Search

In this work, a non-spontaneous martensitic transformation (MT) activated by the hydrostatic pressure has been observed in polycrystalline Ni43Co7Mn35In15 Heusler alloy. This alloy can experience a nearly complete metamagnetic MT with the assistance of an enough pressure. As the change of pressure reaches 20 kbar, the maximum baroresistance (BR) of the studied alloy achieves ~ 825% at 50 K and remains ~ 280% even in the vicinity of room temperature revealing a giant BR effect over a wide temperature range. More interestingly, the perfectly reversible isothermal BR effects as high as over 650% have been also found at the temperatures below 130 K by overcoming a thermal barrier between direct and reverse MTs. Such an interesting behavior could be ascribed to a pressure-induced continuous first-order MT accompanied by a prominent change of spin ordering, which brings about a combined contribution of electron-spin and electron-lattice scatterings. [ABSTRACT FROM AUTHOR]

In the present work, polycrystalline Co52V29+xGa19-x(0 ≤ x ≤ 2) Heusler alloys have been prepared. The related experimental results confirm that each sample undergoes a first-order martensitic transformation (MT) from the L21 cubic austenitic state to the D022 tetragonal martensitic state. With increase of V concentration, both transformation temperature and strain are heightened simultaneously, thus giving rise to an increment of transition entropy change Δ S tr . In addition, the influence of hydrostatic pressure on MT and transition strain have been also carefully studied. With increase of pressure, the transformation temperatures of these samples move to high values apparently, but their reversible strain only exhibit a slight enhancement and quickly approach the saturated values. For different compositions, however, there is no obvious difference in the rate of transformation temperature change with pressure. Such a behavior opens up the potential applications of the functional properties associated with the hydrostatic pressure-induced MT for this system. [ABSTRACT FROM AUTHOR]

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]

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 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]

The evolutions of electrical transport property and Baroresistance (BR) effect at the martensitic transformation (MT) with the change of Co content have been systematically investigated in the Ni 50- x Co x Mn 35 In 15 (0 ≤ x ≤ 7) Heusler system. The structure measurements show that every sample undergoes first-order MT from a L 2 1 cubic structure to a 3 M monoclinic structure. According to magnetic measurements, it is also found that the samples with lower Co content (0 ≤ x ≤ 3) exhibit a paramagnetic MT, i.e. the MT occurs between the paramagnetic austenite and the paramagnetic martensite. At higher Co content, however, the samples display a metamagnetic MT, i.e. the MT occurs between the ferromagnetic austenite and the paramagnetic martensite. Due to the enhancement of the ferromagnetic ordering for the austenitic phase with Co increasing, the difference in resistivity between austenitic and martensitic phases is enlarged significantly. This leads to a giant BR effect with a value of ∼250% associated with the hydrostatic pressure-induced MT can be observed in the sample with x = 6. Moreover, the Hall measurement results indicate that the difference in electrical transport behavior between both phases for the studied alloys mostly relies on the mobility of carriers related to the electro-lattice and the electro-spin scatterings. In this case, the underlying mechanism of the relative contributions originating from these two different scattering processes to the saturated BR effect has been separated quantitively based on the electrical transport measurements under applied different hydrostatic pressures. It demonstrates that the electron-spin scattering acts as a dominant role in improvement of the BR effect for this system. • The MT from a paramagnetic type into a metamagnetic one has been found. • A giant BR effect (∼250%) has been obtained around the room temperature. • The change of electrical transport during MT depends on the mobility of carriers. • Both electro-lattice and electro-spin scatterings has been separated quantitively. • The spin-dependent scattering plays a crucial role to improve the BR effect. [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]