Variable delay lines using magnetostrictive metallic-glass film overlays

Abstract

A variable surface acoustic wave (SAW) delay line was fabricated using a thin (<1 μm) magnetostrictive film, metallic-glass overlay. It is well known that metallic-glasses can be prepared in ribbon form by rapid quenching from the melt. However, it is difficult to prepare thin film overlays of these materials for SAW and other devices with this technique. We have succeeded in preparing film overlays of Fe-B by co-evaporation. Our measured magnetostrictions and magnetizations of these films are virtually the same as in ribbon materials. Delay measurements were made using a vector voltmeter method with a bias magnetic field applied along the direction of SAW propagation and in the two perpendicular directions. The largest delay change is in the plane and perpendicular to the direction of propagation. Although the magnetostriction constants are approximately equal to that of Ni, the changes in delay time, Δτ, in the Fe-B coated SAW delay lines are larger than for Ni coated SAW devices. Also, much lower saturation bias magnetic fields, H, are required. A figure of merit, Δτ/τH, is about 250 times larger for some of the Fe-B films than for Ni.