  Defects ubiquitously exist in crystal materials and usually exhibit a very
different nature than the bulk matrix, and hence, their presence can have
significant impacts on the properties of devices. Although it is well accepted
that the properties of defects are determined by their unique atomic
environments, the precise knowledge of such relationships is far from clear for
most oxides due to the complexity of defects and difficulties in
characterization. Here, we fabricate a 36.8{\deg} SrRuO3 grain boundary of
which the transport measurements show a spin-valve magnetoresistance. We
identify its atomic arrangement, including oxygen, using scanning transmission
electron microscopy and spectroscopy. Based on the as-obtained atomic
structure, the density functional theory calculations suggest that the
spin-valve magnetoresistance is because of the dramatically reduced magnetic
moments at the boundary. The ability to manipulate magnetic properties at the
nanometer scale via defect control allows new strategies to design
magnetic/electronic devices with low-dimensional magnetic order.
