The antiferromagnetic state in ultrathin LaNiO3 layer supported by long-range exchange bias in LaNiO3/SrTiO3/La0.7Sr0.3MnO3 superlattices

Abstract

Research on the novel antiferromagnetic (AFM) state in ultrathin LaNiO₃ (LNO) layers is very significant because bulk LNO is always exhibits paramagnetic state. Recently, an unexpected exchange bias effect has been observed in LNO-based heterostructures, but the reason for this effect is considered as the interfacial localized magnetic moment rather than the AFM state in ultrathin LNO layers. To this end, we have grown a prototypical superlattice composed of non-magnetic spacer layers as a LNO/spacer/La_0.7Sr_0.3MnO₃ (LSMO) system to support the AFM state in ultrathin LNO layers. Verified through X-ray absorption spectroscopy measurements, the interfacial localized magnetic moment induced by charge transfer can be effectively eliminated by inserting a spacer layer. Moreover, the long-range exchange bias effect can still be observed in these LNO/spacer/LSMO superlattices, and the strength of the coupling decreases with increasing non-magnetic spacer layer thickness. Therefore, this phenomenon suggests that the antiferromagnetic state in an ultrathin LNO layer plays a key role in the long-range exchange bias. Our findings will provide important clues for simplifying the behavior of confusing systems.