  The mechanical properties of magnetic materials are instrumental for the
development of the magnetoelastic theory and the optimization of
strain-modulated magnetic devices. In particular, two-dimensional (2D) magnets
hold promise to enlarge these concepts into the realm of low-dimensional
physics and ultrathin devices. However, no experimental study on the intrinsic
mechanical properties of the archetypal 2D magnet family of the chromium
trihalides has thus far been performed. Here, we report the room temperature
layer-dependent mechanical properties of atomically thin CrI3 and CrCl3,
finding that bilayers of CrI3 and CrCl3 have Young's moduli of 62.1 GPa and
43.4 GPa, with the highest sustained strain of 6.09% and 6.49% and breaking
strengths of 3.6 GPa and 2.2 GPa, respectively. Both the elasticity and
strength of the two materials decrease with increased thickness, which is
attributed to a weak interlayer interaction that enables interlayer sliding
under low levels of applied load. The mechanical properties observed in the
few-layer chromium trihalide crystals provide evidence of outstanding
plasticity in these materials, which is qualitatively demonstrated in their
bulk counterparts. This study will contribute to various applications of the
van der Waals magnetic materials, especially for their use in magnetostrictive
and flexible devices.
