Abstract SiO2 (0.8–3.2 nm) ultrathin layers were inserted into Fe/Pt multilayers to introduce controllable defects on the interfaces between SiO2 and Fe/Pt multilayers. The insertion of SiO2 layers effectively reduced the average grain size and the size of magnetic domains. Out-of-plane coercivity of the FePt films decreased with increasing thickness of the SiO2 insert layer. Studies on the angle-dependent coercivity of Fe/Pt multilayers without and with SiO2 insert layer, the magnetization reversal behavior changed from near domain-wall motion type to close to the a Stoner–Wohlfarth type of rotation mode.