Persistent antiferromagnetic order in heavily overdoped Ca$_{1-x}$La$_x$FeAs$_2$

TL;DR

This study reveals persistent antiferromagnetic order in heavily overdoped Ca$_{1-x}$La$_x$FeAs$_2$, challenging the typical suppression of magnetism in overdoped regimes of iron-based superconductors.

Contribution

It demonstrates that antiferromagnetic order persists at high doping levels in Ca$_{1-x}$La$_x$FeAs$_2$, providing new insights into its phase diagram and magnetic properties.

Findings

Antiferromagnetic transition at 120K in heavily overdoped sample

No superconductivity observed down to 1.8 K

Multiband electronic behavior confirmed by Hall effect and Kohler's rule violation

Abstract

In the Ca$_{1-x}$La$_x$FeAs$_2$ (112) family of pnictide superconductors, we have investigated a highly overdoped composition (x = 0.56), prepared by high-pressure, high-temperature synthesis. Magnetic measurements show an antiferromagnetic transition at TN = 120K, well above the one at lower doping (0.15 < x < 0.27). Below the onset of long-range magnetic order at TN, the electrical resistivity is strongly reduced and is dominated by electron-electron interactions, as evident from its temperature dependence. The Seebeck coefficient shows a clear metallic behavior as in narrow band conductors. The temperature dependence of the Hall coefficient and the violation of Kohler's rule agree with the multiband character of the material. No superconductivity was observed down to 1.8 K. The success of the high-pressure synthesis encourages further investigations of the so far only partially explored phase diagram in this family of Iron-based high temperature superconductors.