Explaining all-optical switching in ferrimagnets with heavy rare-earth elements by varying the spin-flip scattering probability of Gd in CoₓGd₁₀₀₋ₓ alloys and Co/Gd bilayers

Using the microscopic three temperature model, we simulate single-pulse all-optical switching (AOS) in alloys and bilayers consisting of Co and Gd. In particular, we investigate its dependence on the spin-flip probability of Gd aₛf,Gd, a material parameter describing the strength of spin-phonon coupling. We do so to elucidate the mechanisms behind all-optical switching in systems where Co is coupled to heavy rare-earth elements with higher damping such as Tb. In alloys, our observations are twofold. First, an increase of aₛf,Gd leads to a broadening of the range of compositions for which AOS is observed. Second, the ideal Co content is decreased as aₛf,Gd is varied. For bilayers, our analysis indicates that switching is most efficient when aₛf,Gd takes on small values. Conversely, increasing the value of aₛf,Gd leads to a general suppression of AOS. Comparing alloys to bilayers, we find that AOS in alloys exhibits greater resilience to variations in aₛf,Gd than it does in bilayers.