Spin currents are used to write information in magnetic random access memory (MRAM) devices by switching the magnetization direction of one of the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) nanopillar. Different physical mechanisms of conversion of charge current to spin current can be used in two-terminal and three-terminal device geometries. In two-terminal devices, charge-to-spin conversion occurs by spin filtering in the MTJ's ferromagnetic electrodes and present day MRAM devices operate near the theoretically expected maximum charge-to-spin conversion efficiency. In three-terminal devices, spin–orbit interactions in a channel material can also be used to generate large spin currents. In this Perspective article, we discuss charge-to-spin conversion processes that can satisfy the requirements of MRAM technology. We emphasize the need to develop channel materials with larger charge-to-spin conversion efficiency—that can equal or exceed that produced by spin filtering—and spin currents with a spin polarization component perpendicular to the channel interface. This would enable high-performance devices based on sub-20 nm diameter perpendicularly magnetized MTJ nanopillars without need of a symmetry breaking field. We also discuss MRAM characteristics essential for CMOS integration. Finally, we identify critical research needs for charge-to-spin conversion measurements and metrics that can be used to optimize device channel materials and interface properties prior to full MTJ nanopillar device fabrication and characterization.

中文翻译：

---

磁性随机存取存储器自旋电流发电的展望

通过切换磁隧道结 (MTJ) 纳米柱的铁磁电极之一的磁化方向，自旋电流用于在磁随机存取存储器 (MRAM) 设备中写入信息。将电荷电流转换为自旋电流的不同物理机制可用于两端和三端器件几何形状。在两端设备中，电荷到自旋的转换是通过 MTJ 的铁磁电极中的自旋过滤发生的，目前的 MRAM 设备在接近理论上预期的最大电荷到自旋转换效率的情况下运行。在三端器件中，通道材料中的自旋轨道相互作用也可用于产生大的自旋电流。在这篇 Perspective 文章中，我们讨论了可以满足 MRAM 技术要求的电荷到自旋转换过程。我们强调需要开发具有更高电荷自旋转换效率的通道材料——可以等于或超过自旋过滤产生的效率——以及具有垂直于通道界面的自旋极化分量的自旋电流。这将使基于直径小于 20 nm 的垂直磁化 MTJ 纳米柱的高性能设备成为可能，而无需对称破断场。我们还讨论了 CMOS 集成所必需的 MRAM 特性。最后，我们确定了电荷到自旋转换测量和指标的关键研究需求，可用于在完整的 MTJ 纳米柱器件制造和表征之前优化器件通道材料和界面特性。