Engineering Magnetic Interactions in Complex Oxide Heterostructures

Complex oxides possess a wide range of technologically relevant functional properties including ferromagnetism, ferroelectricity, and superconductivity. Furthermore, their interfaces exhibit unexpected functional properties not found in the constituent materials due to structural and chemical changes as well as electronic and magnetic interactions. These unique interfacial effects lead to fundamental differences compared to analogous metallic systems. For example, ferromagnetic (FM)/FM interfaces consisting of magnetically hard La_0.7Sr_0.3CoO₃ (LSCO) and soft La_0.7Sr_0.3MnO₃ (LSMO) display exchange-spring behavior where the hard layer pins the moments of the soft layer, however, the hard/soft magnetic interface does not coincide with the chemical interface.¹ Rather, an interfacial LSCO layer forms that is characterized by magnetically active Co²⁺ ions which couple to the soft LSMO layer. The full characterization of the structural and magnetic properties of the LSCO/LSMO bilayers involves synchrotron-radiation and neutron-scattering based techniques as well as high resolution transmission electron microscopy. We find that the proportion of the Co²⁺ ion-rich LSCO layer and magnitude of exchange bias shift depends sensitively on parameters such as individual layer thicknesses, epitaxial strain state, BO₆ octahedral tilt pattern of the underlying substrate, and stacking order of the layers.² These results demonstrate how the competing interactions in complex oxides enable intriguing opportunities to tailor functional properties for new, versatile, and energy efficient spintronic devices.
We are grateful to the support by NSF (DMR 1745450), UC MRPI (No. MR-15-328528), and the DOE SCGSR program. This research utilized DOE user facilities including ALS at LBNL, SSRL at SLAC, SNS at ORNL, and EMSL at PNNL.

¹B. Li, et al., APL, 105, 202401 (2014)
²B. Li, et al., APL 109, 152401 (2016); A.M. Kane, Y. et al., PRM 3, 014413 (2019); J.P. Byers et al., JAP, 125, 082518 (2019).