Probing Phosphorus Solubility and Its Effect on Critical Temperature (T_c) in the Helical Superconducting Magnet RbEuFe₄As_4–xP_x

Abstract

RbEuFe 4 As 4 exhibits a rare combination of hightemperature superconductivity and noncollinear magnetism, originating from the FeAs and Eu layers, respectively. In order to fine-tune its superconducting and magnetic properties, we studied P-doped RbEuFe 4 As 4−x P x . To determine the value of x for which RbEuFe 4 As 4−x P x exists, members of the series have been synthesized in the form of relatively large-sized single crystals by a high-temperature flux growth technique using RbAs flux as well as polycrystalline powder by direct combination reactions between RbFe 2 As 2 and EuFe 2 As 2−x P x . The flux crystal growth reactions indicate that RbEuFe 4 As 4−x P x forms with the values of x ≤ 0.12, which is corroborated by the Rietveld refinement analysis on the products obtained from direct combination reactions. The solubility limit exists primarily due to the preferential site As(2) occupation by P in the RbEuFe 4 As 4 crystal structure. As x increases in RbEuFe 4 As 4−x P x , magnetization measurements reveal that the superconducting critical transition temperature (T c ) decreases, while the magnetic ordering temperature (T N ) remains almost unchanged in comparison to undoped RbEuFe 4 As 4 .