Spectroscopy and structural investigation of iron phosphorus trisulfide -- FePS$_3$

TL;DR

This study reports the growth, structural analysis, and optical characterization of FePS$_3$, revealing its magnetic and optical properties and their correlation with temperature-induced phase transitions, supported by experimental and theoretical methods.

Contribution

It provides a comprehensive analysis of FePS$_3$'s structure, optical properties, and magnetic interactions, combining advanced microscopy, spectroscopy, and density-functional theory.

Findings

Successful growth of large FePS$_3$ crystals with high yield

Identification of structure and composition via electron microscopy and spectroscopy

Correlation between optical behavior and magnetic phase transition

Abstract

Lamellar structures of transition metal phosphorus trisulfides possess strong intralayer bonding, albeit adjacent layers are held by weak van der Waals interactions. Those compounds received enormous interest due to their unique combination of optical and long-range magnetic properties. Among them, iron phosphorus trisulfide (FePS$_3$) gathered special attention for being a semiconductor with an absorption edge in the near-infrared, as well as showing an Ising-like anti-ferromagnetism. We report a successful growth of centimeter size bulk FePS$_3$ crystals with a chemical yield above 70%, whose crystallographic structure and composition were carefully identified by advanced electron microscopy methodologies, including atomic resolution elemental mapping, along with photoelectron spectroscopy. The knowledge on the optical activity of FePS$_3$ is extended utilizing temperature-dependent absorption and photoacoustic spectroscopies, while measurements were corroborated with density-functional theory calculations. Temperature-dependent experiments showed a small and monotonic band-edge energy shift down to 115 K and exposed the interconnected importance of electron-phonon coupling. Most of all, the correlation between the optical behavior and the magnetic phase transition is revealed, which shows the practical utilization of temperature-dependent optical absorption to investigate magnetic interactions.