We report the modification of magnetism in a magnetic insulator ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ thin film by topological surface states (TSS) in an adjacent topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ thin film. Ferromagnetic resonance measurements show that the TSS in ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ produces a perpendicular magnetic anisotropy, results in a decrease in the gyromagnetic ratio, and enhances the damping in ${\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$. Such TSS-induced changes become more pronounced as the temperature decreases from 300 to 50 K. These results suggest a completely new approach for control of magnetism in magnetic thin films.

• Received 13 November 2019
• Revised 13 April 2020
• Accepted 5 June 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.017204