Chengye Yin

The control of interfacial oxygen vacancy provides additional functional tunability to correlated oxide heterostructures. Here, we studied the role of amorphous capping layers, such as LaAlO3 and LaMnO3, in controlling magnetic properties of (La,Sr)MnO3//SrTiO3 heterostructures. When (La,Sr)MnO3 layers are thin (∼4 nm), the amorphous LaAlO3 capping layer significantly suppresses the ferromagnetic interaction, denoted by a decreased Curie temperature TC (ΔTC over −300 K) and saturated moment MS (ΔMS at −2.9 μB/Mn) compared to the uncapped counterparts, irrespective of epitaxial orientations. This ferromagnetic suppression is attributed to the creation of interfacial oxygen vacancies, as evidenced by the recovery of ferromagnetism upon ex situ annealing (1 h at 625 °C in air). Moreover, when replacing LaAlO3 with LaMnO3, the reduction of oxygen affinity in the capping layer results in less pronounced magnetic modulations with ΔTC at −100 K and ΔMS at −1.1 μB/Mn. Also, the increase in (La,Sr)MnO3 layer thickness dilutes the capping-layer effect, leading to negligible changes on TC and MS in the LaAlO3-capped 40-nm-thick (La,Sr)MnO3//SrTiO3 samples. Our results not only shed some light on understanding the capping-layer effect in manganite-based heterostructures but also offer a feasible strategy for functional modulations at other oxide interfaces.

The crucial role of interface engineering in controlling functionality has been well documented in the (001)-orientated perovskite oxide heterostructures; however, limited attention has been given to other epitaxial orientations. In this study, the (La,Sr)MnO3 heterostructure is selected to present the epitaxial-orientation-dependent interface engineering strategies based on magnetoelectric coupling and oxygen octahedral coupling. When capped by a ferroelectric PbTiO3 layer for interlayer magnetoelectric coupling, the (001) (La,Sr)MnO3 layer exhibits the most significant magnetic modulations compared to (110) and (111) counterparts. This can be attributed to the PbTiO3's out-of-plane polarization that depends on the epitaxial orientations. Also, if considering the interfacial oxygen octahedral structure in terms of epitaxial orientations, the buffer (or cap) layer hosts the most part of interfacial oxygen octahedra and, thus, plays a dominant role in controlling oxygen octahedral coupling of (001)-orientated [or (110)-orientated] perovskite heterostructures. This is consistent with our observations that for the (001) [or (110)] (La,Sr)MnO3 heterostructures, the DyScO3 buffer layer offers the more (or less) effective magnetic modulations compared to the cap one. These findings underscore the orientation-dependent nature of interface engineering in manganite heterostructures as well as in other perovskite heterostructures for tailoring functionalities.

Magnetic anisotropy has significant importance in both designing high-efficiency magnetic devices and understanding noncollinear spin textures. Here, La0.67Sr0.33MnO3 layers are epitaxially fabricated on the (001)-, (110)-, and (111)-orientated SrTiO3 substrates to manipulate magnetic anisotropy. While the [11¯0] axis is the in-plane magnetic easy axis for the (001) La0.67Sr0.33MnO3 layer, it becomes the hard axis for the (110) and (111) samples. Interestingly, the (110) samples exhibit a great enhancement in magnetic anisotropy energy, reaching at 6.1 × 105 erg/cm3 that is 1–2 orders of magnitude higher than ones in (001) and (111) films. It is also noted that such improved magnetic anisotropy of (110) samples is maintained up to 30 nm. Those observations can be interpreted in terms of the orientation-modified orbital symmetry. While the energetically favored 3dx2−y2 orbital and degenerated eg orbitals drive the two-dimensional and bulk-like ferromagnetism in (001) and (111) La0.67Sr0.33MnO3 layers, respectively, the 3d3z2−r2 orbital provides the lowest orbital symmetry and results in the highest magnetic anisotropy energy in (110) samples. Meanwhile, this model can also explain the thickness-dependent Curie temperatures with different epitaxial orientations, deepening the understanding of the complex oxide heterostructures for magnetic modulations.