Institute of High Pressure Physics

Experimental data collected for the preparation of the manuscript: "Enhancement of the Superconducting Transition Temperature in Mn-doped CaKFe₄As₄ Processed by the High gas-pressure and High temperature Synthesis Method"

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

Authors: Manasa Manasa, Mohammad Azam, Tatiana Zajarniuk, Svitlana Stelmakh, Tomasz Cetner, Andrzej Morawski, Shiv J. Singh

Journal of Superconductivity and Novel Magnetism 39 (2026) 10

Abstract:

A series of Mn-doped CaKFe₄As₄ samples, CaK(Fe_1−xMn_x)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 (T_c). 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 T_c by 3 to 7 K, particularly at low Mn concentrations. While the critical current density (J_c) of the parent sample (x = 0) shows a significant enhancement under the applied magnetic fields, J_c 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.

Note: In the published article,

• Figure 2 is Backscattered electron (BSE) images and the corresponding elemental mapping for CaK(Fe_1−xMn_x)₄As₄ polycrystal samples. (No dataset for this figure)

Figure. 1 (a) Powder XRD pattern of CaK(Fe_1−xMn_x)₄As₄ polycrystalline samples with x = 0, 0_HIP, 0.02, 0.02_HIP, 0.03 and 0.03_HIP is presented. The variation of (b) Lattice constant ‘a’, (c) Lattice constant ‘c’, and (d) Unit cell volume ‘V’ is shown for all CaK(Fe_1−xMn_x)₄As₄ samples synthesized using the CSP under ambient pressure and the HP-HTS method with the Mn doping contents (x).

Figure. 3 (a) The temperature dependence of electrical resistivity (ρ) up to room temperature, and (b) the low-temperature variation of resistivity up to 40 K for CaK(Fe_1−xMn_x)₄As₄ polycrystalline samples prepared by both the CSP and HP-HTS methods.

Figure. 4 (a) The temperature dependence of the normalized magnetic susceptibility (4πM/H) measured in zero-field-cooled (ZFC) and field cooled (FC) modes for CaK(Fe_1−xMn_x)₄As₄ bulk samples with x = 0, x = 0_HIP, x = 0.02, x = 0.02_HIP under an applied magnetic field of 20 Oe. (b) The magnetic field variation of the critical current density (J_c) at 5 K up to the magnetic field of 9 T for the samples with x = 0, x = 0_HIP, x = 0.005_HIP, x = 0.01_HIP, x = 0.02_HIP and x = 0.03_HIP.

Figure. 5 The variation of (a) the room temperature resistivity (ρ_300K), (b) the superconducting onset transition temperature T_c onset, (c) the residual resistivity ratio (RRR = ρ_300K / ρ_40K), (d) transition width (ΔT = T_c^onset - T_c^offset), and (e) the critical current density (J_c) at 0 T at 5 K as a function of Mn-concentration (x) are presented for CaK(Fe_1−xMn_x)₄As₄ polycrystalline samples prepared by the CSP at ambient pressure and the HP-HTS method.

Figure. 6 Normalized graph of (a) the lattice constant ‘a’, (b) the lattice constant ‘c’, and (c) the unit cell volume ‘V’ as a function of Mn doping content (x) are presented for all CaK(Fe_1−xMn_x)₄As₄ samples synthesized by the CSP method at ambient pressure, compared with previously reported data for Mn-doped SmFeAs(O, F) (denoted as “1111” in the figure) [Phys. C: Superconductivity. 494, 57–61 (2013)] and Mn-doped FeSe_0.5Te_0.5 (denoted as “11” in the figure) [Superconductor Science and Technology, 24, 045009 (2011)]. (d) A comparative summary of the superconducting transition temperatures (T_c) of CaK(Fe_1−xMn_x)₄As₄ bulks prepared by CSP at ambient pressure and HP-HTS methods, together with reported Mn doped CaKFe₄As₄ single-crystals grown by the conventional method at ambient pressure [Journal of Physics: Condensed Matter 35(39), 395801 (2023)], is shown with Mn concentration (x). The transition temperature values are determined from both the resistivity and magnetic measurements