COMPLEX MAGNETIZATION PROCESSES OF EXCHANGE-COUPLED TRILAYERS

The magnetization processes of two series of sandwiches of compositions Sm-Co/Co/Sm-Co' and Sm-Co/Gd-Co/Sm-Co' prepared by dc bias sputtering are presented. The layers of Sm-Co and Sm-Co' have different compositions each with a different coercive field. The central layer consists of a soft magnetic material with a thickness varying from 500 to 5000 angstrom. In these systems, it is possible to stabilize a magnetic configuration with the magnetic moments of the external layers having opposite directions. Due to the magnetic coupling between the layers associated with the strong exchange interactions between cobalt atoms throughout the whole sample, a large planar Bloch wall is formed in the central layer. The width of this wall depends on the intrinsic properties of this central layer, but the magnetization processes vary with the relative magnitude of the wall width to the thickness of this layer. For a large thickness of the central layer, the Bloch wall is very mobile under applied field leading to a very large susceptibility.