Training and temperature effects of epitaxial and polycrystalline Ni_(80)Fe_(20)/Fe_(50)Mn_(50) exchange biased bilayers

摘要

For exchange biased bilayers of Ni_(80)Fe_(20)/Fe_(50)Mn_(50), the effects of crystalline structure on the training effect of the exchange bias field (H_(EB)) and of the coercive field (H_C) have been investigated for (001)- and (110)-oriented epitaxial as well as polycrystalline thin film samples. The training effect of H_(EB) and H_C at 5 K is strongest for the polycrystalline sample as compared to the (110)-oriented sample. The training effect is found to originate from the hysteresis cycle-number dependence of H_1, the switching field of the descending branch of the hysteresis loop. A very good qualitative agreement is observed between the cycle-number dependence of H_(EB) and of the fraction of pinned uncompensated moments of an antiferromagnet (AFM) monolayer. In the temperature range between 5 and 300 K, H_(EB) and H_C are found to depend strongly on the crystalline structure as well as orientation of the ferromagnet (FM)/AFM bilayers.