Fe rich CoFe can be used in AP1 to enhance CPP GMR. However, this is found
to degrade the electro-migration performance of the device. This problem
has been solved by using an AP1 that is a laminate of several CoFe(25%)
layers, separated from one another by copper layers. Ultra-thin layers of
iron-rich CoFe are then inserted at all the copper-CoFe interfaces.