Depth-resolved x-ray characterization of interfacial ferromagnetism in oxide superlattices

Origins of the emergent interfacial ferromagnetism in CaMnO3/CaRuO3 heterostructures have been investigated for nearly two decades. Several experimental and theoretical studies suggest that this phenomenon is stabilized by the charge transfer from Ru to Mn, but they differ in predicting the thicknesses of the resultant ferromagnetic layers [1-4]. In this study, we have carried out polarization-dependent x-ray absorption spectroscopy with circular dichroism and x-ray resonant magnetic scattering (XRMS) measurements to probe the depth-resolved magnetic profile in a CaMnO3/CaRuO3 superlattice. Self-consistent x-ray optical fitting of both non-resonant and resonant XRMS spectra near the Mn L2,3 absorption edge revealed significantly different magnetic moments localized within one unit-cell of the top and bottom interfaces of the CaMnO3 layer. Complementary hard x-ray photoemission spectroscopy was utilized to probe bulk-sensitive core-level and valence-band electronic structure. The experimental results were rationalized using first-principles theoretical calculations.

[1]  K. S. Takahashi et al., Appl. Phys. Lett. 79, 1324 (2001); [2]  B. R. K. Nanda et al., Phys. Rev. Lett. 98, 216804 (2007); [3]  J. W. Freeland et al., Phys. Rev. B 81, 094414 (2010); [4]  A. J. Grutter et al., Nano Lett. 16, 5647 (2016).