High efficiency spin-valve and spin-filter in a doped rhombic graphene quantum dot device

•Spin valve effect in rhombic graphene quantum dot controlled by B/N doping.•The B/N doping gives rise the semiconductor-to-metal transition in rGQD leading to high spin-filter efficiency.•Spin injection in AGNR electrodes from rhombic graphene quantum dot. Spin-polarized transport through a rhombic graphene quantum dot (rGQD) attached to armchair graphene nanoribbon (AGNR) electrodes is investigated by means of the Green’s function technique combined with single-band tight-binding (TB) approach including a Hubbard-like term. The Hubbard repulsion was included within the mean-field approximation. Compared to anti-ferromagnetic (AFM), we show that the ferromagnetic (FM) ordering of the rGQD corresponds to a smaller bandgap, thus resulting in an efficient spin injector. As a consequence, the electron transport spectrum reveals a spin valve effect, which is controlled by doping with B/N atoms creating a p-n-type junction. The calculations point out that such systems can be used as spin-filter devices with efficiency close to a 100%.