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 μm²cell size permalloy devices. The variation of these margin data with permalloy composition and heat treatment are interpreted in terms of this stress/magnetostriction model.