Variation of the temperature coefficient of collapse field in bismuth-based bubble garnets

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Abstract
To achieve wide temperature operation of magnetic bubble devices, the bias magnet field must remain within the material bias margins over the entire temperature range. It is therefore best that the slope of the bubble collapse field be matched to that of the bias magnet field. However, the slope of the collapse field of unmodified Bi:YIG is 50% greater than the slope of the field of the commonly used barium ferrite magnet. We used an approximation to the collapse field formula to show its dependence on magnetization and wall energy and the effect of substitution of various classes of rare earths. In particular, we have tested the effect of additions of Gd, Sm, and Eu on 1-μm Bi:YIG bubble materials. Collapse field, magnetization, and wall energy were fitted to quadratic functions of temperature from −50 to 150 °C. Gd, the traditional slope-reducing additive, affects the collapse field through the magnetization but also introduces substantial nonlinearity, which can lead to large deviations of the collapse field from the bias field at extreme temperatures. Sm introduces a strongly temperature-dependent rare-earth component of anisotropy that reduces the slope of the collapse field through the wall energy. Eu incorporates both these effects and, owing to its singular magnetic properties, results in the most nearly linear temperature dependence of the collapse field and the best approximation to the bias magnet.