Role of hot phonons and layer geometry in spintronic terahertz emission

We compare terahertz (THz) emission from bilayer and trilayer spintronic structures optimized for femtosecond laser excitation. The trilayer shows approximately twice the THz amplitude of the bilayer, owing to constructive spin-to-charge conversion at both interfaces. However, saturation behavior emerges in the trilayer due to hot phonon effects. Time-domain analysis of the extracted charge currents reveals distinct ultrafast spin transport dynamics. These results highlight the role of multilayer design and phonon interactions in enhancing the performance of spintronic THz emitters.