However, with the exception of methods combining more than one source of torque, these schemes all rely on breaking the static in-plane symmetry in the device. To date, these have included in-plane exchange bias fields 14, 15, 16, interlayer exchange coupling 17, 18, in-plane structural, composition, or interfacial oxidation asymmetry 19, 20, 21, 22, 23, 24, 25, and combining multiple competing sources of spin torque in one device 26, 27, 28. Thus, mechanisms to break the in-plane (structural or magnetic) symmetry, instead of H ex, are being investigated to realize practical SOT memory devices 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28. The requirement of external H ex in switching, however, hinders the integration of SOT devices on semiconductor chips. SOTs originating from the spin Hall effect (SHE) in the NM (e.g., heavy metals 2, 10 or topological insulators 11, 12) or from the Rashba effect 1, 13 at the NM/FM interface can drive the adjacent magnetization to switch, while H ex breaks the in-plane inversion symmetry and leads to a deterministic switching direction for a particular direction of the in-plane current. Typically, for memory applications where information is encoded in the direction of the magnetization in magnets with perpendicular magnetic anisotropy (PMA), SOT switching is realized in a non-magnet/ferromagnet (NM/FM) or NM/FIM heterostructure with the assistance of an external in-plane magnetic field H ex along the current direction 1, 2, 10, 11, 12. Hence, FIMs are promising as near-term candidates for practical high-performance SOT devices. They can also utilize the relatively straightforward electrical readout methods available in ferromagnetic material systems (due to their non-zero magnetization) 7, 8, 9. FIMs exhibit the exchange-dominated high-frequency (sub-terahertz) dynamics of antiferromagnets, which can result in high switching speed 5, 6, 7, while avoiding the difficulties of controlling domain size commonly encountered in antiferromagnets 4. SOT switching of ferrimagnetic (FIM) materials, in particular, is of great current interest 5, 6, 7, 8, 9. Spin-orbit torque (SOT) is a leading contender as a fast and low-power method to manipulate magnetic order in spintronic devices, particularly for artificial intelligence and high-performance computing applications where high-speed on-chip memory is required 1, 2, 3, 4. This bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI provides a strategy for efficient and compact SOT device design. Micromagnetic simulations are in agreement with experimental results, and elucidate the role of g-DMI in the deterministic switching processes. The vertical structural inversion asymmetry induces strong intrinsic SOTs and a gradient-driven Dzyaloshinskii–Moriya interaction (g-DMI), which breaks the in-plane symmetry during the switching process. Here, we report bias-field-free SOT switching in a single perpendicular CoTb layer with an engineered vertical composition gradient. Existing methods to do so involve the application of an in-plane bias magnetic field, or incorporation of in-plane structural asymmetry in the device, both of which can be difficult to implement in practical applications. To be deterministic, however, switching of perpendicularly magnetized materials by SOT requires a mechanism for in-plane symmetry breaking. Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices.