标题： 降低CPP-GMR器件中自旋转移矩诱导磁化翻转的临界电流：$Co_2FeGa_{0.5}Ge_{0.5}$Heusler合金中低阻尼和增强的自旋散射不对称性的影响 显示英文标题

标题： Reducing critical current for spin-transfer-torque-induced magnetization reversal in CPP-GMR devices: effect of low damping and enhanced spin scattering asymmetry in $Co_2FeGa_{0.5}Ge_{0.5}$ Heusler alloy

摘要： 自旋转移矩（STT）在磁阻器件中的应用，已实现了诸如STT-磁阻随机存取存储器、自旋转移振荡器和能量辅助磁记录等关键应用。 在器件结构中，自由层（FL）的磁化方向通过来自自旋注入层（SIL）的自旋注入进行操控，操作所需的临界电流密度与FL的阻尼（$\alpha$）常数成正比，并与STT效率成反比，而STT效率取决于材料的自旋极化（$P$）。 在此，我们研究了低 $\alpha$ 和高 $P$ 的 $Co_2FeGa_{0.5}Ge_{0.5}$（CFGG）Heusler合金对垂直于平面巨磁阻器件中STT引起的磁化翻转所需操作电流的影响。 与采用传统NiFe-FL的器件相比，采用CFGG作为FL材料的器件实现了操作电流的大幅降低，这是由于CFGG具有非常低的 $\alpha$，这证明了CFGG作为FL材料的优势。 鉴于CFGG在SIL中具有高自旋极化的优点，我们分析了由CoFe和薄CFGG层组成的双层SIL的影响，重点是利用CoFe/CFGG界面处的自旋散射不对称性。 采用CoFe/CFGG-SIL的器件表现出最低的临界电流，证明了STT效率的增强。 此外，全面研究了STT效率与磁阻比之间的相关性，结果表明，在CoFe/CFGG-SIL中，器件间的STT效率分布较小。 这些发现突显了CFGG Heusler合金和CoFe/CFGG双层结构在开发高效稳定STT基自旋电子器件中的潜在价值。 显示英文摘要

摘要： Spin-transfer torque (STT) in magnetoresistance devices has enabled key applications such as STT-magnetoresistive random access memory, spin torque oscillators, and energy-assisted magnetic recording. In the device structures, where a free layer (FL) magnetization is manipulated by spin injection from a spin injection layer (SIL), the critical current density required for operation is directly proportional to the damping ($\alpha$) constant of FL and inversely proportional to the STT efficiency, which depends on the spin polarization ($P$) of the materials. Here, we investigate the effect of low $\alpha$ and high $P$ of $Co_2FeGa_{0.5}Ge_{0.5}$(CFGG) Heusler alloy on the operation current required for STT-induced magnetization reversal in current perpendicular-to-plane giant magnetoresistance devices. Devices with CFGG as a FL material achieved a large reduction in the operation current, as compared to those with conventional NiFe-FL owing to the very low $\alpha$ of CFGG, demonstrating the advantage of CFGG as a FL material. As the advantage of high spin polarization CFGG for SIL, we analyzed the effect of bilayer SIL consisting of CoFe and thin CFGG layers, focusing on utilizing the spin scattering asymmetry at the CoFe/CFGG interface. Devices with the CoFe/CFGG-SIL exhibited the lowest critical current, demonstrating enhanced STT efficiency. In addition, the correlation of STT efficiency with magnetoresistance ratio were comprehensively investigated, showing that device-to-device distribution in STT-efficiency was smaller in CoFe/CFGG-SIL. These findings highlight the potential of CFGG Heusler alloy and CoFe/CFGG bilayer structures as key components for the development of efficient and stable STT-based spintronic devices.