Ferromagnetic insulator Cr2Ge2Te6 thin films with perpendicular remanence

Ferromagnetic van der Waals (vdW) insulators possess robust magnetic order even in a few layers of two-dimensional sheets. The heterostructures of such vdW materials prepared by molecular-beam epitaxy (MBE) are one of the ideal platforms for exploration of novel electronic/spintronic functionalities based on their ferromagnetism via an abrupt hetero-interface. Here we report successful MBE-growth of a vdW magnetic insulator Cr2Ge2Te6 thin film on a topological insulator (Bi,Sb)2Te3. Metal to insulator transition is observed in Cr–Ge–Te alloy films with increasing Ge content as tuned by the Ge and Cr flux ratio, corresponding to the structural phase change from Cr2Te3 to Cr2Ge2Te6. In the nearly stoichiometric Cr2Ge2Te6 films, a large remanent magnetization with perpendicular magnetic anisotropy appears in contrast to the bulk crystals with no discernible hysteresis. The perpendicular remanence with high Curie temperature of about 80 K remains in the thinnest 6-nm film prepared in this study. Designing of magnetic vdW heterostructures based on the Cr2Ge2Te6 thin films offers great opportunities for exploring unusual physical phenomena via proximity effect at the vdW hetero-interface.