Robust Interfacial Exchange Bias and Metal–Insulator Transition Influenced by the LaNiO₃ Layer Thickness in La_0.7Sr_0.3MnO₃/LaNiO₃ Superlattices

Abstract

Artificial heterostructures based on LaNiO (LNO) have been widely investigated with the aim to realize the insulating antiferromagnetic state of LNO. In this work, we grew [(LaSrMnO)-(LaNiO)] superlattices on (001)-oriented SrTiO substrates by pulsed laser deposition and observed an unexpected exchange bias effect in field-cooled hysteresis loops. Through X-ray absorption spectroscopy and magnetic circular dichroism experiments, we found that the charge transfer at the interfacial Mn and Ni ions can induce a localized magnetic moment. A remarkable increase of exchange bias field and a transition from metal to insulator were simultaneously observed upon decreasing the thickness of the LNO layer, indicating the antiferromagnetic insulator state in 2 unit cells LNO ultrathin layers. The robust exchange bias of 745 Oe in the superlattice is caused by an interfacial localized magnetic moment and an antiferromagnetic state in the ultrathin LNO layer, pinning the ferromagnetic LaSrMnO layers together. Our results demonstrate that artificial interface engineering is a useful method to realize novel magnetic and transport properties.

The Exchange Bias of LaMnO3/LaNiO3 Superlattices Grown along Different Orientations

“…The peak at 533 eV is distinctly visible in all SLs, and its intensity is larger in the (001)-oriented SL, indicating the higher degree of hybridization between Mn and Ni ions. As the Fermi level of LMO is higher than that of LNO layer, the presence of electron transfer from Mn to Ni sites is in good agreement with the results of Mn L -edge and O K -edge spectra 13 . Therefore, it is plausible to consider the charge transfer occurring from interfacial Mn to Ni ions in SLs.

Figure 4Normalized XAS spectra at the ( a ) Mn L -edge and ( b ) O K -edge from different samples recorded in TEY mode at room temperature.

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“…However, Zhou et al . have recently observed exchange bias in the relatively thin layer in (001) stacking of LMO/LNO SLs and found that thicker SLs exhibit lower charge transfer rates compared to thinner SLs 13 . Inspired by these findings, we chose the thin SLs as (3–3) 10 in (001) plane, (4–4) 10 in (110) plane, and (5–5) 10 in (111) plane for comparison.…”

“…Furthermore, 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 reconstruction 13 . In addition, it was found that the exchange bias can be observed in thin LMO/LNO superlattice along the (001) direction 14 .…”

Interfacial Spin Glass State and Exchange Bias in the Epitaxial La0.7Sr0.3MnO3/LaNiO3 Bilayer

“…It is obvious that H EB decreases rapidly with increasing temperature, finally vanishes at the blocking temperature ( T B ) of 120 K. As T B gets smaller than the freezing temperature T F of the spin glass, we suggest that the exchange bias effect in the LSMO/LNO interface is supported by the emergence of the spin glass state. As previously reported, in a range of diverse materials such as LSMO/SMO, the existence of the spin glass state is known to lead an exponential temperature dependent decay of H EB and H C [29, 33–35]. In Fig.…”

High-spin state and magnetic coupling induced through interfacial orbital reconstruction observed in SrRuO3/LaNiO3superlattice

“…The electronic structure at the perovskite-oxide interface between two transition metal oxides features complex interactions among the lattice, charge, spin, and orbital degrees of freedom and shows many emergent physical properties, including high-temperature superconductivity [1], magnetoresistance [2], exchange bias (EB) [3], and ferroelectricity [4]. With regard to these complex oxide structures, many of which are epitaxially compatible, the past decade has seen rapid growth in materials science at the atomic level with the creation of heterostructures with unique properties [5].…”