  Topological insulators (TIs) are a promising class of materials for
manipulating the magnetization of an adjacent ferromagnet (FM) through the
spin-orbit torque (SOT) mechanism. However, current studies combining TIs with
conventional FMs present large device-to-device variations, resulting in a
broad distribution of SOT magnitudes. It has been identified that the
interfacial quality between the TI and the FM is of utmost importance in
determining the nature and efficiency of the SOT. To optimize the SOT magnitude
and enable ultra-low-power magnetization switching, an atomically smooth
interface is necessary. To this end, we have developed the growth of a full van
der Waals FM/TI heterostructure by molecular beam epitaxy. The compensated TI
(Bi0.4Sb0.6)2Te3 and ferromagnetic Fe3GeTe2 (FGT) were chosen because of their
exceptional crystalline quality, low carrier concentration in BST and
relatively large Curie temperature and perpendicular magnetic anisotropy in
FGT. We characterized the magnitude of the SOTs by using thorough harmonic
magnetotransport measurements and showed that the magnetization of an ultrathin
FGT film could be switched with a current density Jc < 10^10 A/m^2. In
comparison to previous studies utilizing traditional FMs, our findings are
highly reliable, displaying little to no variation between devices.
