Spin valves with a thin pinning layer of α-Fe2O3 or α-Fe2O3/NiO

Magnetoresistive (MR) properties of spin valves pinned by a thin alpha-Fe2O3 layer were investigated. In spin valves consisting of alpha-Fe2O3/Ni-Fe(2 nm)/Co(1 nm)/Cu(2 nm)/Co(1 nm)/Ni-Fe(5 nm), the MR ratio remained nearly constant at about 12%, when the alpha-Fe2O3 layer thickness was reduced from 50 to 10 nm, while the exchange anisotropy field H-ex decreased from 22 to 6 kA/m. The spin valves with a thinner alpha-Fe2O3 layer showed higher sensitivity to magnetic field than the ones with a thicker alpha-Fe2O3 layer. The measurement of MR ratio after annealing at 573 K in the alpha-Fe2O3/Co/Cu/Co spin valves revealed that the spin valve with a 30-nm-thick alpha-Fe2O3 layer was more stable against heat treatment than the one with a 50-nm-thick alpha-Fe2O3 layer. Heat treatment increased H-ex in spin valves with both thick and thin alpha-Fe2O3 layers. Spin valves with NiO(10 nm)/alpha-Fe2O3 (10 nm) as a pinning layer showed larger H-ex than spin valves with either alpha-Fe2O3 (10 nm) or NiO(10 nm) pinning layers. (C) 1999 American Institute of Physics. [S0021-8979(99)25408-4].