Control of magnetic, non-magnetic and superconducting states in annealed Ca(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$

TL;DR

This study demonstrates how annealing and Co substitution can tune Ca(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ crystals into various magnetic, non-magnetic, and superconducting states, revealing a comprehensive phase diagram.

Contribution

It introduces a 3D phase diagram controlling magnetic and superconducting states via annealing temperature and Co doping in CaFe2As2.

Findings

Annealing temperature influences phase transitions in Ca(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$.

Co doping separates magnetic and collapsed tetragonal phases.

Bulk superconductivity is observed with specific Co and annealing conditions.

Abstract

We have grown single crystal samples of Co substituted CaFe2As2 using an FeAs flux and systematically studied the effects of annealing/quenching temperature on the physical properties of these samples. Whereas the as-grown samples (quenched from 960C) all enter the collapsed tetragonal phase upon cooling, annealing/quenching temperatures between 350C and 800C can be used to tune the system to low temperature antiferromagnetic/orthorhomic or superconducting states as well. The progression of the transition temperature versus annealing/quenching temperature (T-T$_{anneal}$) phase diagrams with increasing Co concentration shows that, by substituting Co, the antiferromagnetic/orthorhombic and the collapsed tetragonal phase lines are separated and bulk superconductivity is revealed. We established a 3D phase diagram with Co concentration and annealing/quenching temperature as two independent control parameters. At ambient pressure, for modest x and T$_{anneal}$ values, the Ca(Fe1-xCox)2As2 system offers ready access to the salient low temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and non-magnetic/collapsed tetragonal.