Spin–orbit torques (SOT) allow ultrafast, energy-efficient toggling of magnetization state by an in-plane charge current for applications such as magnetic random-access memory (SOT-MRAM). Tailoring the SOT vector comprising of antidamping (T_AD) and fieldlike (T_FL) torques could lead to faster, more reliable, and low-power SOT-MRAM. Here, we establish a method to quantify the longitudinal (T_AD) and transverse (T_FL) components of the SOT vector and its efficiency χ_AD and χ_FL, respectively, in nanoscale three-terminal SOT magnetic tunnel junctions (SOT-MTJ). Modulation of nucleation or switching field (B_SF) for magnetization reversal by SOT effective fields (B_SOT) leads to the modification of SOT-MTJ hysteresis loop behavior from which χ_AD and χ_FL are quantified. Surprisingly, in nanoscale W/CoFeB SOT-MTJ, we find χ_FL to be (i) twice as large as χ_AD and (ii) 6 times as large as χ_FL in micrometer-sized W/CoFeB Hall-bar devices. Our quantification is supported by micromagnetic and macrospin simulations which reproduce experimental SOT-MTJ Stoner–Wohlfarth astroid behavior only for χ_FL > χ_AD. Additionally, from the threshold current for current-induced magnetization switching with a transverse magnetic field, we show that in SOT-MTJ, T_FL plays a more prominent role in magnetization dynamics than T_AD. Due to SOT-MRAM geometry and nanodimensionality, the potential role of nonlocal spin Hall spin current accumulated adjacent to the SOT-MTJ in the mediation of T_FL and χ_FL amplification merits to be explored.

中文翻译：

---

纳米级磁隧道结中的自旋轨道扭矩矢量量化


自旋轨道扭矩 (SOT) 允许通过面内充电电流超快、节能地切换磁化状态，适用于磁性随机存取存储器 (SOT-MRAM) 等应用。定制由抗阻尼 (T _AD ) 和场状 (T _FL ) 扭矩组成的 SOT 矢量可以带来更快、更可靠和低功耗的 SOT-MRAM。在这里，我们建立了一种量化 SOT 向量的纵向 (T _AD ) 和横向 (T _FL ) 分量及其效率 χ _AD 和 χ 的方法 _FL 分别在纳米级三端 SOT 磁隧道结 (SOT-MTJ) 中。通过 SOT 有效场 (B _SOT ) 调制成核或切换场 (B _SF ) 以实现磁化反转，从而改变 SOT-MTJ 磁滞回线行为，其中 χ _AD 和 χ _FL 被量化。令人惊讶的是，在纳米级 W/CoFeB SOT-MTJ 中，我们发现 χ _FL (i) 是 χ _AD 的两倍，(ii) 是 χ _FL 微米级 W/CoFeB 霍尔棒器件。我们的量化得到了微磁和宏观自旋模拟的支持，这些模拟仅再现了 χ _FL > χ _AD 的实验性 SOT-MTJ Stoner–Wohlfarth 小行星行为。此外，从横向磁场下电流感应磁化开关的阈值电流来看，我们表明在 SOT-MTJ 中，T _FL 在磁化动力学中比 T _AD .由于 SOT-MRAM 的几何结构和纳米尺寸，SOT-MTJ 附近积累的非局域自旋霍尔自旋电流在 T _FL 和 χ _FL 放大调节中的潜在作用值得表示为探索过。