  Orbital currents have recently emerged as a promising tool to achieve
electrical control of the magnetization in thin-film ferromagnets. Efficient
orbital-to-spin conversion is required in order to torque the magnetization.
Here we show that the injection of an orbital current in a ferrimagnetic
GdyCo100-y alloy generates strong orbital torques whose sign and magnitude can
be tuned by changing the Gd content and temperature. The effective spin-orbital
Hall angle reaches up to -0.25 in a GdyCo100-y/CuOx bilayer compared to +0.03
in Co/CuOx and +0.13 in GdyCo100-y/Pt. This behavior is attributed to the local
orbital-to-spin conversion taking place at the Gd sites, which is about five
times stronger and of the opposite sign relative to Co. Furthermore, we observe
a manyfold increase in the net orbital torque at low temperature, which we
attribute to the improved conversion efficiency following the magnetic ordering
of the Gd and Co sublattices.
