GIANT SURFACE MAGNETOSTRICTION IN POLYCRYSTALLINE NI AND NIFE FILMS

We have measured the effective magnetoelastic coupling coefficients, B (eff), of polycrystalline NiFe/Ag/Si, NiFe/Cu/Si, and Ni/SiO2/Si films in situ as functions of magnetic layer thickness over the range from 1.5 to 50 nm using magneto-optic Kerr effect and applied static strain . The B(eff),s agree well with bulk values at large thicknesses but ta ke on anomalously large values for thicknesses below about 5 nm. The d ata are well fit by a Neel model, B(eff)=B(bulk)+B(surf)/(t-t0), where t0 may be related to intermixing at the interface with the substrate (verified by Auger depth profiling). These data suggest that the surfa ce conditions are of enhanced importance in controlling magnetic prope rties, particularly anisotropy, permeability, and noise, even in films whose compositions are nominally of zero magnetostriction.