Magnetic Domain Structures of Multilayered permalloy Films Observed by Spin-Polarized SEM

The domain structures in patterned permalloy films were investigated by spin-polarized SEM, as part of the development of thin film magnetic heads with narrow track widths. Spin-polarized SEM made it possible to determine the direction of the magnetization in magnetic cores accurately. For single-layer permalloy films, triangular domains dominate and no 180° walls are observed in pole pieces when the track width is less than 10 μm. For two-layer permalloy films with an alumina intermediate layer of thickness 4 nm, domain structures indicate that the magnetization direction remains oriented along the track width even when the track width is 7 μm. Furthermore, in six-layer permalloy films with alumina intermediate layers 20 nm thick, the length of the 180° walls in the pole pieces becomes longer than that in two-layer permalloy films with a 4 nm alumina layer. It is thus concluded that multilayer permalloy films with single-domain structures are best suited for use in thin film magnetic heads with narrow track widths.