Spin-Flipping Associated With the Antiferromagnet IrMn

We have used current-perpendicular-to-plane magnetoresistance measurements of Py-based exchange-biased spin-valves containing IrMn inserts of thickness t to estimate the spin-flipping probability of the antiferromagnet IrMn. From t=0 to t= 1 nm, we find a rapid decrease in A¿R=A(RAP - RP) , by about a factor of 50-here A is the area through which the CPP current flows, and RAP and RP are the resistances with the moments of the two Py layers oriented anti-parallel (AP) or parallel (P) to each other. We attribute this decrease to very strong spin-flipping in the IrMn/Cu interfacial region, with effective spin diffusion length l _sf ^IrMn/Cu= 0.24 nm, only about 1 monolayer (ML). But for t from 2 to 5 nm, the decrease of A¿R with increasing IrMn thickness is much slower. The reason for this slowing is not yet clear.