Enhancing TMR and spin-filtration by using out-of-plane graphene insulating barrier in MTJs

First principles investigations are performed to understand the spin-polarized transport in Magnetic Tunnel Junctions (MTJs) consisting of an out-of-plane graphene sheet as a barrier in between two CrO₂ Half-Metallic-Ferromagnetic (HMF) electrodes. Upon comparison of the results with the results of in-plane graphene based MTJs reported in the past, it is observed that out-of-plane structures offer a high TMR of ∼100% and the transport phenomenon is tunneling since there are no transmission states near the Fermi level. However, in in-plane structures, the transport phenomenon cannot be tunneling since there are a significant number of transmission states near the Fermi level, although a high Magneto Resistance (MR) of ∼90% is observed. Both the TMR and Spin Injection Efficiency η (Spin-Filtration) are higher in out-of-plane structures in comparison to in-plane structures, which is due to the graphene sheet acting as a perfect barrier in out-of-plane structures, which results in negligible spin down current (I↓) in both the Parallel Configuration (PC) and Antiparallel Configuration (APC).