  Layered ferromagnets with high coercivity have special applications in
nanoscale memory elements in electronic circuits, such as data storage.
Therefore, searching for new hard ferromagnets and effectively tuning or
enhancing the coercivity are the hottest topics in layered magnets today. Here,
we report a strain tunability of perpendicular magnetic anisotropy in van der
Waals (vdW) ferromagnets VI3 using magnetic circular dichroism measurements.
For an unstrained flake, the M-H curve shows a rectangular-shaped hysteresis
loop with perpendicular magnetic anisotropy and a large coercivity (up to 1.775
T at 10 K). Furthermore, the coercivity can be enhanced to a maximum of 2.6 T
at 10 K under a 2.9% in-plane tensile strain. Our DFT calculations show that
the magnetic anisotropy energy (MAE) can be dramatically increased after
applying an in-plain tensile strain, which contributes to the enhancement of
coercivity in the VI3 flake. Meanwhile, the strain tunability on the coercivity
of CrI3, with a similar crystal structure, is limited. The main reason is the
strong spin-orbital coupling in V3+ in VI6 octahedra in comparison with that in
Cr3+. The strain tunability of coercivity in VI3 flakes highlights its
potential for integration into vdW heterostructures, paving the way toward
nanoscale spintronic devices and applications in the future.
