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

Abstract

Two-level fluctuations of the magnetization state of pseudo spin-valve pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires (∼ 40 nm in diameter, 6000 nm in length) are triggered by spin-polarized currents of 10 7 A/cm 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 A/cm 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.

Evidence of high dissipation in magnetization reversal processes of five Co/Cu bilayers

“…However, the nature of this dissipation process is not well understood. It could involve precession phenomena of the layer magnetization induced by a spin transfer mechanism which can occur because the magnetic field is close to the switching field value [17] or possible spin-wave emission processes [18].…”

Telegraph noise due to domain wall motion driven by spin current in perpendicular magnetized nanopillars

“…For nanopillar spin valves with in-plane anisotropy, in the presence of spin transfer torque telegraph noise ͑TN͒ switching has been observed between fully magnetized states: the parallel ͑P͒ and the antiparallel ͑AP͒ states. [8][9][10][11][12][13] In the case of nanopillars exhibiting perpendicular anisotropy no TN effect has been reported, as yet, but has been predicted for certain parts of the currentfield phase diagram. 4 In addition to the switching between the two uniform states, by the application of both field and current additional intermediate states have been observed in perpendicular anisotropy devices.…”

“…Those time scales are slightly larger than the ones observed for in-plane anisotropy nanopillars. In that case, TN is observed between fully magnetized states only with no domain wall involved [8][9][10][11][12][13] and the time scales are shown to vary from 1 s to 1 s. For H eff = −45 Oe the system switches mainly between the P state and a DW state whereas for H eff = −235 Oe the system switches between several DW states and the AP state. Both the magnetic states involved and the typical dwell times are tuned by the magnetic field.…”

Mechanisms limiting the coherence time of spontaneous magnetic oscillations driven by dc spin-polarized currents

“…A plausible mechanism for the strong T dependence is switching between different dynamical magnetic modes, leading to linewidths inversely proportional to the lifetime of the precessional state. Switching between steady-state precessional modes and static states has previously been identified at frequencies from < 100 kHz 8,29,30 to 2 GHz. 31 The consequences on linewidths have been considered within LLG simulations.…”