Enhancement of the Superconducting Transition Temperature in Mn-doped CaKFe4As4 Processed by the High gas-pressure and High-temperature Synthesis Method

A series of Mn-doped CaKFe4As4 samples, CaK(Fe1 − xMnx)4As4 with x values of 0, 0.005, 0.01, 0.02, 0.03, 0.04, and 0.05, are synthesized using two distinct routes: conventional synthesis process at ambient pressure (CSP), and high gas-pressure and high-temperature synthesis (HP-HTS) method. Comprehensive characterizations are performed on these samples to investigate their superconducting properties. This study examines the effects of Mn substitution at Fe sites in the FeAs layer on the superconducting properties of the CaKFe4As4 (1144) material. The HP-HTS process improves the microstructure and phase purity of the parent sample (x = 0), resulting in an enhanced superconducting transition temperature (Tc). In contrast, Mn doping via the CSP method in CaKFe4As4 reduces the sample quality and superconducting performance. Notably, the high-pressure synthesis method leads to an increase in the Tc by 3 to 7 K, particularly at low Mn concentrations. While the critical current density (Jc) of the parent sample (x = 0) shows a significant enhancement under the applied magnetic fields, Jc decreases for Mn-doped CaKFe4As4 bulks. These results demonstrate that high-pressure synthesis is an effective approach to improve the superconducting properties of Mn-doped 1144 compounds.