PtMn spin valve with synthetic ferrimagnet free and pinned layers

Spin valve films with a laminated antiparallel Co/NiFe/Ru/NiFe synthetic ferrimagnet (SF) free layer combined with PtMn/Co/Ru/Co SF pinned layers were demonstrated to maintain large magnetoresistance ratio of ∼8.0% even below ∼10 Å of effective thickness of the Co/NiFe/Ru/NiFe SF free layers, defined as the thickness difference of the two ferromagnetic layers antiferromagnetically coupled through Ru. Spin flopping field Hsf and saturation field Hs of the Co/NiFe/Ru (8 Å)/NiFe SF free layers slightly increased after annealing at 250 °C for 4 h, and then the Hsf of the Co (3 Å)/NiFe(30 Å)/Ru(8 Å)/NiFe(20 Å) SF free layer after annealing remained 600 Oe, even at 200 °C. Further, antiferromagnetic coupling interlayer materials and their thickness dependence of Hsf and Hs were investigated in the Co(3 Å)/NiFe(40 Å)/X/NiFe(25 Å), X=Ru, Cr, Ir, and Rh, sandwich stacks. The oscillatory antiferromagnetic exchange coupling was clearly observed, and the large Hsf and Hs exceeding 2000 Oe and 7 kOe, respectively, were obtained both at Ir 3.8 Å and Rh 6.1 Å, which corresponded to the oscillatory first peak in the Co/NiFe/Ir/NiFe and Co/NiFe/Rh/NiFe sandwiches.