Abstrakt
We report measurements of current-induced magnetic torques in structures containing a similar to 1-nm-thick layer of an antiferromagnet IrMn. We perform ac-electrical measurements in Ta/IrMn/CoFeB and Ta/IrMn structures below and above the Neel temperature of the ultrathin IrMn and compare the results with control experiments in a Ta/CoFeB bilayer.
We employ the second harmonics technique to detect current-induced effects and perform symmetry analysis that enables us to separate distinct contributions to the signal. We identify signals generated by a thermal gradient in the sample and signals originating from current-induced torques.
In the Ta/CoFeB bilayer we observe a current-induced torque acting on CoFeB consistent with the sign and magnitude of the spin Hall effect in Ta. In the Ta/IrMn/CoFeB trilayer, the opposite sign of spin Hall angles in IrMn and Ta results in a strongly suppressed spin torque acting in CoFeB at high temperatures where IrMn is paramagnetic.
In the low temperature antiferromagnetic state of IrMn, the torque acting in CoFeB is enhanced and driven by the spin Hall effect in IrMn with the opposite sign and comparable amplitude to the torque in the Ta/CoFeB bilayer. The spin Hall current from Ta in the Ta/IrMn/CoFeB trilayer at low temperatures is not compensating the spin Hall current from IrMn in the net torque acting on CoFeB but is instead absorbed by the antiferromagnetic moments in IrMn.