Sapozhnikov M.V. Spintronic THz emitters based on graphene and antiferromagnets

We investigate terahertz (THz) emission mechanisms in spintronic emitters – Co (3 nm), graphene (Gr)/Co (3 nm), and Co (3 nm)/FeMn (5 nm) – grown on quartz substrates. Magnetic properties were characterized in the longitudinal magneto-optical Kerr effect (MOKE) geometry, and the emission dynamics by time-domain THz spectroscopy (THz-TDS). In Gr/Co, the graphene interface induces perpendicular magnetic anisotropy; the phase of the THz waveforms is invariant with respect to the pumping side at a fixed field polarity, indicating demagnetization-driven emission. Under back-side pumping the amplitude increases by ≈1.5×, whereas front-side excitation reduces it by about a factor of two, consistent with differences in optical/THz absorption and interference. In Co/FeMn, the antiferromagnetic layer imposes pronounced in-plane uniaxial anisotropy and increases coercivity; a phase inversion upon switching the pumping side indicates a dominant inverse spin Hall effect. No exchange bias is observed at the selected thicknesses and without post-annealing. Additionally, an asymmetry of the THz hysteresis loops in Co/FeMn reveals even-in-magnetization contributions to the emission. These results underscore the central role of interface engineering in Co/AFM and Gr/Co stacks for controlling spin-to-charge conversion and optimizing THz-emitter performance.