The ability to control the electronic and magnetic functional properties of materials by tuning chemical and structural interactions at atomically abrupt interfaces is a powerful

tool for stabilizing novel magnetic and electronic states. Competing structural and magnetic interactions at coherent interfaces between atomically thin complex oxides can lead to magnetic properties not found in bulk. Here, we show that the magnetic anisotropy is reversed from out-of-plane to in-plane in SrRuO₃/ N unit cell LaNiO₃ superlattices compressively strained to (001)-SrTiO₃ when the LaNiO₃ thickness, N, increases from 2 unit cells to 4 unit cells. Using synchrotron X-ray scattering and first-principles theory, we show that the coupling of the oxygen octahedra at the  SrRuO₃-LaNiO₃ interface induces a structural transition in the SrRuO₃ layer, which results in the changes to the magnetocrystalline anisotropy.