Magnetic coupling at the interface between ultrathin tetragonal CuO and La0.7Sr0.3MnO3

High-symmetry rocksalt type tetragonal CuO (T-CuO) does not exist in bulk but can be synthesized via thin film epitaxy limited to a few unit cells (3, 4) thick and above which it relaxes to its bulk tenorite structure. Direct probe into magnetic properties of T-CuO layer has been a challenge because of its ultrathin limit. Here, we demonstrate the interfacial magnetic coupling between ultrathin T-CuO and ferromagnetic (La0.7Sr0.3MnO₃) layers in an epitaxial 0.16em0exCuO/La0.7Sr0.3MnO₃ bilayer grown on (001)-oriented SrTiO₃. We observe a positive exchange bias shift of ~30 Oe at 2 K in CuO/La0.7Sr0.3MnO₃ bilayer. The observation of positive exchange bias indicates that there exists antiferromagnetic exchange coupling between Mn and Cu moments at the interface. Notably, the exchange bias vanishes at 5 K and it is discussed in view of the proposed spin structure revealed from low-energy muon spin rotation and x-ray magnetic circular dichroism study [Phys. Rev. B 103, 224429 (2021)]. Furthermore, an enhanced Gilbert damping, linewidth broadening and larger inhomogeneous 4πMeff value from in-plane ferromagnetic resonance measurements, are the direct consequence of antiferromagnetic exchange coupling at the CuO/La0.7Sr0.3MnO₃ interface. Combining both static and dynamic magnetic characterization, we establish an understanding of interfacial exchange coupling in CuO/La0.7Sr0.3MnO₃ bilayer.