Ultrafast spin dynamics in ferromagnetic Nickel

Abstract

Fast magnetization changes can be achieved in a ferromagnet using optical pulses. Such changes which are due to an increase of the spin temperature above the Curie point are generally induced by the temperature elevation of the lattice induced by pico-nanosecond pulses [1,2]. In this case, the electron and phonon population are in equilibrium, and the delay between spin and lattice dynamics has been attributed to spin phonons interactions. As reported in this paper, the initial hot electron distribution created by femtosecond pulses can induce an ultrafast spin heating via electron-spin collisions. It is shown that in the first picosecond a new situation occurs where the electrons, spins and phonons are out of equilibrium and where an ultrafast demagnetization takes place [3].