ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
The Ni-Mn-Ga shape memory alloy displays the largest shape change of all knownmagnetic Heusler alloys with a strain of the order of 10% in an external magnetic field ofless than one Tesla. In addition, the alloys exhibit a sequence of intermediate martensiteswith the modulated structures usually appearing at c/a 〈 1 while the low-temperature non-modulated tetragonal structures have c/a 〉 1. Typically, in the Ni-based alloys, the martensitictransformation is accompanied by a systematic change of the electronic structure in the vicinityof the Fermi energy, where a peak in the electronic density of states from the non-bonding Nistates is shifted from the occupied region to the unoccupied energy range, which is associatedwith a reconstruction of the Fermi surface, and, in most cases, by pronounced phonon anomalies.The latter appear in high-temperature cubic austenite, premartensite but also in the modulatedphases. In addition, the modulated phases have highly mobile twin boundaries which can berearranged by an external magnetic field due to the high magnetic anisotropy, which builds upin the martensitic phases and which is the origin of the magnetic shape memory effect. Thisoverall scenario is confirmed by first-principles calculations
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.583.21.pdf
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