Christian Illg

Delayed magnetic vortex core reversal

When switching the vortex core in a magnetic disc by a short excitation with an in-plane field, there is an initial global excitation of the magnetization due to a precession of the magnetization in the spatially homogeneous field. Then an energy transport from this global excitation towards the center of the disc takes place leading to a concentration of the energy close to the vortex core which suffices to switch the core. Because this transport requires time, there is a delay between the end of the excitation and the switching. This is demonstrated for switching by in-plane rotating GHz rf-bursts.

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

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.

Ultrafast demagnetization after laser pulse irradiation in Ni: Ab-initio electron-phonon scattering and phase space calculations

Electron-phonon scattering is one possible candidate to explain ultrafast demagnetization in Ni. We calculate the demagnetization time and the demagnetization rate with ab initio density-functional theory and estimate the phase space for scattering which is related to the maximum possible demagnetization. We find that both demagnetization rate and phase space are too small for reasonable excitations to explain the experimental demagnetization.