Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.
Department of Physics, University of Ulsan, Ulsan, 44610, Korea.
Adv Sci (Weinh). 2023 Apr;10(12):e2206800. doi: 10.1002/advs.202206800. Epub 2023 Feb 19.
Spin current, converted from charge current via spin Hall or Rashba effects, can transfer its angular momentum to local moments in a ferromagnetic layer. In this regard, the high charge-to-spin conversion efficiency is required for magnetization manipulation for developing future memory or logic devices including magnetic random-access memory. Here, the bulk Rashba-type charge-to-spin conversion is demonstrated in an artificial superlattice without centrosymmetry. The charge-to-spin conversion in [Pt/Co/W] superlattice with sub-nm scale thickness shows strong W thickness dependence. When the W thickness becomes 0.6 nm, the observed field-like torque efficiency is about 0.6, which is an order larger than other metallic heterostructures. First-principles calculation suggests that such large field-like torque arises from bulk-type Rashba effect due to the vertically broken inversion symmetry inherent from W layers. The result implies that the spin splitting in a band of such an ABC-type artificial SL can be an additional degree of freedom for the large charge-to-spin conversion.
自旋电流可以通过自旋霍尔或拉什巴效应将其角动量转换为铁磁层中的局域磁矩。在这方面，为了发展包括磁随机存取存储器在内的未来存储或逻辑器件，需要对磁化进行操控，这就要求有较高的电荷到自旋转换效率。在这里，在没有中心对称的人工超晶格中演示了体 Rashba 型电荷到自旋转换。在具有亚纳米级厚度的[Pt/Co/W]超晶格中，电荷到自旋的转换强烈依赖于 W 的厚度。当 W 厚度变为 0.6nm 时，观察到的场型转矩效率约为 0.6，比其他金属异质结构大一个数量级。第一性原理计算表明，由于 W 层固有的垂直破缺的反转对称性，这种大的场型转矩源于体 Rashba 效应。该结果表明，这种 ABC 型人工 SL 中能带的自旋劈裂可以为大的电荷到自旋转换提供额外的自由度。
