Occurrence of ferromagnetic shape memory alloys (invited)

This article presents an overview of the necessary conditions for the forma tion of shape memory alloys (SMAs) and how these must overlap with the occu rrence of ferromagnetism so that ferromagnetic shape memory alloys (MSMAs) may be formed. The electronic, elastic, and geometric conditions permit an understanding of the occurrence of Cu- and Fe-based SMAs as well as NiMnGa Heusler MSMAs except that the naively determined critical electron concentr ation for the latter, 7.3, disagrees with the values of 1.5 and 8.6 accepte d for the Hume-Rothery phases and certain Fe-based systems. (C) 2000 Americ an Institute of Physics. [S0021- 8979(00)39908-X].