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The influence of Cu doping on phase transition, thermal strain, and thermal expansion property of polycrystalline Ni50Mn23−xCuxGa27(x = 1, 3, 5, 6 and 7) alloys is investigated. The results show that with increasing Cu concentration, martensitic transformation gradually gets close to Curie transition. A magnetostructural transition (MST) is observed in samples with x = 6 and 7. Such MST can enhance magnitude of transformation strain. Besides, Ni50Mn23−xCuxGa27 alloys possess an isotropic, recoverable, and thermally stable thermal strain. Excitedly, Cu doping can effectively tune the phase transition, thermal strain, and thermal expansion properties of Ni50Mn23−xCuxGa27 alloys. Adjustable coefficients of thermal expansion from positive to negative are obtained by Cu‐doped Ni50Mn23−xCuxGa27 alloys. The average linear expansion coefficient (α) between −140.44 and −207.70 ppm K−1 is observed in samples with x = 6 and 7 for a narrow temperature span of 11–14 K. When the temperature span is about 72 K (x = 6) and 73 K (x = 7), which is the largest temperature span observed in Ni–Mn–Ga‐based alloys recently, the α values decrease to about −36 ppm K−1. These findings are beneficial for manipulating the thermal expansion property of Ni–Mn–Ga–Cu alloys and their multifunctional applications. [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]

The magnetic field effect on phase transition and thermal expansion properties were investigated in Ni 55 Mn 18 Ga 27 alloy. The results show that the alloy has an excellent isotropy, reproducibility and thermostability in thermal strain and exhibits a large negative thermal expansion (NTE) effect in the direct and reverse martensitic transformations (MTs). For the direct MT, the average linear expansion coefficient α is about −225.21 ppm/K and the corresponding temperature span is around 8.2 K. Additionally, the sensitivities of the transformation strain and peak temperatures to field are about 88.5 ppm/T and 1.31 K/T, respectively. The rates of α and temperature spans of NTE to magnetic field are about 8.88 ppm/K T and 0.82 K/T, indicating that the magnetic field can improve the NTE property of the Ni–Mn-Ga alloy. Finally, the NTE mechanism has also been discussed. Our findings are beneficial to improving the thermal expansion and NTE properties of Ni–Mn-Ga alloys. • The thermal strain of the Ni55Mn18Ga27 alloy is highly isotropic, reproducible and thermostable. • The alloy exhibits a large negative thermal expansion (NTE) effect during the martensitic transformations (MTs). • The average linear expansion coefficient α is −225.21 ppm/K for the direct MT and the rate of α to field is ∼8.88 ppm/K T. • The NTE mechanism has also been discussed. • Applying magnetic field can improve the NTE property of the Ni–Mn-Ga alloy. [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]

A large-size single crystal of Mn 4 Ta 2 O 9 with ∼3.5 mm in diameter and ∼65 mm in length was successfully grown for the first time by a newly designed one-step method based on the optical floating zone technique. Both the clear Laue spots and sharp XRD Bragg reflections suggest the high quality of the single crystal. In Mn 4 Ta 2 O 9 single crystal, an antiferromagnetic phase transition was observed below Néel temperature 102 K along c axis, which is similar to the isostructural compound Mn 4 Nb 2 O 9 , but differs from the isostructural Co 4 Nb 2 O 9 . Relative dielectric constant at 30 kOe suggests that no magnetoelectric coupling exists in Mn 4 Ta 2 O 9 . [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 structure, transition properties, and hydrostatic pressure (p) and magnetic field (B) dependence of transition temperatures and operation-temperature window (Δ T , defined as the temperature range of martensitic transition) were investigated in Ni 53 Mn 21 Ga 26 alloy. The results reveal that all the transition temperatures and Δ T increase almost linearly with increasing magnetic field and pressure. Particularly, a stronger dependence of peak temperature (T M) and Δ T on pressure, d T M /d p = 25.7 K/GPa and dΔ T /d p = 18.7–22.7 K/GPa, is observed in contrast with the smaller values of d T M /d B = 1.3 K/T and dΔ T /d B = 1.4–1.7 K/T found in Ni 53 Mn 21 Ga 26 alloy. Furthermore, the value of 25.7 K/GPa may be the largest shift in T M with pressure observed in polycrystalline Ni–Mn-Ga systems. Clearly, the sensitivities of T M and Δ T to pressure are much higher than those to magnetic field. These findings illustrate that applying hydrostatic pressure is beneficial to broaden Δ T in Ni 53 Mn 21 Ga 26 alloy. • Ni 53 Mn 21 Ga 26 alloy exhibits a magnetostructural transformation (MST). • Hydrostatic pressure effects on the phase transition properties and operation-temperature window (Δ T) have been studied. • A large shift in peak temperature with pressure of 25.7 K/GPa was observed. • A strong response of Δ T to pressure p , dΔ T /d p = 18.7–22.7 K/GPa, was reported. • Hydrostatic pressure can effectively broaden the operation-temperature window. [ABSTRACT FROM AUTHOR]