Ultrafast Control of Néel Vector in Collinear Antiferromagnet MnPt

Exchange-bias-coupled spintronic terahertz emitters (EBC-STEs) utilize antiferromagnets (AFMs) as passive pinning layers for ferromagnetic spins and as detectors of spin currents. Conventionally, terahertz (THz) emission from STEs is attributed solely to the ferromagnetic subsystem, with the ultrafast magnetization dynamics of AFM considered undetectable due to its zero magnetic moment. Here, we propose a novel experimental approach to probe the ultrafast control and detection of magnetization dynamics driven by laser-induced optical torque on the Néel vector in collinear AFM MnPt. We isolate the underlying Néel vector dynamics from the ferromagnetic magnetization dynamics by transducing the canted magnetic moment into a distinct THz signal, which is confirmed by the emission observed in Pt/MnPt. We further demonstrate the exceptional robustness of the exchange bias under optical excitation. This work provides the first direct evidence of ultrafast AFM magnetization dynamics in an EBC-STE, transforming it from a passive emitter into a sensitive probe of interfacial ultrafast magnetism and unlocking the potential of antiferromagnetic THz spintronics.