Measurement of energy barrier distribution in the antiferromagnetic layer of exchange biased materials

Summary form only given. In the past we (Hughes et al. J. Appl. Phys. vol.89, p.5585-5591 (2001)) have shown that the antiferromagnetic layer in an exchange bias system can be thermally activated so as to change the exchange field progressively from its optimum value in negative field and eventually to reverse the direction of the exchange bias, although this was done by measuring hysteresis loops at different temperatures while maintaining negative saturation for identical periods of time. In effect what this means is that the measured magnetisation of the ferromagnetic layer essentially represents a measure of the exchange field which acts on the antiferromagnetic layer. As such for a material exhibiting a square hysteresis loop, the exchange field is either at its maximum value in the original direction of the exchange bias (positive magnetisation in the ferromagnet) or is at its maximum value in a direction opposed to that of the original exchange bias (negative magnetisation). Thus the measured magnetisation axis for such a system becomes effectively a measure of the exchange field having two discreet values.