Thermally assisted decay of pinning in polycrystalline exchange biased systems (invited)

The exchange field decays when spin valves are subjected to a field that rotates the pinned layer towards the reverse direction. The decay results from a competition between the torque on the interfacial AF spins from the pinned layer, which lowers the barrier for thermal switching, and the KuV product of the AF grains, which provide stability. Typical values of the decay rates at 125 degreesC vary between 5-35%/decade, depending upon the AF. A comparison of the thermal decay-rates for many AF's important for spin valve heads shows that IrMn (blocking temperature, T-b similar to 250 degreesC) is the most stable, followed by NiMn (350 degreesC), PtMn (325 degreesC) and NiO (200 degreesC). An Arrhenius-type model is presented which fits the data well. This model is used to estimate the anisotropy constants of NiMn and IrMn to be 5 x 10(5) and 2 x 10(6) erg/cm(3), respectively. Thermally activated reversal of the AF results in T-b often being less than T-N, and a peak in the pinned layer coercivity observed near T-b. (C) 2001 American Institute of Physics.