OBSERVATION OF THE DOMAIN STRUCTURES IN SOFT MAGNETIC (Fe97Al₃)85N15 / Al₂O₃ MULTILAYERS

The longitudinal magnetooptical Kerr effect was used to analyse magnetic domains in soft magnetic (Fe_(97)Al₃)_(85)N_(15)/Al₂O₃ multilayers in order to get microscopic understanding of interlayer exchange coupling. The measuring system consists of a Kerr microscope, a CCIR camera (with an 8-bit framegrabber), 16 bit digital camera and computer system for real-time image processing and to control external magnetic field and cameras. The strength of ferromagnetic (FM) coupling as a function of the spacer thickness of Al₂O₃ was investigated. It was found that strong FM-coupling, strong uniaxial anisotropy and coherent rotation of the magnetization have been observed for the spacer thickness in the range of 0.2 ㎚ ≤ t ≤ 1 ㎚, however, weak FM-coupling, patch domains and 360°-walls occur for the spacer thickness of t = 2.5 ㎚. At a spacer thickness of t ≥ 5 ㎚ transition takes place from weak FM-coupling to the decoupled state where complex interlayer interactions and different types of the domain walls were observed.