  After the discovery of magnetism in monolayer CrI3, the magnetic properties
of different 2D materials from the chromium-trihalide family are intuitively
assumed to be similar, yielding magnetic anisotropy from the spin-orbit
coupling on halide ligands. Here we reveal significant differences between the
CrI3 and CrBr3 magnetic monolayers in their magnetic anisotropy, resulting
Curie temperature, hysteresis in external magnetic field, and evolution of
magnetism with strain, all predominantly attributed to distinctly different
interplay of atomic contributions to spin-orbit coupling in two materials.
