  The groundbreaking works in graphene and graphene nanoribbons (GNRs) over the
past decade, and the recent discovery of borophene draw immediate attention to
the underexplored borophene nanoribbons (BNRs). We herein report a density
functional theory (DFT) study of the geometric, electronic and magnetic
properties of BNRs as a function of orientation (denoted as BxNRs and ByNRs
with the orientation along x- and y-axis, respectively), ribbon width (Nx, Ny =
4 to 15), and hydrogenation effects. We found that the anisotropic quasi-planar
geometric structure of BNRand its edge states profoundly govern the electronic
and magnetic properties. Pristine ByNRs adopt a magnetic ground state,
anti-ferromagnetic (AFM) or ferromagnetic (FM) depending on the ribbon width,
while pristine BxNRs are non-magnetic (NM). Upon hydrogenation, all BNRs become
NM. Interestingly, both pristine and hydrogenated ByNRs undergo a
metal-semiconductor-metal transition at Ny = 7, while BxNRs remain metallic.
