Cheng Hao, Wang Yangkai, Liu Zheng, Jia Xiangyu, Huang Qiuping, Lu Yalin
Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, P.R. China.
Hefei National Research Center for Physical Sciences at the Microscale, Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei 230026, P.R. China.
Nanophotonics. 2023 May 11;12(12):2145-2156. doi: 10.1515/nanoph-2023-0089. eCollection 2023 Jun.
Spintronic terahertz (THz) emission via spin-to-charge conversion (SCC) has been widely studied in ferromagnets (FM)/nonmagnets (NM) structures, in which various mechanisms of SCC have been confirmed in different NM materials. However, it is rare to find a material having multiple SCC mechanisms at the same time. Here, we report a ferromagnetic metal Ni film with diverse functions in the SCC process, by performing THz emission experiments in single Ni layer, FM/Ni, Ni/NM bilayers and FM/Ni/NM trilayers. It is demonstrated that in Ni monolayer, THz emission is radiated by the anomalous Hall effect and ultrafast demagnetization of Ni film. In FM/Ni, the Ni film acts as an SCC implementer and THz emission is mainly generated by the inverse spin Hall effect (ISHE) of Ni. In Ni/NM, the Ni film acts as a spin injector and provides spin currents to be converted to charge current via ISHE of heavy metal NM, inducing THz emission. In FM/Ni/NM, THz emission mainly comes from ISHE of FM/Ni, Ni/NM, and FM/NM, and their domination is relative to Ni thickness. Our findings show a ferromagnetic film not only acts as a spin injector but also as an SCC implementer, providing a new concept to design spintronic THz emitters.
通过自旋到电荷转换（SCC）产生的自旋电子太赫兹（THz）发射已在铁磁体（FM）/非磁体（NM）结构中得到广泛研究，其中在不同的NM材料中已证实了各种SCC机制。然而，很少能找到一种同时具有多种SCC机制的材料。在此，我们通过在单Ni层、FM/Ni、Ni/NM双层和FM/Ni/NM三层结构中进行太赫兹发射实验，报道了一种在SCC过程中具有多种功能的铁磁金属Ni薄膜。结果表明，在Ni单层中，太赫兹发射是由Ni薄膜的反常霍尔效应和超快退磁辐射产生的。在FM/Ni中，Ni薄膜充当SCC的实施者，太赫兹发射主要由Ni的逆自旋霍尔效应（ISHE）产生。在Ni/NM中，Ni薄膜充当自旋注入器，并提供自旋电流，通过重金属NM的ISHE将其转换为电荷电流，从而诱导太赫兹发射。在FM/Ni/NM中，太赫兹发射主要来自FM/Ni、Ni/NM和FM/NM的ISHE，它们的主导作用与Ni的厚度有关。我们的研究结果表明，铁磁薄膜不仅可以充当自旋注入器，还可以充当SCC的实施者，为设计自旋电子太赫兹发射器提供了一个新的概念。
