Spin injection efficiency at metallic interfaces probed by THz emission spectroscopy

TL;DR

This study explores the relationship between ultrafast THz emission and steady state ferromagnetic resonance in metallic trilayers, revealing how spin conductance and damping are interconnected and can be modeled with Rashba fields.

Contribution

It demonstrates the connection between ultrafast spin currents and Gilbert damping, extending magneto-circuit concepts to ultrafast spintronics and modeling spin losses with an effective Hamiltonian.

Findings

Ultrafast spin current defines a direct spin conductance.

Gilbert damping relates to an effective spin mixing-conductance.

Spin-memory losses can be modeled via Rashba fields.

Abstract

Terahertz (THz) spin-to-charge conversion has become an increasingly important process for THz pulse generation and as a tool to probe ultrafast spin interactions at magnetic interfaces. However, its relation to traditional, steady state, ferromagnetic resonance techniques is poorly understood. Here we investigate nanometric trilayers of Co/X/Pt (X=Ti, Au or Au0:85W0:15) as a function of the 'X' layer thickness, where THz emission generated by the inverse spin Hall effect is compared to the Gilbert damping of the ferromagnetic resonance. Through the insertion of the 'X' layer we show that the ultrafast spin current injected in the non-magnetic layer defines a direct spin conductance, whereas the Gilbert damping leads to an effective spin mixing-conductance of the trilayer. Importantly, we show that these two parameters are connected to each other and that spin-memory losses can be modeled via an effective Hamiltonian with Rashba fields. This work highlights that magneto-circuits concepts can be successfully extended to ultrafast spintronic devices, as well as enhancing the understanding of spin-to-charge conversion processes through the complementarity between ultrafast THz spectroscopy and steady state techniques.