Terahertz Generation via Picosecond Spin-to-Charge Conversion in IrMn3/Ni−Fe Heterojunction

Experimental investigations of ultrafast electro-optical properties in magnetic materials manifest their great potential for emerging spintronic optoelectronic devices. Here, using time-resolved terahertz emission spectroscopy, we construct a spintronic terahertz emitter consisting of an ${\mathrm{Ir}\mathrm{Mn}}_{3}/\mathrm{Ni}\ensuremath{-}\mathrm{Fe}$ heterojunction. A femtosecond spin current pulse is generated in the thin film of the $\mathrm{Ni}\ensuremath{-}\mathrm{Fe}$ layer when it absorbs a femtosecond laser pulse, and then the spin current is converted into a transient charge current by the metallic ${\mathrm{Ir}\mathrm{Mn}}_{3}$ layer on picosecond timescales. We timely record the terahertz emission associated with this ultrafast conversion process by means of electro-optic sampling. Besides, the spin-to-charge conversion efficiency of the ${\mathrm{Ir}\mathrm{Mn}}_{3}/\mathrm{Ni}\ensuremath{-}\mathrm{Fe}$ heterojunction is determined via quantitative analysis of the spin torque ferromagnetic resonance results. We have both optically verified and electrically studied the spin-to-charge conversion of the ${\mathrm{Ir}\mathrm{Mn}}_{3}/\mathrm{Ni}\ensuremath{-}\mathrm{Fe}$ heterojunction. Our results enlarge the material choice range of spintronic terahertz emitters, which may promote further investigations of ultrafast spin-to-charge conversion in different heterojunction materials.