Positive Exchange Bias in Ion-Beam Sputtered IrMn/CoFeB System Grown on CoFe Seed Layer

In this paper, we report positive exchange bias (PEB) at room temperature in as-deposited ion-beam sputtered Si(100)/SiO₂/CoFe/IrMn/CoFeB trilayers without any field cooling protocol. The appearance of positive exchange bias is attributed to the antiferromagnetic coupling between the uncompensated Mn and ferromagnetic (FM) CoFeB spins at the interface. PEB in our sample is obtained as a consequence of interfacial microstructure control leading to unidirectional exchange anisotropy, brought about by the incident energetic atoms/ions produced during ion-beam sputtering. On magnetic annealing, enhancement in the coercivity and disappearance of exchange bias is observed irrespective of IrMn (111) textured growth due to the irreversible changes in the interfacial spin structure. The coercivity of CoFeB layers can be tuned by varying the seed layer thickness in the magnetically annealed samples. The significance of this work is a new insight into the effect of incident energetic atomic flux on the interfacial microstructure leading to positive exchange bias. Moreover, this study is promising in paving way for the utilization of trilayer stack with independently switchable FM layers in CoFeB based TMR and GMR structures.