Incomplete alignment of the uncompensated AFM interface moment toward the annealing field in AFM/FM bilayers

In antiferromagnet/ferromagnet (AFM/FM) bilayers, the induced unidirectional anisotropy of the ferromagnet (FM) layer has been proposed to come from the uncompensated moment of the AFM at the interface. It is commonly assumed that the uncompensated interface moment of all AFM grains is aligned toward the magnetic field direction applied during film deposition or annealing. However, our model calculation shows that this may not be the case in PtMn-CoFe bilayers. For the samples annealed at 280°C for 2 hours, a significant portion of the grains have higher energy barriers than the threshold and cannot flip their interface moment to reach the global energy minimum. The interface moment directions of these grains remain random after the annealing.