Fermi Level Controlled Ultrafast Demagnetization Mechanism in Half-Metallic Heusler Alloy

The electronic band structure-controlled ultrafast demagnetization mechanism in Co2FexMn1-xSi Heusler alloy is underpinned by systematic variation of composition. We find the spin-flip scattering rate controlled by spin density of states at Fermi level is responsible for non-monotonic variation of ultrafast demagnetization time ({\tau}M) with x with a maximum at x = 0.4. Furthermore, Gilbert damping constant exhibits an inverse relationship with {\tau}M due to the dominance of inter-band scattering mechanism. This establishes a unified mechanism of ultrafast spin dynamics based on Fermi level position.