Nonvolatile phase-programmable spintronic terahertz emitter via laser-induced spin polarization switching

Ultrafast-laser-driven spintronic terahertz (THz) emitters are promising building blocks for future THz technologies, owing to their ability to generate efficient ultrabroadband THz radiation from nanometer-thick metallic heterostructures and to support a variety of functional THz devices. Here, we further extend their functionality by realizing nonvolatile phase encoding in an IrMn₃/Co₂₀Fe₆₀B₂₀/W heterostructure. By implementing fluence-controlled femtosecond laser excitation, we demonstrate robust THz phase reversal governed by a well-defined threshold of 0.78 mJ/cm², attributed to spin-polarization reversal mediated by exchange bias and magnetic anisotropy manipulation. Time-resolved double-pump experiments show that the THz phase switching is driven by ultrafast laser-induced heating and reveal a thermal gating window of about 15 ps. We further achieve reversible optical writing and magnetic reset between two nonvolatile THz phase states, maintaining a phase contrast above 140% over 30 cycles. Finally, we demonstrate optical-THz spatial phase patterning with a signal-to-noise ratio of 53 dB and a phase contrast of 160%. This work paves the way for write-read-reset THz pattern and information encoding, and advances the integration of STEs with on-chip photonic architectures.