  We study spin configurations of classical magnetic impurities placed close to
the edge of a two-dimensional topological superconductor both analytically and
numerically. First, we demonstrate that the spin of a single magnetic impurity
close to the edge of a topological superconductor tends to align along the
edge. The strong easy-axis spin anisotropy behind this effect originates from
the interaction between the impurity and the gapless helical Majorana edge
states. We then compute the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction
between two magnetic impurities placed close to the edge. We show that, in the
limit of large interimpurity distances, the RKKY interaction between the two
impurities is mainly mediated by the Majorana edge states and leads to a
ferromagnetic alignment of both spins along the edge. This effect could be used
to detect helical Majorana edge states.
