  This letter reports the modification of magnetism in a magnetic insulator
Y3Fe5O12 thin film by topological surface states (TSS) in an adjacent
topological insulator Bi2Se3 thin film. Ferromagnetic resonance measurements
show that the TSS in Bi2Se3 produces a perpendicular magnetic anisotropy,
results in a decrease in the gyromagnetic ratio, and enhances the damping in
Y3Fe5O12. Such TSS-induced changes become more pronounced as the temperature
decreases from 300 K to 50 K. These results suggest a completely new approach
for control of magnetism in magnetic thin films.
