Antiferromagnetism and electronic states in 2D Transition Metal Phosphorus Trisulphides

Transition-metal phosphorus trisulphides (TMPS3) represent a class of materials relevant for their spintronic and magnetoelectronic functionalities. Interestingly, the distribution of magnetic moments in these compounds is found to depend on the specific transition metal involved. While antiferromagnetic ordering is well established for these systems in the bulk phase, a systematic in-depth study of the magnetism and of the electronic states in the 2-dimensional (2D) layered arrangement is in its infancy. Here, the fabrication of 2D FePS3, NiPS3 and MnPS3 by mechanical exfoliation and their comprehensive characterization via Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), micro-photoluminescence (m-PL), magneto-photoluminescenc (mag.-PL) and superconducting quantum interference device (SQUID) magnetometry as a function of the layer thickness, are reported. The observed Raman resonant features are consistent with the results from XPS and reveal a coherent thickness-dependent behaviour. The SQUID measurements confirm the antiferromagnetic ordering of the TMPS3. The analysis of the electronic structures carried out by means of polarization-dependent m- and mag.-PL for the three considered compounds as a function of the number of monolayers (MLs) in the samples, points at a transition from indirect- to direct-band gap at the cross-over between single and multiple ML thickness. Moreover, magneto-transport measurements on van der Waals heterostructures based on graphene and NiPS3, allow establishing the electronic properties. These findings pave the way to the controlled band-gap engineering and spin-wave transport, essential for the development of TMPS3-based antiferromagnetic spintronic devices.