Abstract
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.
Highlights
Magnetic van der Waals materials have attracted renewed interest since the longrange ferromagnetic ordering survives down to a two-dimensional monolayer or a few monolayers in magnetic insulators, such as Cr2Ge2Te6 (Ref. 1) and CrI3 (Ref. 2)
Concomitance of ferromagnetism and insulating features in the magnetic van der Waals (vdW) materials provides a feasible arena for exploration of the proximity effect in the stacked heterostructures with other vdW materials such as graphene, transition metal dichalcogenides, and topological insulators.[10,11]
Topological insulators composed of a layered chalcogenide such as (Bi,Sb)2Te3 have been grown by Molecular beam epitaxy (MBE),[18] realizing the quantum anomalous Hall effect in magnetically doped samples grown by tuning their chemical potential and magnetic element composition aAuthor to whom correspondence should be addressed: mogi@cmr.t.u-tokyo.ac.jp
Summary
Magnetic van der Waals (vdW) materials have attracted renewed interest since the longrange ferromagnetic ordering survives down to a two-dimensional monolayer or a few monolayers in magnetic insulators, such as Cr2Ge2Te6 (Ref. 1) and CrI3 (Ref. 2). The crystal structure of Cr2Ge2Te6 is rhombohedral with vdW stacking of hexagonal layers, as shown in Fig. 1(a) (Ref. 26).
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