Interfacial magnetism emerging from orbital hybridization is the key facilitator for practical nanoscale spintronic devices. Most devices require a capping layer, and it is widely assumed that capping-layer variations do not change the fundamental properties of magnetic films underneath. In a model Co−Fe−B/MgO system, interfacial investigations, so far, have been focused on the hybridization of Fe d and O p orbitals. However, the role of the capping layer has largely been ignored by adopting a reductionist scenario of just oxidation or charge modification. Here, we report strong modifications of interfacial magnetism in Co−Fe−B/MgO by systematically changing the Ru capping thickness using element-specific x-ray magnetic circular dichroism and x-ray absorption spectroscopy at Fe L2,3, Co L2,3, and O K edges, along with corresponding spin and orbital magnetic moment calculations and magnetometry measurements. We observe unusual spin-flip-like transitions due to capping layers and find direct evidence for systematic spin and orbital modifications, beyond just charge transformation, strikingly captured by oxygen x-ray absorption and dichroism spectra. Our result shows the importance of the capping layer and provides a complete picture of rich interfacial magnetism in the
This work is supported by the Ministry of Education of Singapore (MOE) AcRF Tier-2 (Grants No. MOE2017-T2-1-135, No. MOE2018-T2-2-117, and No. MOE2019-T2-1-163), MOE AcRF Tier-1 (Grants No. R-144-000-423-114 and No. R-144-000-398-114), and NUS Core Support (Grant No. C-380-003-003-001). The work at A*STAR is funded by SpOT-LITE program (A*STAR Grant No. A18A6b0057) through RIE2020 funds from Singapore.