Pressure-induced structure transformation and collapse of ferromagnetism in van der Waals insulator

Ferromagnetism in van der Waals insulators like CrBr3 is highly sensitive to structural modifications. We explore the pressure-driven structural and magnetic transformations of the van der Waals magnet CrBr₃, establishing it as a model platform for phenomena emerging in layered vdW systems. Single-crystal X-ray diffraction revealed intrinsic trimorphism with two known phases (monoclinic and rhombohedral) and a so far unreported trigonal phase. The paracrystal model well captures the coexistence of the rhombohedral and trigonal phases at ambient conditions. Increasing pressure drives the growth of the AA-stacked trigonal phase at the expense of the rhombohedral phase, which becomes undetectable above 8.4 GPa. Magnetization measurements provided the first direct evidence of a collapse of ferromagnetism above 5.8 GPa. This behavior is attributed to the increasing number of AFM-coupled Cr moments in AA stackings. Ab initio DFT calculations of electronic structure and atomistic simulations of finite-temperature magnetism corroborate the scenario. Ferromagnetism in van der Waals insulators like CrBr₃ is highly sensitive to structural modifications, posing challenges for understanding magnetic behavior under varying conditions. Here, the authors investigate pressure-induced structural and magnetic transformations in CrBr₃, revealing a trigonal phase stabilized at high pressure and demonstrating the collapse of ferromagnetism above 5.8 GPa.