Observation of Distinct Structural Phase Transition in Bulk CrI3 Magnet

Abstract

Exploring structural phase is not only vital for fundamental physical properties, but also crucial for creating innovative devices. The emerging two-dimensional (2D) ferromagnet CrI3 has been widely studied because of its novel magnetic order, stacking order and related properties. Conventionally, it is predicted that the high-temperature monoclinic crystal phase will convert into low-temperature rhombohedral crystal phase in bulk CrI3 at a critical temperature of ~ 220 K. Strikingly, here, a high-temperature monoclinic phase in bulk CrI3 flake is completely preserved upon cooling from 295 to 10 K beyond the conventional phase changes, breaking out the regular cognition. This work indicates that complex structural phases coexist in bulk CrI3 ferromagnet, which are attributed to the difference between the surface and inner layers. These findings not only deepen the understanding of 2D ferromagnetic materials, but also provide opportunities for constructing future 2D-based magneto-optic and magneto-mechanical devices.