Ferromagnetic Shape Memory Alloys: Foams and Microwires

Abstract

Ferromagnetic shape memory alloys exhibit martensite transformation (MT) and magnetic transition and thus may be actuated by thermal and magnetic fields. The working frequency of these alloys may be higher than conventional shape memory alloys, such as Ni-Ti, because the magnetic field may operate at higher frequency. This chapter focuses on some fundamental topics of these multifunctional materials, including the composition-structure relationship, the synthesis of the foams and microwires, the martensite transformation and magnetic transition characters, the properties (magneticfield-induced strain (MFIS), magnetocaloric effects (MCEs), shape memory effects, and superelastic effects), and applications. The improvement of the magnetic-field-induced strain due to the reduced constraint of twin boundary motion caused by grain boundaries in polycrystalline Ni-Mn-Ga foams and the size effects of the superelasticity and magnetocaloric properties in Ni-Mn-X (X = In, Sn, Sb) microwires are detailed and addressed.

Phase Field Simulations of Microstructures in Porous Ferromagnetic Shape Memory Alloy Ni2MnGa

“…Ferromagnetic shape memory alloy (FSMA), as a kind of multi-ferroic material, presents a coupling between ferromagnetic and ferroelastic properties [1]. In particular, the Heusler alloy Ni 2 MnGa exhibits extremely high magnetic field-induced strain (MFIS), more than an order of magnitude larger than conventional magnetostriction materials [1][2][3][4][5][6][7][8][9]. FSMA shows a magneto-structural coupling with a magnetic 90-degree domain wall along twin boundaries and induces a cross-response of strain and applied field [1].…”