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Large magnetocaloric effects can be observed in materials with first-order magneto-structural phase transition. However, materials with large thermal hysteresis show a reduced effect in moderate fields (∼ 2 T) because the external field is insufficient to induce a fully reversible transformation. The hysteresis can be overcome or even exploited by applying a second external stimulus. A multi-stimuli test bench has been built to demonstrate the multicaloric effect in FeRh alloy using a pulsed magnetic field up to 9 T and a uniaxial stress of up to 700 MPa. A cyclic multicaloric effect of ± 2.5 K could be observed for a sequential application of a pulsed field of 3 T and a uniaxial stress of 700 MPa. The interplay among external field strength, thermal hysteresis, and the transition width enables the use of pulsed magnetic fields and allows a decoupling of the applied magnetic field and the heat transfer process in the multi-stimuli cycle. [ABSTRACT FROM AUTHOR]

Magnetic refrigeration working based on the magnetocaloric effect can be the perfect replacement of the conventional gas compression-based refrigeration technology and reduces its harmful effects on the environment. The boundary between a first-order and a second-order phase transition would be where the perfect magnetocaloric material would be found. Therefore, establishing the sequence of phase transitions clearly is essential for the characterization of other phase change materials and for applied magnetocaloric research. A quantitative fingerprint of second-order thermomagnetic phase transitions is reported here in Si-substituted high content Mn-based inverse Heusler alloy systems, which are found to be crystallized in cubic structures. The second-order nature of the phase transition has been confirmed from the Arrott plot analysis and a correlation between magnetocaloric effect and local exponent is established. Using the Arrott plot, the critical exponents are evaluated employing different techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm. Their values are found to be in great agreement with each other and follow the mean-field model signifying the presence of long-range ordering in the materials. The high value of isothermal magnetic entropy change and the reversibility justifies the suitability of the reported materials in the practical application as magnetic refrigerants. [ABSTRACT FROM AUTHOR]

Using commercially available components, a compact laboratory-type prototype has been developed and assembled to demonstrate single and multicaloric effects arising from single and cyclic applications of magnetic fields and uniaxial mechanical loads. Using the example of the LaFe11.4Mn0.3Si1.3H1.6 alloy with a first-order phase transition near room temperature, the possibility of observing magnetocaloric, elastocaloric, and multicaloric effects is demonstrated. It is shown that by selecting protocols for applying combined external influences: magnetic field and mechanical load, it is possible to observe a synergistic effect for adiabatic temperature change, which amounts to 1.17 K (0.31 T and 19 MPa) at a temperature of 291.5 K for the multicaloric effect, which exceeds the corresponding value of |ΔT| = 0.75 K (0.31 T) at a temperature of 291.65 K for the magnetocaloric effect. The proposed approaches and obtained results can be used for the development of new prototypes of multicaloric cooling systems and the optimization of current ones. [ABSTRACT FROM AUTHOR]

In this study, we investigate the magnetocaloric effects (MCE) and critical behavior of Gd-doped La 0. 6 5 Ca 0. 3 5 − x GdxMnO3 (x = 0 , 0. 1 0 , 0. 1 5) polycrystalline materials. Our results reveal excellent MCE in the Gd-doped samples. Under a magnetic field of 7 T, the full-width at half maximum (Δ T FWHM ) increases from 41 K (x = 0. 0 0) to 121 K (x = 0. 1 0) and 112 K (x = 0. 1 5). Additionally, the refrigerant capacity (RC) is enhanced by 149% and 145% at x = 0. 1 0 and x = 0. 1 5 , respectively, compared to the parent phase. We propose that these improvements can be attributed to the introduction of Gd 3 + ions, which possess smaller ionic radii. This reduction in the average A-site ionic radius weakens the double exchange (DE) interactions, resulting in a more continuous phase transition within the system. Supporting this view, we observe a decrease in magnetization strength after doping, a reduction in Curie temperature ( T C) from 250 K (x = 0. 0 0) to 134 K (x = 0. 1 0) and 130 K (x = 0. 1 5) and a transformation from a first-order to a second-order phase transition in the doped samples. To characterize the critical behavior of the phase transition in the doped samples, we employ the K-F method. The obtained critical exponents for x = 0. 1 0 and x = 0. 1 5 are β = 0. 3 8 0 ± 0. 0 0 6 , γ = 1. 3 2 3 ± 0. 0 0 3 , δ = 4. 4 8 2 ± 0. 0 0 5 and β = 0. 4 7 7 ± 0. 0 0 8 , γ = 1. 0 8 3 ± 0. 0 0 4 , δ = 3. 2 7 0 ± 0. 0 0 2 , respectively. Furthermore, the calculation of the n values suggests a transition of the phase transition in the doped samples from short-range ordering to long-range ordering. [ABSTRACT FROM AUTHOR]

La0.7Ca0.3MnO3 (LCMO) is a prominent semi-metallic ferromagnet known for its strong spin polarization and sharp magnetic transition temperature. This makes it a highly attractive candidate for various applications in spintronic technology, memory devices, and multifunctional systems. The structural and physical properties of LCMO can be significantly altered by adjusting the annealing atmosphere during synthesis. Here, we present an in-depth analysis on the influence of oxygen annealing on the structural characteristics, magnetic behavior, and magnetocaloric properties of LCMO compound. The analysis of X-ray diffraction patterns by using Rietveld refinement method revealed that all the samples formed an orthorhombic structure with the Pnma space group with a decrease in cell volume for samples (S2 and S3) annealed in oxygen atmosphere. The samples S1, S2, and S3 undergo ferromagnetic-paramagnetic phase transitions at 247, 263, and 264 K, respectively. This suggests that the oxygenated annealing induce the oxygen homogeneity in the sample. On the other hand, the field-dependent magnetization measurements and Arrott analysis indicated a first-order ferromagnetic phase transition in all the prepared samples. The maximum change in magnetic entropy was evaluated by using numerical approximation of Maxwells thermodynamic relation. It was noted that the maximum change in magnetic entropy shows monotonic behaviour with oxygen annealing. This ability to adjust magnetization and magnetocaloric effect by altering the annealing atmosphere of LCMO presents a novel approach for developing magnetic refrigerants and gaining insight into fundamental phenomena. [ABSTRACT FROM AUTHOR]

