Surface-vacancy-induced metallicity and layer-dependent magnetic anisotropy energy in Cr₂Ge₂Te₆

Two-dimensional van der Waals materials have attracted considerable attention because of their promising applications in spintronic devices. This paper reports on first-principles calculations of the electronic structure and ferromagnetism of Cr 2 Ge 2 Te 6 with surface Ge vacancies. These vacancies are found to remove the bandgap and induce metallicity in Cr 2 Ge 2 Te 6 that persists with decreasing Ge-vacancy concentration. Meanwhile, the Ge vacancies cause an unexpected sharp increase in the magnetic anisotropy energy compared to that of perfect Cr 2 Ge 2 Te 6. More importantly, how thickness affects the magnetic anisotropy energy is studied to show that the latter oscillates upon increasing the number of layers, thereby switching between the out-of-plane and in-plane magnetization directions. The present findings regarding a surface-vacancy-tuned bandgap and magnetism controlled by the layer thickness in a two-dimensional van der Waals magnet could lead to potential applications in next-generation magnetic memory storage, sensors, and spintronics.