The Exchange Bias of LaMnO/LaNiO Superlattices Grown along Different Orientations.

With the goal of observing and explaining the unexpected exchange bias effect in paramagnetic LaNiO-based superlattices, a wide range of theoretical and experimental research has been published. Within the scope of this work, we have grown high-quality epitaxial LaMnO(n)-LaNiO(n) (LMO/LNO) superlattices (SLs) along (001)-, (110)-, and (111)-oriented SrTiO substrates. The exchange bias effect is observed in all cases, regardless of growth orientation of the LMO/LNO SLs. As a result of a combination of a number of synchrotron based x-ray spectroscopy measurements, this effect is attributed to the interfacial charge transfer from Mn to Ni ions that induces localized magnetic moments to pin the ferromagnetic LMO layer. The interaction per area between interfacial Mn and Ni ions is nearly consistent and has no effect on charge transfer for different orientations. The discrepant charge transfer and orbital occupancy can be responsible for the different magnetic properties in LMO/LNO superlattices. Our experimental results present a promising advancement in understanding the origin of magnetic properties along different directions in these materials.