Local magnetism and exchange interactions in the 2D layered van der Waals materials MnPS_xSe_3-x

Two-dimensional (2D) materials are of intense current fundamental and applied interest as a route to create novel quantum phenomena beyond well-established classical behavior within their topologically constrained layers. In this context 2D monolayer graphene, formed from the isolation of weakly connected van der Waals (vdW) bonded 2D layers in graphite by exfoliation, ignited widespread interest. The focus has expanded to “beyond graphene” 2D vdW layered materials, in both single layer and quasi-2D bulk form, with intrinsic properties such as magnetism and semiconductivity not present in graphene. Here, we present results on the series MnPS_xSe_3-x, which are layered magnetic and semiconducting vdW materials. The end members of the series MnPS₃ and MnPSe₃ have magnetic ions forming hexagonal 2D motifs that order at similar temperatures, however have distinct magnetic structures and emergent phenomena. Neutron scattering is uniquely powerful at accessing magnetism and we will present several complimentary elastic and inelastic neutron measurements that investigate MnPS₃ and MnPSe₃ and the behavior as we tune through the series MnPS_xSe_3-x. Total neutron scattering measurements allow a magnetic pair distribution function (mPDF) analysis, this is a new technique that provides insights into the local magnetism in the long range and short range ordered magnetic phases. Inelastic neutron scattering results allow for an understanding of the evolution of the exchange interactions and anisotropy. Collectively the results show a smooth progression of dimensionality and magnetism as the non-magnetic S and Se ion content are varied in MnPS_xSe_3-x.