A Study of Spin-Flipping in Sputtered IrMn using Py-based Exchange-Biased Spin-Valves

To study spin flipping within the antiferromagnet IrMn, we extended prior Current-Perpendicular-to-Plane (CPP) Giant Magnetoresistance (GMR) studies of Py-based exchange-biased-spin-valves containing IrMn inserts to thicker IrMn layers-5 nm less than or equal to t(IrMn) less than or equal to 30 nm. Unexpectedly, A{\Delta}R = A[R(AP) - R(P)]--the difference in specific resistance between the anti-parallel (AP) and parallel (P) magnetic states of the two Py layers-did not decrease with increasing t(IrMn), for t(IrMn) greater than 5 nm, but rather became constant to within our measuring uncertainty. This constant looks to be due mostly to a new, small MR in thin Py layers. The constant complicates isolating the spin-diffusion length, lsf(IrMn), in bulk IrMn, but lsf(IrMn) is probably short, less than or equal to 1 nm. Similar results were found with FeMn.