Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys

Abstract

Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg−1 K−1 or 22 J kg −1 K−1, and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed.

Relative cooling power enhancement by tuning magneto-structural stability in Ni-Mn-In Heusler alloys

“…2, which confirms the statistical disorder occupancy between Mn and In atoms. Hence we conclude the domination of cubic B2 structure and this is consistent with previous studies [24,25]. Rietveld refinements were performed using GSAS software [26,27] and the lattice constants from the refinement are tabulated in Table 2.…”

Orientation Dependence of the Elastocaloric Effect in Ni54Fe19Ga27 Ferromagnetic Shape Memory Alloy

“…The MCE in MSMAs requires large magnetic driving forces from magnetic fields greater than 2 T to achieve reversible temperature changes that are comparable with those of other non‐MSMA solid‐state rare‐earth refrigerants, example Gd. In normal MCE operations, bulky superconducting magnets are needed to produce the magnetic fields large enough to drive the martensitic transformation. Here, the giant elastocaloric effect (ECE) defined by the stress‐induced entropy change was studied in SMAs offering an additional magnetic field‐free method of driving temperature changes applicable to solid state refrigeration.…”

Magnetic Shape Memory Turns to Nano: Microstructure Controlled Actuation of Free‐Standing Nanodisks

“…Magnetic shape memory materials were first introduced in 1996 by Ullako et al who demonstrated magnetic‐field‐induced strain in NiMnGa Heusler single crystals. Since their discovery, they have gathered a continuously increasing attention for revealing emerging properties that in turn have opened new fields of research and application, such as magnetic actuation, ferroic cooling, and energy harvesting …”