The simultaneous occurrence of superparamagnetism and superconductivity in nominal single crystalline (Ca1-xPrx)Fe2As2 with 0 <= x <= 0.13

TL;DR

This study reveals the coexistence of superparamagnetism and superconductivity in (Ca1-xPrx)Fe2As2, linking defects and magnetic clusters to the emergence of superconductivity, and suggests potential routes to enhance Tc.

Contribution

It provides systematic compositional and magnetic evidence for the simultaneous occurrence of superparamagnetism and superconductivity, supporting an interface-mechanism for high Tc in Pr-doped CaFe2As2.

Findings

Superconductivity occurs alongside superparamagnetism across the doping range.

Superconducting volume fraction correlates with magnetic cluster and defect densities.

Tc remains approximately constant (~49 K) regardless of Pr doping level.

Abstract

The observation of non-bulk superconductivity with an unexpectedly high onset transition temperature Tc up to ~ 49 K in non-superconducting single crystalline CaFe2As2 upon rare-earth doping has raised interesting questions concerning its origin. Several possibilities including interfacial mechanism have been proposed to account for the unusual observation. In an attempt to differentiate such propositions, we have carried out a systematic compositional and magnetic study on single crystals of nominal (Ca1-xPrx)Fe2As2 with 0 <= x <= 0.13 throughout the solubility range of Pr, which covers both the non-superconducting and superconducting regions. We found the unusual simultaneous occurrence of superparamagnetism and superconductivity with an x-independent Tc and a close correlation of the superconducting volume fraction with the magnetic cluster density and As-defect density. The finding demonstrates a close relationship among superconductivity, superparamagnetism, and defects, consistent with the previously proposed interface-mechanism, and offers a possible future path to higher Tc.