  We present a novel memory device that consists of a thin ferromagnetic layer
of Fe deposited on topological insulator thin film, Bi2Se3. The ferromagnetic
layer has perpendicular anisotropy, due to MgO deposited on the top surface of
Fe. When current is passed on the surface of Bi2Se3, the surface of the Bi2Se3
becomes spin polarized and strong exchange interaction occurs between the d
electrons in the ferromagnet and the electrons conducting the current on the
surface of the Bi2Se3. Part of the current is shunted through the ferromagnet
which generates spin transfer torque in the ferromagnet. The combination of the
spin transfer torque and exchange interaction torque along with
voltage-controlled magnetic anisotropy (VCMA) allows ultralow-energy switching
of the ferromagnet. We perform micromagnetic simulations and predict switching
time of the order of 2.5 ns and switching energy of the order of 0.45fJ for a
ferromagnetic bit with thermal stability of 43kBT. Such ultralow-energy and
high-speed VCMA-induced switching of a perpendicular anisotropy ferromagnet on
a topological insulator could be utilized for energy-efficient memory design.
