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Proceedings Paper

Magnetic properties of single crystals of Ni-Mn-Ga magnetic shape memory alloys
Author(s): Shannon P. Farrell; Richard A. Dunlap; Leon M. Cheng; Rosaura Ham-Su; Michael A. Gharghouri; Calvin V. Hyatt
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Paper Abstract

The magnetic shape memory (MSM) effect occurs in some ferromagnetic martensitic alloys at temperatures below the martensite finish temperature and involves the re-orientation of martensite variants by twin boundary motion, in response to an applied stress and/or magnetic field. The driving force for twin boundary motion is the magnetic anisotropy. In this study, magnetization measurements as a function of magnetic field were made on several oriented single crystals of Ni-Mn-Ga alloys using a vibrating sample magnetometer. The magnetization versus magnetic field curves were characteristic of magnetically soft materials with magnetic anisotropy consistent with literature estimates for the different martensite structures observed in Ni-Mn-Ga alloys. Differences in the slope of the curves were due to the martensite structure, the relative proportion of martensite variants present, and their respective easy and hard axis orientations. Thermo-magneto-mechanical training was applied in an attempt to transform multi-variant specimens to single variant martensite. Training of the orthorhombic 7M martensites was sufficient to produce a near single variant of martensite, while the tetragonal 5M martensite responded well to training and produced a single-variant state. The strength of the uniaxial magnetic anisotropy constant for single-variant tetragonal 5M martensite, Ni52.9Mn27.3Ga19.8, was calculated to be Ku=1.8 x 105 J/m3, consistent with literature values. To obtain single-variant martensites, heat-treatment of the specimens prior to thermo-magneto-mechanical training is necessary.

Paper Details

Date Published: 21 July 2004
PDF: 12 pages
Proc. SPIE 5387, Smart Structures and Materials 2004: Active Materials: Behavior and Mechanics, (21 July 2004); doi: 10.1117/12.539770
Show Author Affiliations
Shannon P. Farrell, Defence Research and Development Canada (Canada)
Richard A. Dunlap, Dalhousie Univ. (Canada)
Leon M. Cheng, Defence Research and Development Canada (Canada)
Rosaura Ham-Su, Defence Research and Development Canada (Canada)
Michael A. Gharghouri, Dalhousie Univ. (Canada)
Calvin V. Hyatt, Defence Research and Development Canada (Canada)

Published in SPIE Proceedings Vol. 5387:
Smart Structures and Materials 2004: Active Materials: Behavior and Mechanics
Dimitris C. Lagoudas, Editor(s)

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