In 2008, superconductivity was discovered in the iron-based compound LaFeAsO_1-xF_x, making it the first family of iron-based superconductors, now referred to as 1111 compounds. These compounds show evidence for unconventional superconductivity, as do other iron-based superconductors that have been discovered more recently. To understand whether these magnetic properties are a feature of the individual systems, or an indication of an underlying trend requires detailed investigation.

This study, published in Communications Physics, is a comprehensive exploration of the structural and magnetic order in the 1111 compound LaFeAs_1-xP_xO using synchrotron X-ray and neutron diffraction and muon spin relaxation. The researchers' comprehensive work enabled them to create the first complete phase diagram of the series.

Collecting the measurements required for this study was challenging as the magnetic moments in the compound are very small. The experiments required long count times and the high-flux capabilities of the WISH beamline, itself a very sensitive diffractometer. These diffraction results revealed the subtle differences of the magnetic structures across the phase diagram. On the EMU beamline, using muons as an extremely high sensitivity probe of local fields, the researchers were able to accurately determine the bulk nature of the magnetic order and the transition temperature of the various phases.

The researchers found that, unlike any other family of compounds, the LaFeAs_1-xP_xO series displays all three types of magnetic orders known to iron-pnictide systems within the same phase diagram. This inspired the authors to develop a unified theoretical model describing all magnetic phases using a single two-dimensional order parameter. The delicate balance between this parameter and superconductivity leads to a plethora of phases observed in the study.

Further Reading

The full publication can be found at DOI: 10.1038/s42005-022-00911-5