  Artificial perovskite-oxide nanostructures possess intriguing magnetic
properties due to their tailorable electron-electron interactions, which are
extremely sensitive to the oxygen coordination environment. To date,
perovskite-oxide nanodots with sizes below 50 nm have rarely been reported.
Furthermore, the oxygen octahedral distortion and its relation to magnetic
properties in perovskite oxide nanodots remain unexplored yet. Here, we have
studied the magnetic anisotropy in patterned SrRuO3 (SRO) nanodots as small as
30 nm while performing atomic-resolution electron microscopy and spectroscopy
to directly visualize the constituent elements, in particular oxygen ions. We
observe that the magnetic anisotropy and RuO6 octahedra distortion in SRO
nanodots are both nanodots' size-dependent but remain unchanged in the first
3-unit-cell interfacial SRO monolayers regardless of the dots' size. Combined
with the first principle calculations, we unravel a unique structural mechanism
behind the nanodots' size-dependent magnetic anisotropy in SRO nanodots,
sugguesting that the competition between lattice anisotropy and oxygen
octahedral rotation mediates anisotropic exchange interactions in SRO nanodots.
These findings demonstrate a new avenue towards tuning magnetic properties of
correlated perovskite oxides and imply that patterned nanodots could be a
promising playground for engineering emergent functional behaviors.
