Two-dimensional (2D) materials show great promise for building next-generation memristors. However, their application in self-rectifying memristors (SRMs)—crucial for suppressing sneak-path currents in high-density arrays—is still underexplored. In this work, we address this gap by developing ultrathin non-layered Co₃O₄ nanosheets through a vapor-phase growth strategy and precisely engineering their oxygen vacancies (O_V) for high-performance SRMs. Our synergistic approach, combining salt-assisted vapor–liquid–solid, hydrate-assisted, and spatial confinement methods, enables the controlled synthesis of high-quality Co₃O₄ nanosheets as thin as 0.46 nm with a single-atomic-layer thickness. We demonstrate that magnetically driven rapid thermal annealing (MD-RTA) effectively increases the O_V concentration from 15.15% to 33.15%, as quantitatively confirmed by X-ray photoelectron spectroscopy (XPS), Raman, and Kelvin probe force microscopy (KPFM). The resulting memristor exhibits excellent self-rectifying resistive switching behavior, with a high rectification ratio exceeding 10⁴ and a large ON/OFF ratio over 10⁴. The device also achieves high switching uniformity (coefficient of variation, C_v = 0.0979), stable cycling endurance over 100 direction current (DC) cycles, and room-temperature operation. This study provides a reliable synthesis route for 2D non-layered materials and highlights defect engineering as an effective strategy for developing advanced in-memory computing devices with inherent crosstalk immunity.