Origin and location of interfacial conversion in Ni/Ti/X heterostructures

Determine whether the conversion of spin and orbital accumulation into charge current in Ni/Ti/X multilayers is localized at the Ni/Ti interface, at the Ti/X interface, or arises from a combination of both interfaces, and ascertain whether any contribution from the Ti/X interface is mediated by spin-current propagation through the Ti spacer followed by conversion of orbital accumulation at the Ti/X interface.

Background

The paper investigates orbital and spin to charge conversion in Ni/Ti/Au and Ni/Pt/Ti/Au heterostructures using spin/orbital pumping via FMR and thermal gradients. The authors find that the generated charge current is independent of Ti thickness up to 60 nm, implying a dominant interfacial conversion mechanism rather than bulk orbital transport within Ti.

To probe which interface(s) are responsible, the authors vary the capping layer X in Ni/Ti/X stacks and observe strong modulation of the signal, suggesting a role of the secondary interface. However, it remains unresolved whether the conversion occurs at the Ni/Ti interface, the Ti/X interface, or both, and whether spin-current propagation through Ti mediates a subsequent conversion at Ti/X. Clarifying this is critical to fully validate the proposed multistep interfacial mechanism where orbital accumulation is locally converted to spin at one interface, transported as spin through Ti, and reconverted to orbital (and then charge) at the second interface.

References

A fundamental question arises regarding the origin of the measured charge current: where does the conversion of spin and orbital accumulation into $I_c$ occur, and what are the governing mechanisms? Our experimental evidence points to a purely interfacial conversion; however, it remains to be determined whether this process is localized at the primary Ni/Ti interface, the secondary Ti/X interface, or arises from a synergistic contribution of both. Furthermore, if the second interface plays a role, it is essential to discern whether the signal stems from the propagation of a spin current through the Ti spacer and a subsequent conversion of an orbital accumulation at the Ti/X interface.

— Unconventional views on orbitronics supported by experimental results  (2603.28075 - Yactayo et al., 30 Mar 2026) in Main text, paragraph preceding Figure 3 (Dual-interface conversion)