Temperature Dependence of Anisotropy in Ti and Gd Doped NiMnGa-Based Multifunctional Ferromagnetic Shape Memory Alloys

Abstract

<jats:p>The temperature dependence of magnetocrystalline anisotropy was investigated in detail for the polycrystalline Ni50Mn25Ga25, Ni50Mn25Ga20Ti5 and Ni50Mn25Ga20Gd5 ferromagnetic shape memory alloys in the temperature range of 50–400 K. The effective anisotropy constant was estimated from a series of high field magnetization curves based on the fitting procedure according to the law of approach to magnetic saturation. The low temperature martensitic phase was found to have a significantly higher anisotropy energy in comparison to a high temperature austenitic phase, which was observed through a sudden, distinct drop of anisotropy energy. The calculated values of the effective anisotropy constant were comparable to the results published by other authors. Moreover, the strong influence of chemical composition on the first-order phase transition and the second-order ferromagnetic to the paramagnetic transition was revealed. Finally, the strong coupling between the temperature dependence of the coercive field and the temperature dependence of magnetocrystalline anisotropy was also shown and discussed in the present study.</jats:p>

Mechanical and Magnetic Properties of Porous Ni50Mn28Ga22 Shape Memory Alloy

“…The DSC curves and room temperature XRD patterns of the Ni 50 Mn 28 Ga 22 porous alloy with different pore sizes are depicted in Figure 3a and Figure 3b, respectively. The DSC curve reveals a singular endothermic peak during heating and a separate exothermic peak during cooling for samples with various pore sizes, indicating a one-step transformation consistent with the as-cast samples [23]. The phase transition start and finish temperatures (M s , M f , A s , A f ), as well as the Curie point (T c ) of the porous alloy, were determined using the tangent method and are presented in Table 2 for evaluation.…”

“…In addition, the porosity was slightly lower 50%, which is due to the slight melting of the alloy surface during sintering, causing size shrinkage. The DSC curves and room temperature XRD patterns of the Ni50Mn28Ga22 poro loy with different pore sizes are depicted in Figure 3a and Figure 3b, respectively DSC curve reveals a singular endothermic peak during heating and a separate exoth peak during cooling for samples with various pore sizes, indicating a one-step tra mation consistent with the as-cast samples [23]. The phase transition start and Table 1 lists the content and porosity of Ni 50 Mn 28 Ga 22 porous alloy elements obtained using sintering at 1373 K. The actual porosity of the porous alloys was calculated using the following formula:…”