Superconductivity in Co-doped LaFeAsO

TL;DR

This study synthesizes Co-doped LaFeAsO, demonstrating that cobalt doping suppresses antiferromagnetism and induces superconductivity at specific doping levels, revealing the system's tolerance to disorder and the emergence of ferromagnetism at high doping.

Contribution

It provides new insights into how cobalt doping induces superconductivity and affects magnetic properties in LaFeAsO, expanding understanding of doping effects in iron-based superconductors.

Findings

Superconductivity appears at x=0.05 and 0.11 with T_c up to 14.3 K.

Superconductivity is absent at higher doping levels like x=0.2 and 0.5.

High cobalt doping (x=1) leads to ferromagnetic behavior.

Abstract

Here we report the synthesis and basic characterization of LaFe1-xCoxAsO for several values of x. The parent phase LaFeAsO orders antiferromagnetically (TN ~ 145 K). Replacing Fe with Co is expected to both electron dope the system and introduce disorder in the FeAs layer. For x = 0.05 antiferromagnetic order is destroyed and superconductivity is observed at Tconset = 11.2 K. For x = 0.11 superconductivity is observed at Tc(onset) = 14.3 K, and for x = 0.15 Tc = 6.0 K. Superconductivity is not observed for x = 0.2 and 0.5, but for x = 1, the material appears to be ferromagnetic (Tc ~ 56 K) as judged by magnetization measurements. We conclude that Co is an effective dopant to induce superconductivity. Somewhat surprisingly, the system appears to tolerate considerable disorder in the FeAs planes.