Spin orientation-dependent antiferromagnetic proximity effect

Summary form only given. The interface magnetic phenomenon, which forms the backbone of modern information technology, is of great interest for several decades. When two or more dissimilar materials with different long-range magnetic orderings and/or functionalities are combined together, it may give rise to new interfacial properties, such as the proximity effect. The exchange coupling between two FM layers, as well as that between a FM layer and an AFM layer, has been widely studied before, but the exchange coupling between the AFM spins in two AFM layers has not been paid enough attention due to the technique difficulty to directly measure the AFM properties in AFM layers. In this report, antiferromagnetic proximity effect was systematically studied in epitaxial CoO/NiO/ MgO(001) system with x-ray linear dichroism (XMLD) and magneto-optic Kerr effect (MOKE) measurement. NiO AFM spin undergoes a spin reorientation transition from in-plane to out-of-plane or spin canting with increasing NiO thickness owning to the competition between the strain-induced out-of-plane anisotropy of the NiO AFM spin and the AFM interfacial exchange coupling driven by the in-plane CoO AFM spins. The Néel temperatures of CoO layer and NiO layer can be determined directly by temperature dependent XMLD effect. We found the Néel temperature of CoO layer could be greatly enhanced by the adjacent NiO layer, but the enhancement closely depends on the spin orientation of adjacent NiO AFM. The T_N of the 2nm single CoO layer is ~220K, and increases to ~400K while grown on 2nm NiO layer with the in-plane anisotropy, then CoO´s TN decreases to ~300K while grown on 12nm NiO layer with the out-of-plane anisotropy. Moreover, we found the Néel temperatures of CoO layer strongly depends on the CoO thickness, and the T_N of top CoO interface decreases when it is away from CoO/NiO interface. Through the CoO-thickness-dependent T_N measurement, we- can estimated the antiferromagnetic correlation length, which is ~2 .2nm. Our results give clear evidence that magnetic proximity effect between antiferromagnetic bilayers could influence the spin direction and the ordering temperature.