纵向自旋电流密度梯度对垂直磁化自旋轨道矩翻转的影响

中文摘要 AI 辅助

纵向自旋电流梯度（例如，由于厚度、成分或宽度的梯度）能否替代法向金属/铁磁异质结构中具有垂直磁各向异性的确定性自旋轨道矩翻转所需的纵向磁场，一直是一个关键未解问题。在此，我们报告了稳健的微磁学和实验证据，表明任何实际的纵向自旋电流密度梯度都不能有效替代纵向磁场来实现垂直磁各向异性器件的确定性翻转。相反，纵向自旋电流密度只能修改磁畴的成核和脉冲时序敏感的振荡，从而影响皮秒尺度的条状非确定性翻转窗口。当考虑与自旋电流脉冲相关的横向有效场（奥斯特场和类场力矩之和）时，同样的结论依然稳健成立。这种非确定性翻转在存在有限的器件间差异、写电流脉冲漂移以及器件参数热波动的情况下阻碍了应用。我们还通过实验表明，与纵向自旋电流密度梯度相比，垂直自旋在垂直自旋力矩器件的确定性翻转中更为有效。

英文摘要

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.

发表机构

• State Key Laboratory of Semiconductor Physics and Chip Technologies, Institute of Semiconductors, Chinese Academy of Sciences（中国科学院半导体研究所半导体物理与芯片技术国家重点实验室）
• Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences（中国科学院大学材料科学与光电技术研究中心）

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