Oscillatory interlayer exchange coupling in MgO tunnel junctions with perpendicular magnetic anisotropy

The influence of magnetic layer thickness on the interlayer coupling through a tunnel barrier is investigated in Co/MgO/Co structures with perpendicular anisotropy. Despite the rather large MgO thickness, a clear antiferromagnetic coupling is observed. It oscillates with increasing magnetic layer thickness, in agreement with theories on indirect coupling through insulating spacers. Although the average interlayer coupling strength decreases with increasing annealing temperature, constant period and amplitude of these oscillations are observed for all annealing temperatures.