Modification of the exchange bias effect by He ion irradiation

FeNi/FeMn exchange bias samples with a large exchange bias field at room temperature have been prepared. Upon irradiation with He ions, both the exchange bias field and the coercive field are modified. For low ion doses the exchange bias field is enhanced by about 70%. Above a threshold dose of 0.3/spl middot/1/sup 15/ ions/cm/sup 2/, the exchange bias field decreases continuously as the ion dose increases. The observed modifications can be explained in terms of defect creation acting as pinning sites for domain walls and atomic intermixing.