Internal bias effect of double layer epitaxial garnet films

A method of eliminating the external magnetic bias field necessary to sustain stable cylindrical magnetic domains (magnetic bubbles) is presented. This method uses double-layer garnet films. The films were grown on the (111) surface of Gd3Ga5O12by the LPE method under different conditions for each film. There is an exchange coupling interaction across the interface of the double layer. This interaction acts as an effective magnetic bias field by which stable bubbles can be maintained without any additional external magnetic field. The largest effective bias field, approximately 19 Oe, was obtained for a double layer consisting of Y2.55Gd0.45Ga1.37Fe3.63O12(upper film) and Y2.5Gd0.5Ga1.4Fe3.6O12(lower film). Temperature characteristics of the internal bias effect and the relation between the normalized effective field and normalized film thickness are discussed. The bubble domains in the double layer films, when propagated by means of the usual permalloy T-bar patterns but with no external bias field, showed somewhat different operating margin characteristics from those of the bubbles in the usual single-layer garnet films.