Martensitic and Magnetic Transformation Behaviors in Heusler-Type NiMnIn and NiCoMnIn Metamagnetic Shape Memory Alloys

Abstract

Martensitic and magnetic transformation behaviors of Ni 50 MnIn, Ni 45 Co 5 MnIn, and Ni 42.5 Co 7.5 MnIn Heusler alloys were investigated by differential scanning calorimetry (DSC), vibrating sample magnetometry (VSM), and transmission electron microscopy (TEM). The martensitic transformation starting temperature (M s ) decreases with increasing In composition, while the Curie temperatures (T c ) of the parent phase are almost independent in each alloy series. On the other hand, the addition of Co resulted in a decrease of the M s and an increase of the T c , and the degree of the decline of M s was accelerated by magnetic transformation of the parent phase. The M s temperature change induced by the magnetic field was also confirmed. It was found that the degree of M s change is strongly related to the entropy change by the martensitic transformation, which shows a correlation with T c -M s . These behaviors can be qualitatively explained on the basis of thermodynamic considerations.

Contributions to the Transformation Entropy Change and Influencing Factors in Metamagnetic Ni-Co-Mn-Ga Shape Memory Alloys

“…T -Ap), the greater the magnetic contribution to the entropy change, hence the overall transformation entropy diminishes, as it has been observed for many different metamagnetic alloys [14,15,[24][25][26]. Owing to the thermal hysteresis of the MT, ( ⏐, which can only be fulfilled if "paramagnetic" martensite has higher degree of magnetic order than paramagnetic austenite [14].…”

“…A C T -TO) has been widely proven for different metamagnetic alloys [14,15,[24][25][26]], a phenomenological model has been recently developed, based on a BraggWilliams approximation, accounting for the magnetic contribution. The model achieves excellent agreement between calculated and experimental ΔS for different composition and atomic order degrees, corroborating the magnetic origin of changes in transformation entropy [23,27].…”

Shape Memory Response in Ni<SUB>40</SUB>Co<SUB>10</SUB>Mn<SUB>33</SUB>Al<SUB>17</SUB> Polycrystalline Alloy

“…2) Especially, the Co-doped Ni-Mn-In and -Sn quaternary alloys show a drastic change of magnetization by martensitic transformation from a ferromagnetic P phase to a very weakly magnetic M phase. [3][4][5] The martensitic transformation temperatures of these alloys are drastically decreased by the application of a magnetic field, and magnetic field-induced reverse transformation (MFIRT) has been confirmed.…”

Giant magnetocaloric effect from reverse martensitic transformation in Ni–Mn–Ga–Cu ferromagnetic shape memory alloys

“…Table 2. T 0 is the transformation temperature where the parent phase has the same Gibbs energy as that of the product martensite phase and is approximated by (A f + M s )/2 [33][34][35][36]. martenstite (x > 6.5) from austenite (0 < x < 6.5) at room temperature.…”