Annealing of Oblique-Incidence Permalloy Films

The anisotropy of evaporated Permalloy films (composition near zero magnetostriction) deposited on glass at 45° to the substrate normal and at a substrate temperature of 200°C has been studied after anneal for several hours at 300°C. After anneal the room temperature easy axis of films with positive magnetostriction is in the original direction. However, films with negative magnetostriction develop a new room temperature easy axis 90° to the original one; at 300°C the easy axis is in the original direction. Application of a large magnetic field in any direction during anneal does not influence the final magnetic anisotropy in either case. These effects are qualitatively explained by assuming the anneal to increase the tension along the long axis of oblique-incidence chains, a process which converts surface energy into strain energy. Anisotropy was measured by resonance in a coaxial bridge over the frequency range 50 Mc to 2100 Mc. A rectangular coaxial cavity is used which can be heated to 500°C in a vacuum of ${10}^{\text{−6}}\hspace{0.17em}\mathrm{mm}$ Hg; continuous angular orientation of the film is possible with a resolution of ±0.5°. Bridge balance is good enough to permit samples of less than 100 A thickness to be measured.