Ultrafast Control of Néel Vector in Collinear Antiferromagnet MnPt

Exchange-bias-coupled spintronic terahertz emitters (EBC-STEs) utilize an antiferromagnet (AFM) as both a passive pinning layer for ferromagnetic spins and a detector of spin currents. Conventionally, terahertz (THz) emission from spintronic terahertz emitters (STEs) is attributed solely to the ferromagnetic subsystem, with the ultrafast magnetization dynamics of AFM considered undetectable due to its zero net magnetic moment. Here, we demonstrate a novel experimental approach to probe and control ultrafast magnetization dynamics driven by laser-induced optical torque on the Néel vector in collinear AFM MnPt. The Néel vector induced transient magnetization is isolated from ferromagnetic magnetization dynamics by detecting the distinct THz emission from the canted magnetic moment, as confirmed in Pt/MnPt bilayers. We further investigate the stability of the EBC-STE compared to conventional STEs under optical excitation. This work provides 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.