Ultrafast Spin Current Excitation and Controlled Terahertz Radiation from Noncollinear Antiferromagnets

Noncollinear antiferromagnets (AFMs) are promising candidates for next-generation spintronic devices due to their terahertz (THz) magnetic resonance, robustness against external field interferences, and strong magneto-optical responses. Using femtosecond laser excitation, spin current generation and THz radiation mechanisms are systematically investigated via inverse spin Hall effect in Mn₃Ga/Pt bilayers with multiple magnetic phases. The results reveal that spin currents in ferrimagnetic Mn₃Ga originate from common hot electron excitation. In contrast, the stronger THz fields from samples containing both ferrimagnetic and noncollinear AFM phases are field-independent, with spin currents arising from pulsed magnetizations through magnetic dipole transitions, observed exclusively in the AFM phase. Furthermore, theoretical models incorporating magnetic group symmetry and nonlinear optical effects are developed, offering accurate explanations for the THz filed dependence on sample azimuth, pump polarization, and pump helicity. These findings open new avenues for generating ultrafast spin currents in noncollinear AFMs, presenting significant potential for high-speed spintronic applications.