Thi Huong Giang, D: Giant Magnetostrictive Films Based On Tb

This thesis deals with the magnetostriction of sputtered films based on the new composition Tb(Fe0.45Co0.55)1.5. For the single layer film, a magnetostriction as high as 1140 ppm was obtained. In Fe/TbFeCo/Fe sandwich films, further improvement of magnetostrictive characteristics thanks to the interfacial coupling was observed. The best performances were obtained for "sping-magnet" magnetostrictive {TbFeCo/YFeCo}50 multilayers. The microstructure of the individual soft magnetic Fe or FeCo-layer depends on the Y-concentration and/or heat treatments. An excellent magnetostrictive magnetostriction (720 ppm) was obtained in the sample with nanocrystalline soft layers. For this system, models of the magnetization and magnetostriction process including the interfacial domain wall have been proposed. Using these magnetostrictive films, magnetoelectric TbFeCo/PZT composites have been fabricated that exhibit a maximum ME voltage coefficient as large as 9650 (V/m)/(kA/m). Based on this ME composite, a promising magnetic sensor with a very high sensitivity (130 mV/mT) have successfully manufactured, which allows to determine not only the strength of the magnetic field but also its direction.