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We report effect of hydrostatic pressure on martensitic transformation in polycrystalline Ni 44.6 Co 5.5 Mn 35.5 In 14.4 . With applying pressure, the transformation moves to high temperatures at a rate of 4.4 K/kbar. Utilizing an indirect method, the calculated maximum isothermal entropy changes achieve ~ 14.3 J/kg K at 2.76 kbar and ~ 15.6 J/kg K at 5.98 kbar, which respectively output the values of ~ 5 K and ~ 6 K for the adiabatic temperature change near room temperature. After deducting the average hysteretic loss (~ 152 J/kg), the effective refrigeration capacities still reach ~ 38 J/kg at 2.76 kbar and ~ 247 J/kg at 5.98 kbar, performing an enhanced barocaloric effect. [ABSTRACT FROM AUTHOR]

Both the barocaloric effect (BCE) and its reversible behavior during martensitic transformation (MT) have been experimentally investigated in Ni 42.3 Co 7.9 Mn 38.8 Sn 11 quaternary Heusler alloy. The experimental results show that the studied alloy experiences the MT from the ferromagnetic L 2 1 -type cubic structure to the paramagnetic-like three-layered (3 M ) modulated monoclinic structure, resulting in a value of ∼1.1% for the relative volume change ε between two phases. Due to appearance of an enhanced ε , the migration rate of martensitic transformation with respect to the hydrostatic pressure reaches ∼4.7 K/kbar, while a high transition entropy change (∼28 J/kg K) is still maintained. Based on an indirectly estimated method, the calculated maximum value for isothermal entropy change Δ S T achieves ∼ -23 J/kg K with the pressure change of 6.2 kbar, which yields the values of ∼10 K for adiabatic temperature change Δ T a d and ∼786 J/kg for relative cooling power (RCP), performing a large BCE. According to the change of phase fraction at selected hydrostatic pressures, a detailed schematic diagram has been established to evaluate the reversibility of this effect. With applying an external cyclic pressure of 6.2 kbar, the maximum repeatable values calculated for both Δ S T and Δ T a d are decreased to ∼ -15 J/kg K and ∼5 K, respectively. This is attributed to an insufficient driving force, which can only partially transform this material, leading to a reversible MT appeared in the mixed state. [ABSTRACT FROM AUTHOR]

The evolutions of phase transformation, magnetic and electrical transport properties with the change of Fe concentration have been systematically investigated in a series of Ni 60- x Fe 13+ x Ga 27 (x = 0–10) Heusler alloys. The structure and heat flow measurements reveal every sample undergoes a disordered-ordered transition from a disordered B 2 structure to a L 2 1 ordered structure, and a first-order structural transformation from the L 2 1 cubic structure to a L 1 0 tetragonal structure is corresponding to the martensitic transformation (MT). With increasing Fe concentration, the disordered-ordered transition and ferromagnetic transition shift to higher temperature, while the MT shifts to lower temperature. According to phase diagram established in the present investigation, it is also found that the increase of Fe content can convert the first-order MT from a paramagnetic type to a ferromagnetic one, which is accompanying by an obvious increase of both effective and spontaneous magnetic moments. Furthermore, the calculated magnetocrystalline anisotropy constant (K 1) of the studied alloys monotonically increases as Fe increases. It is evident that the magnetic degrees of freedom in these two MTs remain almost unchanged so that the electron-spin scattering doesn't change, which results in the resistivity difference between the austenitic and martensitic states is feeble. Such an intrinsic nature leads to a weak magnetoresistance (MR) and baroresistance (BR) effects in the studied samples because of only contribution of electron-lattice scattering change on the resistivity. This demonstrates from a negative perspective that the electron-spin scattering change originated from the variation in the magnetic degrees of freedom acts as a dominant role in improvement of the MR and BR effects for the Heusler system possessed the first-order MT. • The phase diagram including the structural ordering transition for Ni-Fe-Ga alloys was established. • Ni 60- x Fe 13+ x Ga 27 alloys undergo a disordered-ordered transition from a disordered B 2 structure to a L 2 1 ordered structure. • The magnetocrystalline anisotropy constant monotonically increases as Fe increases. • The baroresistance and magnetoresistance effect of Ni-Fe-Ga has been obtained around the room temperature. • The electron-spin scattering change acts as a crucial role to improve the MR and BR effects. [ABSTRACT FROM AUTHOR]

• Applying hydrostatic pressure can push the MT to a higher temperature. • Curie transition almost remains unchanged under hydrostatic pressure. • The average magnetic moment and mass susceptibility of SPM cluster are reduced. • The strength of FM/AFM interactions are suppressed by hydrostatic pressure. • The application of hydrostatic pressure suppresses the exchange bias effect. The effect of hydrostatic pressure on martensitic transformation (MT), superparamagnetic (SPM) and exchange bias (EB) behaviors in polycrystalline Ni 45 Cu 5 Mn 35 In 15 has been intensively investigated by various experimental methods. The experimental results show that the studied alloy experiences a MT from the austenitic state with a L 2 1 -type cubic structure to the martensitic state with a seven-layer (7 M) modulated orthorhombic structure with decreasing temperature, accompanied by a significant change in magnetization. It is found that applying hydrostatic pressure can induce the MT to occur in the higher temperature, while the Curie transition almost remains unchanged due to the suppression of ferromagnetic (FM) coupling. In addition, the applied hydrostatic pressure can suppress the EB field and coercivity of the studied alloy due to the reduction of the competition between FM and AFM interactions. This phenomenon can be attributed to the fact that the application of hydrostatic pressure reduces the size of the SPM cluster and its average magnetic moment. [ABSTRACT FROM AUTHOR]