Role of ion implantation in exchange bias systems

Summary form only given. Applying ion irradiation to exchange bias bilayers we report that both the direction and the strength of the exchange bias field H/sub eb/ can be manipulated locally by He ion irradiation in an applied magnetic field. As a test system NiFe/FeMn double layers are chosen. In this case the magnitude of H/sub eb/ is enhanced over its initial value in the low ion dose regime. Above a threshold irradiation dose a reduction and eventually a suppression of H/sub eb/ is found. The direction of H/sub eb/ is initialized by the field direction during irradiation. The data are well described by a model based on the competition between the enhancement of the exchange bias field strength due to defect creation in the antiferromagnetic layer and the decrease induced by intermixing at the ferromagnet/antiferromagnet interface. In a second series of experiments the role of the chemical ordering of the antiferromagnetic material is addressed employing PtMn instead of FeMn. In this case only a reduction of the exchange bias field is observed and the corresponding dose range is reduced by a factor of 10 compared to the FeMn samples. This can be attributed to the ion-induced chemical disordering. Employing CrMn, the coercivity can be tailored prior to the onset of exchange bias. The applications of ion irradiation to sensor structures are discussed.