Training effect in an exchange bias system: The role of interfacial domain walls

Abstract

Polarized neutron reflectivity (PNR) is used to obtain the magnetic depth profile of an antiferromagnetically coupled ferrimagnetic/ferrimagnetic bilayer, Gd40Fe60/Tb12Fe88. This system shows a transition from positive to negative exchange bias field HE as the cooling field Hcf is increased from small to large positive value. It also exhibits training behavior upon field cycling which affects HE and the coercive field HC. From the PNR measurements at room temperature and at 15K, we confirm that the magnetic configuration inside the TbFe layer is frozen when the sample is cooled in various Hcf. The thickness and pitch of the magnetic twist inside the TbFe layer depend on Hcf and give rise to the observed differences in the bias field. Irreversible reorganization of the TbFe magnetization at the interface occurs upon GdFe magnetization reversal and is found to explain the training effect as well as the overall reduction in coercivity. © 2006 The American Physical Society.