Multiferroic materials are strong candidates for reducing the energy consumption of voltage-controlled spintronic devices because of the coexistence of ferroelectric (FE) and magnetic orders in a single phase. In this article, we present a new multiferroic perovskite, GdNi x Fe 1−x O 3 (GFNO), produced via sputtering on a SrTiO 3 substrate. The proposed GFNO is FE and canted antiferromagnetic (AFM) within a monoclinic framework at room temperature. The FE polarization of the GFNO is up to 37 μC/cm 2 . When capped with a Co layer, the resulting heterostructure exhibits voltage-controlled magnetism (VCM). The heterostructured device exhibits two distinct features. First, its VCM depends on the magnitude as well as the polarity of the applied bias, thereby doubling the number of available magnetic readout states under a fixed voltage. Furthermore, the magnetic order of the device can be controlled very effectively within ±1 V. These two characteristics satisfy the requirements for low-power and highstorage technology. Theoretical analysis and experimental results indicate the importance of Ni dopant in regulating the polarity-dependent multiferroicity of this gadolinium ferrite system.