Thermal strain, magnetostriction and magnetization measurements of Ni 41 Co 9 Mn 31.5 Ga 18.5 polycrystalline ferromagnetic shape memory alloy (FSMA) were performed across the martensitic transition temperature, T M , and the reverse martensitic transition temperature, T R , at atmospheric pressure. When cooling from the austenite phase, a steep decrease in thermal expansion due to the martensitic transition at T M was found. When heating from the martensitic phase, a steep increase in the thermal expansion due to the reverse martensitic transition at T R was observed. These transition temperatures decreased gradually with increasing magnetic field. The field dependence of the martensitic transition temperature, dT M /dB, is ¹4.2 K/T and that of the reverse martensitic transition temperature, dT R /dB, is ¹7.9 K/T. The metamagnetic transition appeared between 330 and 390 K. The results of thermal strain and magnetization measurements indicate that a magneto-structural transition occurred at T M . The region above T M or T R is the ferromagnetic austenite phase and that below T M or T R is the paramagnetic or weak ferromagnetic martensitic phase. At constant temperature, a magnetic field-induced strain was observed with a value of 1.0 © 10 ¹3 , which indicates that this alloy is sensitive to magnetic fields. Strong magneto-structural coupling was revealed by the magnetic properties and phase transitions.

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Thermal expansion, permeability and magnetization measurements of the ferromagnetic shape memory alloys, Ni 2 MnGa 0.88 Cu 0.12 , were carried out across the martensitic transition temperature T M and the reverse martensitic transition temperature T R at atmospheric pressure. When cooling from the austenite phase, a steep decrease in the thermal expansion due to the martensitic transition was found. The permeability indicates a sharp peak around T M and ferromagnetism below T M . Considering the permeability and magnetization results of Ni 2 MnGa 0.88 Cu 0.12 , the region above T M or T R is the paramagnetic-austenite phase and the region below T M or T R is the ferromagnetic-martensite phase. Magnetic phase diagrams were constructed based on the results of the temperature dependence of thermal expansion. T M and T R increased gradually with increasing magnetic field. The shift of T M in magnetic fields (B) around zero magnetic fields was estimated as dT M /dB = 1.3 K T −1 . The shift of T M indicates that magnetization influences the martensitic transition, and the increase of T M with magnetic field is proportional to the difference in the magnetization between the austenite and martensite phases.

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