Ferromagnetism and superconductivity in P-doped CeFeAsO

TL;DR

This study reports the coexistence of superconductivity and ferromagnetism in P-doped CeFeAsO, revealing unique magnetic and structural properties that challenge existing quantum-critical point theories for iron-based superconductors.

Contribution

It demonstrates the coexistence of superconductivity and ferromagnetism in CeFeAs1-xPxO and provides insights into magnetic ordering without orthorhombic distortion.

Findings

Superconductivity and ferromagnetism coexist at x ≈ 30%.

Fe antiferromagnetic order is suppressed but does not shift with P doping.

Absence of orthorhombic distortion despite AFM Fe-ordering.

Abstract

We report on superconductivity in CeFeAs1-xPxO and the possible coexistence with Ce- ferromagnetism (FM) in a small homogeneity range around x = 30% with ordering temperatures of T_SC = T_C = 4K. The antiferromagnetic (AFM) ordering temperature of Fe at this critical concentration is suppressed to T^N_Fe ~ 40K and does not shift to lower temperatures with further increase of the P concentration. Therefore, a quantum-critical-point scenario with T^N_Fe -> 0K which is widely discussed for the iron based superconductors can be excluded for this alloy series. Surprisingly, thermal expansion and X-ray powder diffraction indicate the absence of an orthorhombic distortion despite clear evidence for short range AFM Fe-ordering from muon-spin-rotation measurements. Furthermore, we discovered the formation of a sharp electron spin resonance signal unambiguously connected with the emergence of FM ordering.