Ferromagnetic resonance in single-crystal nickel films

Abstract

Ferromagnetic resonance measurements have been carried out on single-crystal nickel films obtained by epitaxial evaporation on NaCl under various evaporation conditions. Resonance measurements on thin films by previous investigators have yielded anomalous values of 4M which have tentatively been attributed to stress in the films. In this paper it is shown that there is a second factor which must be taken in consideration to explain the shift in resonance peak. Films that were grown at high temperatures (400°C) and in good vacuum (10-10 mm Hg) exhibited an apparent saturation magnetization only 60-70 of the bulk value. This is in accord with the results of ferromagnetic resonance experiments of Kuriyama et al., who attempted to explain their results by the presence of large tensile stresses in the films. However, electron microscope studies of films grown under the above conditions indicated that the films formed discrete, well-separated islands of nickel. The observed particle sizes are such that the demagnetizing factor perpendicular to the film is 60-70 of the value for a continuous planar film. This implies that the shift in the resonance peak was caused not by stresses but by a lowering of the demagnetizing field resulting from the discrete particle growth. To further substantiate this, continuous films grown at lower temperatures (300°C) and in technical vacuum (10-5 mm Hg) exhibited a magnetization approximately 60 higher than the bulk material values. X-ray diffraction indicated the presence of large compressive stresses in these films. That the increased magnetization was induced by these compressive stresses was convincingly shown by the decrease of the saturation magnetization to bulk value when the stress was relieved by the introduction of water vapor into the cavity. No such change in the external field at resonance was observed for the discontinuous films under a similar exposure to water vapor. © 1962 The American Institute of Physics.