Magnetic-field-controlled twin boundaries motion and giant magneto-mechanical effects in Ni–Mn–Ga shape memory alloy

Abstract

This report represents some new experimental results and the quantitative model describing large magneto-strain effect and main mechanical and magnetic properties observed in several ferromagnetic shape-memory alloys. The model application to giant magneto-strain effect recently found in some non-stoichiometric Ni-Mn-Ga alloys is discussed.

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

“…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].…”

“…Likhachev et al [17] stated that the magnetic driving force responsible for twin boundary motion is practically equal to the magnetocrystalline anisotropy constant K U . The magnetic driving force applied to twin boundaries is equal to a difference in magnetization free energies between the different twin variants of martensite.…”

<i>Ab-Initio</i> Study of Electronic Structure of Martensitic Twin Boundary in Ni₂MnGa Alloy

“…Wang et al calculated the energy consumed for the martensite/parent interfacial motion during the martensitic transformation using a boundary friction phenomenological theory 7) . Likhacheö et al suggested that the magnetic driving force applied to twin boundaries is equal to a difference in magnetization free energies between the different twin variants of martensite and this kind of force will achieve its maximal value 0.13 MN/m 2 in a magnetic eld based on the experimental results and the theoretical model 8) . The martensitic structure in the Ni-Mn-Ga alloy has been studied intensively and was found to be composition-, stressand temperature-dependence [9][10][11][12][13] .…”

Thermal Strain and Magnetization Studies of the Ferromagnetic Heusler Shape Memory Alloys Ni2MnGa and the Effect of Selective Substitution in 3d Elements on the Structural and Magnetic Phase

“…Several studies on Ni-Mn-Ga alloys address the martensite transition and correlation between magnetism and crystallographic structures [6][7][8][9][10][11][12][13][14][15][16][17][18]. Ma et al studied the crystallography of Ni50+xMn25Ga25-x alloys (x = 2-11) by powder X-ray diffraction and optical microspectroscopy [7].…”