Magnetic evolution of Cr_2Te_3 epitaxially grown on graphene with post-growth annealing

Two-dimensional and van der Waals ferromagnets are ideal platform to study low dimensional magnetism and proximity effects in van der Waals heterostructures. Their ultimate two dimensional character offers also the opportunity to easily adjust their magnetic properties using strain or electric fields. Among 2D ferromagnets, the Cr_1+xTe_2 compounds with x=0-1 are very promising because their magnetic properties depend on the amount of self-intercalated Cr atoms between pure CrTe_2 layers and the Curie temperature (T_C) can reach room temperature for certain compositions. Here, we investigate the evolution of the composition, structural and magnetic properties of thin Cr_1.33Te_2 (Cr_2Te_3) films epitaxially grown on graphene upon annealing. We observe a transition above 450C from the Cr_1.33Te_2 phase with perpendicular magnetic anisotropy and a T_C of 180 K to a composition close to Cr_1.39Te_2 with in-plane magnetic anisotropy and a T_C of 240-250 K. This phase remains stable up to 650C above which a pure Cr film starts to form. This work demonstrates the complex interplay between intercalated Cr, lattice parameters and magnetic properties in Cr_1+xTe_2 compounds.