Achieving deterministic field-free switching of perpendicular magnetization via the spin-orbit torque (SOT) effect is one of the central challenges in developing low-power, high-density SOT-type magnetic random-access memory (SOT-MRAM). Although all-electric control of perpendicular magnetization switching has been realized in materials with low crystal symmetry or low magnetic symmetry, achieving this goal using conventional heavy metals (e.g., $\mathrm{Ta}$)—which are compatible with large-area magnetron sputtering fabrication processes—remains critically important for practical applications. In this study, we introduce in-plane structural asymmetry into the heavy metal $\mathrm{Ta}$, which breaks the mirror symmetry of the thin-film system while preserving the perpendicular magnetic anisotropy of the ferromagnetic layer. This structural modification induces spin currents with out-of-plane polarization, enabling deterministic field-free switching of perpendicular magnetization in a $\mathrm{Pt}/\mathrm{Co}/\mathrm{Ta}$ heterostructure. Notably, the switching exhibits a pronounced directional dependence: effective magnetization reversal occurs exclusively when pulsed currents are applied along the low-symmetry axis, whereas no switching is observed along the high-symmetry axis. This discovery demonstrates that low-symmetry structural engineering can directly generate out-of-plane spin polarization by tailoring the spin polarization direction, offering an innovative solution for the practical implementation of high-density, low-power spintronic devices.

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• Magnetic anisotropy
• Magnetization switching
• Spin current
• Spin-orbit torque
• Devices for digital logic, storage & processing
• Magnetic multilayers
• Magnetization measurements
• Sample preparation