Epitaxial growth of Bi$_2$Te$_3$ on the Ferromagnetic Insulator Cr$_2$Ge$_2$Te$_6$*

We report the experimental realization of a new topological insulator-ferromagnetic insulator (TI-FI) material system: the Cr$_2$Ge$_2$Te$_6$-Bi$_2$Te$_3$ heterostructure. The layered chalcogenide FI Cr$_2$Ge$_2$Te$_6$ exhibits a high Curie temperature of 61 K and a resistivity greater than $10^3$ $\Omega$-cm below 77 K, which suit it well for the study of magnetic proximity effects in TI-FI heterostructures. We fabricate heterostructures by growing single crystalline Cr$_2$Ge$_2$Te$_6$ substrates and depositing Bi$_2$Te$_3$ thin films using metalorganic chemical vapor deposition. Cross-sectional transmission electron microscopy reveals a sharp interface along the (0 0 1) planes of the two crystals, with the structures uniformly oriented as Cr$_2$Ge$_2$Te$_6$[1$\bar 1$0]//Bi$_2$Te$_3$[0$\bar 1$0]. The coupling between the Cr$_2$Ge$_2$Te$_6$ and Bi$_2$Te$_3$ layers is studied via the anomalous hall effect.