  The discovery of efficient magnetization switching activated by the spin Hall
effect (SHE)-induced spin-orbit torque (SOT) changed the course of magnetic
random-access memory (MRAM) research and development. However, for systems with
perpendicular magnetic anisotropy (PMA), the use of SOT is still hampered by
the necessity of a longitudinal magnetic field to break the magnetic symmetry
to achieve deterministic switching. In this work, we first demonstrate that a
robust and tunable field-free current-driven SOT switching of perpendicular
magnetization can be controlled by the growth protocol in Pt-based magnetic
heterostructures. It is further elucidated that such growth-dependent symmetry
breaking is originated from the laterally tilted magnetic anisotropy of the
ferromagnetic layer with PMA, which has been largely neglected in previous
studies and its critical role should be re-focused. We show by both experiments
and simulations that in a PMA system with tilted anisotropy, the deterministic
field-free switching possesses a conventional SHE-induced damping-like torque
feature and the resulting current-induced effective field has a non-linear
dependence on the applied current density, which could be potentially
misattributed to an unconventional SOT origin.
