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

Abstract

The irreversible thermoremanent magnetization (${m}_{\mathrm{TRM}}^{irr}$) of a sole, magnetically diluted epitaxial antiferromagnetic Co${}_{1\ensuremath{-}y}$O(100) layer is determined by the mean of its thermoremanent magnetizations (${m}_{\mathrm{TRM}}$) at positive and negative remanence. During hysteresis-loop field cycling, ${m}_{\mathrm{TRM}}^{irr}$ exhibits successive reductions, consistent with the training effect (TE) of the exchange bias measured for the corresponding Co${}_{1\ensuremath{-}y}$O(100)/Co($11\overline{2}0$) bilayer. The TE of exchange bias is shown to have its microscopic origin in the TE of ${m}_{\mathrm{TRM}}^{irr}$ of the magnetically diluted antiferromagnet.