Magnetic Properties of the Ferromagnetic Shape Memory Alloys Ni(50+x)Mn(27−x)Ga(23) in Magnetic Fields

Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni(50+x)Mn(27−x)Ga(23) (x = 2.0, 2.5, 2.7) were performed. For x = 2.7, in which the martensite transition and the ferromagnetic transition occur at the same temperature, the martensite transition starting temperature T(Ms) shift in magnetic fields around a zero magnetic field was estimated to be dT(Ms)/dB = 1.1 ± 0.2 K/T, thus indicating that magnetic fields influences martensite transition. We discussed the itinerant electron magnetism of x = 2.0 and 2.5. As for x = 2.5, the M(4) vs. B/M plot crosses the origin of the coordinate axis at the Curie temperature, and the plot indicates a good linear relation behavior around the Curie temperature. The result is in agreement with the theory by Takahashi, concerning itinerant electron ferromagnets.