Understanding the Giant Enhancement of Exchange Interaction in Bi2Se3−EuS Heterostructures

A recent experiment indicated that a ferromagnetic EuS film in contact with a topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ might show a largely enhanced Curie temperature and perpendicular magnetic anisotropy [F. Katmis et al., Nature (London) 533, 513 (2016).]. Through systematic density functional calculations, we demonstrate that in addition to the factor that ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ has a strong spin orbit coupling, the topological surface states are crucial to make these unusual behaviors robust as they hybridize with EuS states and extend rather far into the magnetic layers. The magnetic moments of Eu atoms are nevertheless not much enhanced, unlike what was…