Magnetostriction of amorphous Tb<i>x</i>Fe1−<i>x</i> thin films

Abstract

A systematic investigation was made of magnetostriction and magnetization in amorphous thin films (∼1 micron) of TbxFe1−x with x=0 to 0.5 prepared by electron-beam co-evaporation. The amorphous or crystalline character of the films was determined using x-ray and Mössbauer techniques. Net magnetization, coercivity, and the initial in-plane and out-of-plane distribution of magnetization was determined using a vibrating sample magnetometer. Both the sign and magnitude of the magnetostriction was measured as a function of magnetic field using a capacitance method. Over most of the concentration range the amorphous samples have a positive magnetostriction with a maximum of Δl/l=285×10−6 at x=0.4 and going to zero at the compensation point (x=0.22) and near x=0.5 where the amorphous alloys are no longer magnetically ordered at room temperature. In the region x=0.1 to 0.2 the magnetostriction is more complex, being negative for fields up to 5 kOe and positive at higher fields. All the films studied with x?0.1 were magnetically very hard and required fields much greater than 15 kOe to saturate. The relatively large magnetostrictions compared with crystalline materials indicate that the large Tb single-ion magnetostriction mechanism continues to play a strong role in the amorphous lattice structure.