Study of spin-transfer-induced dynamics in spin-valves for current-perpendicular-to-plane magnetoresistive heads

We have investigated spin-transfer effects in complex spin-valve pillars developed for current-perpendicular-to-plane (CPP) magnetoresistive heads. The structure of the samples included an exchange-biased synthetic pinned layer; both the reference and the free layer were laminated by inserting ultrathin Cu layers. Despite the low thickness of the polarizer, our results show that the free layer can be switched between the parallel (P) and the antiparallel (AP) states by applying current densities of the order of 107 A cm−2. Due to the use of exchange-biased structures, the stability phase diagrams could be obtained in the four quadrants of the field (H)–current (I) plane, for static as well as for dynamic experiments. Microwave measurements demonstrate the existence of several spin-transfer induced precession regimes, as well as the non-equivalence of the two bias polarities, given the influence of the non-homogeneous fields in the system.