Polarization characteristics of Ni/Pt-based spintronic terahertz emitters based on spin electron dynamics

We report on the terahertz (THz) emission polarization characteristics of spintronic nickel/platinum (Ni/Pt) bilayer films. The films were deposited on MgO substrates via electron beam deposition with varying Ni thicknesses of 5, 7, and 9 nm and a constant Pt thickness of 6 nm. Results from B-field polarity-dependent THz measurements exhibited different THz emission characteristics for the p- and s-polarized components. We attribute the strong, wide-bandwidth B-field dependent p-polarized component to the inverse spin Hall effect (ISHE) and the weak, low-bandwidth B-field independent s-polarized component to the ultrafast demagnetization (UDM) process. The peak-to-peak THz emission amplitudes were demonstrated to be dependent on the sample rotational angle about the optical axis which suggests sample inhomogeneity from the deposited Ni/Pt spintronic films. These results are crucial for the material design and development of more intense spintronic THz sources.