Trapped flux in pure and Mn-substituted CaKFe₄As₄ and MgB₂ superconducting single crystals

Measurements of temperature dependent magnetization associated with trapped magnetic flux in single crystals of CaKFe4As4, CaK(Fe0.983Mn0.017)(4)As-4 and MgB2 using zero-field-cooled and field-cooled protocols are presented. The results allow for the determination of the values of superconducting transition temperature, lower critical field and self-field critical current density. These are compared with the literature data. Possible experimental concerns are briefly outlined. Our results, on these known superconductors at ambient pressure, are qualitatively similar to those recently measured on superhydrides at megabar pressures (Minkov et al 2023 Nat. Phys.https://doi.org/10.1038/s41567-023-02089-1) and, as such, hopefully serve as a baseline for the interpretation of high pressure, trapped flux measurements.