Tuning fieldlike torque by the orbital Hall effect in Ta/ferromagnetic metal structures

We investigate the influence of different $3d$ ferromagnetic metals on the fieldlike torque in Ta. We find that the fieldlike torque and dampinglike torque exhibit the same trend: As the orbital-to-spin conversion coefficient of the ferromagnetic metal increases, the orbital torque with a positive sign in Ta also increases, while the spin torque with a negative sign remains nearly constant. Therefore, under the competition between spin torque and orbital torque, both dampinglike torque and fieldlike torque show the same trend. Additionally, we introduce a 1 nm Cu layer at the interface to exclude the interference of spin-orbit torque generated by the spin Rashba-Edelstein effect or the orbital Rashba-Edelstein effect. Due to the significant orbital Hall conductivity in Ta, we identify that an important source of fieldlike torque is the orbital current generated by the orbital Hall effect, which can be tuned through orbital-to-spin conversion.