Origin of interfacial energy in coupled films of permalloy and cobalt

The mechanism of magnetic coupling in multilayer films was investigated by analyzing the shape of the magnetoresistance hysteresis loops. A magnetic field was applied during the deposition of the layers in a high vacuum. Each film consisted of a soft layer of Ni-Fe and a hard layer of Co separated by intermediate laminations of SiO or Ag. The thickness of the intermediate lamination varied from 100 to about 5000 Å. The magnetoresistance hysteresis loop of the soft layer was displaced along the driving field axis. The displacement reaches a maximum value when the intermediate lamination has a thickness of about 700 Å and seems to be caused by a negative magnetic coupling. It was also found that the material of the intermediate lamination does not materially alter the characteristics of the films. Both phenomena were discussed in terms of magnetostatic interactions between uniaxial single-domain particles. The explanation for the interfacial energy based on long-range interactions points out that short-range interactions between the separated layers can be neglected.