Tuning terahertz emission generated by anomalous Nernst effect in ferromagnetic metal

Despite intensive research, the mechanism determining terahertz (THz) emission of ferromagnetic (FM) metallic monolayers remains elusive. Here, we report on results a systematic investigation THz generated by pumping Ni80Fe20 Al2O3 substrates with femtosecond laser. We found solid evidence that is dominated anomalous Nernst effect (ANE), in which transient spin-polarized charge current can be induced an ultrafast electron temperature gradient picosecond timescale, outputting emission. polarity reversal waveform after introduction SiO2 buffer layer to sample and that, based simulation, it was consequence direction gradient. Comparing different FM further confirms also strongly depends sign ANE coefficient. These phenomena unambiguously indicate plays decisive role process The present work shows importance spin caloritronics for spintronic emitter. principle demonstrated here applied other materials.