Interlayer Coupling and Magnetoresistance of MnIr-Based Spin Valves: Dependencies on Deposition Rate, Spacer Thickness, and Temperature

We present a study of the dependence of Cu spacer interlayer coupling field (H_coupl) on the thickness t of the Cu and the deposition rate of the layers in spin valves (SVs). We considered two series of SVs made of NiFe/CoFe/Cu/CoFe/Mnlr with Cu t ranging from 16 to 26 Aring. In series 1, the deposition rates were 0.49 A/s for Cu and 0.29 Aring/s for CoFe. In series 2, the deposition rates were lower: 0.28 Aring/s for Cu and 0.23 Aring/s for CoFe. We found that lowering the deposition rates led to considerably lower H_coupl; about ~24 Oe in series 1 versus about 13 Oe in series 2, both with t = 19 A and temperature T = 300 K. In both series, we observed an increase of H_coupl when t is reduced (as would be expected from Neel coupling dominance). The increase is weaker in the low deposition rate series. The difference is related to the different roughness of the ferromagnetic/nonferromagnetic interfaces under the two deposition rates. We also measured the temperature dependence of the magnetoresistance (MR), starting at 20 K, observing values between 9% and 16% for series 2 and between 13% and 16% for series 1. MR then decreased linearly with increasing T for all SVs, vanishing at a temperature T₀ of about 600 K, well below the bulk Curie point. However, we observed a striking difference between series 1 and series 2 in the temperature dependence of the dGMR/dT slopes, where GMR is the giant magnetoresistance.