Isotropic non-local Gilbert damping driven by spin currents in epitaxial Pd/Fe/MgO(001) films

TL;DR

This study demonstrates that both local and non-local Gilbert damping are isotropic in epitaxial Pd/Fe/MgO(001) films, indicating spin current absorption is independent of magnetization orientation, which advances understanding in spintronics.

Contribution

It provides the first experimental and theoretical evidence that non-local Gilbert damping driven by spin currents is isotropic in epitaxial Pd/Fe heterostructures.

Findings

Both local and non-local Gilbert damping are isotropic in Fe(001) plane.

Effective spin mixing conductance of Pd/Fe interface is nearly invariant across magnetization directions.

First principles calculations agree with experimental results, confirming isotropic spin current absorption.

Abstract

Although both theoretical predications and experimental observations demonstrated that the damping factor is anisotropic at ferromagnet/semiconductor interface with robust interfacial spin-orbit coupling, it is not well understood whether non-local Gilbert damping driven by spin currents in heavy metal/ferromagnetic metal (HM/FM) bilayers is anisotropic or not. Here, we investigated the in-plane angular- and frequency- dependence of magnetic relaxation of epitaxial Fe/MgO(001) films with different capping layers of Pd and Cu. After disentangling the parasitic contributions, such as two-magnon scattering (TMS), mosaicity, and field-dragging effect, we unambiguously observed that both local and non-local Gilbert damping are isotropic in Fe(001) plane, suggesting that the pure spin currents absorption is independent of Fe magnetization orientation in the epitaxial Pd/Fe heterostructure. First principles calculation reveals that the effective spin mixing conductance of Pd/Fe interface is nearly invariant for different magnetization directions in good agreement with the experimental observations. These results offer a valuable insight into the transmission and absorption of pure spin currents, and facilitate us to utilize next-generation spintronic devices.