Field-Induced Strain Under Load in Ni-Mn-Ga Magnetic Shape Memory Materials

Magneto-Structural Properties of Ni2MnGa Ferromagnetic Shape Memory Alloy in Magnetic Fields

“…The sudden changes in permeability indicate that the ferromagnetic transition occurs around 358 K. The temperature dependence of permeability for Ni 52 Mn 25 Ga 23 is similar to that for Ni 52 Mn 12.5 Fe 12.5 Ga 23 , which shows the transition from a ferromagnetic-martensite (Ferro-M) phase to a ferromagnetic-austenite (Ferro-A) phase [20]. The step around 333 K (heating process) and 327 K (cooling process) for Ni 52 Mn 25 Ga 23 in Figure 1a reflects stronger magnetocrystalline anisotropy in the tetragonal martensite phase [8,18] [9,18,20] below the field of 10 mT. (Figure 4), the magnetization at B = 0.5 T, 1 T, and 5 T just above T M is smaller than that below T M , which is different from the temperature dependence of the permeability in Figure 2.…”

“…Therefore, the magnetostriction is smaller than the strain at T M in the linear strain measurements. The magnetostriction of the polycrystalline Ni 50 Mn 28 Ga 22 alloy was reported by Murray et al [18]. They mentioned that the strain in the martensite phase below T M is an order of magnitude smaller than that of a single crystal of the stoichiometric compounds [1].…”

“…Several studies on Ni-Mn-Ga alloys have addressed martensite transformation and correlation between magnetism and crystallographic structures [6][7][8][9][10][11][12][13][14][15][16][17][18]. Ma et al [7] studied the crystallography of Ni 50+x Mn 25 Ga 25-x alloys (x = 2-11) by powder X-ray diffraction and optical microspectroscopy.…”

“…The typical width of a variant is about 1 μm, by means of the TEM image of Ni 54 Mn 25 Ga 21 , which is shown in [7], and the strict twin structure of the microstructure is beneficial to the thermoelasticity of its martensitic transformation. A few studies discussed the interaction between magnetism and crystallographic rearrangements [1,8,9,17,18]. The memory strain, which means the second thermal cycle and the relative elongation obtained before the pre-deformation, was observed in single crystal Ni 2 MnGa and polycrystal Ni 53.6 Mn 27.1 Ga 19.3 [10].…”

“…Chernenko et al [12] also studied about magnetization and X-ray powder diffractions, and clear changes were found at T M for both measurements. Murray et al [18] studied the polycrystal Ni-Mn-Ga alloys. The magnetization step at T M was also observed, which is a reflection of the magnetocrystalline anisotropy in the tetragonal martensite phase.…”