The effect of aliovalent substitution on magnetic properties of polycrystalline Ca/K-1144

Among IBSC superconductors, the 1144 family ( AAE Fe4As4 with A =alkali metal, AE =alkaline-earth metal), has attracted considerable interest in recent years because of their propensity to form lattice defects that positively influence the flux pinning properties. Extensive research is underway to optimize this class of materials for the low-temperature high-field regime, both in the form of single crystal and polycrystalline powder. The latter is of particular interest because the 1144 material has been shown to be suitable for wire production through the easy and well-assessed Powder In Tube (PIT) process. In our recent experiments, it has been shown that the 1144 structure can be tailored to obtain a doped compound with a different chemical formula ( A x AE 1-x )( AE y A 1-y )Fe 4 As 4 , that is characterized by unaltered critical temperature values despite the high level of substitution up to 15 at.%. In order to unveil the influence of the double substitution on the grain boundary and pinning properties of doped samples, we recently started an extensive characterization campaign whose preliminary results are presented here. Both structural and morphological properties of the compound are not affected by the simultaneous doping with 10 at.% Na and 5 at.% Ba, as revealed by XRD and SEM analyses. On the contrary, the study of magnetic properties shows that although there is no improvement in transport properties, the aliovalent substitution induces a clear change in the in-field behavior which deserves further investigations.