Alexandre Magnus Gomes Carvalho

This work investigates the magnetostructural transition and magnetocaloric effect (MCE) in the Ni₅₀Mn_(37-x)Fe_xSn₁₃ Heusler alloy series (with x=0, 1, 2, 3, 4 and 5). The polycrystalline ingots were prepared by arc melting and annealed at 850°C for 3 days. Temperature-dependent X-ray diffraction revealed a reversible first-order martensitic transformation from a high-temperature cubic austenite phase to a low-temperature orthorhombic martensite phase. Magnetic and calorimetric measurements showed that the substitution of Mn by Fe systematically shifts the martensitic transition to lower temperatures, leading to its complete suppression for x=5. The alloys exhibit both inverse and conventional MCE, associated with the martensitic and ferromagnetic transitions, respectively. Notably, the sample with x=3 displayed an optimized magnetocaloric performance, achieving a maximum inverse magnetic entropy change (ΔS_T) of +6.6 J kg⁻¹K⁻¹ and a conventional ΔS_T of −3.8 J kg⁻¹K⁻¹ under a magnetic field strength change of 50 kOe. Consequently, a large relative cooling power of approximately 491 J kg⁻¹ was obtained for this composition. These results demonstrate that small stoichiometric adjustments in the Fe concentration, combined with precise thermal treatment, allow bulk alloys to achieve refrigerant capacities typically restricted to melt-spun ribbons, establishing the Ni-Mn-Fe-Sn system as a cost-effective and high-performance candidate for solid-state refrigeration.

Diamonds from the Guiratinga region (southeastern Mato Grosso, central Brazil) provide constraints on the structure, metasomatism, redox state, and thermal evolution of the subcontinental lithospheric mantle beneath the northern Paraná Basin, along the southeastern margin of the Amazonian Craton. A multi-analytical approach integrating synchrotron μ-XRD, Raman spectroscopy, μ-FTIR, EPMA, and LA-ICP-MS was applied to characterize mineral inclusions, mineral chemistry, and nitrogen systematics. The inclusion assemblage is dominated by a peridotitic suite comprising forsteritic olivine (Mg# = 92.1–93.3), enstatite (Mg# = 94.3–94.8), clinopyroxene, and garnet, indicating derivation from a strongly depleted lithospheric mantle keel. Temperatures derived from the Al-in-olivine thermometer projected onto a 40 mW/m2 geotherm yield P–T estimates of 4.5–5.0 GPa and 1059–1156 °C. The occurrence of phlogopite indicates infiltration of volatile-rich metasomatic agents. A subordinate eclogitic signature is recorded by high-pressure phases (coesite and kyanite) and mineral associations compatible with transformed crustal protoliths. Hydrous to retrograde phases (amphibole, sodic plagioclase, epidote, and quartz) are interpreted as products of post-entrapment re-equilibration during hydration–oxidation processes. Hematite occurs as an isolated inclusion lacking microfracture connectivity, suggesting deep redox re-equilibration. FTIR spectra reveal total nitrogen contents of 0–970 at.ppm and aggregation states dominated by Type IaAB diamonds, with subordinate IaB, IaA, Ia, and IIa populations, indicating heterogeneous time–temperature histories. Nitrogen aggregation thermochronometry suggests prolonged mantle residence at ~1145–1261 °C for ~1.0 Ga.

Energy conversion materials represent a rapidly evolving field that is core to future sustainable technologies. Caloric effect materials, which convert magnetic, electrical, or mechanical stress into thermal energy, are particularly promising for their potential application in solid-state cooling. In particular, the torsiocaloric effect—where materials convert pure shear stress into thermal energy—remains relatively underexplored despite its immense technological potential. However, progress in this area has been hindered by the lack of commercial instrumentation designed to study the thermomechanical properties of materials under shear stress. In this work, we present a device capable of characterizing materials under shear stress and directly measuring the torsiocaloric effect efficiently. The system was tested using two distinct materials—a rigid polymer and a shape memory alloy—demonstrating its versatility. Our results show that the device can successfully generate torque versus angular displacement curves, conduct fatigue tests, measure adiabatic temperature change, and evaluate caloric reversibility. These outcomes highlight the device’s excellent performance and its potential to advance the research in the torsiocaloric field.

Effect of temperature on straining of AISI 304 austenitic stainless steel

We report a theoretical simulation of the barocaloric effect in spin crossover systems starting from a model Hamiltonian, which includes the crystalline electrical field, elastic, and phonon interactions. A systematic study, through the model parameters, allowed the construction of phase diagrams, and the contributions of configurational, magnetic, and phonon entropies for the barocaloric effect were investigated. The majority contribution comes from the phonons (about 76%, in our simulation), which were associated with the large cell volume change during the low-spin-(SL) ↔ high-spin-(HS) phase transition. Besides, the refrigerant capacity due to the barocaloric effect was discussed in the first- and second-order (LS) ↔ (HS) phase transition regimes. We find out that when hysteresis increases, with an increase in pressure, a higher barocaloric effect can be obtained.

Long-chain n -alkanes exhibit a remarkable barocaloric effect in a wide range of temperatures, enhanced by the onset of a liquid–solid pressure-induced phase transition, and are promising candidates for the development of solid-state cooling systems.