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An experimental investigation was conducted to understand the influence of hydrostatic pressure on phase transition, thermal expansion and barocaloric property of a polycrystalline Ni 54 Mn 23 Ga 23 alloy. Two pressure ranges of 0–1.28 GPa and 0–0.74 GPa were selected for thermal expansion and barocaloric property measurements due to the different test limits of instrumentals. The pressure dependence of fourteen parameters was studied systematically. It was found that the sample experiences a martensitic transformation (MT) near room temperature and the response of MT peak temperature (T M) to pressure is about 15.89 K/GPa. The phase transition strain (λ tr), transformation width (Δ T tr) relative volume change (|Δ V / V |) and maximum adiabatic temperature change (Δ T ad) max increase linearly with pressure and their shifting rates are about 0.071 %/GPa, 7.5 K/GPa, 0.211 %/GPa and 12.2 K/GPa, respectively. Simultaneously, applying hydrostatic pressure can also enhance the barocaloric property of the sample, leading to a large increase in the absolute value of the maximum entropy change (|Δ S | max), the refrigerating capacity (RC) and their reversible values. On cooling, the sensitivities of the reversible RC and its proportion to pressure are around 185.52 J/kg GPa and 16.7 %/GPa, respectively. Finally, the average linear expansion coefficient (α ave) of both martensite and austenite phases keeps unchanged while in the MT region it decreases from -99.84×10–6/K to -86.04×10–6/K with increasing pressure from 0 to 1.28 GPa. These findings indicate that applying hydrostatic pressure can effectively adjust the phase transformation, thermal expansion and barocaloric property of Ni-Mn-Ga alloys, which are meaningful for their application in solid-state refrigeration. • Pressure can effectively adjust phase transformation, thermal expansion and barocaloric property of Ni 54 Mn 23 Ga 23 alloy. • A large response of martensitic transformation (MT) peak temperature to pressure is reported. • The barocaloric property and its reversibility are highly sensitive to pressure. • The average linear expansion coefficient during MT decreases with increasing pressure. [ABSTRACT FROM AUTHOR]

The structural, magnetic, magnetocaloric and barocaloric properties were investigated in Ni 55.5 Mn 17.8 Ga 26.7 alloy. The results show that the sample experiences two successive magnetostructural transformations (MSTs) with decreasing/increasing temperature. The field-induced entropy change and pressure-induced entropy change are only −7.55 J/kg K for a field change of Δ H = 3 T and −10.52 J/kg K for a pressure change of Δ P = 0.622 GPa while the corresponding refrigeration capacity (RC) achieves 68.80 J/kg and 247.83 J/kg, respectively. Such considerable RC values can be ascribed to the broadening of the full-width at half maximum (FWHM) due to the two successive MSTs. It was observed that RC and FWHM increase with magnetic field and pressure, which results in an enhancement of magnetocaloric and barocaloric effects. Importantly, RC and FWHM under Δ P = 0.622 GPa are comparable to and even larger than those reported in some expensive rare-earth-based magnetic refrigerants. The responses of RC and FWHM to pressure are 89.05 J/kg GPa and 4.77 K/GPa for 0 ≤ P ≤ 0.3 GPa and the values are 654.57 J/kg GPa and 73.86 K/GPa for 0.3 ≤ P ≤ 0.622 GPa. The FWHMs of 11.23 K under Δ H = 3 T and of 32.83 K under Δ P = 0.622 GPa are obtained. All these excellent properties originated from two successive MSTs would make Ni 55.5 Mn 17.8 Ga 26.7 alloy promising as a new and inexpensive multicaloric material used in the solid refrigeration technology. • Ni 55.5 Mn 17.8 Ga 26.7 alloy exhibits two successive magnetostructural transformations (MSTs). • Large magnetocaloric and barocaloric effects were observed due to the two successive MSTs. • Two successive MSTs and hydrostatic pressure can effectively broaden the phase transforming temperature span. • A large refrigerant capacity of 247.83 J/kg was obtained under a pressure change of 0.622 GPa. • An inexpensive multicaloric material Ni 55.5 Mn 17.8 Ga 26.7 alloy was reported. [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 Sm 0.5 Y 0.5 FeO 3 single crystal was successfully synthesized using the optical floating zone method. A systematic study was conducted to investigate the spin reorientation transition process in the Sm 0.5 Y 0.5 FeO 3 single crystal, as well as the effects of applied magnetic fields and isostatic pressure on the spin reorientation transition. Analysis of the M (T) curves revealed that the spin reorientation transition process in the single crystal occurs from Γ 4 to Γ 2 between 310 and 350 K. In addition, the spin reorientation phase transition is quite sensitive to magnetic fields and isostatic pressure, particularly when the isostatic pressure exceeds 0.81 GPa, where the rare Γ 3 phase is observed. The M (T) curve under different measurements of isostatic pressure indicates that the spin reorientation phase transition occurs in the sequence of Γ 4 → Γ 2 + Γ 3 + Γ 4 → Γ 2 + Γ 3 with a decrease in temperature once the isostatic pressure exceeds ∼0.72 GPa. Notably, to provide a more comprehensive description of the changes in phase transition configurations with temperature under different isostatic pressure, a detailed phase diagram was established. These findings present new avenues and possibilities for the development of ultrafast spintronic devices and optical magnetic memory systems operating at near room temperature. • Sm 0.5 Y 0.5 FeO 3 single crystals are grown by optical floating zone method. • Laue and X-ray studies confirmed high crystalline quality of the single crystal. • Magnetic fields and isostatic pressures can effectively regulate the spin reorientation phase transition. • The spin reorientation phase transition under high pressure occurs in the sequence Γ 4 → Γ 2 + Γ 3 + Γ 4 → Γ 2 + Γ 3. • A detailed phase diagram was established to depict the spin configuration vary with temperature and isostatic pressure. [ABSTRACT FROM AUTHOR]

