  Hard-soft bilayers are analogous to prototype exchange-biased ferromagnetic
-antiferromagnetic systems as the minor loop of the soft layer is biased by the
hard and furthermore they offer bias layer tunability. In sputtered CoPt/Co
hard-soft bilayers we demonstrate that the exchange bias field shows a linear
dependence on the hard layer magnetization, while the coercivity shows a
quadratic dependence. Analysis of the minor hysteresis loop features supported
by Monte-Carlo simulations provide clear evidence that the coercivity of the
soft layer is mainly determined by the tunable randomness of the domain state
of the hard layer.
