Spintronic terahertz (THz) emitter has the advantages such as lower cost, broader spectrum and easier operation compared with the commercial THz emitters, and thus has become the focus of research towards the next generation THz source. However, in such spintronic THz emitter, an external magnetic field is technological required to align the orientations of the magnetization, which is detrimental for practical applications. Here, a spintronic terahertz emitters based on IrMn/Fe/Pt exchange bias structure is presented. By means of ultrafast spin injection on Fe/Pt interface followed by the spin-to-charge conversion in Pt, plus the effective magnetic field originating from the IrMn/Fe interface, THz pulse with considerable intensity can be generated in such structure without the assist of external field. Besides, the remanent magnetization for thin Fe is enhanced by the insertion of ultrathin Cu to IrMn/Fe interface, which is beneficial to the field-free THz emission. The range of obtained dynamic THz spectrum exceeds 60 dB and the positive saturation field can reach up to ~ -10 mT by optimizing the multilayer thickness, meeting the standard for commercial application. By rotating the sample, it is found that the polarization direction of the generated THz wave circulates simultaneously and keeps perpendicular to the direction of exchange bias field in the film plane. Moreover, we designed a spin valve THz emitter based on the structure of IrMn/Fe/Pt/Fe by adding a free ferromagnetic Fe layer to the exchange bias multilayers. The emitted THz pulse amplitude is larger for the antiparallel alignment of the Fe layers at zero field compared with the parallel alignment or exchange bias structure. The work show that the spin terahertz emitter based on IrMn/Fe/Pt exchange bias structure can produce considerable terahertz signal without external field. What’s more, the polarization direction of the emitted THz signal can be easily manipulated by rotating the sample. Because of this series of advantages, such exchange bias heterostructures is expected to play an important role in the design of next generation THz source.
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