Effects of gas exposure on the surface-acoustic-wave attenuation and magnetoresistance of nickel thin films

Abstract

We present experimental data showing that both the magnetic bias field H-dependent attenuation response to microwave (0.6 GHz) surface acoustic waves A(H) and the dc magnetoresistance ΔR(H) of vacuum-evaporated nickel thin films (100–250 Å) can significantly decrease or ‘‘age’’ when the samples are maintained in vacuum after film deposition. However, these losses in A(H) and ΔR(H) response can be recovered by exposing the samples to air. These effects are reversible, that is, if the samples are again placed in vacuum; their A(H), ΔR(H) responses again decrease while subsequent exposure to air again results in a recovery of sample response. Exposure of vacuum-aged samples to Ar results in no change in sample response and a passivation of the sample against the subsequent effects of other gases. These phenomena are apparently due to reversible physiabsorption processes that affect the magnetostriction-stress contribution to film coercivity. Apart from their significance for the study of the impact of physical absorption processes on thin film micromagnetic structure, these ‘‘gas effects’’ may have practical applications for modifying the response characteristics of magnetoelastic surface-wave devices and sensors.