We report a large cryogenic magnetocaloric effect stemming from an unconventional borderline first-order magnetic phase transition with negligibly small thermomagnetic hysteresis in a rare-earth-based intermetallic compound PrNdIn. The sample exhibits maximum magnetic field-induced entropy change as large as −10 J/Kg K (for 20 kOe magnetic field change) near the boiling point of oxygen. Magnetocaloric properties of PrNdIn are comparable to those of other known potential magnetocaloric materials with operating temperatures ranging between 50 and 125 K. The magnetic properties of the present sample are qualitatively reminiscent of those of the binary Pr2In and Nd2In, including the emergence of a second low-temperature anomaly in the temperature dependence of magnetization. [ABSTRACT FROM AUTHOR]

In order to improve the magnetocaloric properties of MnNiSi-based alloys, a new type of high-entropy magnetocaloric alloy was constructed. In this work, Mn0.6Ni1−xSi0.62Fe0.4CoxGe0.38 (x = 0.4, 0.45, and 0.5) are found to exhibit magnetostructural first-order phase transitions from high-temperature Ni2In-type phases to low-temperature TiNiSi-type phases so that the alloys can achieve giant magnetocaloric effects. We investigate why chexagonal/ahexagonal (chexa/ahexa) gradually increases upon Co substitution, while phase transition temperature (Ttr) and isothermal magnetic entropy change (ΔSM) tend to gradually decrease. In particular, the x = 0.4 alloy with remarkable magnetocaloric properties is obtained by tuning Co/Ni, which shows a giant entropy change of 48.5 J∙kg−1K−1 at 309 K for 5 T and an adiabatic temperature change (ΔTad) of 8.6 K at 306.5 K. Moreover, the x = 0.55 HEA shows great hardness and compressive strength with values of 552 HV2 and 267 MPa, respectively, indicating that the mechanical properties undergo an effective enhancement. The large ΔSM and ΔTad may enable the MnNiSi-based HEAs to become a potential commercialized magnetocaloric material. [ABSTRACT FROM AUTHOR]

The crystal structure, magnetic phase transitions and magnetocaloric effect of DyCo2−xGex (x = 0.0–0.2) compounds were studied. X-ray diffraction coupled with Rietveld analysis shows that all DyCo2−xGex samples maintain the cubic Laves structure (MgCu2-type, Fd-3 m space group), and the lattice parameter increases as x increases. Under an applied field change of 0–5 T, the maximum magnetic entropy change of DyCo2−xGex (x = 0.0, 0.05, 0.15 and 0.2) compounds are 10.4, 10.3, 7.3 and 6.3 J/kg K, and the values of relative cooling power are 290.6, 309.6, 290.4 and 271.8 J/kg, respectively. According to Arrott plots and the Inoue-Shimizu model, DyCo2 and DyCo1.95Ge0.05 compounds still maintain the first-order magnetic phase transition. But when the Ge content exceeds 0.05, a magnetic phase transition from first-order to second-order occurs. Magnetic measurement reveals that the Ge content increases the Curie temperature from 151 (for x = 0.0) to 179 K (for x = 0.2). This suggests that the DyCo2−xGex compounds are candidate materials for cryogenic magnetic cooling, which can be used in natural gas liquefaction, biological organ storage in medicine and quantum computer heat dissipation. [ABSTRACT FROM AUTHOR]

In this paper, the magnetocaloric properties and magnetic phase transition of the (La–Ca) MnO3 system after secondary doping with the large magnetic moment rare earth element Gd are investigated. Analysis reveals that the polycrystalline material La0.65Ca0.3Gd0.05MnO3 exhibits a magnetocaloric effect superior to both the un-secondary doped and similar types of materials at the critical point of the ferromagnetic–paramagnetic phase transition (TC = 173 K). Under 7 T magnetic field, the maximum magnetic entropy change |∆SMmax|, refrigerant capacity RC, and relative cooling capacity RCP are 8.10 J kg−1 K−1, 350.54 J kg−1, and 422.17 J kg−1, respectively. The high overlap between TEC (4 K) and |∆SMmax| at the same magnetic field indicates its good utility. Landau theory yields a negative slope of the Arrott plot at TC, and the fit of Landau coefficients b (TC) obtains negative values verifying the ferromagnetic–paramagnetic first-order phase transition. Further calculation of the n value and the universal curve plot using the magnetocaloric effect confirmed this type of magnetic phase transition and revealed the origin of the large magnetocaloric effect. The material provides new ideas for applications in cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In this paper, the magnetocaloric properties and magnetic phase transition of the (La–Ca) MnO3 system after secondary doping with the large magnetic moment rare earth element Gd are investigated. Analysis reveals that the polycrystalline material La0.65Ca0.3Gd0.05MnO3 exhibits a magnetocaloric effect superior to both the un-secondary doped and similar types of materials at the critical point of the ferromagnetic–paramagnetic phase transition (TC = 173 K). Under 7 T magnetic field, the maximum magnetic entropy change |∆SMmax|, refrigerant capacity RC, and relative cooling capacity RCP are 8.10 J kg−1 K−1, 350.54 J kg−1, and 422.17 J kg−1, respectively. The high overlap between TEC (4 K) and |∆SMmax| at the same magnetic field indicates its good utility. Landau theory yields a negative slope of the Arrott plot at TC, and the fit of Landau coefficients b (TC) obtains negative values verifying the ferromagnetic–paramagnetic first-order phase transition. Further calculation of the n value and the universal curve plot using the magnetocaloric effect confirmed this type of magnetic phase transition and revealed the origin of the large magnetocaloric effect. The material provides new ideas for applications in cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In this study, polycrystalline samples of La0.7Ca0.3−xSrxMnO3 (x = 0.00, 0.10, and 0.25) were prepared using the conventional solid-phase reaction method. The magnetocaloric effects and critical behavior of this series of polycrystalline materials were investigated. The research results indicate that all the samples are single-phase with an orthorhombic structure, belonging to the space group Pbnm. Under a magnetic field of 7 T, the maximum magnetic entropy changes of the samples were 9.74, 7.37, and 6.11 J·kg−1·K−1, respectively, and the relative cooling power are 360.53, 361.04, and 366.50 J·kg−1, respectively. The doped samples demonstrate superior magnetic refrigeration ability compared to the parent phase. It is noteworthy that the Curie temperature increases from 243 K (x = 0.00) to 295 K (x = 0.10) and 350 K (x = 0.25). In addition, there is a transition from a first-order to a second-order phase transition in the sample with x = 0.25. The critical behavior of the compounds with x = 0.25 was analyzed using various methods, including modified Arrott plots, the Kouvel-Fisher method, and critical isotherm, to determine critical exponents (β, γ, and δ). The results obtained from both methods are close and indicate that the critical behavior of the sample crosses between mean field model and 3D-Heisenberg model. The temperature dependence of the order parameter n for different magnetic fields is studied using the relation |∆SM|∝ Hn. The values of n not only reveal the type of phase transition of the system but also validate the critical exponents. The results indicate that La0.7Ca0.3−xSrxMnO3 (x = 0.10, and 0.25) ceramics have the potential to be used as room-temperature magnetic refrigeration materials. [ABSTRACT FROM AUTHOR]

