Observation of spin wave resonance in Ni thin films after adsorption of oxygen

Ni thin films were deposited in ultrahigh vacuum (UHV) onto soft glass substrates. Film thicknesses ranged from 74 to 837 Å. On films in UHV, only the uniform precession mode was observed during the microwave experiments. Admission of gases such as H2, H2O, O2, N2O, and air caused a lowering of the resonance field of the uniform precession mode. This effect was interpreted earlier as a relief of compressive stress related to surface tension. After adsorption of gases the films were virtually stress free. In the case of O2, N2O, and air admission a standing spin wave resonance (SWR) mode (p=1) slowly developed in films thicker than 400 Å after the lowering of the resonance field of the uniform precession mode was observed. From the fact that in UHV and in the presence of H2 and H2O no SWR was found, while development of the first mode was slow in oxygen-containing atmosphere and was thought to be related to the growth of a NiO layer, it may be concluded that spin wave excitation is made possible in this case as a result of surface spin pinning due to ferromagnetic-antiferromagnetic exchange coupling (Meiklejohn and Bean) rather than surface anisotropy (Néel). The surface spin pinning was found to be weak but the intensity of the first mode increased rapidly with film thicknesses above 400 Å. On the basis of the surface spin pinning model proposed by Kittel the exchange constant A was assigned an average value of 0.74×10-6 erg/cm