Yang T, Hirohata A, Kimura T, Otani Y
Frontier Research System, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
J Nanosci Nanotechnol. 2007 Jan;7(1):259-64.
Because of the capability to switch the magnetization of a nanoscale magnet, the spin transfer effect is critical for the application of magnetic random access memory. For this purpose, it is important to enhance the spin current carried by the charge current. Calculations based on the diffusive spin-dependent transport equations reveal that the magnitude of spin current can be tuned by modifying the ferromagnetic layer and the spin relaxation process in the device. Increasing the ferromagnetic layer thickness is found to enhance both the spin current and the spin accumulation. On the other hand, a strong spin relaxation in the capping layer also increases the spin current but suppresses the spin accumulation. To demonstrate the theoretical results, nanopillar structures with the size of approximately 100 nm are fabricated and the current-induced magnetization switching behaviors are experimentally studied. When the ferromagnetic layer thickness is increased from 3 nm to 20 nm, the critical switching current for the current-induced magnetization switching is significantly reduced, indicating the enhancement of the spin current. When the Au capping layer with a short spin-diffusion length replaces the Cu capping layer with a long spin-diffusion length, the reduction of the critical switching current is also observed.
由于能够切换纳米级磁体的磁化，自旋转移效应对于磁性随机存取存储器的应用至关重要。为此，增强由电荷电流携带的自旋电流很重要。基于扩散自旋相关输运方程的计算表明，自旋电流的大小可以通过修改铁磁层和器件中的自旋弛豫过程来调节。发现增加铁磁层厚度会增强自旋电流和自旋积累。另一方面，覆盖层中的强自旋弛豫也会增加自旋电流，但会抑制自旋积累。为了证明理论结果，制备了尺寸约为100nm的纳米柱结构，并对电流诱导的磁化翻转行为进行了实验研究。当铁磁层厚度从3nm增加到20nm时，电流诱导磁化翻转的临界开关电流显著降低，表明自旋电流增强。当具有短自旋扩散长度的金覆盖层取代具有长自旋扩散长度的铜覆盖层时，也观察到临界开关电流的降低。
