Abstract
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.
Highlights
Ferromagnetic shape memory alloys (FSMA) are recently one of the most extensively studied group of modern smart materials [1,2,3]
The influence of elemental doping with Ti and Gd on the temperature dependence of magnetic behavior in the Ni50Mn25Ga20-xZx (x = 0 or 5, Z = Gd, Ti) ferromagnetic shape memory alloys were studied in detail
The influence of elemental doping with Ti and Gd on the temperature dependence of magnetic behavior in the Ni50 Mn25 Ga20-x Zx (x = 0 or 5, Z = Gd, Ti) ferromagnetic shape memory alloys were studied in detail
Summary
Ferromagnetic shape memory alloys (FSMA) are recently one of the most extensively studied group of modern smart materials [1,2,3]. NiMnGa-based Heusler compounds stand out as the most complex alloys due to their unique magnetomechanical properties, such as magnetic field induced strains [4,5,6], pseudoelasticity/superelasticity [7,8,9], magnetoresistance [10,11] or magnetoand mechanocaloric effects [12,13,14,15,16]. The strong correlation between the microstructure and the magnetic properties of the austenitic and martensitic phases leads to the abrupt drop of magnetization in the vicinity of the martensitic transformation. This significant difference in magnetization strongly influences the majority of magnetomechanical properties in NiMnGa-based materials. It is well documented that the magnetism of NiMnGa-based alloys varies significantly with composition in and near stoichiometric Ni2 MnGa samples depending on the Ni [19,20,21], Mn [22,23] or Ga [24,25]
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