Magnetisation process and magneto striction in Fe/TerfecoHan/Fe sandwich films with perpendicular magnetic anisotropy

A new magnetostrictive film with out-of-plane magnetic anisotropy is realised in sandwich type of Fe/Tb(Fe0.55CO0.45)(1.5)/Fe (denoted as Fe/TerfecoHan/Fe) films with a fixed individual TerfecoHan-layer thickness t(TbFeCo) = 600 nm and variable Fe layer thickness t(Fe) = 0, 10, 15 and 60 nm. As-deposited Fe/TerfecoHan/Fe films exhibit a magnetostriction as large as 10(-3) in an applied field of mu(0)H = 0.6 T. This magnetostriction is exclusively observed in the field direction parallel to the sample length. The development of giant low-field magnetostriction has been performed by heat treatment. A maximal magnetostrictive susceptibility chi(lambdaparallel to) = 2.3 x 10(-2) T-1 is reached in mu(0)H = 6 mT for the TerfecoHan film annealed at T-A = 450degreesC. For Fe/TerfecoHan/Fe sandwich films, however, the magnetic softness is just slightly improved with T-A = 250degreesC and 350degreesC. At T-A = 450degreesC, both the perpendicular magnetic anisotropy and the magnetic coercivity are reinforced. These magnetic behaviours are associated to the fact that the additional Fe-layers accelerated the crystallisation process in the TerfecoHan layer. The sandwich films are favourable for making the Fe/TerfecoHan/Fe a low-field magnetostrictive material for microelectromechanical systems as well as a perpendicular recording medium. Mechanisms of the magnetisation process and huge parallel magnetostriction are discussed for the films under investigation. (C) 2002 Elsevier Science B.V. All rights reserved.