Proximity effects in graphene and ferromagnetic CrBr3 van der Waals heterostructures.

Herein, we report first-principles calculations for the magnetic proximity effect in a van der Waals heterostructure formed by a graphene monolayer, induced by its interaction with a two-dimensional (2D) ferromagnet (chromium tribromide, CrBr3). We observed that the magnetic proximity effect arising from the spin-dependent interlayer coupling depends on the interlayer electronic configuration. The proximity effect results in the spin polarization of the graphene orbital by up to 63.6%, together with a miniband splitting of about 73.4 meV, and 8% enhancement in the magnetic moment (3.47 µB per cell) in the heterostructure. The position of the Fermi level in the Dirac cone is shown to depend strongly on the graphene-CrBr3 interlayer separation of 3.77 Å. Consequently, we also show that a perpendicular electric field can be used to control the miniband spin splitting and transmission spectrum. Also, the interfacial polarization effect due to the existence of two different constituents reinforces the conductivity via electrostatic screening in the heterolayer. These findings point towards the application potential of this unique system in nanoscale devices, where the electric field-driven magnetic proximity effect can lead to spin controllability and possible engineering of spin gating.

Ion transport mechanisms in pectin-containing EC-LiTFSI electrolytes.

Using all-atom molecular dynamics simulations, we report the structure and ion transport characteristics of a new class of solid polymer electrolytes that contain the biodegradable and mechanically stable biopolymer pectin. We used highly conducting ethylene carbonate (EC) as a solvent for simulating lithium-trifluoromethanesulfonimide (LiTFSI) salt containing different weight percentages of pectin. Our simulations reveal that the pectin chains reduce the coordination number of lithium ions around their counterions (and vice versa) because of stronger lithium-pectin interactions compared to lithium-TFSI interactions. Furthermore, the pectin is found to promote smaller ionic aggregates over larger ones, in contrast to the results typically reported for liquid and polymer electrolytes. We observed that the loading of pectin in EC-LiTFSI electrolytes increases their viscosity (η) and relaxation timescales (τc), indicating higher mechanical stability, and, consequently, a decrease of the mean squared displacement, diffusion coefficient (D), and Nernst-Einstein conductivity (σNE). Interestingly, while the lithium diffusivities are related to the ion-pair relaxation timescales as D+ ∼ τc-3.1, the TFSI- diffusivities exhibit excellent correlations with ion-pair relaxation timescales as D- ∼ τc-0.95. On the other hand, the NE conductivities are dictated by distinct transport mechanisms and scales with ion-pair relaxation timescales as σNE ∼ τc-1.85.