Abstract
With the goal of observing and explaining the unexpected exchange bias effect in paramagnetic LaNiO3-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 LaMnO3(n)-LaNiO3(n) (LMO/LNO) superlattices (SLs) along (001)-, (110)-, and (111)-oriented SrTiO3 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.
Highlights
Transition-metal oxides have long been a major focus of condensed-matter research due to their strong correlation between charge, spin, lattice and orbital degrees of freedom1
Previous research found that the charge transfer in interfacial Mn and Ni ions can result in local magnetic moment pinning the ferromagnetic LMO layer and causing exchange bias in LMO/LNO SLs31
The relationships between structure, magnetic behavior, charge transfer and orbital occupancy have been investigated for different orientations in LMO/LNO superlattices using X-ray absorption spectroscopy (XAS) and X-ray linear dichroism (XLD) measurements
Summary
Transition-metal oxides have long been a major focus of condensed-matter research due to their strong correlation between charge, spin, lattice and orbital degrees of freedom1. Taking Gibert et al as an example, the exchange bias (EB) effect was observed in (111)-oriented superlattices that consist of ferromagnetic LaMnO3 (LMO) and paramagnetic LaNiO3 (LNO), while it was not observed in SLs grown along the (001) direction6. Zhou et al have recently indicated the absence of exchange bias in the relatively thick LMO/LNO superlattice along (001) orientation is due to charge transfer being suppressed by orbital reconstruction13.
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