Giant magnetostriction of TbFe monolayers with improved field-induced sensitivity

Giant magnetostriction, (GMS), reported until now in thin films using rare earth-transition metal RM/sub 2/ (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/sub rf/ and the sputtering gas pressure P/sub Ar/. The magnetostriction increases with P/sub rf/ up to very large saturation values not observed until now in TbFe films (/spl Delta/l/l=1300 ppm or b/sup /spl gamma/,2/=50 MPa at 20 kOe) due to a structural change from amorphous at low P/sub rf/ to crystallized phase at a high P/sub rf/ as confirmed from XRD. When a bias magnetic field H/sub d/ is applied on the film during deposition a strong change is seen in the structural, elastic, magnetic and ME properties, H/sub d/ keeps the amorphous phase even at high P/sub rf/ which induces a reduction of the ME "linewidth" but an increase of the GMS sensitivity.