A large moment antiferromagnetic order in overdoped high-Tc superconductor 154SmFeAsO1-xDx

TL;DR

This study reveals a new antiferromagnetic phase with a large magnetic moment in overdoped 154SmFeAsO1-xDx, providing insights into the relationship between magnetic order and high-temperature superconductivity in electron-doped iron pnictides.

Contribution

It reports the discovery of a novel long-range antiferromagnetic order with a record magnetic moment in overdoped iron-based superconductor 154SmFeAsO1-xDx, and links it to the phase diagram and superconductivity.

Findings

Largest Fe magnetic moment of 2.73 μB/Fe in non-doped iron pnictides.

Antiferromagnetic phase (AFM2) appears at doping level x >= 0.56.

The AFM2 phase is associated with a structural transition and kinetic frustration of the Fe-3dxy orbital.

Abstract

In iron-based superconductors, high critical temperature (Tc) superconductivity over 50 K has only been accomplished in electron-doped hREFeAsO (hRE = heavy rare earth (RE) element). While hREFeAsO has the highest bulk Tc (58 K), progress in understanding its physical properties has been relatively slow due to difficulties in achieving high concentration electron-doping and carrying out neutron-experiments. Here, we present a systematic neutron powder diffraction (NPD) study of 154SmFeAsO1-xDx, and the discovery of a new long-range antiferromagnetic ordering with x >= 0.56 (AFM2) accompanying a structural transition from tetragonal to orthorhombic. Surprisingly, the Fe magnetic moment in AFM2 reaches a magnitude of 2.73 muB/Fe, which is the largest in all non-doped iron pnictides and chalcogenides. Theoretical calculations suggest that the AFM2 phase originates in kinetic frustration of the Fe-3dxy orbital, in which the nearest neighbor hopping parameter becomes zero. The unique phase diagram, i. e., highest-Tc superconducting phase is adjacent to the strongly correlated phase in electron-overdoped regime, yields important clues to the unconventional origins of superconductivity.