In this study, polycrystalline samples of La0.7Ca0.3−xSrxMnO3 (x = 0.00, 0.10, and 0.25) were prepared using the conventional solid-phase reaction method. The magnetocaloric effects and critical behavior of this series of polycrystalline materials were investigated. The research results indicate that all the samples are single-phase with an orthorhombic structure, belonging to the space group Pbnm. Under a magnetic field of 7 T, the maximum magnetic entropy changes of the samples were 9.74, 7.37, and 6.11 J·kg−1·K−1, respectively, and the relative cooling power are 360.53, 361.04, and 366.50 J·kg−1, respectively. The doped samples demonstrate superior magnetic refrigeration ability compared to the parent phase. It is noteworthy that the Curie temperature increases from 243 K (x = 0.00) to 295 K (x = 0.10) and 350 K (x = 0.25). In addition, there is a transition from a first-order to a second-order phase transition in the sample with x = 0.25. The critical behavior of the compounds with x = 0.25 was analyzed using various methods, including modified Arrott plots, the Kouvel-Fisher method, and critical isotherm, to determine critical exponents (β, γ, and δ). The results obtained from both methods are close and indicate that the critical behavior of the sample crosses between mean field model and 3D-Heisenberg model. The temperature dependence of the order parameter n for different magnetic fields is studied using the relation |∆SM|∝ Hn. The values of n not only reveal the type of phase transition of the system but also validate the critical exponents. The results indicate that La0.7Ca0.3−xSrxMnO3 (x = 0.10, and 0.25) ceramics have the potential to be used as room-temperature magnetic refrigeration materials. [ABSTRACT FROM AUTHOR]

In this article, we have investigated the temperature and magnetic field-induced complex magnetic phases and magnetocaloric properties of the nanocrystalline Nd 0.5 Ca 0.5 MnO 3 (NCMO) compound in detail. The compound exhibits charge-ordered antiferromagnetic (CO-AFM) and charge-orbital-ordered antiferromagnetic (AFM) phases at T C O ≃ 225 K and T N = 160 K respectively. At the intermediate temperature range, i.e. T N ≤ T ≤ T C O , an unfamiliar magnetic state is present where the orbital ordering of manganese ions sets progressively. Both the short-range and zig-zag ordered ferromagnetic (FM) chains and an AFM phase coexist within this temperature window. The effect of magnetic field and temperature drastically modifies the fragile magnetic ground state and this change is also reflected in the magnetocaloric properties of the studied compound. At the low-temperature region, an inverse magnetocaloric effect (MCE) is noticed due to the kinetically arrested magnetic moments of the AFM phase. However, a conventional MCE is noticed in the high-temperature regime. The anomalous behavior of the MCE in the nanocrystalline NCMO compound is analyzed by considering the effect of the reduction of particle size and the meta-stable nature of the magnetic ground state. In addition, we have paid attention to the hysteretic losses associated with the first-order phase transition (FOPT) in order to estimate the magnetic cooling capacity for the material. These studies carry notable importance for the usefulness of nanocrystalline half-doped manganite compounds not only for basic scientific research purpose, but also having possible practical utilization in the magnetic refrigeration industries. [Display omitted] • The nanocrystalline Nd 0. 5 Ca 0. 5 MnO 3 compound exhibits multiple complex magnetic phases. • A peculiar magnetic state has been observed in the temperature window of (T CO , T N). • In addition to a conventional magnetocaloric effect (MCE), inverse MCE has also been noticed in the studied system. [ABSTRACT FROM AUTHOR]

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones. [ABSTRACT FROM AUTHOR]

The paper considers the influence of magnetic phase separation on the magnitude of the magnetocaloric effect. A general thermodynamic generalized Landau's theory with a variable number of particles is proposed, which allows a simple and consistent description of the first-order phase transition between magnetically ordered and disordered phases, considering phase separation. The calculation of the magnetic susceptibility and entropy of the phases involved in phase separation is considered. It is shown that the magnetic susceptibility of the magnetically ordered (disordered) phase involved in phase separation is negative (positive) in the vicinity of the tricritical point, which can lead to an inversion of the sign of the magnetocaloric effect. [ABSTRACT FROM AUTHOR]

The isobaric temperature dependences of the magnetization and the magnetocaloric characteristics of alloys of the Mn1 – xCrxNiGe system are studied in a constant magnetic field up to 10 kOe in the range of hydrostatic pressures up to 12 kbar. It has been established that, with increasing pressure, the implementation of helimagnetic ordering undergoes qualitative changes from the smooth hysteresis-free second-order phase transition to the first-order phase transitions accompanied by the appearance of a temperature hysteresis and an increase in the magnetocaloric effect. Based on the exchange-structural model, an explanation is given for the mechanism of baric transformation of magnetic and magnetocaloric properties. [ABSTRACT FROM AUTHOR]

The structural characterization, and the electronic, magnetic and magnetocaloric properties of polycrystalline samples of La0.7Ca0.3Mn1-xCuxO3 (x = 0, 0.04, 0.06, 0.08) have been investigated. X-ray powder diffraction analysis indicates all samples having an orthorhombic structure, belonging to the Pbnm space group. X-ray absorption fine structure spectra reveal that Mn is in the mixed state of Mn3+ and Mn4+ while Cu has divalent state (Cu2+). With the substitution of Cu2+ for Mn, the Curie temperature, TC, decreases monotonically from 248K for x = 0 to 156K for x = 0.08, which is due to weakened exchange interactions. The downturn in the temperature dependencies of the inverse magnetic susceptibility, »-1(T), curves observed above TC for x = 0 and 0.08 is characteristic of the Griffiths-like phase. The analysis of isothermal magnetization data M(T,H) based on the Banerjee's criteria has indicated x = 0, 0.04, and 0.06 samples undergoing a first-order magnetic phase transition. However, the x = 0.08 sample, the coexistences of second-order magnetic phase transition at low magnetic fields below 8 kOe and first-order magnetic phase transition at high magnetic fields were observed. The maximum magnetic entropy change measured at a magnetic field span of 50 kOe occurring near the TC decreases from 10.3 to 4.8 J/kg.K with increasing x from 0 to 0.08. However, the relative cooling power (RCP) tends to increase, in which a maximum RCP of 360 J/kg for x = 0.08 that is about 1.3 times greater than that observed for the parent sample (x = 0). [ABSTRACT FROM AUTHOR]

