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

The exchange field decays when spin valves are subjected to a field that ro tates the pinned layer towards the reverse direction. The decay results fro m a competition between the torque on the interfacial AF spins from the pin ned layer, which lowers the barrier for thermal switching, and the KuV prod uct 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 c omparison 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) an d NiO (200 degreesC). An Arrhenius-type model is presented which fits the d ata well. This model is used to estimate the anisotropy constants of NiMn a nd IrMn to be 5 x 10(5) and 2 x 10(6) erg/cm(3), respectively. Thermally ac tivated 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 In stitute of Physics.