Optimization of magnetostriction, coercive field and magnetic transition temperature in nanocrystalline TbDyFe plus Zr Nb multilayers

The magnetostrictive properties of TbDyFe/Nb multilayers containing 2 at % Zr as an additive have been investigated after different annealing treatmen ts for the (Terfenol-D near) composition of [Tb0.27Dy0.73](0.27)Fe-0.73. Th e multilayer structure has been produced by ion-beam sputtering on a sapphi re substrate. After 10 min annealing of the multilayers at temperatures fro m 873 to 973 K the parallel magnetostriction increased from lambda(parallel to)(0.8 T) = 265 to 520 ppm accompanied ky an increase of the magnetic pha se transition temperature from T-C = 333 to 592 K, while the increase of th e coercive fields from mu(0)H(c) < 5 to 75 mT lies distinctively below 100 mT. These properties are suitable for applications of giant magnetostrictiv e films in microsystems where values of lambda > 500 ppm, T-C > 500 K and m u(0)H(c) much less than 100 mT are required. Establishing a nanocrystalline microstructure with grain sizes d < d(c) similar to 15 nm (d(c) is the cri tical grain diameter) smaller than the exchange length is essential for the combination of intrinsic magnetic properties (increased lambda and T-C) wi th soft magnetic properties (mu(0)H(c) of a few mT) as typical for an amorp hous microstructure. It is shown by microstructural XRD and TEM investigati ons that such a nanocrystalline microstructure can be realized by a suitabl e heat treatment of TbDyFe + Zr/Nb multilayers. Introducing Nb spacer layer s effectively reduces grain growth for certain annealing temperatures while Zr is assumed to play a dominant role in forming nucleation centers of nan ograins. In combination, both effects can be well used to optimize the magn etostrictive layer properties. (C) 1999 Elsevier Science B.V. All rights re served.