Separation of emission mechanisms in spintronic terahertz emitters

Spintronic thin films were shown to be promising high-performance broadband terahertz (THz) emitters. For spintronic ferromagnet/heavy metal heterostructures, THz emission arises from three mechanisms: the magnetic dipolar radiation due to the ultrafast demagnetization, the transient current radiation due to spin-charge conversion, and anomalous Hall effect. Here, we demonstrate that the three mechanisms show distinct dependences on the thickness of the ferromagnetic layer. With the insertion of an ultrathin Al2O3 layer between the ferromagnetic and heavy metal layer, the spin-charge conversion is suppressed when the Al2O3 thickness exceeds 1 nm. Our results agree with the theoretical predictions based on a simple spin-diffusion model.

Automated summary

Spintronic thin films have been found to be high-performance broadband terahertz emitters, with emission mechanisms depending on the thickness of the ferromagnetic layer. The suppression of spin-charge conversion was observed when an ultrathin Al2O3 layer was inserted between the ferromagnetic and heavy metal layers, in agreement with theoretical predictions based on a simple spin-diffusion model.