Dislocations in Gadolinium Gallium Garnet (Gd3Ga5O12): III. Nature of Prismatic Loops and Helical Dislocations

Thin garnet films suitable for magnetic bubble devices can be made by depositing the film material onto nonmagnetic garnets such as Gd
3
Ga
5
O
12
(GGG). The performance of these devices is influenced by the dislocation content of the films. This, in turn, depends on the dislocation content of the substrate. Dislocations in the substrate can be detected by means of the birefringence they induce, or from the etch pits formed where they meet the sample surface. Most of the dislocations revealed by these techniques have been climb loops around inclusions and helical dislocations. This paper describes an optical method for determining the sign of the stresses at inclusions and nature of loops and helical dislocations. The method has shown that iridium inclusions are compressed by the matrix and that the loops and helices in GGG are extrinsic; they grow either by the emission of vacancies or the absorption of interstitial atoms.