  We demonstrate that zero-energy Majorana bound state, in the ferromagnetic
insulator (FI)-superconductor (SC) junction formed on the edge of
two-dimensional topological insulator, exhibits three types of spin-triplet
pairing correlations and its spin polarization direction is position
independent in ferromagnetic insulator. When an electron is injected with a
spin (anti-)parallel to this direction, equal-spin Andreev reflection exhibits
the widest (narrowest) resonance peak. Similar behaviour is found when the
coupling between two Majorana bound states in a FI-SC-FI junction is invoked,
though an additional weak spin-singlet pairing correlation is generated. These
signatures can readily facilitate the experimental detection of spin-triplet
correlations and spin polarization of Majorana bound states.

Mesoscale and Nanoscale Physics