Athermal training due to exchange and dipolar coupling within a granular model for exchange bias

Athermal training effects in static magnetization curves of exchange-coupled systems have been obtained within a model for polycrystalline antiferromagnetic/ferromagnetic bilayers with a granular interface. Together with parallel coupling between each ferromagnetic grain and stable interface grains that sit underneath it, magnetic exchange and/or dipolar interactions between neighboring stable and partially stable interface grains have been considered. Using realistic anisotropy and coupling parameters in the simulations, training effects have been obtained regardless of the anisotropy type (uniaxial or biaxial) of the interface grains with uncompensated spins. The partial recovery of training effects after application of strong magnetic fields or a change of the sign of the exchange-bias field after training experimentally observed by some authors has been naturally achieved in the framework of the present model.