Attenuation of 618 MHz SAW in multilayer Ni-Cu-Ni thin films

The authors report on the magnetic field (H) dependence of attenuation α(H) of 618-MHz SAW (surface acoustic waves) propagating in vacuum-evaporated multilayer Ni-Cu-Ni thin-film samples. Experimental results indicate that the magnetoelastic α( H) response of ≈200-Å single layers of Ni (α(H)≈22 dB/cm) is not affected by the deposition of overlayers of 75 Å and 180 Å of Cu; however, the deposition of a second ≈200-Å layer of Ni onto the Ni-Cu structure reduces the α(H) response of the resultant Ni-Cu-Ni composite sample by over two orders of magnitude (from 22 dB/cm to ≈1 dB/cm). Interpretation of these results in terms of a theoretical model for SAW attenuation in magnetostrictive thin films indicates that mutual magnetostatic coupling between the two Ni layers of the Ni-Cu-Ni composite films may be effectively self biasing the samples into a magnetically saturated low-α(H)-response operating regime. It is concluded that if multilayer magnetic-film-nonmagnetic-film structures are to be used in magnetically controllable SAW devices it appears that the effective magnetostatic coupling between the magnetic layers should be reduced