Development of giant low-field magnetostriction in a-TerfecoHan-based single layer, multilayer and sandwich films

Abstract

Giant magnetostriction in low magnetic field has been achieved with different approaches, among which single, multilayer and sandwich films with rare-earth base are considered as most promising ones. Enhancement of the 3d(Fe,Co)-magnetic moment with respect to those of 3d(Fe) and 3d(Co) strengthens the Tb–FeCo exchange energies in amorphous Tb(Fe 0.55Co 0.45) 1.5 (named as a-TerfecoHan) films. This is thought to cause diminishing of the Tb-sperimagnetic cone-angle and, thus, leading to enhancement of the magnetostriction. Indeed, a saturation magnetostriction of λ γ,2 ∼10 −3 has been obtained. After annealing, a parallel magnetostrictive susceptibility of χ λ∥ =1.8×10 −2 T −1 has been achieved at μ o H=10 mT. TbFeCo/YFe multilayers combining exchange-coupled giant magnetostrictive TerfecoHan layers and large-magnetisation Y 0.2Fe 0.8 ones exhibit an excellent magnetic and magnetostrictive softness. Subsequent annealing at 350°C leads to the relaxation of the a-TbFeCo layers and to a nanocrystallisation of the YFe layers. In this state, a magnetic coercive field μ o H C=0.3 mT and a huge magnetostrictive susceptibility, χ λ∥ =13×10 −2 T −1 have been obtained. Mössbauer studies indicate that the magnetic softness as observed is associated to the evolution of the nanocrystalline Fe-particles. Magnetostriction is also presented for Fe/TerfecoHan/Fe sandwiches. In this case, giant magnetostriction is already developed at low fields in as-deposited films. Technologically, this seems to be one of the simplest ways to prepare magnetostrictive films for microsystem applications.