PtMn single and dual spin valves with synthetic ferrimagnet pinned layers

Spin valve films with the PtMn/Co/Ru/Co synthetic ferrimagnet pinned layer, in which the magnetization of the two Co layers is strongly coupled in an antiparallel orientation and the magnetization direction of one of the Co layers is pinned by unidirectional exchange coupling with PtMn, were investigated. PtMn synthetic ferrimagnet pinned layers were demonstrated to exhibit strong unidirectional exchange field H-ex exceeding 2500 Oe at an optimum PtMn/Co/Ru/Co thickness combination for either PtMn on top or at the bottom. The H-ex of PtMn/Co/Ru/Co rapidly increased at the PtMn layer thickness around 10-12 nm and was nearly constant from 12 to 30 nm. It was also found that the saturation field of the Co(3 nm)/Ru(0.8 nm)/Co(2 nm) sandwich, which represents the antiparallel interlayer coupling strength through Ru, remained 2200 Oe even at 300 degrees C. Thus the combination of the high blocking temperature of 380 degrees C for PtMn and the large antiparallel exchange interaction of Co/Ru/Co up to 300 degrees C makes the pinned layer highly stable against various magnetic fields during Joule heating of spin valve sensor stripes. Further, the PtMn synthetic-ferri-pinned-type dual spin valve films showed a large unidirectional exchange field of 2000 Oe and a giant magnetoresistance ratio of 11.0%. (C) 1999 American Institute of Physics. [S0021-8979(99)39408-1].