Elimination of domain wall velocity saturation and local coercivity variations by multilayer garnet materials

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Abstract
Experiments involving the growth of hard‐bubble‐suppressing 90° capping layers below, on top of, and surrounding the bubble film have been conducted. The investigation of the wall domain dynamics of the triple layer structure (suppression layer‐bubble film‐suppression layer) has shown that the velocity saturation associated with dynamic conversion is removed. Domain wall velocities of 12,000 cm/sec have been observed, presumably as a result of the large shape and stress anisotropy at the bubble surfaces preventing the formation of horizontal Bloch lines. Further insights as to the origin of dynamic conversion are offered by the data taken on structures involving the bubble film and a single 90° suppression layer. In these cases, the horizontal Bloch line model predicts dynamic behavior not dependent on the direction of the applied biasing field. However, experiments show that for both types of double‐layer structures, velocity saturation is removed only when the biasing field is applied with the correct polarity. Application of the biasing field with the opposite polarity gives velocity saturation results identical to those observed with ionimplanted films. These results suggest either the horizontal Bloch line model is incorrect or that other complex wall structures are important in these layered films. Multi‐layered structures also offer improved static properties over over ion‐implanted films. A large variation in the coercivity has been seen over over the surface of ion‐implanted films. The origin of this local coercivity is unknown but may be related to the post‐growth leadrich film observed on the surface of garnet bubble films. The effects of this local coercivity become increasingly important as the device operation frequency tends toward the dynamic conversion point. No such local coercivity variations were observed in the triple layer structures. The suppression layer also has been shown to improve the temperature stability properties of the stripwidth and the mobility, as well as to increase the wall energy.

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