  The orbital Hall effect in light materials has attracted considerable
attention for developing novel orbitronic devices. Here we investigate the
orbital torque efficiency and demonstrate the switching of the perpendicularly
magnetized materials through the orbital Hall material (OHM), i.e., Zirconium
(Zr). The orbital torque efficiency of approximately 0.78 is achieved in the Zr
OHM with the perpendicularly magnetized [Co/Pt]3 sample, which significantly
surpasses that of the perpendicularly magnetized CoFeB/Gd/CoFeB sample
(approximately 0.04). Such notable difference is attributed to the different
spin-orbit correlation strength between the [Co/Pt]3 sample and the
CoFeB/Gd/CoFeB sample, which has been confirmed through the theoretical
calculations. Furthermore, the full magnetization switching of the [Co/Pt]3
sample with a switching current density of approximately 2.6x106 A/cm2 has been
realized through Zr, which even outperforms that of the W spin Hall material.
Our finding provides a guideline to understand orbital torque efficiency and
paves the way to develop energy-efficient orbitronic devices.
