Coexistence of the uniaxial anisotropy and the antiferromagnetic coupling in Co/Ir(1 1 1) superlattices

We have investigated the structural and the magnetic properties of carefully grown Co/Ir(1 1 1) superlattices composed of a few atomic mono-layers (MLs) of each element. We found that the superlattice of [Co(3 ML)/Ir(3 ML)] has its magnetic easy-axis perpendicular to the surface and has quite large antiferromagnetic (AF) coupling between adjacent Co layers. As a result, the magnetic hysteresis curve shows a spin-flip at H∼53 kOe . Adopting a simple two sublattice coherent rotation model, we analyzed the MH curves and obtained the AF coupling strength J AF and the perpendicular anisotropy K as well. The estimated K of [Co(3 ML)/Ir(3 ML)](1 1 1) is even larger than that of Co/Pt multilayer which is known as a typical strong perpendicular anisotropy system.