Training effect of the exchange bias in Co/CoO bilayers originates from the irreversible thermoremanent magnetization of the magnetically diluted antiferromagnet

The irreversible thermoremanent magnetization (mTRMⁱʳʳ) of a sole, magnetically diluted epitaxial antiferromagnetic Co_1-yO(100) layer is determined by the mean of its thermoremanent magnetizations (mTRM) at positive and negative remanence. During hysteresis-loop field cycling, mTRMⁱʳʳ exhibits successive reductions, consistent with the training effect (TE) of the exchange bias measured for the corresponding Co_1-yO(100)/Co(112̄0) bilayer. The TE of exchange bias is shown to have its microscopic origin in the TE of mTRMⁱʳʳ of the magnetically diluted antiferromagnet.