Effects of GaAs Buffer Layer on Structural, Magnetic, and Transport Properties of Magnetic Topological Insulators Cr_<i>y</i>(Bi_<i>x</i>Sb_1−<i>x</i>)_2−<i>y</i>Te₃ and V_<i>y</i>(Bi<sub><

Herein, the effects of a GaAs buffer layer on the structural, magnetic, and transport properties of Cr y (Bi x Sb 1− x ) 2− y Te 3 magnetic topological insulator (MTI) thin films are studied and compared with those of V y (Bi x Sb 1− x ) 2− y Te 3 , which are recently reported. Similar to the case of V y (Bi x Sb 1− x ) 2− y Te 3 , growth on a GaAs buffer layer leads to some distinctly different properties than direct growth on InP substrates. These include improved interface quality confirmed by transmission electron microscopy, enhanced magnetic coercive fields, and smaller resistivity peaks at the magnetization reversals. Furthermore, the Bi‐ratio dependence of the carrier density reveals that the interface property also affects the Fermi level. These results demonstrate the importance of the buffer layer in controlling the electronic properties of the MTI films.