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

Magnetoresistive (MR) properties of spin valves pinned by a thin α-Fe2O3 layer were investigated. In spin valves consisting of α-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 α-Fe2O3 layer thickness was reduced from 50 to 10 nm, while the exchange anisotropy field Hex decreased from 22 to 6 kA/m. The spin valves with a thinner α-Fe2O3 layer showed higher sensitivity to magnetic field than the ones with a thicker α-Fe2O3 layer. The measurement of MR ratio after annealing at 573 K in the α-Fe2O3/Co/Cu/Co spin valves revealed that the spin valve with a 30-nm-thick α-Fe2O3 layer was more stable against heat treatment than the one with a 50-nm-thick α-Fe2O3 layer. Heat treatment increased Hex in spin valves with both thick and thin α-Fe2O3 layers. Spin valves with NiO(10 nm)/α-Fe2O3(10 nm) as a pinning layer showed larger Hex than spin valves with either α-Fe2O3(10 nm) or NiO(10 nm) pinning layers.