Structural, electrical and magnetic properties of evaporated permalloy thin films: effect of substrate and thickness

We have studied the effects of the substrate and the thickness on the structural, electrical and magnetic properties of permalloy thin films Ni81Fe19 (Py). Series of Py thin films were evaporated on four various substrates: glass, kapton, Si(1 0 0) and Si(1 1 1). The thickness ranges from 13 nm to 190 nm. We show that evaporated permalloy on kapton and Si(1 1 1) present a strong < 1 1 1 > preferred orientation for samples thicker than 85 nm; however, the films grown on glass and Si(1 0 0) present a weak (1 1 1) texture for most of these samples. Generally, the lattice constant for Py/glass, Py/Si(1 0 0) and Py/Si(1 1 1) samples is found to be smaller than the bulk value (a(bulk)), while for the Py/kapton, it is larger than a(bulk). There is an overall increase of the grain sizes (100 angstrom-480 angstrom) with thickness for Py/Si(1 1 1), Py/Si(1 0 0) and Py/glass. For the Py/kapton samples, the grain sizes (about 130 angstrom) seem to be independent of the thickness. The resistivity, rho, decreases with increasing thickness for all samples. The highest values of rho were observed in the Py/kapton thin films, diffusion at the grain boundaries might be in part responsible for these high values. The magnetization easy axis is found to be in the film plane for all samples. For all series, the two thinner films seem to exhibit a perpendicular magnetocrystalline anisotropy. The coercive field, H-C//, values range from 1 Oe to 67 Oe. A peak in the H-C// vs. t curve is observed for Py/Si while for Py on glass and Py/kapton, H-C// seems to be constant. We also observed that for the thicker Py/Si(1 1 1) samples, the coercivity decreases as the grain sizes increase.