  The reversal of perpendicular magnetization (PM) by electric control is
crucial for high-density integration of low-power magnetic random-access memory
(MRAM). Although the spin-transfer torque (STT) and spin-orbit torque (SOT)
technologies have been used to switch the magnetization of a free layer with
perpendicular magnetic anisotropy, the former has limited endurance because of
the high current density directly through the junction, while the latter
requires an external magnetic field or unconventional configuration to break
the symmetry. Here we propose and realize the orbit-transfer torque (OTT), that
is, exerting torque on the magnetization using the orbital magnetic moments,
and thus demonstrate a new strategy for current-driven PM reversal without
external magnetic field. The perpendicular polarization of orbital magnetic
moments is generated by a direct current in a few-layer WTe2 due to the
existence of nonzero Berry curvature dipole, and the polarization direction can
be switched by changing the current polarity. Guided by this principle, we
construct the WTe2/Fe3GeTe2 heterostructures, where the OTT driven field-free
deterministic switching of PM is achieved.
