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.