A direct method was used to study the magnetocaloric effect (MCE) for samples of the compound Mn5Si3 under adiabatic conditions in magnetic fields up to 2 T at cryogenic temperatures in the range from 25 to 125 K. According to the results of measurements, it is shown that at temperatures near the first-order metamagnetostructural phase transition from a noncollinear antiferromagnetic to a collinear antiferromagnetic state, both inverse and сonventional MCE are observed. The maximum value of the inverse MCE was ∆Tad = –0.27 K at initial temperature T0 = 55 K in a magnetic field of 2 T. Conventional MCE with maximum value ∆Tad = +0.23 K is observed at T0 = 70 K in a field of 2 T. [ABSTRACT FROM AUTHOR]

In this study, polycrystalline samples of La0.7Ca0.3-xDyxMnO3 (x = 0, 0.15) were synthesized via the solid-state reaction method. Their structures, magnetic properties, magnetocaloric effects, and critical behaviors associated with phase transitions were systematically investigated. All samples exhibited structures belonging to the Pbnm space group, characterized by precise compositions and good single-phase. The samples underwent paramagnetic-ferromagnetic (PM-FM) phase transitions at Curie temperatures (TC) of approximately 244 K for x = 0 and 132 K for x = 0.15. The incorporation of Dy significantly broadened the half height wide temperature range (ΔTFWHM) from 39.36 K (x = 0) to 121.92 K (x = 0.15). Consequently, the relative cooling capacity (RCP) of the samples was markedly increased, rising from 369.76 J·kg−1 (x = 0) to 721.09 J·kg−1 (x = 0.15). Furthermore, upon doping with x = 0.15, the phase transition type shifted from the first-order phase transition (FOPT) of the parent phase to a second-order phase transition (SOPT). This shift is attributed to the substitution of some Ca2+ ions by Dy3+, which weakened the double-exchange interaction and altered the phase transition type. Analysis of the critical behavior using the Kouvel-Fisher (K-F) and Modified Arrott plot (MAP) methods revealed that the critical features of the phase transition in La0.7Ca0.15Dy0.15MnO3 are better described by a Mean-Field Model with long-range ordering. Therefore, this study not only enriches our understanding of the physical properties of this class of materials but also enhances their potential for magnetic refrigeration (MR) applications. [ABSTRACT FROM AUTHOR]

In this study, a series of polycrystalline La 0.65 Ca 0.35- x Ba x MnO 3 (x = 0,0.1,0.2,0.3) samples were synthesized through high-pressure heat treatment processing. Their magnetic properties, magnetocaloric effects, and critical behaviors associated with phase transitions were investigated. The substitution of Ba2+ for Ca2+ resulted in lattice expansion, which in turn increased the Mn-O-Mn bond angle and enhanced the double-exchange interaction within the system. It was revealed by experimental magnetic studies and Density functional theory calculations that the magnetic interactions, dominated by Mn-3d in the ferromagnetic ground state, were strengthened, leading to an increase in the Curie temperature from 219 K (x = 0) to 249 K (x = 0.1), 272 K (x = 0.2) and 300 K (x = 0.3). Under a magnetic field of 7 T, the maximum magnetic entropy change was found to be 4.47 J·kg−1·K−1 (x = 0), 4.25 J·kg−1·K−1 (x = 0.1), 3.60 J·kg−1·K−1 (x = 0.2) and 3.28 J·kg−1·K−1 (x = 0.3), respectively. Notably, compared to solid-state reaction method samples, the refrigerating temperature range broadened by 131.25 %, 57.44 %, and 47.45 % for x = 0, 0.1, and 0.2, respectively, using high-pressure heat treatment. Additionally, the x = 0.1 sample exhibited a first-to-second-order phase transition. Analysis of Arrott plots confirmed the first-order phase transition in the parent sample and the second-order phase transition in the doped samples. Furthermore, the Modified Arrott plot, Kouver-Fisher, and local exponent methods revealed that, as the Ba content increased, the critical exponents β , γ , and δ of the samples with second-order phase transition characteristics (doped samples) approached 0.5, 1.0, and 0.667, respectively. The introduction of Ba was found to facilitate the establishment of a second-order phase transition pattern that is more consistent with the mean-field theory model. • High-pressure heat treatment significantly improves Δ T FWHM compared to solid-phase reaction. • High-pressure heat treatment resulted in the transformation of La 0.65 Ca 0.25 Ba 0.1 MnO 3 into FM-PM SOPT type. • The average overlap between TEC (4 K) and |-∆ S M max| is more than 98 %. [ABSTRACT FROM AUTHOR]

Ni-Co-Mn-Ti all- d Heusler alloys are attracting considerable attention for solid-state caloric cooling applications due to their promising combination of excellent caloric and mechanical properties. Here, we report on the maximum attainable magnetocaloric effect in Ni 37 Co 13 Mn 34.5 Ti 15.5 , which shows a first-order magnetostructural martensitic transformation around room temperature. Heat capacity measurements reveal a giant transition entropy change of 43.5 J(kgK)−1 and are utilized to estimate the magnetocaloric effect as well as the magnetic fields required to saturate it in isothermal and adiabatic conditions. Confirming the results based on this approach, we achieve maximum isothermal entropy changes and directly measured adiabatic temperature changes of 37.8 J(kgK)−1 and − 20.2 K, respectively. Thus, the herein reported maximum attainable magnetocaloric effect outperforms classical Ni-Mn-based Heusler alloys, such as Ni(-Co)-Mn-In. Especially the saturated adiabatic temperature change surpasses all previously published values of magnetic field-induced first-order phase transitions measured around room temperature in pulsed magnetic fields in recent years. Thereby, we demonstrate that Ni(-Co)-Mn-Ti Heusler alloys are particularly suitable for the application of sufficiently large external stimuli to fully induce the phase transition and exploit their intrinsically large caloric effect. [Display omitted] [ABSTRACT FROM AUTHOR]

