Giant magnetostriction of TbFe monolayers with improved field-induced sensitivity

Giant magnetostriction, (GMS), reported until now in thin films using rare earth-transition metal RM₂ (R=Tb, Sm, and M=Fe, Co) compounds, presents in most cases an isotropic or quasi-isotropic magnetoelastic (ME) behavior. A large change of the ME coefficient b under the lowest possible external field is required in order to improve the sensitivity of these materials which are interesting for their application in microelectromechanical systems (MEMS). The present paper shows the possibility of improving strongly both the ME coefficient and sensitivity. Optimized ME properties are correlated with the sputtering parameters such as the RF power P_rf and the sputtering gas pressure P_Ar. The magnetostriction increases with P_rf up to very large saturation values not observed until now in TbFe films (Δl/l=1300 ppm or b^γ,2=50 MPa at 20 kOe) due to a structural change from amorphous at low P_rf to crystallized phase at a high P_rf as confirmed from XRD. When a bias magnetic field H_d is applied on the film during deposition a strong change is seen in the structural, elastic, magnetic and ME properties, H_d keeps the amorphous phase even at high P_rf which induces a reduction of the ME “linewidth” but an increase of the GMS sensitivity