Magnetic-Electronic Coupling in The Van der Waals Metal-Phosphorous-Trichalcogenides

The recent discovery of magnetic van der Waals materials- opens a new paradigm in solid-state research, offering an exploration of magnetism at the nearly atomistic limit, with an impact on the development of newly emerging spintronics, memory and information devices. In particular, antiferromagnetic (AFM) materials are catching special attention at the current time, due to their low stray magnetic field, and fast spin response (in the THz). The talk will include a thorough investigation of the fundamental magnetic properties and their coupling to the electronic nature of two representative materials: MnPS₃ and FePS₃. With a single AFM layer, the metals are positioned in a honeycomb arrangement. The AFM character is generated via a spin-exchange interaction among metal next neighbours (NNs), when the metal spins are mainly oriented normally to the layer plane arranged either in Nèel or zigzag configurations. It is important to note that second and third NNs intralayer interactions are not negligible in the MPX₃ layers, governed by super-exchange AFM coupling through the metal(d)-chalcogen(p) bonding. An interlayer interaction adds small tuning with weak super-super spin-exchange interaction, which despite being weak, may change the magnetic properties by having either AFM or FM stacking or by inducing a magnetic torque.<br/>A MnPS₃ layer with a Nèel magnetic configuration and lack of spin-orbit coupling was a suitable platform for examining the contribution of the long spin-exchange interaction. The study implemented dilution of the Mn content (forming alloyed compounds with the general chemical formula MnxZn1-xS₃), examining the sustain of AFM arrangement down to a composition of x=0.5, hence, supporting the weight of 2^nd and 3^rd spin-exchange coupling to the long-range magnetic ordering. A FePS₃, having a zigzag magnetic configuration, represents a case with a pronounced distortion of the honeycomb symmetry, due to local distortion around a metal site by a strong spin-orbit coupling. The two examples mentioned here showed a strong correlation between the magnetic ordering and the optical transitions, showing obvious changes in the photoluminescence at the Nèel temperature (a point possessing a magnetic transition from AFM to paramagnetic phase), as well as an optical polarization character along the magnetic directionality. It was mainly distinct in the appearance of an exceptionally sharp emission line in the FePS₃ single layer with a strong linear polarization along the zigzag direction.<br/>The accompanied DFT calculations simulated the spin-exchange coupling process and its impact on the electronic band structure (will be shown at the presentation by a short movie). Furthermore, the theoretical calculations exposed a fundamental character in which the electronic transitions show a hybrid property between local metal transitions and band-edge transitions. The exploration of these fundamental points is an ongoing process at the current moment.<br/><br/><br/>Acknowledgement: The authors express their gratitude to the collaborators in the project: Dr. Milosz Rybak and Prof. Magdalena Birowska (Warsaw University) and Dr. Thomas Brume and Prof. Thomas Heine (The University of Dresden).