Thickness Effect on Magnetostriction of Fe and Fe $_{98}$ B $_{2}$ Thin Films

Film thickness effect on saturation magnetostriction of Fe and Fe₉₈B₂ thin films has been investigated in relation to the film strain. Saturation magnetostriction varies from -4 × 10^-6 to +3 × 10^-6 with decreasing the film thickness from 40 to 10 nm, changing the sign at around 15 nm for both the Fe and the Fe₉₈B₂ films. The saturation magnetostrictions of Fe₉₈B₂ films of 7 and 5 nm thicknesses are +10 × 10^-6 and +17 × 10^-6, respectively. XRD patterns observed for these films show only the bcc(110) reflection, which indicates that the films consist of oriented nanocrystals with bcc structure. The lattice spacing, d_bcc(110); increases with decreasing the film thickness from 20 to 10 nm for both Alms. With decreasing the film thicknesses, both magnetostriction and strain increase. These experimental results support the theoretical study which suggests a strain effect on magnetostriction.