The saturation magnetostriction of thin polycrystalline films of iron, cobalt, and nickel

The saturation magnetostriction λs of Fe, Co, and Ni films was measured by the cantilevered substrate technique. The values of λs, -6.8×10-6 and -38×10-6, obtained for Fe and Ni, respectively, are in accord with bulk published values. A unique value of λs could not be obtained for Co because the sputtered or evaporated Co films were admixtures of face-centered-cubic and hexagonal close packed phases and the magnitude and sign of λ varied with the fcc content. Increasing the substrate temperatures during film deposition decreases the fcc content; however, this also caused the development of a C-axis hexagonal texture normal to the film plane. Annealing the films at ∼500°C caused a similar but more pronounced texture. Then, because of the uniaxial anisotropy of Co, the films could not be magnetically saturated and the magnetostrictive behavior changed; i.e., the transverse and longitudinal λ were both negative and in some instances the transverse λ was larger than the longitudinal λ.