On the origin of uniaxial anisotropy in permalloy thin films

Abstract

Variation of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> during isothermal magnetic annealing has been systematically investigated to make clear the origin of the induced anisotropy in evaporated Permalloy films of the composition ranging from 70- to 90-percent Ni. The anisotropy of films deposited at room temperature comes from six different origins, whose activation energies are <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{1} &lt; 0.2</tex> eV (0.17-0.2 eV), <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{2} \simeq E_{3} \simeq 0.5</tex> eV, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{4} \simeq E_{5} \simeq 1.1</tex> eV, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{6} = 2.0</tex> eV, respectively. The compositional dependence of contributions from each origin can be used in order to elucidate the whole mechanism of the anisotropy in detail. The component of activation energy from 0.2 to 0.5 eV is closely related to the magnetoelastic anisotropy, while that of 1.1 eV is almost independent of the film composition. The component with the activation energy of 2.0 eV proved to be the same as that found in bulk Permalloy. Furthermore, the effects of the preparation condition of films on the anisotropy are also discussed.