Shape memory and magnetic properties of Co–Al ferromagnetic shape memory alloys

Martensitic transformation from the face-centered cubic to the hexagonal close-packed structure, shape memory (SM) effect and magnetic properties in the Co–14 at.% Al alloy were investigated and the microstructures of the martensite were examined using transmission electron microscopy. It was found that the SM effect occurs at temperatures between 200 and 300 °C corresponding to the reverse transformation temperatures, and that a metastable L12-structured phase is formed in Co–14 at.% Al aged at 600 °C. The magnetic properties were measured by a vibrating sample magnetometer, and the Curie temperature and saturation magnetization were determined to be 689 °C and 120 emu/g at 25 °C. All these results indicate that Co–Al alloys can be listed as a new class of ferromagnetic SM alloys.