Layer-dependent mechanical properties and enhanced plasticity in the van der Waals chromium trihalide magnets*

The knowledge of the mechanical properties of 2D magnets provides valuable information for the development of magneto-mechanic theory and the construction of optimal strain-modulated magnetic devices. Despite seminal works studying the effect of pressure in 2D magnets, there has been no experimental study on the intrinsic mechanical properties of the chromium trihalides to the date. Here we report the room temperature values of the Young’s modulus and the fracture strength of CrI₃ and CrCl₃ from bulk down to the few-layer limit. The materials show a Young’s modulus (~50 GPa) / breaking strength (~5 GPa) ratio comparable to the best 2D materials, 50 times above that of any other polycrystalline bulk material, withstanding maximum strains of 6.5%. This enlarges the possibilities of application in mechanical and magnetostrictive devices, so far highly restricted to the semiconducting 2D materials. At the same time, these results place the bulk counterparts of the two atomically-thin crystals as strong candidates to show an enhanced plastic behavior, which we have qualitatively tested in the bulk form of the crystals.