Northwestern University

Boise State University

Markus Chmielus

David C Dunand

Peter Mullner

Yuttanant Boonyongmaneerat

Xuexi Zhang

Cassie Witherspoon

Magnetic materials and methods exhibit large magnetic-field-induced deformation/strain (MFIS) through the magnetic-field-induced motion of crystallographic interfaces. The preferred materials are porous, polycrystalline composite structures of nodes connected by struts wherein the struts may be monocrystalline or polycrystalline. The materials are preferably made from magnetic shape memory alloy, including polycrystalline Ni&#x2014;Mn&#x2014;Ga, formed into an open-pore foam, for example, by space-holder technique. Removal of constraints that interfere with MFIS has been accomplished by introducing pores with sizes similar to grains, resulting in MFIS values of 0.12% in polycrystalline Ni&#x2014;Mn&#x2014;Ga foams, close to the best commercial magnetostrictive materials. Further removal of constraints has been accomplished by introducing pores smaller than the grain size, dramatically increasing MFIS to 2.0-8.7%. These strains, which remain stable over &#x3e;200,000 cycles, are much larger than those of any polycrystalline, active material.

Polycrystalline foams exhibiting giant magnetic-field-induced deformation and methods of making and using same

A magnetic materials construct and a method to produce the construct are disclosed. The construct exhibits large magnetic-field-induced deformation through the magnetic-field-induced motion of crystallographic interfaces. The construct is a porous, polycrystalline composite structure of nodes connected by struts wherein the struts may be monocrystalline or polycrystalline. If the struts are polycrystalline, they have a 'bamboo' microstructure wherein the grain boundaries traverse the entire width of the strut. The material from which the construct is made is preferably a magnetic shape memory alloy, including polycrystalline Ni&#x2014;Mn&#x2014;Ga. The construct is preferably an open-pore foam. The foam is preferably produced with a space-holder technique. Space holders may be dissolvable ceramics and salts including NaAlO.

Magnetic material with large magnetic-field-induced deformation

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Boise, ID, United States of America

Markus Chmielus