Giant magnetic-field-induced strains in polycrystalline Ni-Mn-Ga foams

M. Chmielus, X. X. Zhang, C. Witherspoon, D. C. Dunand, P. Müllner*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

241 Scopus citations

Abstract

The magnetic shape-memory alloy Ni-Mn-Ga shows, in monocrystalline form, a reversible magnetic-field-induced strain (MFIS) up to 10%. This strain, which is produced by twin boundaries moving solely by internal stresses generated by magnetic anisotropy energy, can be used in actuators, sensors and energy-harvesting devices. Compared with monocrystalline Ni-Mn-Ga, fine-grained Ni-Mn-Ga is much easier to process but shows near-zero MFIS because twin boundary motion is inhibited by constraints imposed by grain boundaries. Recently, we showed that partial removal of these constraints, by introducing pores with sizes similar to grains, resulted in MFIS values of 0.12% in polycrystalline Ni-Mn-Ga foams, close to those of the best commercial magnetostrictive materials. Here, we demonstrate that introducing pores smaller than the grain size further reduces constraints and markedly increases MFIS to 2.0-8.7%. These strains, which remain stable over 200,000 cycles, are much larger than those of any polycrystalline, active material.

Original languageEnglish (US)
Pages (from-to)863-866
Number of pages4
JournalNature materials
Volume8
Issue number11
DOIs
StatePublished - Nov 2009

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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