Quantitative analysis of vectorial torques in thin 3d Co ferromagnet using orbital-spin conversion

TL;DR

This paper quantitatively analyzes the orbital and spin currents responsible for magnetic torques in thin Co ferromagnets, revealing enhanced currents and interfacial orbital current generation via the Orbital Rashba-Edelstein effect.

Contribution

It introduces a method to measure and distinguish orbital and spin currents in Co ferromagnets using second harmonic Hall techniques and orbital-to-spin conversion layers.

Findings

Both orbital and spin currents are enhanced in the studied systems.

Interfacial orbital currents are generated via the Orbital Rashba-Edelstein effect.

Decoherence length measurements confirm interfacial orbital current generation.

Abstract

Recent findings in orbitronics pointed out large current-induced torques originating, in the current understanding, from incident orbital currents. These are generated by orbital Rashba-Edelstein effect (OREE) produced at the interface between some light metal and oxides films e.g. by naturally oxidized copper layer (Cu*). In the present work, by using second harmonic Hall techniques, we determine the ratio of orbital vs spin currents exerting torques on thin transition metals Co ferromagnet in systems using an orbit-to-spin Pt converter as interlayer with Cu*. Our results quantifying damping like torques show that both orbital and spin currents are enhanced in these systems. Moreover, the experimental determination of the decoherence length in a sample series with varying Co thickness clearly demonstrates the interfacial generation of the orbital currents in Cu* by Orbital Rashba-Edelstein effects (REE) leading to subsequent magnetic torque in Co over a typical lengthscale of several nanometers