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Room temperature elastocaloric effect as well as the effects of strain rate and loading stress have been studied in polycrystalline Ni51Mn34In8Sn7. The increase of strain rate reduces plastic deformation and lattice invariant strain, thus improving the superelasticity. Higher strain rate and stress facilitate the stress-induced structural transition and adiabatic environment, and so the temperature change (ΔT) increases at a rate of 1.77 K (1% s−1)−1 and 1.78 K (102 MPa)−1. A large ΔT of 4.2 K is obtained by optimizing the strain rate and loading stress, which is comparable to or even larger than those of many NiMn-based alloys at room temperature. This result suggests polycrystalline Ni51Mn34In8Sn7 as a desirable material for room temperature elastocaloric refrigeration.

The effects of Cu substitution for Ni atoms on the magnetic and magnetocaloric properties have been investigated in Mn0.8Fe0.2Ni1-xCuxGe (x = 0.05–0.3) compounds. The substitution of Cu leads to the larger separation of Mn atoms, which stabilizes the hexagonal phase and thus reduces the structural transition temperature Tstr. Moreover, the larger separation of nearest-neighbor Mn atoms weakens the ferromagnetic (FM) coupling in TiNiSi-type orthorhombic phase and results in the spiral antiferromagnetic (AFM) and more antiparallel AFM state with increasing Cu content. Similarly, the Ni2In-type hexagonal phase also changes from FM state to weak-magnetic spin-glass-like state with the introduction of Cu. The x = 0.05 compound shows a conventional magnetocaloric effect (MCE) due to the magnetostructural transformation from PM hexagonal phase to FM orthorhombic phase. On the contrary, the x = 0.1 compound undergoes the antiferromagnetically magnetostructural transition from FM hexagonal phase to AFM orthorhombic phase, which leads to a high inverse MCE. This large inverse MCE could be utilized in novel magnetic refrigerator to improve the refrigeration efficiency and applied for magnetic refrigeration of natural gas liquefaction.

The magnetic and rotating magnetocaloric properties in textured Tb3NiGe2 compound were investigated. Two successive magnetic transitions, a ferrimagnetic to antiferromagnetic (AFM)-like transition at Tt = 130 K and an AFM to paramagnetic (PM)-like transition at TN = 144 K, are observed. Besides, a magnetic-field-induced antiferromagnetic-ferromagnetic metamagnetic transition occurs in the temperature range of Tt ∼ TN. Large rotating magnetic entropy changes, together with considerable adiabatic temperature changes and refrigeration capacity, are obtained in textured Tb3NiGe2 compound. Moreover, the equivalence of different calculation methods for rotating magnetocaloric effect (RMCE) is discussed mathematically. The large RMCE with excellent thermal and magnetic reversibility suggests textured Tb3NiGe2 compound as an attractive candidate for novel magnetic refrigerant.

Textured Ho2GdAl2 alloy exhibits highly anisotropic magnetic properties due to the coexistence of preferred crystallographic orientation and magnetocrystalline anisotropy (MCA). The variation in MCA energy (Ea) induced by the rotation of textured Ho2GdAl2 from a perpendicular to parallel direction under constant field results in a rotating magnetocaloric effect (MCE), which is larger than the conventional MCE. Moreover, the peaks of rotating magnetic entropy change (ΔSR) and rotating adiabatic temperature change (ΔTad,R) broaden asymmetrically towards low temperatures due to the different variation of MCA below and above the Curie temperature TC, thus leading to a table-like rotating MCE over the liquefaction temperature of natural gas.

The Gd x Ho 3−x Al 2 ( x = 0.5–2.5) compounds undergo two successive magnetic transitions: a second-order magnetic transition from paramagnetism (PM) to ferromagnetism (FM) around T C followed by a FM to ferrimagnetism (FIM)-like transition at T t . The T C increases linearly with the increase of Gd content due to the de Gennes factor of Gd being larger than that of Ho, while the T t remains nearly constant around 45 K independent of the variation of Gd content. The working temperature range is expanded by substituting Ho with Gd atoms due to the higher transition temperature of Gd 3 Al 2 and the different composition dependence of successive magnetic transitions, and thus leading to an enhanced refrigerant capacity ( RC ). For a relatively low field change of 2 T, a giant RC value of 272 J/kg with a wide working temperature range of ∼80 K is obtained for x = 1.0 compound due to the partial overlap of successive Δ S M peaks. This is probably the largest RC value so far reported in the temperature range of liquid natural gas (111 K). Consequently, the large Δ S M and giant RC suggest that Gd x Ho 3−x Al 2 compounds could be good candidates of magnetic refrigerants in a wide temperature range.

The phase relationships, magnetic transitions, and magnetocaloric effect (MCE) of MnCo1 − xCuxGe (x = 0–0.5) alloys have been investigated. The substitution of Cu for Co reduces the structural transition temperature between Ni2In-type hexagonal phase and TiNiSi-type orthorhombic phase. The Curie temperature of orthorhombic martensite (TCM) also decreases with increasing x from 0 to 0.2, which is likely due to the weakening of Co-Mn and/or Co-Co interactions by non-magnetic element Cu substitution for Co atoms. In addition, two successive first-order magnetic transitions, a ferromagnetic (FM) to antiferromagnetic (AFM)-like transition around T2 followed by an AFM to FM-like transition around T1, are observed for 0.17 ≤ x ≤ 0.27, which have not been reported in MnCoGe-based alloys so far. An inverse MCE is observed under low field changes and then a universal curve of ΔSM is successfully constructed, proving the applicability of universal curve for AFM materials with inverse MCE. Finally, the variation of magnetic states is explained in terms of the expansion of nearest-neighbor Mn-Mn distance d1. These new findings and related discussions are very helpful for future tailoring of magnetostructural coupling and metamagnetic transition in MM'X (M, M′ = transition metals, X = carbon or boron group elements) alloys. Keywords: Magnetic properties, Martensitic transformations, Magnetocaloric effect