Magnetic Phases and Zone-Folded Phonons in a Frustrated van der Waals Magnet

2D magnetic materials have attracted extensive research interest due to their potential application in nanospintronics, optospintronics, and magnonics. Ferromagnetic- and antiferromagnetic-layered materials have been demonstrated and successfully inserted into van der Waals heterostructures. However, the effects of magnetic frustration in van der Waals materials and the possibilities offered by spin configurations characterized by nonlinear spin arrangements have not been fully considered yet. Herein, we establish the magnetic phase diagram of bulk CrOCl, a frustrated van der Waals magnet, using magnetization and magneto-optical spectroscopy techniques. In particular, we use the magnetic superstructures relative to the crystallographic unit cell and the associated rich zone-folded phonon series to describe the magnetic-field-induced phases. Theoretical calculations taking into account the competing nearest neighbors' magnetic exchange interactions provide insight into the lattice vibrations of this class of magnetic system. This study expands the scope of 2D magnetic materials and provides a methodology to characterize frustrated van der Waals magnets.