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轻金属材料Cr具有较大的轨道霍尔电导, 并且不依赖强自旋-轨道耦合即可实现高效的电荷-轨道流的转换, 这些优点在自旋电子领域具有重要的应用前景, 有助于开发新型的轨道-自旋电子器件. 本研究采用磁控溅射的方法在Al2O3衬底上制备了Cr薄膜和Cr/Ni异质结. 通过太赫兹发射谱测量观察到Cr中的逆轨道霍尔效应. 在Cr/Ni异质结中由铁磁层Ni中自旋-轨道耦合所产生的轨道流通过Cr的逆轨道霍尔效应转换为电荷流. 此外, 研究了太赫兹信号对Ni层厚度的依赖性, Ni厚度的增加显著地提高了自旋流-轨道流的转换效率, 增强了轨道太赫兹发射信号.Cr的逆轨道霍尔效应为轨道-自旋电子器件的设计与性能调控提供了新的研究思路.Orbitronic devices have aroused considerable interest due to their unique advantage of being independent of strong spin-orbit coupling. Light metal chromium (Cr) with high orbital Hall conductivity has significant potential for application in orbit-spintronic devices. In this study, we present experimental verification of the inverse orbital Hall effect (IOHE) in Cr thin films and systematically investigate the underlying physical mechanisms of orbital-to-charge current conversion. The Cr/Ni and Pt/Ni heterostructures are fabricated on Al2O3 substrates via magnetron sputtering. Terahertz time-domain spectroscopy is employed to measure the terahertz emission signal. The Cr/Ni heterostructure exhibits the same positive terahertz polarity as the ISHE-dominant Pt/Ni heterostructure, despite the Cr layer owing negative spin Hall angle, which confirms the IOHE of Cr/Ni heterostructure. In the Cr/Ni heterostructures, femtosecond laser excitation generates spin current in the ferromagnetic Ni layer, which is converted into orbital current via its spin-orbit coupling. This orbital current propagates into the Cr layer where it is transformed into charge current through the IOHE. Furthermore, the increase of the Cr thickness (2–40 nm) weakens the terahertz emission of Cr/Ni heterostructures due to enhanced optical absorption of Cr layers reducing spin current generation in Ni layers. However, the optimization of Ni thickness (3–10 nm) significantly enhances the terahertz emission by improving the spin-orbital conversion efficiency. This work provides experimental evidence for IOHE in Cr films and demonstrates the crucial role of ferromagnetic layer engineering in spin-to-orbit conversion efficiency, providing innovative perspectives for designing and optimizing the performance of orbitronic devices.
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Keywords:
- light material Cr film /
- inverse orbital Hall effect /
- terahertz
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图 1 (a) Al2O3/Cr (40 nm), (b) Al2O3/Cr (10 nm)/Ni (5 nm)和(c) Al2O3/Cr (40 nm)/Ni (5 nm)的原子力显微镜图像
Fig. 1. AFM images of (a) Al2O3/Cr (40 nm), (b) Al2O3/Cr (10 nm)/Ni (5 nm) and (c) Al2O3/Cr (40 nm)/Ni (5 nm) samples
图 2 (a)—(e) Cr (2—40 nm)/Ni (5 nm)结构的太赫兹信号
Fig. 2. (a)–(e) The THz signals of the Cr (2–40 nm)/Ni (5 nm) structures.
图 3 (a) Pt (1 nm)/Ni (5 nm)和(b) Pt (3 nm)/Ni (5 nm)结构的太赫兹信号
Fig. 3. The THz signals of the (a) Pt (1 nm)/Ni (5 nm) and (b) Pt (3 nm)/Ni (5 nm) structures
图 4 (a) Cr (10 nm)/Ni (3 nm), (b) Cr (10 nm)/Ni (5 nm)和Cr (10 nm)/Ni (10 nm)结构的太赫兹信号
Fig. 4. The THz signals of the (a) Cr (10 nm)/Ni (3 nm) structures, (b) Cr (10 nm)/Ni (5 nm) and (c) Cr (10 nm)/Ni (10 nm) structures
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