Role of magnetic dopants in the phase diagram of Sm1111 pnictides: The Mn case

TL;DR

This study investigates how magnetic Mn dopants affect the electronic and magnetic phases of SmFeAsO0.88-F0.12 superconductors, revealing a transition from superconductivity to magnetic order with increasing Mn content.

Contribution

It provides a detailed phase diagram showing the coexistence and suppression of superconductivity and magnetism due to Mn doping, supported by muon-spin spectroscopy data.

Findings

Superconductivity persists at low Mn levels (x<0.03).

Magnetic order coexists with superconductivity at intermediate Mn levels (0.03<=x<0.08).

Superconductivity is suppressed and magnetic correlations strengthen at higher Mn content (x=0.08).

Abstract

The deliberate insertion of magnetic Mn dopants in the Fe sites of the optimally-doped SmFeAsO0.88-F0.12 iron-based superconductor can modify in a controlled way its electronic properties. The resulting phase diagram was investigated across a wide range of manganese contents (x) by means of muon-spin spectroscopy (muSR), both in zero- and in transverse fields, respectively, to probe the magnetic and the superconducting order. The pure superconducting phase (at x < 0.03) is replaced by a crossover region at intermediate Mn values (0.03 =< x < 0.08), where superconductivity coexists with static magnetic order. After completely suppressing superconductivity for x = 0.08, a further increase in Mn content reinforces the natural tendency towards antiferromagnetic correlations among the magnetic Mn ions. The sharp drop of Tc and the induced magnetic order in the presence of magnetic disorder/dopants, such as Mn, are both consistent with a recent theoretical model of unconventional superconductors [M. Gastiasoro et al., ArXiv 1606.09495], which includes correlation-enhanced RKKY-couplings between the impurity moments.