  Spin-orbit torques (SOTs) generated through the conventional spin Hall effect
and/or Rashba-Edelstein effect are promising for manipulating magnetization.
However, this approach typically exhibits non-deterministic and inefficient
behaviour when it comes to switching perpendicular ferromagnets. This
limitation posed a challenge for write-in operations in high-density magnetic
memory devices. Here, we determine an effective solution to overcome this
challenge by simultaneously leveraging both a planar Hall effect (PHE) and an
orbital Hall effect (OHE). Using a representative Co/PtGd/Mo trilayer SOT
device, we demonstrate that the PHE of Co is enhanced by the interfacial
coupling of Co/PtGd, giving rise to a finite out-of-plane damping-like torque
within the Co layer. Simultaneously, the OHE in Mo layer induces a strong
out-of-plane orbital current, significantly amplifying the in-plane
damping-like torque through orbital-to-spin conversion. While either the PHE or
OHE alone proves insufficient for reversing the perpendicular magnetization of
Co, their collaborative action enables high-efficiency field-free deterministic
switching. Our work provides a straightforward strategy to realize high-speed
and low-power spintronics.