Abstract Hollow SnO 2 nanospheres have been successfully fabricated through a simple hydrothermal method by using carbon spheres as template. Microstructure observation showed that the hollow SnO 2 had uniform nanoscale size and single-shelled structure assembled by individual nanocrystallines. Being employed as the supercapacitor electrode materials, the resultant hollow SnO 2 nanospheres displayed a considerable specific capacitance of 332.7 F/g at a current density of 1 A/g, much higher than the pristine SnO 2 particles (143.5 F/g). The hollow SnO 2 also exhibited good rate capability remained relatively high capacitance of 174.9 F/g at a large current density of 20 A/g, as well as excellent cycling properties without capacitance degradation over 2000 charging/discharging cycles. Such excellent electrochemical performance of the hollow SnO 2 nanosphere can be attributed to its unique nanosized and single-shelled hollow structure which greatly increases the available surface area and providing hierarchical porosity for the electrode materials. Highlights • Hollow SnO 2 nanospheres were successfully fabricated by a hydrothermal method. • The hollow SnO 2 possesses novel nanoscale size and single-shelled structure. • The hollow SnO 2 exhibited enhanced capacitive properties. [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]

The influence of isotropic physical pressure, applied either during the high-pressure-high-temperature (HPHT) annealing or the measuring processes, on the magnetic properties of NdFeO 3 single crystal, has been investigated. In comparison to the complete spin reorientation (SR) in an as-grown NdFeO 3 single crystal, the thermomagnetic M (T) and isothermal M (H) curves for a HPHT-annealed sample indicates an incomplete SR transition from a Γ 2 -rich to a Γ 4 -rich Γ 24 mixed phase. Moreover, the M (T) curves of the as-grown sample under different measuring hydrostatic pressures suggest that the SR transition takes place in the sequence of Γ 2 → Γ 1 + Γ 2 + Γ 4 → Γ 1 + Γ 4 → Γ 4 , instead of the Γ 2 → Γ 2 + Γ 4 → Γ 4, without applying pressure during the measuring process. Such manipulation of the magnetic configuration reveals that the 3 d -4 f interaction in the NdFeO 3 could be greatly affected by the isotropic pressure. These findings may provide a new perspective and possibility for the tuning of the magnetism and corresponding microscopic interactions. • A comparative study of isotropic pressure on NdFeO3 single crystal is carried out. • High-pressure-high-temperature annealing leads to an incomplete spin reorientation • Hydrostatic pressure in the measuring process introduces an intermediate phase. • Isotropic pressure can tune the magnetism and microscopic interactions in NdFeO3. [ABSTRACT FROM AUTHOR]