The magnetism of spins localized on a two-dimensional crystal lattice is an intensively studied area of modern solid state physics, since this system is on the verge of long-range order at finite temperatures. While in the Heisenberg model with isotropic spin space any long-range order is destroyed by the thermal fluctuations, the strongly anisotropic Ising model leads to long-range order up to a critical temperature.

The well-insulated hexagonal layers of van der Waals magnets with a variety of possible magnetic anisotropies and ordering textures provide an ideal hunting ground for the realization of abstract spin models. Moreover, the spin anisotropy and the weak coupling between the layers can be tuned by applied pressure, as the hexagonal layers can be shifted with respect to each other. Depending on the symmetry of the spin texture, the inversion and time reversal symmetries of the crystal lattice can be broken by the magnetic order, leading to possible magnetoelectric phenomena. This effect allows magnetic control of the electric polarization and can lead to surprising optical properties such as one-way transparency.

The experimental infrastructure of the Complex Magnetism Group (broadband optical spectroscopy at cryogenic temperatures and high magnetic fields) in combination with the magnetometric and magnetoelectric measurement capabilities at our international partners (Institute of Solid State Physics, TU Wien (Austria), High Field Magnet Laboratory Nijmegen (The Netherlands)) will allow the discovery of static and dynamic magnetoelectric effects in our single crystal samples of van der Waals magnets (MnPS₃, MnPSe₃, FePS₃, NiPS₃).

The candidate will investigate the magnetic field and temperature dependence of the magnetization as well as the electric polarization of the single crystal samples along the relevant crystallographic directions. To further elucidate the magnetic ordering structures, the candidate will perform optical magnetic resonance spectroscopy experiments in the GHz-THz frequency range up to high magnetic fields. The observed static and dynamic magnetic and magnetoelectric properties will be interpreted using a mean-field spin model.