Study of Spin Valves With L 10-FePt Pinning Layer and Different Pinned Layers

L1₀ FePt pinned spin valves (SVs) with different pinning/pinned layers: FePt/CoFe, FePt/Ru/CoFe, and FePt/CoFe/Ru/CoFe, were fabricated and investigated. Samples with rigidly ferromagnetic coupled bilayer of FePt (6.0 nm)/CoFe (4.0 nm) show giant magnetoresistance (GMR) ratio up to 7.06%, which is similar to that in the conventional MnIr-based SVs. Whereas the free layer coercivity (H _cf) of CoFe (3.0 nm)/NiFe (4.0 nm) is as high as 45 Oe. This is mainly due to the exchange coupling between the free layer and (111) textured FePt layer. Synthetic antiferromagnetic structures, FePt/Ru/CoFe and FePt/CoFe/Ru/CoFe, were proved to be very effective in reducing the H_cf value by forming a closed flux pathway in the bottom electrode. Compared with FePt/Ru/CoFe SVs, the FePt/CoFe/Ru/CoFe ones show higher pinned layer switching field. The optimized SV structure in this study is glass/FePt (6.0)/CoFe (2.0)/Ru (0.8)/CoFe (2.5)/Cu (2.4)/CoFe (3.0)/NiFe (4.0)/Pt (2.0) (in unit of nm), which exhibits a GMR ratio of 7.04%, a free layer H_cf of 22 Oe, and a pinned layer switching field of 1824 Oe