Memory effect and temperature behavior in spin valves with and without antiferromagnetic subsystems

Temperature behavior and memory effect in standard spin valves (SV) and SVs with synthetic antiferromagnetic (Co/Ru/Co) (SV-SAF) subsystems have been studied. SV-SAFs show much better temperature stability. Memory effect refe rs to the phenomenon that the exchange bias can be altered at temperatures (T-R's) much lower than the blocking temperature (T-B), and these temperatu res (T-R's) are imprinted into SVs. The memory effect greatly deteriorates the magnetoresistance behaviors in SV. Our results suggest that the memory effect is caused by a distribution of local blocking temperatures (T-b's). The magnetization state in the pinned layer is critical in determining the temperature behavior of H-E and magnetoresistance. By partially reversing t he magnetization in the pinned ferromagnetic (FM) layers, we are able to se parate the temperature dependencies of the local exchange bias (H-e) associ ated with regions consisting of different T-b's. Two features have been obs erved: (1) the local exchange bias (H-e) with a narrow T-b distribution has a weak temperature dependence; (2) the simple algebraic sum of local H-e's nearly reproduce the total H-E with the difference between these two quant ities representing the domain wall energy in the FM layer. On the other han d, SV-SAFs show strong resistance to memory effects because of two factors; the strong exchange coupling through the Ru layer, and the net magnetic mo ment of Co/Ru/Co layers in SV-SAF being close to zero. The former makes the two SV-SAF FM layers behave coherently, while the latter makes the interac tion between the SV-SAF and the external field negligibly small. (C) 1999 A merican Institute of Physics. [S0021-8979(99)08621-1].