Experiments of spin injection on magnetic nanostructures show that the magnetization can be switched with high current pulses, and without the need of a magnetic field. The mechanism responsible for this effect is still not known, but some experiments show that it is related to fluctuations and noise in magnetic systems. The response of a magnetic nanostructure shows typical processes of activation out of a metastable state and two level fluctuations. An effective temperature is measured is measured through the effective barrier variation. The effective temperature depends on the magnetic configuration and to the current direction. This approach leads to conclude that the transfer of energy is due to a transfer of spin from the current to the magnetization. A new mechanism is proposed as a consequence of the s-d relaxation at the interface in 3d ferromagnets. This mechanism couples the electronic transport (Boltzmann equations) to the dynamics of the magnetization (Landau-Lifshitz-Gilbert equation).