Tunnel spin injection into graphene through ALD-grown tunnel barrier

Graphene is a promising material for spintronics devices because of its long spin relaxation time due to weak spin-orbit interaction and hyperfine interaction. For the spintronics, it is very essential to develop a reliable method to inject spin polarized electrons into graphene from ferromagnetic electrodes. In this study, between ferromagnetic electrodes and graphene we fabricated a new type of Al$_{2}$O$_{3}$ tunnel barrier grown by atomic layer deposition (ALD). Before ALD of Al$_{2}$O$_{3}$, we functionalized the surface of graphene with a self-assembled monolayer of 3, 4, 9, 10 perylene tetracarboxylic acid (PTCA) to improve adhesion and growth of Al$_{2}$O$_{3}$. Using ALD-Al$_{2}$O$_{3}$/PTCA composite barrier, large nonlocal magnetoresistance of 30 $\Omega $ was observed at 45 K. Nonlocal magnetoresistance reached maximum around charge neutrality point, and $I-V$ characteristics of the contacts are nonlinear. These results indicate the achievement of tunnel spin injection into graphene, revealing potentially high performance of ALD-Al$_{2}$O$_{3}$/PTCA tunnel barrier [1]. [1] T. Yamaguchi et al., J. Magn. Magn. Mater. (2011), doi: 10. 1016/j.jmmm. 2011. 09. 031