Co₂FeAl Full Heusler Compound Based Spintronic Terahertz Emitter

Abstract To achieve a large terahertz (THz) amplitude from a spintronic THz emitter (STE), materials with 100% spin polarisation such as Co‐based Heusler compounds as ferromagnetic layer are required. However, these compounds are known to loose their half‐metallicity in the ultrathin film regime, as it is difficult to achieve L2₁ ordering, which has become a bottleneck for the film growth. Here, the successful deposition using room temperature DC sputtering of the L2₁ and B2 ordered phases of the Co₂FeAl full Heusler compound is reported. Co₂FeAl is used as ferromagnetic layer together with highly orientated Pt as nonferromagnetic layer in the Co₂FeAl/Pt STE, where an MgO (10 nm) seed layer plays an important role to achieve the L2₁ and B2 ordering of Co₂FeAl. The THz generation in the Co₂FeAl/Pt STE is presented, which has a bandwidth of 0.2–4 THz. The THz electric field amplitude is optimized with respect to thickness, orientation, and growth parameters using a thickness dependent model considering the optically induced spin current, superdiffusive spin current, inverse spin Hall effect, and the THz attenuation in the layers. This study, based on the full Heusler Co₂FeAl compound opens up a plethora of possibilities in STE research involving full Heusler compounds.