Influence of composition on the magnetisation reversal of IrMn/CoFe exchange bias systems

The magnetisation reversal in IrxMn1−x/CoFe exchange bias bilayers has been investigated as a function of the level of Ir content,'x', in the stack where x = 0.15, 0.19 and 0.22. Values of the anisotropy constant of IrMn in excess of 107 erg/cc were obtained for the samples with a lower Ir content. Increasing the Ir content to 22% decreases the value of the anisotropy by ∼40% which results in a significant reduction in the thermal stability of the samples. While a higher thermal stability is desired for high temperature applications, the stronger anisotropy observed for the x = 0.15 samples results in an increased shearing of the hysteresis loops and, as a consequence, a much wider switching field distribution. Hence, in practice, approaches that combine the high anisotropy of low Ir content with the narrower switching field distribution observed in systems with high levels of Ir might be required.