Strain insensitive Ni-Co films over a wide composition range

The magnetic properties of vacuum deposited Ni-Co films have been studied as a function of film composition, film thickness, and substrate temperature. The experimental parameters ranged from 400-1000 Å for thickness 17-41-percent Ni for composition and room temperature to 300°C for the substrate temperature. It was found that the magnetoelastic strain coefficient approaches zero in the vicinity of 35-percent Ni in agreement with Tolman's result[1] and remains insensitive to film composition from 30-40- percent Ni. These results are in reasonably good agreement with calculations based on single crystal data and the expression of Callen and Goldberg [10]. The coercive force and anisotropy field are an order of magnitude larger than of nonmagnetostrictive Permalloy films. An unexpected result is an increased coercive field with increasing film thickness while the anisotropy field remains practically constant; the films become inverted at a critical thickness in the order of 750 Å For a wide variation of preparation parameters the crystallite size remained less than 100 Å