Magnetization reversal and two-level fluctuations by spin injection in a ferromagnetic metallic layer

Slow magnetic relaxation and two-level fluctuations measurements under high current injection are performed in single-contacted ferromagnetic nanostructures. The magnetic configurations of the samples are described by two metastable states of the uniform magnetization. The current-dependent effective energy barrier due to spin transfer from the current to the magnetic layer is measured. The comparison between the results obtained with Ni nanowires of 6 mum length and 60 nm diameter, and Co (10 nm)/Cu (10 nm)/ Co(30 nm) nanometric pillars of about 40 nm in diameter refined the characterization of this effect. It is shown that all observed features cannot be reduced to the action of a current dependent effective field. Instead, all measurements can be described in terms of an effective temperature, which depends on the current amplitude and direction. The system is then analogous to an unstable open system. The effect of current-induced magnetization reversal is interpreted as the balance of spin injection between both interfaces of the ferromagnetic layer.