Seminarium Fizyki Ciała Stałego

In this talk, I will describe the properties of an orthorhombic frustrated van der Waals magnet, CrOCl, that shows a wide variety of magnetic phases characterized by magnetic cells much larger than the crystallographic cell. The frustration in this material originates from competing magnetic exchange interactions [1,2]. Together with a strong magneto-elastic coupling, this leads to pronounced zone folding effects in the phonon spectrum that provide a unique possibility to describe the B-field induced magnetic phases using Raman scattering techniques. Investigating for different values of the magnetic field the energies and the number of Raman active phonon modes, we are able to describe the evolution of the size of the magnetic unit cell in the different phases. Using this methodology based on the spectroscopy of zone folded phonons, together high field magnetization and ab-initio calculations of the phonon band structure, I will describe the cascade of magnetic phases that bulk CrOCl exhibits when it is subjected to an external magnetic field, before the spin saturation at B=30T [3]. Finally, taking advantage of the weak van der Waals interlayer interaction, we can thin down these materials and I will describe from the view point of magneto-Raman scattering spectroscopy, the properties of thin layers of CrOCl, down to the monolayer limit. We demonstrate that monolayers of CrOCl are air-stable on the time scale of a week, and we that the magnetic phase diagram depends on the number of layers with the emergence of a new magnetic phase stabilized in the few-layers limit [4]. [1] P. G. Reuvekamp, Phd thesis, Universität Stuttgart, (2014) [2] P. Gu et al., Nano Lett. 22 1233, (2022). [3] A. Pawbake et al., ACS Nano 19, 23693, 2025 [4] T. Riccardi et al., arxiv :2603.09836