First order transition material (FOM) usually exhibits magnetocaloric effects in a narrow temperature range which complicates their use in an active magnetic regenerator (AMR) refrigerator. In addition, the magnetocaloric effect in first order materials can vary with field and temperature history of the material. This study examines the behavior of a MnFe(P,Si) FOM sample in an AMR cycle using a numerical model and experimental measurements. For certain operating conditions, multiple points of equilibrium (MPE) exist for a fixed hot rejection temperature. Stable and unstable points of equilibriums (PEs) are identified and the impacts of heat loads, operating conditions, and configuration losses on the number of PEs are discussed. It is shown that the existence of multiple PEs can affect the performance of an AMR significantly for certain operating conditions. In addition, the points where MPEs exist appear to be linked to the device itself, not just the material, suggesting the need to layer a regenerator in a way that avoids MPE conditions and to layer with a specific device in mind. [ABSTRACT FROM AUTHOR]

In this study, we further subject the recently found Fe-Mn-Ni-Ge-Si high-entropy alloys (HEAs) exhibiting first-order thermomagnetic phase transition to designed heat treatments. The results reveal that the standard heat treatments transform the as-cast dual-phase microstructure into a single phase without influencing the magnetocaloric response or average composition. A crucial observation is the substantial enhancement in magnetocaloric effects and transition temperatures achieved through a low-temperature heat treatment at 673 K, while maintaining the microstructures and compositions of the alloys. The optimized annealed Fe-Mn-Ni-Ge-Si HEA samples show exceptional magnetocaloric effects, surpassing previous studies and positioning them as strong contenders against established conventional high-performing magnetocaloric materials. The changes in magnetic anisotropy distribution are indicative of the stress relaxation induced by low-temperature annealing. This work shows that stress relaxation can have a significant effect on the optimization of magnetocaloric response, even more important than achieving a single phase by annealing at higher temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

• The anisotropy of the MCE was determined using MnAs single crystal. • The influence of the sample shape on the estimation of the Δ S m value was investigated. • The Δ S m value depends on the magnetic history of the sample. • The role of the calculation method in the estimation of Δ S m is shown. The magnetic and magnetocaloric properties of a MnAs single crystal have been studied along different crystallographic directions in the temperature range of the first-order magnetic phase transition. The constants of magnetocrystalline anisotropy, K 1 and K 2 , were determined below the transition temperature by the Sucksmith-Thompson method. It was found that the energy of magnetocrystalline anisotropy decreases with increasing temperature. The results highlighted the impact of shape anisotropy and the magnetic prehistory of the sample on the maximum value of −Δ S m. The anisotropy of the −Δ S m value was observed for different crystallographic directions; the −Δ S m value reaches its maximum of 35 J∙kg−1∙K−1 in the [001] direction, while 29 J∙kg−1∙K−1 in the [110] direction. The probability of overestimating the Δ S m (T) values when using Maxwell's equation instead of the Clausius-Clapeyron formula is shown. [ABSTRACT FROM AUTHOR]

This work investigates magnetic properties and the magnetocaloric effect in the scope of continuous and first-order phase transitions in different stability regimes of a system described by the Ashkin–Teller model. Mean Field Theory is implemented through the Gibbs–Bogoliubov variational principle to obtain expressions for free energy, entropy and magnetization, in addition to computing the magnetocaloric properties of the system under analysis. The starting point is a detailed analysis of magnetic properties as a function of temperature, coupling configurations and external fields. Continuous and first-order phase transitions are observed. The impact of having the system under the influence of an external field is studied, showing and discussing the most favorable conditions for the manifestation of the magnetocaloric potential. In addition, phase transitions between metastable and stable states due to the hysteresis effect when varying the external field are obtained from two different methods, Maxwell relations and the use of entropy variation to compute the correct magnetocaloric effect properties. • Study of the Magnetocaloric Effect in the Ashkin–Teller model. • Magnetizations as a function of temperature varying the external field. • Free energy as a function of magnetizations varying the external field. • Magnetocaloric Effect for the different phases present in the model. • Continuous and first-order phase transitions. [ABSTRACT FROM AUTHOR]

In this study, a homemade uniaxial strain pressure cell was designed to be directly used in the standard magnetometers whereby the magnetic properties of samples subjected to a uniaxial strain and magnetic field were characterized. Its feasibility has been demonstrated by the uniaxial strain control of the phase transition and magnetocaloric effect in Ni40Co10Mn40Sn10 (NCMS) alloys. With the assistance of a uniaxial strain of ~0.5%, the cooling temperature span of NCMS alloys is broadened by 2 K, and the refrigeration capacity under a 3 T magnetic field change increases from 246 to 277 J/kg. This research provides not only direct experimental assistance for the tuning of phase transition by the uniaxial strain but also possibilities for studying the coupled caloric effect in first-order phase transition materials under a combined uniaxial strain and magnetic field by the thermodynamic analysis. [ABSTRACT FROM AUTHOR]

Considerable interest to magnetism of MnAs both in bulk or in the form of epitaxial films is stimulated by its applications as a magnetocaloric material and in spintronic devices. Since the MnAs films deposited on GaAs reproduce well a magnetic transformation related to α–β magnetostructural transition that occurs in bulk MnAs, this first-order phase transition occurs through a phase coexistence over a wide temperature range. Here, we considered the same magnetostructural transition in a bulk hybrid structure based on micrometer-scaled MnAs inclusions embedded into the Cd3As2 matrix. In particular, the effect of high pressure and magnetic fields on the ferromagnetic transition temperature, TC, in a composite Cd3As2 + 30 mol. % MnAs has been studied. We found that at ambient pressure, the transition from α-MnAs to β-MnAs is accompanied by the absence of thermal hysteresis of magnetization, implying a phase coexistence regime. The hysteresis width does not markedly increase even at pressures about P = 0.35 GPa, and displacement of TC occurs with a rate of dTC/dP ∼ −91.42 K/GPa. In the temperature region of the α–β phase coexistence, a local peak at T = 283 K and P = 1 GPa is observed, which is associated with an antiferromagnetic order of MnAs inclusions. Direct measurements of isothermal magnetization vs pressure indicate both the stabilization of the ferromagnetic hexagonal α phase at P < Pmax and the development of an orthorhombic antiferromagnetic long-range order, which propagate up to 5 GPa. [ABSTRACT FROM AUTHOR]

