  Effects of an open surface on a magnetic Chern insulator are investigated in
comparison with those of an interface to a capping magnetic layer. In magnets,
an open surface often perturbs the magnetic order by a reconstruction of the
magnetic moment directions near the surface. On the other hand, in topological
insulators, it leads to the formation of topologically protected surface
states. These two contrasting effects may coexist in magnetic Chern insulators,
which give rise to nontrivial surface reconstruction. For instance, the chiral
edge current is largely enhanced by the edge reconstruction in a
two-dimensional magnetic Chern insulator realized in a quarter-filled Kondo
lattice model on a triangular lattice. We here show that the edge
reconstruction can be described semiquantitatively by a simple junction model
between the bulk topological magnetic state and a ferromagnetic capping layer.
We further clarify how the chiral edge current is affected by the magnetic
structure in the capping layer. Our results indicate that the topological edge
state can be controlled magnetically through the junctions.
