World Library  
Flag as Inappropriate
Email this Article

Magnetic shape-memory alloy

Article Id: WHEBN0000665738
Reproduction Date:

Title: Magnetic shape-memory alloy  
Author: World Heritage Encyclopedia
Language: English
Subject: MSMA, Actuator, Smart materials
Publisher: World Heritage Encyclopedia

Magnetic shape-memory alloy

Magnetic shape-memory alloys (MSMAs), or ferromagnetic shape-memory alloys (FSMAs), are ferromagnetic materials which exhibit large strains under the influence of an applied magnetic field due to martensitic phase transformation. Magnetic shape-memory alloys, with near-stoichiometric Ni2MnGa being the most studied example, differ from other magnetostrictive materials, such as Terfenol-D and Galfenol, as they produce much larger strains by twinning, sometimes as large as 9%, under relatively low bias magnetic fields. The mechanism is based on the magnetic anisotropy of the material.

MSMAs produce a similar phase transformation between martensite 1 and martensite 2 (the two variants), as other shape memory alloys (SMAs) which change phase between austenite and martensite with the application of thermal energy. Few models have been developed which describe the constitutive response of MSMAs. Typically, thermodynamic modeling is used to describe the materials behavior.

When finding strain for MSMA the total strain equals the sum of the parts: εtotal = εelastic + εreorientation where εreorientation is defined as εreorientation = εr,max*ξ. ξ and εr,max are defined as variant two volume fraction and maximum reorientation strain, respectively.

ξ may be found analytically from a driving force function found from the Gibbs free energy using the relations of a polynomial or trigonometric hardening function. Variant 2 volume fraction (the variant which expands the specimen when exposed to magnetic energy) is a function of the magnitude of bias magnetic field, applied stress, heat, magnetic anisotropy energy, and other material properties such as magnetization saturation.

Due to the nature of MSMA, a shift in the direction of magnetization is produced when applying a stress to a fully strained element exposed to a bias field. The magnitude of this shift is dependent on the strength of the applied field and material properties. Using Faraday's law of induction, it is evident that MSMAs may be used for energy harvesting using a pickup coil, or inductor.

[1] [2]

Compared to the typical shape-memory alloy (SMA), MSMA can actuate at higher frequencies (up to 1 kHz). However, MSMAs are stiff, very brittle and only recommended for low temperature and actuation force applications.


  1. ^ B. Kiefer and D. C. Lagoudas, "Magnetic field-induced martensitic variant reorientation in magnetic shape memory alloys", Philosophical Magazine, vol. 85, nos. 33-35, 21 Nov. -11 Dec. 2005, 4285-4329
  2. ^ Karaman et al., "Energy harvesting using martensite variant reorientation mechanism in NiMnGa magnetic shape memory alloy", Applied physics letters, 90, 172505 (2007)

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.