In this study, perovskite manganese oxide Pr(0.87-x ) Dy x Ca 0.13 MnO3 ( x - 0, 0.05, 0.1, 0.15) series polycrystalline samples were prepared via high temperature solid reaction method. The effect of the doping amount of Dy on the crystal structure, magnetism and magnetothermal effects of the parent phase Pr0. 87 Ca 0.13 MnO³ were studied. Samples with doping amounts of 0, 0.05 and 0.1 meet the typical characteristics of the preformed cluster phase, while the samples with doping amount of 0.15 meet the typical characteristics of the class Griffiths phase. When T< TN, the ferromagnetism of this group of samples is weakened, antiferromagnetism is enhanced. In the temperature range of Tc ~ 220K, the samples are in a paramagnetic and ferromagnetic coexistence state. For Pr0.72 Dy0.15 Ca 0.13 MnO³, the sample is in a pure paramagnetic state at T > Tc (330K). When the external magnetic field is 7 T, the maximum magnetic entropy of the samples was – ΔSM(0)≈ 4.607 70, - ΔSM(0.05) ≈ 4.112 22, - ΔSM(0.1) ≈3. 878 18, – ΔSM(0.15) ≈ 3. 848 90 J/(kg • K ), respectively, indicating that with the addition of Dy3+ ions, the maximum magnetic entropy decreases, but the temperature range of half high and wide is broaden. According to Arrottcurve and recalculation curve, the parent phase sample of Pr0.87 Ca 0.13 MnO³ and Pr0.82 Dy0.05 Ca 0.13 MnO³ sample undergo a second-order phase transition. In contrast, both Pr0.77 Dy0.1 Ca 0.13 MnO³ sample and Pr0.72Dy0.15 Ca 0.13 MnO³ sample undergo first-order phase transition. [ABSTRACT FROM AUTHOR]

Phase transitions and magnetic structures in the ground state of the two-dimensional Potts model with four spin states on a triangular lattice with competing exchange interactions of the first, J1, and second, J2, nearest neighbors have been studied using the Wang–Landau Monte Carlo algorithm. The phase diagram of the critical temperature versus J2 has been obtained. It has been revealed that the transition from the ferromagnetic phase to the paramagnetic one is a second-order phase transition, whereas the transition from the stripe and stripe–triplet phases to the paramagnetic one is a first-order phase transition. The magnetic structures of the ground state corresponding to different regions of the phase diagram have been determined. It has been found that the competition between exchange interactions in the range of leads to strong frustration and breaking of magnetic order. [ABSTRACT FROM AUTHOR]

Following our previous work on the magnetocaloric compounds FeMnAsxP 1 − x , we obtain thermomagnetic properties for the barocaloric antiperovskite Mn3GaN, which has been investigated in recent years in view of its thermal response under pressure cycling. Its structure displays canting of spins and a volume dilation in the antiferromagnetic (AFM) transition, related to magnetoelastic coupling. A random-phase-approximation (RPA) Green function theoretical treatment is applied to a two-exchange parameter Heisenberg model, and the canting of the spins orientation in the (111) planes of the structure is considered in the model. The observed first-order AFM phase transitions are reproduced by the introduction of a biquadratic spin term in the Hamiltonian, coupled to the volume dilation in the transition. The model is able to predict a greater stability for the canted spin structure as compared with conventional AFM, if the magnitudes of Mn magnetic moments in these structures are taken from the literature. The calculations of quantities of interest for barocaloric applications reproduce quite well the available data on temperature changes and latent heat under pressure cycling, at adiabatic and isothermal conditions, respectively. [ABSTRACT FROM AUTHOR]

In the family compounds of RMn6Ge6, GdMn6Ge6 exhibits excellent magnetic properties and a complex magnetic transition behavior. The samples of GdMn6Ge6−xSix were successful prepared by a vacuum arc furnace. The XRD analysis and Rietveld refinement results show that GdMn6Ge6−xSix crystallize in a hexagonal HfFe6Ge6-type structure with space group P6/mmm, and their lattice parameters a and c decrease with the increasing Si content. The M-T curves in the range of 100–600 K indicates that the compounds experienced two magnetic transitions (AFM-FM and FM-PM) and a large thermal hysteresis between ZFC and FCC curves. The AFM-FM transition occurred at Tt for GdMn6Ge6-xSix is a first-order phase transition and the FM-PM transition belongs to a second-order one. The magnetic transition temperature Tt is greatly influenced by the Si content, and the Curie temperature (Tc) for the all samples is roughly the same. The −∆SM for the x = 0, 0.2, 0.4, 0.6 compounds under the applied magnetic field of 1.6 T are 0.83, 1.06, 1.21 and 1.19 J kg−1·K−1 around 486 K, respectively. This relatively large −∆SM of GdMn6Ge6−xSix occurred in a relatively high temperature region and under low applied magnetic field provide a potential material choices in new magnetic refrigeration application. [ABSTRACT FROM AUTHOR]

Polycrystalline materials are critical to various applications, especially Room-temperature magnetic refrigeration technology, for which limited research has been conducted. In this study, polycrystalline La0.8Ca0.2Mn1−xNixO3 (x = 0 and x = 0.3) samples were prepared using solid-phase reaction method. The influence of Ni doping on the phase of the preformed clusters of polycrystalline samples, magnetic entropy change, and critical behavior were studied. The results revealed that all the samples have cubic orthogonal structures. The two prepared samples exhibited the presence of preformed clusters at temperatures above the low-temperature magnetic transition temperature. The critical behavior parameters of both samples fit the tri-critical model best. The parent material exhibited a first-order to second-order phase transition. The Ni-doped sample exhibited a second-order transition. The maximum magnetic entropy changes of the La0.8Ca0.2Mn1−xNixO3 samples with x = 0 and x = 0.3 were determined to be 6.21 J kg−1 K−1 and 2.57 J kg−1 K−1, respectively. Moreover, Ni doping decreased the magnetic entropy change to a level lower than that without doping. [ABSTRACT FROM AUTHOR]

