Magnetoresistance of antiferromagnetic Ir22Mn78-pinned spin filter specular spin valves

Abstract

Specular spin valves (SSVs) having the spin filter layer (SFL) in contact with the ultrathin free layer of composition Ta-3/NiFe2/IrMn7/CoFe1/(NOL1)/CoFe2/Cu-1.8/CoFe(t(F))/Cu(t(SF))/(NOL2)/Ta-3.5 (in nm) deposited by magnetron sputtering were studied. For these antiferromagnetic Ir22Mn78-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness (t(F)) and the SFL thickness (t(SF)) were 1.5 nm, and a MR ratio higher than 11% was maintained even when t(F) was reduced to 1.0 nm. This was due to an increase of specular electrons by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field (H-int) between the free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer (H-cf) was significantly reduced as compared to traditional spin valves (TSV), and remained as low as 4 Oe when t(F) varied from 1 to 4 nm. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.