Spin-transfer is a typical spintronics effect that allows a ferromagnetic layer to be switched by spin-injection. Most of the experimental results about spin transfer (quasi-static hysteresis loops or AC resonance measurements) are described on the basis of the Landau-Lifshitz-Gilbert equation of the magnetization, in which additional current-dependent damping factors are added, and can be positive or negative. The origin of the damping can be investigated further by performing stochastic experiments, like one shot relaxation experiments under spin-injection in the activation regime of the magnetization. In this regime, the Néel-Brown activation law is observed which leads to the introduction of a current-dependent effective temperature. In order to justify the introduction of these counterintuitive parameters (effective temperature and negative damping), a detailed thermokinetic analysis of the different sub-systems involved is performed. We propose a thermokinetic description of the different forms of energy exchanged between the electric and the ferromagnetic sub-systems at a Normal/Ferromagnetic junction.The derivation of the Fokker-Planck equation in the framework of the thermokinetic theory allows the damping parameters to be defined from the entropy variation and refined with the Onsager reciprocity relations and symmetry properties of the magnetic system. The contribution of the spin-polarized current is introduced as an external source term in the conservation laws of the ferromagnetic layer. Due to the relaxation time separation, this contribution can be reduced to an effective damping. The flux of energy transferred between the ferromagnet and the spin-polarized current can be positive or negative, depending on spin accumulation configuration. The effective temperature is deduced in the activation (stationary) regime, providing that the relaxation time that couples the magnetization to the spin-polarized current is shorter than the relaxation to the lattice.

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Spin injection in metallic normal/ferromagnetic junctions is investigated taking into account the anisotropic magnetoresistance occurring in the ferromagnetic layer. On the basis of a generalized two-channel model, it is shown that there is an interface resistance contribution due to anisotropic scattering, besides spin accumulation and giant magnetoresistance. The corresponding expression of the thermoelectric power is derived and compared with the expression accounting for the thermoelectric power produced by the giant magnetoresistance. Measurements of anisotropic magneto-thermoelectric power are presented in electrodeposited Ni nanowires contacted with Ni, Au, and Cu. It is shown that this thermoelectric power is generated at the interfaces of the nanowire. The results of this study indicate that, while the giant magnetoresistance and the corresponding thermoelectric power indicate the role of spin-flip scattering, the observed anisotropic magneto-thermoelectric power might be the fingertint of interband s-d relaxation mechanisms.