FMR study of surface‐tension‐related stress effects in ultraclean Ni thin films

Ni thin films, 19-837 .ANG. thick, were deposited under ultrahigh vacuum conditions (10-9 to 10-10 torr) onto extremely well degassed substrates. Intrinsic isotropic stress values in the films were detd. by ferromagnetic resonance; these measurements were carried out while the films were in the vacuum system in which they had been prepd. Films deposited onto substrates at 25-35 Deg were in a state of compressive stress when measured in UHV (ultrahigh vacuum). The surface tension provides an explanation for these stresses; the stress levels obey a simple model. After adsorption of O, N2O, or air, the stress levels in the films dropped to very low values, while adsorption of H, H2O, CO, and pyridine resulted in slightly smaller effects. Admission of N to the films caused no stress release. A small degree of reversibility of the latter effect was found for H and H2O. Adsorption of gases had a marked effect on the ferromagnetic resonance linewidths. Films thinner than 100 .ANG. showed deviations from the surface-tension model and the possible discontinuity of such films is indicated as the reason. Expts. on annealed films and expts. with films deposited onto substrates at elevated temps. were performed. The influence of vacuum conditions other than UHV during film deposition was investigated. The relevance of this study to the soln. of the problems of stress-corrosion cracking and H embrittlement is pointed out

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