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

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Abstract
Magnetoresistive (MR) properties of spin valves pinned by a thin α- Fe 2 O 3 layer were investigated. In spin valves consisting of α- Fe 2 O 3 /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 α- Fe 2 O 3 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 α- Fe 2 O 3 layer showed higher sensitivity to magnetic field than the ones with a thicker α- Fe 2 O 3 layer. The measurement of MR ratio after annealing at 573 K in the α- Fe 2 O 3 /Co/Cu/Co spin valves revealed that the spin valve with a 30-nm-thick α- Fe 2 O 3 layer was more stable against heat treatment than the one with a 50-nm-thick α- Fe 2 O 3 layer. Heat treatment increased H ex in spin valves with both thick and thin α- Fe 2 O 3 layers. Spin valves with NiO(10 nm) /α- Fe 2 O 3 (10 nm) as a pinning layer showed larger H ex than spin valves with either α- Fe 2 O 3 (10 nm) or NiO(10 nm) pinning layers.