The magnetic properties of antiferromagnetic (AFM) spins were investigated using x-ray magnetic linear dichroism (XMLD) in epitaxial NiO/CoO/MgO(001) films as a function of film thickness, temperature, and interface modulation. We found that the NiO AFM spins undergo a spin reorientation transition (SRT) from the in-plane orientation to the out-of-plane orientation at a critical NiO thickness. The NiO AFM SRT can be attributed to the competition between the out-of-plane anisotropy of the NiO AFM spins and the AFM interfacial exchange coupling with the CoO in-plane spins. The NiO SRT thickness increases with the CoO thickness and also with the interfacial coupling strength. The temperature-dependent XMLD measurement indicates that the exchange coupling at the NiO/CoO interface can greatly enhance the Néel temperature of the CoO layer

Step-induced antiferromagnetic (AFM) uniaxial anisotropy and its effects on the exchange coupling have been systematically investigated in the epitaxial Fe/CoO bilayers on MgO(001) vicinal surface. X-ray magnetic linear dichroism measurements proved that the atomic steps induced a strong in-plane AFM uniaxial anisotropy in the CoO film. We found that the thermal activation induced in-plane 90-degree switching of CoO AFM in-plane spins. The competition among the step-induced AFM anisotropy, the interface exchange coupling and thermal activation generate novel multiple in-plane spin reorientation transition of the Fe magnetization, which can further provide new insights on the exchange coupling in FM/AFM systems.2