Magnetic proximity effect of a topological insulator and a ferromagnet in thin-film bilayers of Bi0.5Sb1.5Te3 and SrRuO3

Magnetic proximity effect of a topological insulator in contact with a ferromagnet is reported in thin-film bilayers of 15-nm-thick ${\mathrm{Bi}}_0.5{\mathrm{Sb}}_1.5{\mathrm{Te}}₃$ on either 15- or 40-nm-thick ${\mathrm{SrRuO}}₃$ on (100) ${\mathrm{SrTiO}}₃$ wafers. ${\mathrm{SrRuO}}₃$ is an itinerant ferromagnet which has long been considered weak, thus any observation of a significant magnetic proximity effect in the present system should help elucidate the mechanism of this magnetism and might be utilized in device applications. Magnetotransport results of the bilayers were compared with those of reference films of 15-nm ${\mathrm{Bi}}_0.5{\mathrm{Sb}}_1.5{\mathrm{Te}}₃$ and 15- or 40-nm ${\mathrm{SrRuO}}₃$. Comparison of the temperature coefficient of resistance $[(1/R)\ifmmode\times\else\texttimes\fi{}dR/dT$, which is qualitatively proportional to the magnetization] of the bilayer and reference ferromagnetic film normalized above ${T}_c$ shows a clear suppression in the bilayer by about 50% just below ${T}_c$, indicating a weaker proximity magnetization in the bilayer. Resistance hysteresis loops versus field at $1.85\ifmmode\pm\else\textpm\fi{}0.05$ K in the bilayer and reference films show a clear magnetic proximity effect, where the peak resistance of the bilayer at the coercive field shifts to lower fields by $\ensuremath{\sim}30%$ compared to a hypothetical bilayer of two resistors connected in parallel with no interaction between the layers. Narrowing of the coercive peaks of the bilayers as compared to those of the reference ferromagnetic films by 25--35% was also observed, which represents another signature of the magnetic proximity effect.