ORIGINAL MAGNETIZATION PROCESSES IN THE ARTIFICIAL FERRIMAGNET Y-CO/GD-CO/Y-CO

Sandwiches consisting of three amorphous layers, each about 1000 angstrom thick, have been prepared by dc triode sputtering. The approximate composition of each layer is R0.33Co0.67. These systems are such that the Co moments are coupled parallel to each other throughout the thickness of the sandwich while the RE moments are aligned either parallel (for light RE) or antiparallel (for heavy RE) to the Co moments. In this paper, we report experimental and analytical results obtained on the model system Y-Co/Gd-Co/Y-Co. In low fields, both Y-Co and Gd-Co magnetizations are saturated in opposite directions, the Gd moments being antiparallel to the field. As a result, the macroscopic magnetization alternates from one layer to another giving rise to a macroscopic ferrimagnetic arrangement (artificial ferrimagnet). When a field is applied, the magnetization of the Gd-Co layer reverses in the firection of the field. This transition is retarded by the necessary creation of planar Bloch walls at the two interfaces within the Co sublattice. In higher fields, the whole approach to saturation is governed by the reversible shrinking or broadening of these two Bloch walls.