Ultrafast heating-induced magnetization switching in ferrimagnets

We study theoretically the light-induced magnetization switching in a binary ferrimagnet of the type $A_p{B}_{1-p}$, randomly occupied by two different species of magnetic ions. The localized spins are coupled with spins of itinerant electrons via s-d exchange interaction. Model parameters are chosen so that to achieve similarity between magnetic characteristics of the model and those of ferrimagnetic rare-earth-transition metal GdFeCo alloys. The switching is triggered by heating of the itinerant electrons by a laser pulse. The spin dynamics is governed by the cooling of itinerant electrons, exchange scattering, induced by the s-d exchange interaction and spin-lattice relaxation of the itinerant spins with a characteristic time ${\tau }_s$. The dynamics of the localized and itinerant spins is described by coupled rate equations. The main conclusion of this study is that the switching occurs only in a certain temperature range depending on ${\tau }_s$. For long ${\tau }_s$ the switching occurs only below the magnetisation compensation temperature T _K. For physically reasonable values of ${\tau }_s$ this temperature range extends from 0 K to $T_f\left({\tau }_s\right)$, where $T_f\left({\tau }_s\right)$ is slightly higher than the compensation temperature T _K. With further decrease of ${\tau }_s$ this temperature range shifts to temperatures higher than T _K. (paper)