Multiferroic and Related Hysteretic Behavior in Ferromagnetic Shape Memory Alloys

Abstract

We combine a Ginzburg-Landau model for a ferroelastic transition with the theory of micromagnetism to study the magnetostructural behavior leading to multicaloric effects in ferromagnetic shape memory alloys. We analyze the ferroelastic transition under different conditions of temperature, stress and magnetic field and establish the corresponding phase diagram. On the one hand, our results show that the proper combination of both fields may be used to reduce the transition hysteresis and thus improve the reversibility of the related elastocaloric effects, superelasticity and stress-mediated magnetocaloric effects. On the other hand, the stress-free magnetic field-driven and thermally driven magnetostructural evolution provides physical insight into the low-temperature field-induced domain reorientation, from which we derive strategies to modify the operational temperature ranges and thus the corresponding (magnetic) shape-memory effect.

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].…”

“…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]. Therefore, martensite variants rearrangement and variant twin boundaries motion occur under the action of the external magnetic field [10].…”

“…Ke et al [14] investigated the influence of pores on the phase transformation in NiTi shape memory alloys through phase-field simulation. Gebbia et al [1] discussed the hysteresis and MFIS of Ni 2 MnGa at various temperatures by combining the Ginzburg-Landau model and micromagnetism theory. Multi-phase models using the Eshebly theory and Mori-Tanaka method were also employed to investigate the mechanical behaviors and magneto-mechanical coupling between porous FSMAs and FSMA composites under different conditions [12,20].…”