Abstract
Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni50+xMn27−xGa23 (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 TMs shift in magnetic fields around a zero magnetic field was estimated to be dTMs/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 M4 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.
Highlights
Ferromagnetic shape memory alloys have been extensively studied as potential candidates for smart materials
We focused on the physical effects of magnetic fields
Thermal strain, permeability, and magnetization measurements were performed on the Heusler alloys Ni52.5Mn24.5Ga23 (x = 2.5) and Ni52.7Mn24.3Ga23 (x = 2.7)
Summary
Ferromagnetic shape memory alloys have been extensively studied as potential candidates for smart materials. NMR experiments indicate Mn-Mn indirect exchange via the faults in Mn-Ga layers interchange, which are caused by excessive amounts of Ga [13] This result indicates that the exchange interaction between Mn-Mn magnetic moments is sensitive to lattice transformation: during such a transformation, the magnetism changes from that of a soft magnet in the austenite phase to that of a hard magnet in the martensite phase; this is due to higher magnetic anisotropy. Thermal strain and magnetization results of Ni52Mn25Ga23 (x = 2.0) were used for discussing the magnetic field dependence of the martensite transition temperature and magnetization [24]. The experimental results were compared with those of other Ni-Mn-Ga single crystalline or polycrystalline alloys, and correlations between magnetism and martensite transition were found. To define these temperatures clearly, we used TM and TR as the martensite transition starting temperature TMs and the reverse martensite temperature finishing temperature TRf in our research results
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