Microstructure and magnetoelastic coupling coefficients in thin NiFe and Ni films

The effective magnetoelastic (ME) coupling coefficients B-eff of polycrystalline Ni79Fe21 and Ni films have been reported as functions of thickness t. B-eff was observed to have a thickness-independent bulk term, B-b, and a thickness-dependent surface term, B-s/t consistent with the Neel model. For thickness below 50 Angstrom the surface term is important; it can change the sign of the effective ME coupling constant and dramatically increase its magnitude. We expect that the surface ME coupling we observe in polycrystalline thin films may be a combination of the intrinsic Neel surface effect and extrinsic microstructure effects. Our transmission electron microscopy, Auger depth profiling, and atomic force microscopy rule out film discontinuity and compositional gradients as significant sources of he surface ME effect. (C) 1996 American Institute of Physics.