Coexistence of ferromagnetism, antiferromagnetism, and superconductivity in magnetically anisotropic (Eu,La)FeAs2

TL;DR

This study explores the coexistence of ferromagnetism, antiferromagnetism, and superconductivity in (Eu,La)FeAs2, revealing doping-tunable magnetic phases and their relation to superconductivity, offering insights into high-temperature superconductivity mechanisms.

Contribution

It demonstrates the simultaneous presence of multiple magnetic orders and superconductivity in (Eu,La)FeAs2, and establishes an electronic phase diagram linking these phenomena.

Findings

Eu-related ferromagnetism enhanced by La doping

Robust Fe-related antiferromagnetism against doping

Coexistence of ferromagnetism, antiferromagnetism, and superconductivity

Abstract

Materials with exceptional magnetism and superconductivity usually conceive emergent physical phenomena. Here, we investigate the physical properties of the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2 shows anisotropy-associated magnetic behaviors, such as Eu-related moment canting and exchange bias. Through La doping, the magnetic anisotropy is enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a special exchange bias of the superposed ferromagnetic/superconducting loop revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows unusual robustness against La doping. Theoretical calculation and 57Fe M\"ossbauer spectroscopy investigation reveal a doping-tunable dual itinerant/localized nature of the Fe-related antiferromagnetism. Coexistence of the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform for further exploration of potential applications and emergent physics. Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the whole superconducting dome adjacent to the Fe-related antiferromagnetic phase, which is of benefit for seeking underlying clues to high-temperature superconductivity.