MAGNETOSTRICTION CHARACTERISTICS OF ULTRATHIN PERMALLOY-FILMS

An abrupt and large increase in the absolute magnitude of lambda(s) in sputtered polycrystalline permalloy (Ni81Fe19) films for thicknesses below 7 nm was observed. Permalloy films maintain near-zero magnetostr iction with film thicknesses above 7 nm. Film surface studies and micr ostructural characterizations suggest that the magnetostriction observ ed in this study is possibly due to an altered surface morphology of m icrostructural origin. This observation appears to be critical from th e viewpoint of permalloy-based giant magnetoresistive or spin-valve se nsor fabrication where typical permalloy film thicknesses are 3-10 nm. Because thin films with nonzero magnetostriction can induce an undesi rable magnetoelastic anisotropy during sensor operation, the control a nd adjustment of the film composition seems necessary to minimize magn etostriction. (C) 1996 American Institute of Physics.