Synthesis and physical properties of $\rm\bf LaO_{1-x}F_xFeAs$

TL;DR

This study synthesizes LaO_{1-x}F_xFeAs, revealing a transition from antiferromagnetic order to superconductivity with increasing fluorine doping, and maps the evolution of critical temperatures.

Contribution

It provides the first detailed experimental investigation of structural, magnetic, and superconducting properties across different doping levels in LaO_{1-x}F_xFeAs.

Findings

Antiferromagnetic order and structural transition are suppressed with doping.

Superconductivity emerges at x≈0.05 with T_c up to 26.8 K.

T_c varies non-monotonically with doping, peaking at x=0.1.

Abstract

We have prepared the newly discovered Fe-based superconducting material $\rm LaO_{1-x}F_xFeAs$ ($0\leq x\leq 0.2$) in polycrystalline form and have investigated the samples by means of structural, thermodynamic and transport measurements. Our investigations reveal a non superconducting phase at $0\leq x\lesssim0.04$ which for $x=0$ is characterized by a structural transition towards an orthorhombic distortion at $T_s\approx 160$ K and antiferromagnetic spin order at $T_N\approx138$ K. Both transitions lead to strong anomalies in various transport properties as well as in magnetization and in specific heat. Remarkably, the transition temperatures are only weakly doping dependent up $x\lesssim 0.04$. However, the transitions are abruptly suppressed at $x\geq0.05$ in favour of a superconducting phase with a critical temperature $T_c\gtrsim 20$ K. Upon further increasing the F-doping $T_c$ increases up to a maximum of $T_c=26.8$ K at $x=0.1$ which is followed by a decrease down to $T_c\approx10$ K at $x\geq0.15$.