Two-dimensional (2D) semiconductors are of a wide interest in recent years due to their unprecedented electrical and optical characteristics. The 2D endeavor, beyond the discovery of graphene, includes the study of inorganic van der Waals (vdW) transition metal dichalcogenides and solution based-2D semiconductors. Despite the striking electronic and optical properties of the mentioned 2D materials, those are lacking long-range magnetic properties or unique magnetic textures. The current study describes the exploration of a new family of semiconductor vdW compounds that possess magnetism along with their electrical and optical properties – these compounds are transition metal phosphorous trichalcogenides (TMPTs) with a honeycomb arrangement of magnetic metal elements.  Furthermore, diamagnetic TMPTs doped with magnetic impurities will be addressed - in comparison with diluted magnetic colloidal nanoplatelets from the II-VI family.

The TMPTs have a chemical formula MPX₃ (X=S, Se) with the metals (M) from the first row of transition metals, arranged in a honeycomb array with P-P at the center of each metal hexagon. These vdW materials permit the isolation of single layers down to a molecular limit via chemical or mechanical exfoliation. The 2D limit ease the Mermin-Wagner thermal agitation restriction and therefore, support intrinsic protected long-range ferromagnetic (FM) or antiferromagnetic (AFM) order, as well as spin textures (e.g., skyrmions) that are impossible in regular 3D materials. The honeycomb arrangement renders some of the TMPTs with a valley degree of freedom, similar to that found in MoS₂ single layers. Above all, TMPT layers permit coupling of long-range magnetic ordering or/and magnetic doping with the semiconducting properties of the materials.

The lecture will include description of experimental observation exposing the magneto-optical properties of FePS₃, MnPS₃ and Mn:ZnPS₃ TMPTs, and Mn-doped II-VI nanoplatelets.  The properties were investigated using circularly polarized magneto-photoluminescence at variable temperatures and optically detected magnetic resonance spectroscopy.  The preliminary observations indicated a removal of valleys' energy degeneracy by the coupling to the AFM magnetic arrangement.  Furthermore, Mn-doped diamagnetic TMPT showed a coupling between dopant and photo-generated carriers with a behavior similar to exciton-polaron found in doped colloidal II-VI nanoplatelets.  

Overall, the TMPT and magnetically doped 2D materials open a new paradigm in science and technology, from the basic understanding of magnetism, to the discovery of a plethora of new physical phenomena, thus being a base for the development of modern memory devices, spintronics, quantum computation and information.