Large magnetic-field-induced strains have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.

The itinerant-electron metamagnetic ͑IEM͒ transition and magnetocaloric effects ͑MCE's͒ in the La(Fe x Si 1Ϫx) 13 and La(Fe x Si 1Ϫx) 13 H y compounds have been investigated. The La(Fe x Si 1Ϫx) 13 compounds exhibit large values of both the isothermal entropy change ⌬S m and the adiabatic temperature change ⌬T ad around the Curie temperature T C in relatively low magnetic fields. Such large MCE's are explained by a large magnetization change at T C and a strong temperature dependence of the critical field B C for the IEM transition. By hydrogen absorption into the compounds, T C is increased up to about 330 K, keeping the metamagnetic transition properties. Accordingly, the extension of the working temperature range having the large MCE's in relatively low magnetic fields is demonstrated by controlling y in the La(Fe x Si 1Ϫx) 13 H y compounds. The correlation between the increase of T C and the large MCE's in the La(Fe x Si 1Ϫx) 13 H y compounds is discussed by taking the magnetovolume effects into consideration.

The magnetocaloric effect (MCE) originated from the itinerant-electron metamagnetic transition for La(FexSi1−x)13 compounds has been investigated. With increasing Fe concentration, the MCE is enhanced and both the isothermal magnetic entropy change ΔSm and the adiabatic temperature change ΔTad for the compound with x=0.90 are −28 J/kg K and 8.1 K, respectively, by changing the magnetic field from 0 to 2 T. Similar large MCE values are achieved around room temperature by controlling the Curie temperature by means of hydrogen absorption. Consequently, La(FexSi1−x)13 compounds are promising as magnetic refrigerant materials working in relatively low magnetic fields.

A first-order transition above the Curie temperature for ferromagnetic La(FexSi1−x)13 (x=0.86 and 0.88) compounds has been confirmed by applying a magnetic field. The magnetic state changes from the paramagnetic to the ferromagnetic state and the transition field increases with temperature, indicating an itinerant electron metamagnetic (IEM) transition. The IEM transition is broad in x=0.86 and becomes clearer in x=0.88, which takes a negative slope of the Arrott plot. The volume change just above the Curie temperature for x=0.88 is huge, about 1.5%, which is caused by a large magnetic moment induced by the IEM transition.

A system of ferromagnetic β phase Ni–Co–Al alloys with an ordered B2 structure that exhibits the shape memory effect has been developed. The alloys of this system within the composition range Ni (30–45 at. %) Co–(27–32 at. %) Al, undergo a paramagnetic/ferromagnetic transition as well as a thermoelastic martensitic transformation from the β to the β′(L10) phase. The Curie and the martensitic start temperatures in the β phase can be controlled independently to fall within the range of 120–420 K. The specimens from some of the alloys undergoing martensitic transformation from ferromagnetic β phase to ferromagnetic β′ phase are accompanied by the shape memory effect. These ferromagnetic shape memory alloys hold great promise as new smart materials.