Initial rotational susceptibility of exchange coupled Permalloy/copper/cobalt multilayers

Exchange coupled Permalloy/copper/cobalt multilayers are observed by Kerr microscopy. The stability of 180° walls is investigated by applying fields transverse to the initial saturation field. The experiments show that the anisotropy is not as small as previously assumed, but is determined by the initial field. In contrast to the samples with ferromagnetic coupling, the preexisting walls in antiferromagnetically coupled samples can easily be annihilated using transverse fields. This can be explained by particular combinations of coupling strength and anisotropy