Controlled compensation walls and compromise compensation walls in garnet films by the silicon annealing technique

The Si annealing technique has been used on Ga‐substituted LPE bubble garnet films to reduce 4πM through zero and produce controlled, well‐defined compensation walls. A Si film was deposited on a garnet film, patterned photolithographically, and annealed at 525°C for 40 hours in O2. This produced light and dark Faraday contrast regions separated by compensation walls which were independent of the bias field Ho. In the course of annealing, a new type of domain was observed. After 20 hrs. of annealing, the walls between the light and dark areas became fuzzy at Ho ∼ 80 Oe. At ∼ 120 Oe they abruptly began expanding over large areas forming a grey (or 3rd color) domain corresponding to ∼ 0° Faraday rotation. Our model is as follows: At 20 hrs., under the Si, a compensation plane (πM = 0) is produced near the middle of the film and approximately parallel to the surface. In small Ho a "compromise compensation wall" perpendicular to the surface separates the light and dark areas. As Ho is increased >80 Oe, the wall changes its shape to conform to the zero 4πM plane producing a true compensation wall. The two regions above and below this plane tend to cancel in rotation and create the new kind of grey domain. A new type of mobile grey bubble is also described.