Electronic Correlations in Fe_xNi_yPS₃ Van der Waals Materials: Insights from Angle-Resolved Photoelectron Spectroscopy and DFT

Abstract

Recently layered antiferromagnetic materials with different magnetic orderings attract increased attention. It was found that these properties can be preserved down to the monolayer limit opening large perspectives for their applications in (opto)spintronics and sensing, however, lacking the experimental results on electronic structure studies. Here the results of angle-resolved photoelectron spectroscopy (ARPES) studies accompanied by DFT calculations for Fe x Ni y PS 3 layered van der Waals (vdW) alloys are presented, addressing the effects of electronic correlations in these materials. It is demonstrated that in the case of FePS 3 the top of the valence band is formed by the hybrid Fe 3d−S 3p states and is of pure S 3p character for NiPS 3 , respectively, whereas for the mixed Fe−Ni-based vdW alloy the electronic structure is a sum of contributions from the parent compounds. The obtained results give a clear understanding of the nature of the insulating state in studied MPX 3 materials and pave the way on their applications in different areas.

Electronic Correlations in Multiferroic Van der Waals CuCrP2S6: Insights from X-ray Spectroscopy and DFT

“…Figure S10 of the Supporting Information also presents the “ON” ( h ν = 576.21 eV) and “OFF” ( h ν = 570 eV) resonance spectra recorded in a wide energy range at the Cr L 3 absorption edge. Generally, the valence band XPS spectrum of MPX 3 materials, which are wide band gap semiconducting materials, typically exhibits a wide intensive peak in the vicinity of the Fermi level, which is assigned to the 3 d n L̲ final state for the charge-transfer type insulators ( U dd > Δ) and 3d n –1 final state for the Mott–Hubbard type insulator ( U dd < Δ), and a series of weaker satellites at higher binding energies, which are assigned to the opposite final states in both cases, respectively ( L̲ is the hole on the ligand site; U dd is the d–d correlation energy; and Δ is the charge transfer energy between d-states of the metal and p-states of the ligand). − ,− , This is also valid for CuCrP 2 S 6 , whose valence band XPS spectrum is shown in Figure g. In ResPES of MPX 3 materials (see schemes in Figure S11 of the Supporting Information) the interference between the processes of (i) direct photoemission (2p 6 3d n + h ν → 2p 6 3d n –1 + e) and (ii) photoabsorption followed by a participator-Auger Coster–Kronig decay (2p 6 3d n + h ν → 2p 5 3d n +1 → 2p 6 3d n –1 + e) leads to the Fano-type resonance for the identical final state 3d n –1 .…”

“…For example, near-edge X-ray absorption fine structure (NEXAFS) and resonant photoelectron spectroscopy (ResPES) allowed one to assign MnPX 3 and FePX 3 to the class of Mott–Hubbard insulators, − NiPS 3 to the class of charge-transfer insulators, , whereas CoPS 3 has a mixed character of the insulating state . It is interesting that mixed Fe x Ni y PS 3 alloys demonstrate a dual character of the insulating state in their electronic structure pointing to very weak (if any) hybridization of Fe- and Ni-derived electronic states. , Recent angle-resolved photoelectron spectroscopy experiments on different MPX 3 materials demonstrate a rather good agreement with available calculated band structures, allowing us to identify partial elemental and orbital contributions in the electronic structure. ,− …”

XPS Analysis of FexNiyPS3 vdW Materials Used in the Hydrogen Evolution Processes

“…The Fe-and Ni-based MPX 3 materials studied in the present study were synthesised using CVT method and then were rigorously characterized using different methods as discussed in Refs. [22,25]. Figure 2 show the light absorption spectra of the MPX 3 materials obtained using UV-Vis diffuse reflectance spectroscopy before HER investigations.…”