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

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(Fe0.55Co0.45)(1.5) (named as a-TeifecoHan) 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 lambda(gamma,2) similar to 10(-3) has been obtained. After annealing, a parallel magnetostrictive susceptibility of chi(lambdaparallel to) = 1.8 x 10(-2) T-1 has been achieved at mu(o)H = 10 mT, TbFeCo/YFe multilayers combining exchange-coupled giant magnetostrictive TerfecoHan layers and large-magnetisation Y0.2Fe0.8 ones exhibit an excellent magnetic and magnetostrictive softness. Subsequent annealing at 350degreesC leads to the relaxation of the a-TbFeCo layers and to a nanocrystallisation of the YFe layers. In this state, a magnetic coercive field mu(o)H(C) = 0.3 mT and a huge magnetostrictive susceptibility, chi(lambdaparallel to) = 13 x 10(-2) T-1 have been obtained. Mossbauer 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. (C) 2002 Elsevier Science B.V. All rights reserved.