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arXiv · 2609.36489

Effects of Longitudinal Spin Current Density Gradient on Spin-Orbit Torque Switching of Perpendicular Magnetization

Guowen Gong·Qianbiao Liu·Lijun Zhu
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Abstract

It has remained a critical open question as to whether a longitudinal spin current gradient (e.g., due to a gradient in the thickness, composition, or width) can replace the longitudinal magnetic field required for deterministic spin-orbit torque switching of normal metal/ferromagnet heterostructures with perpendicular magnetic anisotropy. Here, we report robust micromagnetic and experimental evidence that any realistic longitudinal spin-current density gradient cannot be an effective replacement for a longitudinal magnetic field to enable deterministic switching of a perpendicular magnetic anisotropy device. Instead, the longitudinal spin current density can only modify the nucleation and pulse-timing-sensitive oscillations of magnetic domains and thus the picosecond-scale strip-like indeterministic switching windows. The same conclusions hold robustly when the transverse effective field associated with the spin-current pulse (the sum of the Oersted field and field-like torque) is taken into account. The indeterministic switching prevents applications in the presence of finite device-to-device variations and drifts in write current pulse and thermal fluctuations of device parameters. We also experimentally show that, instead of a longitudinal spin current density gradient, perpendicular spins are much more effective in deterministic switching of perpendicular spin torque devices.

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Guowen Gong, Qianbiao Liu, Lijun Zhu. 2026-09-29. Effects of Longitudinal Spin Current Density Gradient on Spin-Orbit Torque Switching of Perpendicular Magnetization. https://arxiv.org/abs/2609.36489

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