14 Search Results

MnNiSi-based alloys and isostructural systems have traditionally demonstrated impressive magnetocaloric properties near room temperature associated with a highly tunable first-order magnetostructural transition that involves large latent heat. However, these materials are limited by a small field-sensitivity of the transition, preventing significant reversible effects usable for cooling applications. Instead, the concomitant large transition volume changes prompt a high pressure-sensitivity, and therefore, promise substantial barocaloric performances, but they have been sparsely studied in these materials. Here, we study the barocaloric response in a series of composition-related (MnNiSi)_1-x(FeCoGe)_x (x = 0.39, 0.40, 0.41) alloys that span continuously over a wide temperature range aroundmore » ambient. We report on giant reversible effects of ~40 J K^-1 kg^-1 and up to ~4 K upon application of ~2 kbar and find a degradation of the first-order transition properties with pressure that limits the barocaloric effects at high pressures. Our results confirm the potential of this type of alloys for barocaloric applications, where multicaloric and composite possibilities, along with the high density and relatively high thermal conductivity, constructively add to the magnitude of the caloric effects.« less

(MnNiSi)_1-x(FeCoGe)_x undergoes a magnetostructural phase transition near room temperature that is acutely sensitive to applied hydrostatic pressure, which presents as a marked shift in the martensitic transition temperature (T_M) by about –7.5 K/kbar. The magnetostructural transition can therefore be induced by applied hydrostatic pressure or by magnetic field. The barocaloric and magnetocaloric effects were measured across T_M (for the sample with x = 0.38), and the corresponding entropy changes were +74 J/kg K (P = 2.7 kbar) and –58 J/kg K (μ₀ H = 5 T), respectively. It was observed here that the transition entropy change increases with pressure, whichmore » results in an enhancement of the barocaloric effect. Our measurements show that the transformed phase fraction associated with magnetostructural transition does not depend on pressure and, therefore, this enhancement cannot be attributed to a pressure-assisted completion of the phase transformation.« less

In this paper, we report the magnetic and magnetocaloric properties of the tetragonal rare-earth compound DyRu₂Si₂ under applied hydrostatic pressure. The isothermal entropy change (ΔS) and the adiabatic temperature change (ΔT_ad) were calculated from magnetization data collected at different applied pressures and from heat capacity measurements conducted at atmospheric pressure, respectively. The application of hydrostatic pressure significantly modified the multi-step magnetization curve and the saturation magnetization. A suppression of the magnetization was observed for P = 0.588 GPa and P = 0.654 GPa whereas, at about P ≈1 GPa, the saturation magnetization increased and the magnetization isotherms again resembled themore » curves measured at atmospheric pressure. A small thermal hysteresis was observed between the heating and cooling M(T) curves at T_t=3.4 K, with an applied magnetic field of H = 0.1 T. This thermal hysteresis indicates a first-order like transition which was also supported by the Arrott plot analysis. Finally, the volume magnetostriction was estimated from the pressure-dependent magnetization measurements using a Maxwell relation.« less

Here, the structural, magnetic, magnetocaloric, transport, and magnetoresistance properties of the rare-earth intermetallic compounds GdNi₂Mn_x (0.5 ≤ x ≤ 1.5) have been studied. The compounds with x = 0.5 and 0.6 crystallize in the cubic MgCu₂ type phase, whereas samples with x ≥ 0.8 form a mixed MgCu₂ and rhombohedral PuNi₃ phase. A second order magnetic phase transition from a ferromagnetic to paramagnetic state was observed near the Curie temperature (T_C). The GdNi₂Mn_x (0.5 ≤ x ≤ 1.5) compounds order in a ferrimagnetic structure in the ground state. The largest observed values of magnetic entropy changes (at T_C for ΔHmore » = 5T) were 3.9, 3.5, and 3.1 J/kg K for x = 0.5, 0.6, and 0.8, respectively. The respective relative values of the cooling power were 395, 483, and 220 J/kg. These values are greater than some well-known prototype magnetocaloric materials such as Gd (400 J/kg) and Gd₅Si₂Ge₂ (240 J/kg). Analysis of the resistivity data showed a T² dependence at low temperatures, suggesting strong electron-phonon interactions, whereas at higher temperatures s-d scattering was dominated by the electron-phonon contribution, resulting in a slow increase in resistivity. Magnetoresistance values of ~–1.1% were found for x = 0.5 near T_C, and –7% for x = 1.5 near T = 80 K.« less