Magnetic and magnetostrictive hysteresis loops of TbCo/CoFe multilayers under field applied along the hard magnetization axis are studied using vectorial magnetization measurements, optical deflectometry and magneto optical Kerr microscopy. Even a very small angle misalignment between hard axis and magnetic field direction is shown to drastically change the shape of magnetization and magnetostrictive torsion hysteresis loops. Two kinds of magnetic domains are revealed during the magnetization: big regions with opposite rotation of spontaneous magnetization vector and spontaneous magnetic domains which appear in a narrow field interval and provide an inversion of this rotation.We show that the details of the hysteresis loops of our exchange-coupled films can be described using the classical model of homogeneous magnetization rotation of single uniaxial films and the configuration of observed domains. The understanding of these features is crucial for applications (for MEMS or microactuators) which benefit from the greatly enhanced sensitivity near the point of magnetic saturation at the transverse applied field.

In the present paper, giant magnetostrictive thin films have been investigated for future microelectromechanical systems (MEMS) purposes. For this goal, flexural and torsional motions have been studied in low field anisotropic giant magnetostrictive (GMS) single domain state (SDS) exchange-coupled TbFe/FeCo multilayers (ECML). The magnetoelastic (ME) coefficient b γ,2 depend strongly on the ECML structures, compositions, and sputtering deposition parameters. Giant magnetostrictive Multilayers with a high b γ,2 (18M P a for T bF e 2 /F e 0.6 Co 0.4 compared to 11M P a for T bF e 2 /F e) were obtained with or without an in-plane easy axis with a controlled direction, and without any annealing post-process. Dynamical excitations of the actuators have been investigated under various conditions. An enhancement up to a factor 5 of the oscillations compared to the TbFe/Fe multilayers is observed with the possibility to tune the flexural/torsional dynamical behavior of these cantilevers. The corresponding very large dynamical ME susceptibility of these improved uniaxial ECML gives the possibility to control GMS MEMS with further reduction of the excitation field down to a few oersteds.

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