Interplay of composition, structure, magnetism, and superconductivity in SmFeAs1-xPxO1-y

TL;DR

This study explores how composition, structure, magnetism, and superconductivity interact in SmFeAs1-xPxO1-y, revealing how phosphorus substitution and oxygen deficiency influence magnetic and superconducting states through synthesis and characterization techniques.

Contribution

It provides new insights into the effects of phosphorus substitution and oxygen deficiency on the magnetic and superconducting properties of SmFeAsO-based compounds.

Findings

Phosphorus suppresses the SDW Nél temperature and reduces local magnetic fields.

Superconductivity appears only in oxygen-deficient samples after high-pressure heat treatment.

Two superconducting gaps are observed in point contact spectra.

Abstract

Polycrystalline samples and single crystals of SmFeAs1-xPxO1-y were synthesized and grown employing different synthesis methods and annealing conditions. Depending on the phosphorus and oxygen content, the samples are either magnetic or superconducting. In the fully oxygenated compounds the main impact of phosphorus substitution is to suppress the N\'eel temperature TN of the spin density wave (SDW) state, and to strongly reduce the local magnetic field in the SDW state, as deduced from muon spin rotation measurements. On the other hand the superconducting state is observed in the oxygen deficient samples only after heat treatment under high pressure. Oxygen deficiency as a result of synthesis at high pressure brings the Sm-O layer closer to the superconducting As/P-Fe-As/P block and provides additional electron transfer. Interestingly, the structural modifications in response to this variation of the electron count are significantly different when phosphorus is partly substituting arsenic. Point contact spectra are well described with two superconducting gaps. Magnetic and resistance measurements on single crystals indicate an in-plane magnetic penetration depth of 200 nm and an anisotropy of the upper critical field slope of 4-5. PACS number(s): 74.70.Xa, 74.62.Bf, 74.25.-q, 81.20.-n