Phase diagram of iron-arsenide superconductors Ca(Fe1-xCox)2As2 (0 <= x <= 0.2)

TL;DR

This study maps the phase diagram of Ca(Fe1-xCox)2As2 superconductors, revealing how Co doping influences structural, magnetic, and superconducting transitions, with notable differences from BaFe2As2 due to pressure sensitivity.

Contribution

First detailed phase diagram of Ca(Fe1-xCox)2As2 showing doping effects on structural, magnetic, and superconducting phases, highlighting differences from BaFe2As2.

Findings

Superconductivity appears at x ≥ 0.05 with T_C around 20 K.

Transitions shift and split with increasing Co doping.

Superconducting volume fraction peaks at x = 0.09.

Abstract

Platelet-like single crystals of the Ca(Fe1-xCox)2As2 series having lateral dimensions up to 15 mm and thickness up to 0.5 mm were obtained from the high temperature solution growth technique using Sn flux. Upon Co doping, the c-axis of the tetragonal unit cell decreases, while the a-axis shows a less significant variation. Pristine CaFe2As2 shows a combined spin-density-wave and structural transition near T = 166 K which gradually shifts to lower temperatures and splits with increasing Co-doping. Both transitions terminate abruptly at a critical Co-concentration of xc = 0.075. For x \geq 0.05, superconductivity appears at low temperatures with a maximum transition temperature TC of around 20 K. The superconducting volume fraction increases with Co concentration up to x = 0.09 followed by a gradual decrease with further increase of the doping level. The electronic phase diagram of Ca(Fe1-xCox)2As2 (0 \leq x \leq 0.2) series is constructed from the magnetization and electric resistivity data. We show that the low-temperature superconducting properties of Co-doped CaFe2As2 differ considerably from those of BaFe2As2 reported previously. These differences seem to be related to the extreme pressure sensitivity of CaFe2As2 relative to its Ba counterpart.