Electronic and Magnetic Phase Diagram of a Superconductor, SmFeAsO1-xFx

TL;DR

This study maps the complex interplay of magnetic and superconducting phases in SmFeAsO1-xFx, revealing coexistence of antiferromagnetic Sm order with superconductivity and suppression of Fe magnetism upon doping.

Contribution

It provides a detailed phase diagram of SmFeAsO1-xFx, combining multiple experimental techniques to clarify magnetic ordering and its relation to superconductivity.

Findings

Fe magnetic moments are antiferromagnetically ordered at ~144 K in undoped samples.

Fe magnetism is quenched in F-doped superconducting samples.

Sm moments order antiferromagnetically below ~5 K, coexisting with superconductivity.

Abstract

A crystallographic and magnetic phase diagram of SmFeAsO1-xFx is determined as a function of x in terms of temperature based on electrical transport and magnetization, synchrotron powder x-ray diffraction, 57Fe Mossbauer spectra (MS), and 149Sm nuclear resonant forward scattering (NRFS) measurements. MS revealed that the magnetic moments of Fe were aligned antiferromagnetically at ~144 K (TN(Fe)). The magnetic moment of Fe (MFe) is estimated to be 0.34 myuB/Fe at 4.2 K for undoped SmFeAsO; MFe is quenched in superconducting F-doped SmFeAsO. 149Sm NRFS spectra revealed that the magnetic moments of Sm start to order antiferromagnetically at 5.6 K (undoped) and 4.4 K (TN(Sm)) (x = 0.069). Results clearly indicate that the antiferromagnetic Sm sublattice coexists with the superconducting phase in SmFeAsO1-xFx below TN(Sm), while antiferromagnetic Fe sublattice does not coexist with the superconducting phase.