Investigation of the Coercive Forces of Ni, Fe, and Ni–Fe Films during Evaporation

Abstract

The dependence of the coercive force of Ni, Fe, and Ni–Fe films upon film thickness and amount of trapped gas was evaluated in vacuo. The magneto-optic Kerr effect was utilized for this investigation. Although the penetration depth of light into the film material was determined to be 150±25 A, measurements of Hc could commence for film thicknesses <100 A. It was found that the coercive force Hc is independent of film thickness if the content of trapped gas, as indicated by the p/r (residual gas pressure over deposition rate) ratio is very small, e.g., 5×10−8 torr/A/sec for Ni films. At higher p/r ratios, the coercive force of Ni films displays initially a steep rise which is followed by a shallow minimum, while in Ni–Fe films a maximum appears at about 750 A. The different behavior of Fe films is ascribed to higher gas absorption on this material rather than a principal change in the mechanism of the coercive force. A hypothesis is proposed as explanation for the observed effects.