Demagnetization on the fs time-scale by the Elliott-Yafet mechanism

Abstract

An ultrashort laser pulse can change the magnetization of ferromagnetic metals such as Ni in less than a picosecond. Thereby, angular momentum is transferred from the spin system to the lattice. One possible candidate for this transfer is the Elliott-Yafet mechanism of spin-orbit mediated spin-flip scattering of electrons at phonons. Former ab-initio calculations have shown that for Ni and Co the Elliott-Yafet spin-mixing parameter which describes the degree of mixing of the two spin states for the electronic eigenstates – averaged over all states involved in the demagnetization process – is large enough to explain the experimentally observed demagnetization rates. In the present paper we calculate in addition the spin-mixing for the individual electronic states as function of their wavevector. Furthermore, the theory is extended to the case of Gd for which experiments have revealed a slower demagnetization dynamics than for Ni.