Wideband and on-chip excitation for dynamical spin injection into graphene

TL;DR

This paper demonstrates broadband on-chip spin pumping into graphene using ferromagnetic resonance, enabling efficient spin injection in micron-scale devices and facilitating future complex spintronic applications.

Contribution

It introduces a compact, broadband on-chip RF excitation method for dynamical spin injection into graphene via spin pumping, overcoming electrical injection challenges.

Findings

Clear spin current signals detected over 2-8 GHz range

Spin pumping effective at power levels of a few milliwatts

Device enables exploration of novel materials and complex structures

Abstract

Graphene is an ideal material for spin transport as very long spin relaxation times and lengths can be achieved even at room temperature. However, electrical spin injection is challenging due to the conductivity mismatch problem. Spin pumping driven by ferromagnetic resonance is a neat way to circumvent this problem as it produces a pure spin current in the absence of a charge current. Here, we show spin pumping into single layer graphene in micron scale devices. A broadband on-chip RF current line is used to bring micron scale permalloy (Ni$_{80}$Fe$_{20}$) pads to ferromagnetic resonance with a magnetic field tunable resonance condition. At resonance, a spin current is emitted into graphene, which is detected by the inverse spin hall voltage in a close-by platinum electrode. Clear spin current signals are detected down to a power of a few milliwatts over a frequency range of 2 GHz to 8 GHz. This compact device scheme paves the way for more complex device structures and allows the investigation of novel materials.