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Structure And Magnetic Properties Of Fe-Mn-Ga Magnetic Shape Memory Alloys

Posted on:2014-04-05Degree:MasterType:Thesis
Country:ChinaCandidate:K YaoFull Text:PDF
GTID:2191330473951067Subject:Materials science
Abstract/Summary:PDF Full Text Request
Magnetic shape memory alloys are a kind of functional materials developed in 1990’s. Compared with traditional shape memory alloy, magnetic shape memory alloys not only have the thermal elastic shape memory effect controlled by the temperature field, but also have magnetic shape memory effect controlled by magnetic field.Fe-Mn-Ga alloys exhibit martensitic transformation from paramagnetic P phase to the ferromagnetic M phase. The alloys combine the two mechanisms which include reorientation of martensitic variants and magnetic field-induced phase transformation. In this article, Fe-Mn-Ga alloys were prepared and structure and magnetic properties were analyzed through different methods.1. In this study, the structure of Fe-Mn-Ga alloys were greatly influenced by the composition and the heat treatment. Furthermore,27at.%(Mn) is the critical component to achieve ordered austenitic phase of Fe-Mn-Ga alloys in a small composition range.2. The crystal structure of Fe46Mn26Ga28 alloy was investigated by in situ neutron diffraction technique. The crystal structure of Fe46Mn26Ga28 alloy at 300K is L21 (Heusler) phase. The lattice parameters of which is a=0.5864nm. The GSAS refinement result shows that the Fe atoms occupy the Wyckoff Position 8c (1/4,1/4,1/4), the Ga are placed at 4b (1/2,1/2,1/2) and Mn are located at 4a (0,0,0) in the unit cell, and fits the 225 space group.3. The magnetic properties of Fe-Mn-Ga alloys at variable temperatures and room temperature were investigated. The L21 (Heusler) phase exhibits paramagnetic property at room temperature. The magnetic field-induced martensitic transformation from paramagnetic austenite to ferromagnetic martensite is obtained in Fe45.5Mn25.5Ga28 and Fe46Mn26Ga28 under the applied magnetic field of 5T. The △Ms for the alloys are 18.39K and 15.66K, respectively.4. In this study, the magnetization measured under the applied magnetic field of 0.05T demonstrates two marked changes in the slope when heating in Fe45.5Mn25.5Ga28、Fe46Mn26Ga28 and Fe44Mn26.5Ga29.5 alloys while this anomaly disappears in the stronger magnetic field of 5T. This phenomenon can be ascribed to the Curie temperature of the austenitic phase TcA.
Keywords/Search Tags:Fe-Mn-Ga alloy, reorientation of martensitic variants, magnetic field-induced phase transformation, L21 structure, magnetic properties
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