From spin diffusion to magnetization reversal: The four channel approach

Experiments of spin injection, from a normal metal to a ferromagnet, show that the magnetization of the ferromagnet can be switched with high current pulses, without the need of a magnetic field. In order to describe the experimental observations, two different kinds of electronic populations are defined for the transport: the spin polarized current inside the normal metal (paramagnetic spin-polarized current) and the spin-polarized current inside the ferromagnet (ferromagnetic spin polarization). The redistribution of the electronic populations is then investigated in the framework of a four-channel approach (up and down spin polarization for paramagnetic and ferromagnetic currents). This mechanism couples the electronic transport (Boltzmann equations) to the dynamics of the magnetization (Landau-Lifshitz-Gilbert equation), and leads to define a magnetic temperature which depends on the current injection.