Magnetostriction and magnetic properties of iron-cobalt alloys multilayered with silver

Commercially available Fe-Co alloys with Co contents of 50 and 24 wt. % have been rf sputtered to produce multilayers with noble metal (Ag or Cu) interlayers. Series with fixed Fe-Co or noble metal thicknesses have been produced, as have plain Fe-Co films. In all cases, the coercivities of the multilayers are significantly reduced from those exhibited by the plain alloy films. For example, a film of the alloy containing 50 wt. % Co had H _c=6.9 kA m^-1, whereas a multilayer with 12 nm Fe-Co layers and 2 nm Ag layers had H_c=480 A m^-1. The saturation magnetostriction is also enhanced, in some cases increasing by 60% over the expected bulk polycrystalline alloy value. For example, the literature λ_s value for a Fe-Co alloy containing 24% Co is about 28 ppm; in a multilayer with 12 nm alloy layers and 8 nm Ag layers, λ _s=45 ppm. The combination of high magnetostriction and low coercivity makes such materials as these attractive for their potential as stress sensor and actuation transducer elements.