Spin injection characteristics of Py/graphene/Pt by gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulse

TL;DR

This study investigates spin transport along the c-axis in Py/graphene/Pt structures using gigahertz and terahertz magnetization dynamics driven by femtosecond laser pulses, revealing that graphene blocks vertical spin injection.

Contribution

It provides experimental evidence that graphene suppresses vertical spin transport in Py/graphene/Pt heterostructures using time-resolved magneto-optical Kerr effect and THz emission measurements.

Findings

Gilbert damping constant decreases with graphene layer, indicating spin injection blocking.

THz emission is reduced by graphene, confirming suppression of spin transport.

Graphene's anisotropic resistivity contributes to spin transport blockade.

Abstract

Spin transport characteristics of graphene has been extensively studied so far. The spin transport along c-axis is however reported by rather limited number of papers. We have studied spin transport characteristics through graphene along c-axis with permalloy(Py)/graphene(Gr)/Pt by gigahertz (GHz) and terahertz (THz) magnetization dynamics driven by femtosecond laser pulses. The relatively simple sample structure does not require electrodes on the sample. The graphene layer was prepared by chemical vapor deposition and transferred on Pt film. The quality of graphene layer was characterized by Raman microscopy. Time resolved magneto-optical Kerr effect is used to characterize gigahertz magnetization dynamics. Magnetization precession is clearly observed both for Pt/Py and Pt/Gr/Py. The Gilbert damping constant of Pt/Py was 0.015, indicates spin pumping effect from Py to Pt. The Gilbert damping constant of Pt/Gr/Py is found to be 0.011, indicates spin injection is blocked by graphene layer. We have also performed the measurement of THz emission for Pt/Py and Pt/Gr/Py. While the THz emission is clearly observed for Pt/Py, a strong reduction of THz emission is observed for Pt/Gr/Py. With these two different experiments, and highly anisotropic resistivity of graphite, we conclude that the vertical spin transport is strongly suppressed by the graphene layer.