Permalloy stress/magnetostriction effects in bubble devices

Coercivities as large as 25 Oe are observed in negative magnetostriction permalloy full films following heat treatment at temperatures greater than 300°C. The coercivity is shown to be linearly related to the perpendicular anisotropy that develops in these films. The perpendicular anisotropy results from the interaction of the film's negative magnetostriction and the tensile stress generated during heat treatment. Using elasticity solutions derived by Eshelby, a quantitative evaluation is presented of the stress state expected in similarly heat treated, micron size, permalloy elements embedded in a dielectric matrix. Based on this stress analysis the expected effect of this stress/magnetostriction interaction on bubble device components is discussed. Margin data are presented for the passive bubble generator and start/stop operation in 120 μm
²
cell size permalloy devices. The variation of these margin data with permalloy composition and heat treatment are interpreted in terms of this stress/magnetostriction model.