Structural, Thermal and Magnetic Characterization of Polycrystalline Ni-Mn-Ga Ferromagnetic Shape Memory Alloys

Abstract

Shape memory alloys (SMA) are now widely studied in academia and have increasing usage in industry, as they allow efficient performance compared to mechanic actuators with reduced dimensions and the possibility of sensing temperature through the material itself. A subclass of the SMAs are the alloys with magnetic shape memory, still little explored as intelligent materials in Brazil. They combine the best properties of SMAs and common magnetostrictive materials. The magnetic shape memory alloys (MSMA) can be activated not only by the presence of a thermal stimulus, but also by the presence of an applied magnetic field. In this research, the polycrystalline magnetic shape memory alloys Ni51.3Mn24Ga24.7 and Ni54Mn21Ga25 were manufactured and characterized. Differential scanning calorimetry, X-Ray diffraction, energy dispersive X-ray spectrometry and scanning electron microscopy analyzes were performed to thermoanalytically and crystallographically characterize the alloys. Magnetic characterizations were also performed using Magnetic force microscopy. The results of the characterizations showed that the production process and the heat treatment were satisfactory for the fabrication of the ferromagnetic polycrystalline alloys. Besides that, the compositions Ni51.3Mn24Ga24.7 and Ni54Mn21Ga25, presented austenitic and martensitic 5M structures, respectively, at room temperature and it was possible to observe the alignment of the magnetic domains after magnetization.

Keywords

• Magnetic shape memory alloy
• Ni-Mn-Ga
• Heusler alloys
• NiMnGa polycrystals