AI 中文总结
本研究利用Cr本征氧化物，将NiFe/Cr双层膜转化为自包含双轨道电流源，开发漂移-扩散模型揭示Cr-CrOₓ界面的轨道电流增强效应，实现高效无场磁化翻转，确立本征氧化为可扩展的轨道力矩器件制备策略。
AI 中文摘要
轨道电流可实现超出传统重金属自旋霍尔源效率极限的电荷-自旋转换，但此前利用轨道电流要么需要厚的轨道霍尔材料，要么需要额外的重金属转换层。本研究表明，通常被视为寄生效应的铬本征氧化物，可将简单的NiFe/Cr双层膜转变为无需任何转换层的自包含双轨道电流源。第一性原理计算预测，在Cr(3d)-O(2p)杂化驱动下，表面氧化可使轨道霍尔电导率提升近三倍。实验上，自然氧化的NiFe/Cr异质结构展现出3.9×10⁶ Ω⁻¹ m⁻¹的类阻尼力矩效率，分别比Pt、Ta高出1个、2个数量级；该力矩呈现非单调的Cr厚度依赖关系，无法用传统模型解释。本研究开发了含氧化门控界面源的漂移-扩散模型，定量复现了实验数据，揭示Cr-CrOₓ界面产生的轨道电流比体相轨道霍尔通道强一个数量级，轨道输运长度约为4 nm。增强的力矩可在1.58×10¹¹ A m⁻²下实现无场磁化翻转，性能优于重金属及CuOₓ基准。这些结果确立了本征氧化是实现高效轨道力矩器件的可扩展策略。
英文摘要
Orbital currents offer charge-to-spin conversion beyond the efficiency limit of conventional heavy-metal Spin Hall sources. However, harnessing them has so far required either thick orbital-Hall materials or additional heavy-metal conversion layers. Here, we show that the native oxide of chromium, typically regarded as parasitic, transforms a simple NiFe\Cr bilayer into a self-contained dual-channel orbital-current source without the need for any conversion layer. First-principles calculations predict a nearly threefold enhancement of the orbital Hall conductivity upon surface oxygenation, driven by Cr(3d)-O(2p) hybridization. Experimentally, naturally oxidized NiFe\Cr heterostructures exhibit a giant damping-like torque efficiency of $3.9 \times 10^{6}$ $Ω^{-1}$ m$^{-1}$, exceeding Pt (Ta) by one (two) orders of magnitude. The torque depicts a non-monotonic Cr-thickness dependence which cannot be explained by a conventional model. We have developed a drift-diffusion model with an oxidation-gated interfacial source which quantitatively reproduces the data, revealing that the Cr-CrO$_x$ interface generates orbital currents over an order of magnitude stronger than the bulk orbital Hall channel with an orbital transport length of $\approx 4$ nm. The enhanced torque enables field-free magnetization switching at $1.58 \times 10^{11}$ A m$^{-2}$, outperforming heavy-metal and CuO$_x$ benchmarks. These results establish native oxidation as a scalable strategy for realizing efficient orbital-torque devices.
Comments21 pages ,8 figures
