Coercivity

The temperature scans showed the 20/10 and 40/20 samples to be ferromagnetically coupled or uncoupled. Both of these samples have different loop shapes compared to all of the other, antiferromagnetically coupled layers.

The hysteresis loops for both the 20/10 and 40/20 samples have a higher coercive field than the coupled samples, of $154\pm10\ensuremath{\unskip\,\mathrm{Oe}}$. The coercive field gives the typical field necessary to produce magnetisation reversal in the sample. Assuming a bistable system the uncoupled layers have to overcome a much larger energy gradient to change their magnetisation direction than the coupled layers. The more magnetically continuous coupled layers have a smaller gradient to overcome.

The coercivity of the antiferromagnetically coupled samples seen in Figure 7.9 is exaggerated by the lack of resolution. The coercive field for these samples is of the order of $100\ensuremath{\unskip\,\mathrm{Oe}}$ yet the step size in the loop is also $100\ensuremath{\unskip\,\mathrm{Oe}}$. Whilst this is still less than the uncoupled layers it is most probably much smaller still.