperature (Tc) of FeSe0.7Te0.3 thin films is
strongly correlated with their a-axis lattice parameter. The highest Tc of over
19 K was observed for the film on bare CaF2 substrate, which is related to
unexpectedly large in-plane compressive strain originating mostly from the
thermal expansion mismatch between the FeSe0.7Te0.3 film and the substrate.Comment: Accepted in AIP Advances, 4 figure
Universal scaling behavior of the upper critical field in strained FeSe0.7Te0.3 thin films
open15Revealing the universal behaviors of iron-based superconductors (FBS) is important to elucidate the microscopic theory of superconductivity. In this work, we investigate the effect of in-plane strain on the slope of the upper critical field H c2 at the superconducting transition temperature T c (i.e. -dH c2/dT) for FeSe0.7Te0.3 thin films. The in-plane strain tunes T c in a broad range, while the composition and disorder are almost unchanged. We show that -dH c2/dT scales linearly with T c, indicating that FeSe0.7Te0.3 follows the same universal behavior as observed for pnictide FBS. The observed behavior is consistent with a multiband superconductivity paired by interband interaction such as sign change s ± superconductivity.openYuan, Feifei; Grinenko, Vadim; Iida, Kazumasa; Richter, Stefan; Pukenas, Aurimas; Skrotzki, Werner; Sakoda, Masahito; Naito, Michio; Sala, Alberto; Putti, Marina; Yamashita, Aichi; Takano, Yoshihiko; Shi, Zhixiang; Nielsch, Kornelius; Hühne, RubenYuan, Feifei; Grinenko, Vadim; Iida, Kazumasa; Richter, Stefan; Pukenas, Aurimas; Skrotzki, Werner; Sakoda, Masahito; Naito, Michio; Sala, Alberto; Putti, Marina; Yamashita, Aichi; Takano, Yoshihiko; Shi, Zhixiang; Nielsch, Kornelius; Hühne, Rube
Probing the Martensitic Microstructure of Magnetocaloric Heusler Films by Synchrotron Diffraction
First‐order, magnetocaloric materials are promising for energy efficient solid‐state cooling because of their high entropy changes, but they have the drawback of a hysteresis due to the nucleation and growth of the involved phases. Here, synchrotron based X‐ray diffraction is used to investigate epitaxial Ni−Mn−Ga−Co thin films grown on Pb(MgNb)TiO (PMN‐PT). This integral method is used to test several hypotheses regarding structure and orientation of the martensite, whose nucleation was proposed to be the decisive contribution to hysteresis in Heusler materials. The measurements are compared to a recently proposed model of the martensitic nuclei, combining the phenomenological martensite theory with the adaptive concept. This investigation demonstrates that the diffraction patterns are consistent with a martensitic nucleus built from 8 variants forming a‐b laminates. Additionally, it is shown that in accordance with the surface morphology of these films only a subset of nuclei occur, namely those needed to form type X martensite