Ultrafast demagnetization of metals: Collapsed exchange versus collective excitations

Abstract

We have investigated the magneto-optical response of Fe epitaxial films by femtosecond pump-probe polarimetry in a broad probe spectral region (1.8-2.6 eV). From the extrapolated photoinduced variation of the conductivity tensor, spin and charge dynamics have been disentangled. In particular, the analysis of the off-diagonal tensor element rules out any appreciable modification of the electronic band structure upon laser excitation and suggests that ultrafast demagnetization is determined by collective excitations, i.e., spin fluctuations. Our experimental evidence provides significant insight into the microscopic mechanisms governing the complex spin dynamics of metals in the subpicosecond time scale.

Exchange scattering as the driving force for ultrafast all-optical and bias-controlled reversal in ferrimagnetic metallic structures

“…Indeed, in our model the Stoner excitations are considered to be the mechanism of the quenching of magnetization of the sublattices A and B. The physical picture of the demagnetization process is more complicated and may include spin fluctuations, 35 arising e.g. from magnons.…”

Stoner versus Heisenberg: Ultrafast exchange reduction and magnon generation during laser-induced demagnetization

“…The possible contributions of reduced exchange splitting and magnon excitation have been discussed over the last years, but without strong consensus to date 9,10,22,28,30,38,[43][44][45][46] . Some authors observe a change of exchange splitting during ultrafast demagnetization 38,[44][45][46] , while others do not 30 .…”

Speed and efficiency of femtosecond spin current injection into a nonmagnetic material

“…Although this is a good approximation (as deduced by the demagnetization time constants of Ni on Au and Ni on MgO), it is not perfect. In real systems, additional microscopic mechanisms such as Elliott-Yafet spin-flip scattering [32] and ultrafast magnon generation [33][34][35][36] can have additional contributions to the loss of magnetic moments in 3d ferromagnetic materials. These effects reduce the amount of magnetic moments transported towards the Ni-Au interface and hence result in a larger spin injection efficiency into Au.…”