Antiferromagnetic–Ferromagnetic Heterostructure‐Based Field‐Free Terahertz Emitters

• Published in: Advanced materials (Weinheim) 2022-10, Vol.34 (42), p.e2204373-n/a
• Main Authors: Wu, Xiaojun, Wang, Hanchen, Liu, Haijiang, Wang, Yizhan, Chen, Xinhou, Chen, Peng, Li, Peiyan, Han, Xiufeng, Miao, Jungang, Yu, Haiming, Wan, Caihua, Zhao, Jimin, Chen, Sai
• Format: Article
• Language: English
• Subjects: Anisotropy; Antiferromagnetism; Bias; Electrons; Emission; Emitters; Exchanging; Ferromagnetism; Heterostructures; Magnetic fields; Materials science; Optoelectronic devices; Polarization; Radiation; terahertz emitters; THz spin currents
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202204373

Recently, ferromagnetic‐heterostructure spintronic terahertz (THz) emitters have been recognized as one of the most promising candidates for next‐generation THz sources, owing to their peculiarities of high efficiency, high stability, low cost, ultrabroad bandwidth, controllable polarization, and high scalability. Despite the substantial efforts, they rely on external magnetic fields to initiate the spin‐to‐charge conversion, which hitherto greatly limits their proliferation as practical devices. Here, a unique antiferromagnetic–ferromagnetic (IrMn3|Co20Fe60B20) heterostructure is innovated, and it is demonstrated that it can efficiently generate THz radiation without any external magnetic field. It is assigned to the exchange bias or interfacial exchange coupling effect and enhanced anisotropy. By precisely balancing the exchange bias effect and enhanced THz radiation efficiency, an optimized 5.6 nm‐thick IrMn3|Co20Fe60B20|W trilayer heterostructure is successfully realized, yielding an intensity surpassing that of Pt|Co20Fe60B20|W. Moreover, the intensity of THz emission is further boosted by togethering the trilayer sample and bilayer sample. Besides, the THz polarization may be flexibly controlled by rotating the sample azimuthal angle, manifesting sophisticated active THz field manipulation capability. The field‐free coherent THz emission that is demonstrated here shines light on the development of spintronic THz optoelectronic devices. A field‐free spintronic THz emitter is successfully realized in an antiferromagnetic–ferromagnetic (IrMn3|Co20Fe60B20) heterostructure, which facilitates the exchange bias or interfacial exchange coupling effect. Significantly, stronger spintronic THz radiation is generated using the coherent superposition of two heterojunctions with opposite pinning orientations.