Superconductivity inLaFe1−xCoxAsO
Here we report the synthesis and basic characterization of ${\text{LaFe}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{AsO}$ for several values of $x$. The parent phase LaFeAsO orders antiferromagnetically $({T}_{N}\ensuremath{\approx}145\text{ }\text{K})$. Replacing Fe with Co is expected both to electron dope and introduce disorder in the FeAs layer. For $x=0.05$ antiferromagnetic order is destroyed and superconductivity is observed at ${T}_{c}^{\text{onset}}=11.2\text{ }\text{K}$. For $x=0.11$ superconductivity is observed at ${T}_{c}^{\text{onset}}=14.3\text{ }\text{K}$ and for $x=0.15$ it is observed at ${T}_{c}^{\text{onset}}=6.0\text{ }\text{K}$. For $x=1$, and the material appears to be ferromagnetic 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.