A controlled shunting of polycrystalline oxide thin films on the nanometer length scale opens the door to significantly modify their transport properties. In this paper, the low energy Ar⁺ irradiation induced shunting effect of forming-free, non-volatile resistive switching in polycrystalline BiFeO ₃ thin film capacitor-like structures with macroscopic bottom and top contacts was investigated. Oxygen atoms at the BiFeO₃ surface are preferentially sputtered by Ar⁺ ion irradiation and oxygen vacancies and a metallic Bi phase are formed at the surface of the BiFeO₃ thin film before deposition of the top contacts. A phenomenological model is that of nanoscale shunt resistors formed in parallel to the actual BiFeO₃ thin film capacitor-like structure. This model fits the noticeable increase of the retention stability and current density after irradiation. The formation of stable and conductive shunts is further evidenced by conductive atomic force microscopy measurements.