This work investigates the magnetic properties and the magnetocaloric effect in the spin-1 Blume-Capel model. The study was carried out using the mean-field theory from the Bogoliubov inequality to obtain the expressions of free energy, magnetization and entropy. The magnetocaloric effect was calculated from the variation of the entropy obtained by the mean-field theory. Due to the dependence on the external magnetic field and the anisotropy included in the model, the results for the magnetocaloric effect provided the system with first-order and continuous phase transitions. To ensure the results, the Maxwell relations were used in the intervals where the model presents continuous variations in magnetization and the Clausius-Clapeyron equation in the intervals where the model presents discontinuity in the magnetization. The methods and models for the analysis of a magnetic entropy change and first-order and continuous magnetic phase transitions, such as mean-field theory and the Blume-Capel model, are useful tools in understanding the nature of the magnetocaloric effect and its physical relevance. [ABSTRACT FROM AUTHOR]

• First order antiferromagnetic phase transition in CeMg. • Cubic-tetragonal coupled magnetic phase transition in CeMg. • Normal and inverse magnetocaloric effect in an antiferromagnetic system. • Influence of magnetic anisotropy on the magnetocaloric effect. We report the magnetic and magnetocaloric properties of the antiferromagnetic intermetallic compound CeMg, focusing on its coupled magnetic and structural phase transition within first-order processes. Our study utilizes a model Hamiltonian incorporating interactions such as: crystalline electrical field, intra and inter sublattice exchange interactions, as well as quadrupolar and magnetoelastic to elucidate the behavior of CeMg. Through simulation, we predict and discuss both normal and inverse magnetocaloric effects, providing insights into the magnetocaloric behavior under different magnetic field directions. These findings contribute to a deeper understanding of the complex magnetism in CeMg and lay the groundwork for future experimental investigations. [ABSTRACT FROM AUTHOR]

• Regulating the stoichiometric ratio in chemistry can reduce T tr , with little effect on T c. • A structural and magnetic phase diagram of Mn 1- x CoGe alloys was proposed. • Stoichiometric control can cause magnetic structure coupling and lead to a giant magnetocaloric effect. • A magnetic entropy change of 27.6 J kg−1K−1 and a cooling capacity of 212.1 J kg−1 were obtained under magnetic field of 5 T. As a family of rare-earth-free magnetocaloric materials, MnCoGe-based alloys have attracted intensive attention in the past few years. In this study, we reveal that the deficiency of either Mn or Co reduces the valence electron concentration of MnCoGe system, thereby lowering its structural transition temperature (T tr) by pushing the Fermi level away from the Mn-Mn antibonding electronic states. Moreover, T tr is found to be more sensitive to Co content. By systematically analyzing the temperature dependent magnetization plots and Arrott curves, it is proven that the magnetic and structural degrees of freedom are coupled in the Mn 0.97 CoGe alloy, resulting in a first-order magnetic phase transition. On the contrary, MnCo 0.98 Ge undergoes a second-order transition. As a consequence, the Mn 0.97 CoGe alloy exhibits a maximum magnetic entropy change of 27.6 J kg−1K−1 under a magnetic field of 5 T near the Curie temperature of 265 K, corresponding to a refrigeration capacity of 212.1 J kg−1. Our work demonstrates Mn/Co vacant MnCoGe alloy as a robust candidate of magnetic substance for room temperature magnetocaloric refrigeration. [ABSTRACT FROM AUTHOR]

This study explores the reversibility of the martensitic transformation (MT) and magnetocaloric (MC) response of the Ga-doped Ni 50 Mn 35 In 15 magnetic shape memory alloys (MSMAs) with a Heusler structure. The direct and reverse MT occurs between temperatures T M ≈ 257 K and T A ≈ 266 K, respectively. The large MC effects resulting from the magnetic-field-induced first-order MT render these materials promising for room-temperature magnetic refrigeration. On account of both a low thermal hysteresis of MT (Δ T hyst = 4 K) at a magnetic field of 2 T and a highly reproducible peak value of the adiabatic temperature change at MT (|∆ T ad | ≈ 1.3 K for µ 0 H = 1.9 T), Ni 50 Mn 34 In 15 Ga 1 MSMA emerges as a benchmark material for studying a cyclic stability of MC effects. During the first magnetic switching cycle, a reduction of ∆ T ad at MT by approximately 1.3 is observed, significantly lower than the reported one for other MC materials undergoing similar first-order phase transitions. Subsequent cycles revealed a consistent stability of the magnetic-field-induced ∆ T ad even after more than 200 magnetic field switching cycles. These findings suggest a notable degree of reversibility of the MT in the studied MSMA, which was also confirmed in the present work by a Temperature-First Order Reverse Curve distribution analysis. • Thermal hysteresis is reduced from 9 K to 4 K with a 2 T magnetic field. • Reversible adiabatic temperature change is seen across magnetostructural transition. • Reproducible cyclic behavior of adiabatic temperature change is observed. [ABSTRACT FROM AUTHOR]

First order phase transitions may occur in several magnetic systems, with two structural phases having different magnetic properties each and a structural transition between them. Here, a novel physics based phenomenological model of such systems is proposed, in which magnetization is represented by the volumetric amounts of ferromagnetism (described by extended Jiles-Atherton theory) and paramagnetism (described by the Curie-Weiss law) in respective phases. An identification procedure to extract material parameters from experimental data is proposed. The proposed phenomenological approach was successfully applied to magnetocaloric Gd5(SixGe1-x)4 system and also has the potential to describe the behavior of Griffiths phase magnetic systems. [ABSTRACT FROM AUTHOR]

Magnetocaloric materials with first-order phase transition are potential refrigerant media for solid state refrigeration. In this work, the Ni45Co5Mn35In15 alloy possesses a representative first-order martensitic transition (MT), which is found to be sensitive to both magnetic field and isostatic pressure with rates of ∼−6.4 K T−1 and ∼4.24 K kbar−1. Such an active response to multi-stimuli derives from the strong coupling of the spin and the lattice. A low magnetic field of 1 T can drive nearly 100% of the total entropy change corresponding to the whole transformation in this alloy. However, the prominent magnetocaloric effect (MCE) is almost irreversible owing to the intrinsic hysteresis of the first-order phase transition. By virtue of the strong magnetostructural coupling during the MT, a hydrostatic pressure assisted magnetic field loading loop has been constructed for eliminating the hysteresis and to a large extent improve the reversibility of the MCE. [ABSTRACT FROM AUTHOR]

