Current-Induced Two-Level Fluctuations in Pseudo-Spin-Valve (Co/Cu/Co) Nanostructures

Two-level fluctuations of the magnetization state of pseudo-spin-valve pillars $\mathrm{C}\mathrm{o}(10\mathrm{n}\mathrm{m})/\mathrm{C}\mathrm{u}(10\mathrm{n}\mathrm{m})/\mathrm{C}\mathrm{o}(30\mathrm{n}\mathrm{m})$ embedded in electrodeposited nanowires ($\sim 40\mathrm{n}\mathrm{m}$ in diameter, 6000 nm in length) are triggered by spin-polarized currents of ${10}^7\mathrm{A}/{\mathrm{c}\mathrm{m}}^2$ at room temperature. The statistical properties of the residence times in the parallel and antiparallel magnetization states reveal two effects with qualitatively different dependences on current intensity. The current appears to have the effect of a field determined as the bias field required to equalize these times. The bias field changes sign when the current polarity is reversed. At this field, the effect of a current density of ${10}^7\mathrm{A}/{\mathrm{c}\mathrm{m}}^2$ is to lower the mean time for switching down to the microsecond range. This effect is independent of the sign of the current and is interpreted in terms of an effective temperature for the magnetization.