Explaining all-optical switching in ferrimagnets with heavy rare-earth elements by varying the spin-flip scattering probability of Gd in Co$_x$Gd$_{100-x}$ alloys and Co/Gd bilayers

Abstract: 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 $a_\mathrm{sf,Gd}$, 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 $a_\mathrm{sf,Gd}$ leads to a broadening of the range of compositions for which AOS is observed. Second, the ideal Co content is decreased as $a_\mathrm{sf,Gd}$ is varied. For bilayers, our analysis indicates that switching is most efficient when $a_\mathrm{sf,Gd}$ takes on small values. Conversely, increasing the value of $a_\mathrm{sf,Gd}$ leads to a general suppression of AOS. Comparing alloys to bilayers, we find that AOS in alloys exhibits greater resilience to variations in $a_\mathrm{sf,Gd}$ than it does in bilayers.