Ferro-magnetic resonance in thin ni-films

Abstract

A description is given of experiments of ferromagnetic resonance in thin films of nickel. The films were prepared by evaporation onto mica and were from 0.1μ to 3μ thick. It was found that the value of magnetic field for which the absorption was a maximum appeared to be dependent on the thickness of the film. The results are interpreted in terms of Kittel's equation which involves the quantity ( N y − N z ) I where N y and N z are the demagnetising factors normal to the plane of the film and in the direction of the static magnetic field respectively and I is the saturation intensity of magnetisation. A new oscillation type of magnetometer is described by which both I and ( N y − N z ) may be measured. Results of these measurements combined with the ferromagnetic resonance measurements on the same samples of thin films, show that the g value for nickel is independent of thickness and that the change in resonance magnetic field is, in nearly all cases, due to a change in ( N y − N z ). This is interpreted as arising from strain in the nickel film, due to differential contraction of the nickel and the mica substrate on cooling from the annealing temperature. Calculations show that this should give a change of the right order of magnitude and other experiments are described which support this view.