Temperature dependence of magnetic field-induced strain in Fe3Pt ferromagnetic SMA

A partly ordered Fe₃Pt exhibits a martensitic transformation from the L1₂-type cubic phase to a tetragonal martensite, which is frequently referred to as the FCT martensite. Below the transformation temperature of about 85K, the FCT martensite phase exhibits a large magnetic field-induced strain in association with rearrangement of martensite variants under the magnetic field. A part of the magnetic field-induced strain is reversible, being different behavior from the magnetic field-induced strain of Ni₂MnGa. The magnitude of the reversible strain depends on temperature, and maximum value of about 1% is obtained at 20 K. Under a magnetic field, the variant whose easy axis lies in the field direction
 is the preferable variant, which grows consuming other variants. The fraction of the preferable variant at a temperature is higher in the specimen which is cooled down to the temperature under a magnetic field compared with the specimen
 which is cooled down to the same temperature under zero magnetic field followed by the application of the same magnetic field. Some fundamental physical properties, such as magnetocrstalline anisotropy and twinning stress, in Fe₃Pt are also presented.