  Spintronic THz emitters have attracted much attention due to their desirable
properties, such as affordability, ultra-wideband capability, high efficiency,
and tunable polarization. In this study, we investigate the characteristics of
THz signals, including their frequency, bandwidth, and amplitude, emitted from
a series of heterostructures with ferromagnetic (FM) and nonmagnetic (NM)
materials. The FM layer consists of a wedge-shaped CoFeB layer with a thickness
of 0 to 5 nm, while the NM materials include various metals such as Pt, Au, W,
Ru, Pt$_{\%92}$Bi$_{\%8}$, and Ag$_{\%90}$Bi$_{\%10}$ alloys. Our experiments
show that the emitter with Pt-NM layer has the highest amplitude of the emitted
THz signal. However, the PtBi-based emitter exhibits a higher central THz peak
and wider bandwidth, making it a promising candidate for broadband THz
emitters. These results pave the way for further exploration of the specific
compositions of Pt$_{1-x}$Bi$_{x}$ for THz emitter design, especially with the
goal of generating higher frequency and wider bandwidth THz signals. These
advances hold significant potential for applications in various fields such as
high-resolution imaging, spectroscopy, communications, medical diagnostics, and
more.
