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

Abstract

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°C 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, Tb∼250°C) is the most stable, followed by NiMn (350°C), PtMn (325°C) and NiO (200°C). 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 × 105 and 2 × 106 erg/cm3, respectively. Thermally activated reversal of the AF results in Tb often being less than TN, and a peak in the pinned layer coercivity observed near Tb. © 2001 American Institute of Physics.