Ultrafast demagnetization mechanism in half-metallic Heusler alloy thin films controlled by the Fermi level

The electronic band-structure controlled ultrafast demagnetization mechanism in $\mathrm{C}{\mathrm{o}}₂\mathrm{F}{\mathrm{e}}_x\mathrm{M}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{Si}$ Heusler alloy is underpinned by systematic variation of composition. We find the spin-flip scattering rate controlled by spin density of states at the Fermi level is responsible for nonmonotonic variation of ultrafast demagnetization time (${\ensuremath{\tau}}_{\mathrm{M}}$) with $x$ with a maximum at $x=0.4$. Furthermore, Gilbert damping constant exhibits an inverse relationship with ${\ensuremath{\tau}}_{\mathrm{M}}$ due to the dominance of interband scattering mechanism. This demonstrates a connection between ultrafast demagnetization and magnetic damping based on Fermi-level position in this Heusler alloy system.