Optimisation of overlay properties for use in magnetic bubble devices

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Abstract
Some of the properties required of a magnetic film for use as an overlay in a magnetic bubble device are considered, and it is seen that the function of the overlay in both propagating domains and also acting as a magnetoresistive detector leads to somewhat conflicting requirements. A figure of merit is proposed embracing the fractional magnetoresistive coefficient, saturation magnetisation, resistivity and anisotropy field. Some vacuum-deposited alloys of nickel-iron, nickel-cobalt-iron and nickel-iron-molybdenum are compared on the basis of this figure of merit, as are electroplated nickel-iron and electroless-deposited nickel-cobalt-phosphorus. It is concluded that nickel-iron-molybdenum films merit consideration in place of the normal Permalloy for use in devices with bubble domains of small size.