Proximity Effects Induced in Graphene by Magnetic Insulators: First-Principles Calculations on Spin Filtering and Exchange-Splitting Gaps

We report on first-principles calculations of spin-dependent properties in graphene induced by its interaction with a nearby magnetic insulator (europium oxide, EuO). The magnetic proximity effect results in spin polarization of graphene $\pi$ orbitals by up to 24%, together with a large exchange-splitting band gap of about 36 meV. The position of the Dirac cone is further shown to depend strongly on the graphene-EuO interlayer. These findings point toward the possible engineering of spin gating by the proximity effect at a relatively high temperature, which stands as a hallmark for future all-spin information processing technologies.

Figure 1

(a) side view and (b) top view of the calculated crystalline structures for graphene on top of a six bilayer EuO film. The bottom of EuO is terminated with hydrogen atoms. (c) relative energy (to the optimized structure) of graphene-EuO as a function of shifting distance (${\Delta }_{\mathrm{Z}}$) between the graphene and the substrate.

Figure 2

(a) The six sublattices of graphene on EuO represented with different colors and letters. (b) Total density of states of $p_z$ orbitals of graphene. (c), (d), (e), (f), (g), (h) Local density of states on each inequivalent atom of the supercell shown in (a). The spin polarizations in (b) to (h) are calculated by comparing the density of states between minority and majority states normalized by the total density of states at Fermi level, i.e., $p=(n^{\downarrow }-n^{\uparrow })/(n^{\downarrow }+n^{\uparrow })$.

Figure 3

Band structure of graphene on EuO. Green (blue) and black (red) represent spin up and spin down bands of EuO (graphene), respectively. Inset: zoom around the Dirac cone, the symbols correspond to DFT data while the lines correspond to the fit according to Eq. (2).

Figure 4

Band structures for graphene on EuO with graphene shifted (a) inward (compared to optimized structure) 0.5 Å, (b) outward 1.0 Å, (c) outward 2.0 Å, and (d) outward 5.0 Å, respectively.