Magnetic bubbles, walls, and fine structure in ion-implanted garnets

Abstract

The description and interpretation of bubbles with associated domains and charged walls in Sm YIG garnets implanted with H+ ions are presented. The nature of the contrast obtained with Bitter solution is shown to result from the polarization of the grains by the external bias field. The use of this contrast allows the determination of the direction of the magnetization in the plane of the film and perpendicular to it. The domain arrangements around the bubbles are found to be strongly dependent on the presence of an in-plane anisotropy. In the specimen studied here, the magnetocrystalline threefold symmetry and in-plane easy direction coming from a crystallographic tilt are predominent. The shape of the domains associated with bubbles changes significantly with the magnitude and the direction of the applied in-plane field. The structure can be interpreted in terms of the flux closure and bubble-wall configurations for the S=+1 states investigated here. The fine structure inside the bubbles is revealed and shown to be linked with external walls. The charged walls are attached to unimplanted disks. Their position, polarity, and shape are found to be highly dependent on the symmetry properties of the film as well as the characteristics of the applied in-plane field. Bubbles with charged walls of opposite polarity are strongly attracted to each other; however, a simple model based on magnetostatic interaction is found to be insufficient as the charged walls and the bubbles do not always rotate with exactly the same phase.