From bulk to film magnetostrictive actuators

Bulk 3d-4f intermetallic compounds exhibiting a giant magnetostriction at room temperature have been developed since 1975 by A.E. Clark. Until recently, attempts to obtain thin films with high magnetoelastic coupling had failed, due to the sperimagnetic character of amorphous R-Fe-2 alloys. Two ways have been recently proposed for overcoming this problem, namely preparing (i) R-Fe-2 nanocrystalline alloys, and (ii) R-Co-2 amorphous alloys. Both methods have shown to be promising while still further improved performances have been reached using composite materials as for example multilayer systems (similar to the spring-magnets), which exhibit giant magnetostrictivity (exceeding 1000 MPaT-1 under only 2 mT). We shall review these new materials of interest for microsystems. (C) 1998 Elsevier Science S.A.