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 2-terminal and 3-terminal device geometries. In 2-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 3-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.
On the Temperature-dependent Characteristics of Perpendicular Shape Anisotropy-Spin Transfer Torque-Magnetic Random Access Memories (PSA-STT-MRAMs)
垂直形状各向异性-自旋转移矩-磁性随机存取存储器（PSASTT-MRAM）利用纳米柱自由层几何形状来确保来自纳米磁体的形状各向异性的良好热稳定因子。这种概念特别适合于小到几纳米的小结。在这样的体积尺寸下，纳米柱可以被有效地建模为斯通-沃尔法斯（SW）颗粒，形状各向异性与自发磁化强度的比例为~ Ms ^[2]。对于几乎所有的铁磁体，Ms是温度的强函数，因此，温度相关的形状各向异性是PSA-STT-MRAM的温度相关性能的任何建模中要考虑的重要因素。在这项工作中，我们总结和讨论各种可能的温度依赖性的贡献的PSA-STT-MRAM的热稳定性因子和介电常数的建模和比较不同的温度标度和参数。我们揭示了非平凡的修正的热稳定性因子，同时考虑温度相关的形状和界面各向异性。结合这样的温度依赖性的介电性，阻断温度，和电气开关特性，导致也进行了讨论，在共轭与纳米磁体的尺寸和相干体积。
Electrical detection of magnetization reversal without auxiliary magnets
基于各向异性磁阻的第一代磁性随机存取存储器需要磁场来进行写入和读取。现代的全电读/写存储器使用非相对论自旋输运将存储磁性层与参考铁磁体连接。最近的研究集中在不需要参考铁磁体的相对论自旋力矩对磁矩的电操纵上。在这里，我们报告的观测对应的磁阻效应，在这样一个相对论系统，使我们能够电气检测的符号磁化没有辅助磁场或铁磁体。我们观察到的效果在一个几何形状中，其中的单轴（Ga，Mn）As外延层的磁化设置为平行或反平行的电流诱导的非平衡自旋极化的载流子。在我们的结构中，当电流密度为$10^6$ A cm $^{-2}$时，线性电流磁电阻达到0.2%.
DSTT-MRAM: Differential Spin Hall MRAM for On-chip Memories
提出了一种新的基于自旋转移矩的磁随机存储器器件结构。我们的器件结构利用自旋霍尔效应来创建差分存储器单元，该差分存储器单元表现出快速且节能的写入操作。此外，由于固有的差分器件结构，可以执行快速和可靠的读取操作。我们的模拟研究显示，与标准1 T1 R STT-MRAM存储单元相比，写入能量提高了10倍，与单端感测（如标准1 T1 R STT-MRAM）相比，读取操作快了1.6倍。位单元特性对于高性能片上存储器应用是有希望的。
