π -magnetism and spin-dependent transport in boron pair doped armchair graphene nanoribbons

Carbon-based magnetic nanostructures have long spin coherent length and are promising for spintronics applications in data storage and information processing. Recent experiments demonstrate that a pair of substitutional boron atoms (B2) doped 7-atom-wide armchair graphene nanoribbons (B2-7AGNRs) have intrinsic magnetism, providing a quasi-1D magnetic material platform for spintronics. In this work, we demonstrate that the magnetism in B2-7AGNRs is contributed by π-electrons, originating from the imbalance of electrons in two spin channels in response to boron dopants. The spin-dependent transport across single and double boron pair doped 7AGNRs (B2-7AGNRs and 2B2-7AGNRs) by constructing lateral graphene nanoribbon heterojunctions has been investigated by using first-principles calculations. We show that for B2-7AGNRs with spin splitting π-electronic states near the Fermi level, by applying a bias voltage, one can obtain a current spin polarization over 90% and a negative differential resistance effect. For 2B2-7AGNRs, two spin centers have been found to be antiferromagnetically coupled. We demonstrate a magnetoresistance effect over 15 000% by setting those two spin centers to be ferromagnetic and antiferromagnetic alignments. Based on the above spin-polarized transport properties, we reveal that GNR heterojunctions based on B2-7AGNRs could be potentially applied in quasi-1D spintronic devices.