IrMn microstructural effects on exchange bias variability in patterned arrays of IrMn/Co square dots

The influence of the microstructure on the exchange bias properties of antiferromagnetic/ferromagnetic submicronic dots was investigated in arrays of IrMn/Co square dots of lateral dimensions ranging between 200 and 50nm. IrMn grain size and distributions were tuned by changing the Cu buffer layer or IrMn thicknesses. Exchange bias variability was analysed through focused Kerr measurements on small groups of dots. The average exchange bias field in the patterned samples have similar values as in full sheet samples and with similar variations versus Cu and IrMn thicknesses. Concerning the exchange bias variability, an increase in variability was observed in the patterned samples caused by grain cutting at the dot edges during the patterning process. This increase in exchange bias variability is observed to be even more important in samples having large average grain sizes, particularly for small dots. These effects are correlated with the grain size distributions on full sheet samples. © 2014 IOP Publishing Ltd.