Investigation of domain-wall formation and motion in magnetic multilayers

Abstract

The magnetization-reversal processes in two electrodeposited [Co 64Ni 31Cu 52 nm/Cu] 200 multilayers are investigated using an advanced magneto-optical indicator film (MOIF) technique together with SQUID and vector vibrating sample magnetometry. The non-magnetic Cu spacers are ⋟ 1 nm thick in one specimen leading to predominantly antiferromagnetic exchange coupling between the ferromagnetic Co 64Ni 31Cu 5 layers, and ⋟ 3 nm in the other, with ferromagnetic coupling. The hysteresis loop of the ferromagnetic multilayer is conventional, indicating the stages of domain-wall formation, motion and saturation. Nucleation and movement of domain walls in different layers proceed in a partially uncorrelated manner, and are determined by defects near the surface edge and inside of the multilayer. As a result, the front of the magnetization reversal has a staggered configuration. The antiferromagnetic multilayer has an atypical loop, first with one susceptibility, then a step to a new value, then another susceptibility, and with non-symmetrical behavior about the field axis. Narrow and non-staggered domain-wall images in antiferromagnetically coupled layers are observed. The MOIF technique is used to provide a portrait of the vertical component of the magnetostatic field intensity, helping to elucidate the spin-flip and/or spin-flop processes which are apparently responsible for the hysteresis behavior.