Enhanced spin accumulation at room temperature in graphene spin valves with amorphous carbon interfacial layers

Abstract

We demonstrate a large enhancement of the spin accumulation in monolayer graphene following electron-beam induced deposition of an amorphous carbon layer at the ferromagnet-graphene interface. The enhancement is 10 4 -fold when graphene is deposited onto poly(methyl metacrylate) (PMMA) and exposed with sufficient electron-beam dose to cross-link the PMMA, and 10 3 -fold when graphene is deposited directly onto SiO 2 and exposed with identical dose. We attribute the difference to a more efficient carbon deposition in the former case due to an increase in the presence of compounds containing carbon, which are released by the PMMA. The amorphous carbon interface can sustain very large current densities without degrading, which leads to very large spin accumulations exceeding 500 µeV at room temperature.

Graphene spintronics: Spin injection and proximity effects from first principles

“…12, we expect that a more efficient spin injection using Ni would be readily available, without relying on conventional tunnel barriers. There are already experimental demonstrations of a robust spin injection inserting either a layer of amorphous C atoms or a layer of a fluorinated Gr in F/Gr junctions [19,20].…”

“…In such structures graphene can provide effective spin filtering [7] or replace a tunnel barrier, having an advantage of low resistance and a small number of defects [8][9][10]. F/Gr junctions display magnetic proximity effects [11][12][13][14][15][16] and a robust spin injection, larger than in other materials [17][18][19][20]. Both phenomena induce a magnetic moment in graphene, which in the first case already occurs spontaneously in equilibrium, while the second case represents a nonequilibrium process [21,22].…”

“…F/Gr junctions can sustain large current densities and are suitable spin injectors in a semiconductor [8,19], useful for spin lasers. Through the angular momentum transfer, the injection of spin-polarized carriers leads to a stimulated emission of circularly polarized light [28][29][30][31].…”

Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport

“…In addition, the mobility of graphene is significantly degraded by coupling to phonons or charged impurities/defects in an adjacent oxide. Consequently, significant effort has focused on exploiting other carbon-thin films and 2D materials such as h-BN or MoS 2 as a substrate, gate dielectric or tunnel barrier for graphene devices 7,8,10,18,19 . This improves operating characteristics, but significantly complicates the fabrication, and often relies on sequential mechanical exfoliation to produce a few device structures.…”

Homoepitaxial graphene tunnel barriers for spin transport

“…Most studies use oxides for a tunnel barrier, which contain defects and pinholes, non-uniformities, and offer severe difficulties in wetting the surface of the graphene consistently. 9,10 Promising new candidates to replace oxides for tunnel barriers on graphene include other 2D materials such as BN 11 or amorphous carbon films. 12 Perhaps the most promising candidate is a homoepitaxial tunnel barrier made from graphene itself, 13,14 lightly functionalized with either fluorine or hydrogen.…”