Inhomogeneous Spin Reorientation Transition (SRT) in Giant Magnetostrictive TbCo2/FeCo Multilayers

This article presents a detailed study of the local magnetic behaviour in TbCo₂/FeCo films near the spin reorientation transition (SRT), and explains the behaviour of giant magnetostrictive (GMS) actuators under different driving conditions. 25times(TbCo₂ 5 nm/FeCo 5 nm) GMS thin films were deposited onto 3times25 mm², 50 mum Si beams using RF sputtering method. The magnetoelastic coefficient was found to be 6 MPa. An in-plane easy axis (EA) was obtained by applying a magnetic field during deposition. Deformations of the clamped beams were measured using a laser deflectometry method, and a Kerr-effect measurement setup was used to simultaneously visualize the magnetic moment distribution and measure magnetization cycles. This work shows that the behaviour of devices using the SRT can be described by models involving homogeneous rotation of the magnetic moments, only if the applied magnetic field is slightly mis-aligned. Domain creation has to be taken into account in order to describe the perfectly aligned case. Measurements on dynamic actuation of magnetostrictive systems show that understanding these behaviour will help to optimize the use of the SRT properties.