Measurement protocols for exchange biased systems

A study of exchange biased systems has been made focused on the development of
measurement protocols that yield measurement reproducibility. The materials studied
were IrMn(tAF)/CoFe(10nm) thin films, with tAF being 3nm and 5nm. These materials
were selected due to their industrial applications. The thicknesses were chosen as they
were the most appropriate for the purpose of this study.
Vibrating sample magnetometry has been used to investigate thermal activation
properties in the set of samples. The measurement protocols developed allowed
measurement reproducibility. They lead to a better understanding of the exchange
biased phenomenon. It was found that the changes occurring in the exchange biased
systemsd uring measuremenat re due to thermal activation in the antiferromagneticl ayer
which reduced the degree of order within the antiferromagnet. It was observed that the
peak in the coercivity with the temperature of thermal activation does not correlate with
the median blocking temperature.
A study of training effects and their behaviour with temperature has led to the
identification of three different contributions to exchange bias which are spin freezing,
spin reorientation, and thermal activation. Each of these effects contribute to the shift of
the hysteresis loop and the coercivity of exchange biased systems through different
mechanisms.
The results obtained are consistentw ith a grain size dependenceo f the exchangeb ias
phenomenon, and are in accordance with grain models of exchange bias. Also, the
measurement protocols obtained have been used by other researchers in FeMn/NiFe
exchange coupled bilayers. The results obtained were in accordance with the
conclusions of this thesis