The potential applicability of a magnetocaloric material for solid-state refrigeration purposes mainly relies on its magnetocaloric effect (MCE). Since conventional measurements to assess MCE are generally time–consuming, it is uneasy to fast screen prominent magnetocaloric materials. Here, we have developed a high-throughput infrared characterization technique to feasibly evaluate the adiabatic temperature change of magnetocaloric materials. This method is applicable to both the second-order phase transition Gd and the first-order phase transition (FOPT) La–Fe–Si–based materials, allowing simultaneous measurement of the temperature changes induced by MCE of multiple samples. Moreover, it greatly facilitates the examination of the functional stability of FOPT magnetocaloric materials by accomplishing the cycling test in a short time. By repeatedly changing the magnetic field of 0–1.3–0 T in 0.25 Hz for La1.2Ce0.8Fe11Si2Hy, we observed the adiabatic temperature changes of 2.12 K for the first cycle and 1.85 K upon 100000 cycles. Correspondingly, the change in magnetocaloric response of the sample is visualized by the high-resolution infrared image, giving explanations for the evolution of MCE during cycling. [ABSTRACT FROM AUTHOR]

• 1D regenerator model with hysteresis is used to assess caloric cooler's performance. • Modeling of six hypothetical materials with different caloric properties. • Effect of hysteresis is greater on coefficient of performance than on cooling power. • Materials with low isothermal entropy change are very sensitive to hysteresis. • Materials with low specific heat can tolerate high hysteresis values. Caloric cooling relies on reversible temperature changes in solids driven by an externally applied field, such as a magnetic field, electric field, uniaxial stress or hydrostatic pressure. Materials exhibiting such a solid-state caloric effect may provide the basis for an alternative to conventional vapor compression technologies. First-order phase transition materials are promising caloric materials, as they yield large reported adiabatic temperature changes compared to second-order phase transition materials, but exhibit hysteresis behavior that leads to possible degradation in the cooling performance. This work quantifies numerically the impact of hysteresis on the performance of a cooling cycle using different modeled caloric materials and a regenerator with a fixed geometry. A previously developed 1D active regenerator model has been used with an additional hysteresis term to predict how modeled materials with a range of realistic hysteresis values affect the cooling performance. The performance is quantified in terms of cooling power, coefficient of performance (COP), and second-law efficiency for a range of operating conditions. The model shows that hysteresis reduces efficiency, with COP falling by up to 50% as the hysteresis entropy generation (q hys) increases from 0.5% to 1%. At higher working frequencies, the cooling performance decreases further due to increased internal heating of the material. Regenerator beds using materials with lower specific heat and higher isothermal entropy change are less affected by hysteresis. Low specific heat materials show positive COP and cooling power up to 2% of q hys whereas high specific heat materials cannot tolerate more than 0.04% of q hys. [ABSTRACT FROM AUTHOR]

The effects of Ta substitution on the first-order phase transition have been firstly studied in Hf1-xTaxFe2 (x = 0.15, 0.165, 0.18) alloys with kagome-type lattice. Higher Ta substitution leads to the reduced metamagnetic transition temperature (Tt) from low-temperature ferromagnetism to high-temperature antiferromagnetism and paramagnetism. By doping C atoms, the Tt is gradually reduced and thermal hysteresis becomes widened in the alloys with higher Ta substitution. The critical field which triggers the metamagnetic phase transition is not substantially affected by interstitial C atoms. With increased Ta substitution, for the field change of 7 T, the maximum of magnetic entropy change (ΔSmax) of 3.7 J kg−1 K−1 is obtained at x = 0.15 and enhanced to 4 J kg−1 K−1 at x = 0.165 but reduced to ~ 3.21 J kg−1 K−1 in Hf0.82Ta0.18Fe2 alloy. By C addition, both Tt and the temperature where ΔS is maximized are shifted to a lower temperature, especially in the higher Ta-contained alloys. [ABSTRACT FROM AUTHOR]

The theory of the giant conventional and inverse magnetocaloric effects (MCEs) is advanced on the basis of the theory of magnetism developed by A. I. Akhiezer, V. G. Bar'yakhtar, and S. V. Peletminsky in the classic monograph "Spin Waves". The MCE in the shape memory alloy undergoing the first-order phase transition from the cubic ferromagnetic (FM) phase to the tetragonal antiferromagnetic (AFM) phase is considered. The agreement between the theoretical results and existing experimental data is demonstrated. It is argued that the alloys undergoing the phase transition to AFM phases with weak exchange interaction between the magnetic sublattices are promising for use in the magnetic refrigeration technique. The possibility of observation of the giant MCE in the layered magnetic structure with weak spin-exchange coupling between the FM layers is discussed. [ABSTRACT FROM AUTHOR]

La1.3−xYxSr1.7Mn2O7 (x = 0, 0.025) samples are prepared by the conventional solid-state reaction. X-ray diffraction spectrum reveals that the samples are in the Sr3Ti2O7-type tetragonal phase with the space group I4/mmm. By decreasing the temperature, two samples exhibit the paramagnetic phase at high temperatures to two-dimensional short-range-ordered ferromagnetic states at the intermediate temperatures and finally three-dimensional long-range-ordered ferromagnetic states. Furthermore, the doped sample also demonstrates antiferromagnetic ordering in the low-temperature region. The Arrott curve and calibration curve indicate that the sample behaves as a first-order phase transition. When the applied magnetic field is 6 T, the maximum magnetic entropy change ( Δ S M ) occurs in the two samples in the vicinity of the three-dimensional ordered temperature (Tc3D), and the value of Δ S M for the two samples reaches—4.81 J/kg K and—3.82 J/kg K, respectively. In addition, the relative cooling power is 108 J/kg and 112.2 J/kg at μ 0 H = 3 T , respectively. Although the doping of Y reduces Tc3D, Δ S M and the first-order phase transition character, the relative cooling power is enhanced, thus indicating its potential to realize magnetic refrigeration in high-temperature regions (T > 77 K). [ABSTRACT FROM AUTHOR]

Phase transition and the magnetocaloric effect (MCE) in Nd0.5Sr0.5MnO3 (NSMO) epitaxial thin films were tailored through controlling the lattice-mismatch-induced-strain by depositing on (011)—(La0.18Sr0.82)(Al0.59Ta0.41)O3 and SrTiO3 (STO) single crystalline substrates, respectively. The NSMO film grown on STO, exhibiting uniaxial like tensile strain of 1.3% along the in-plane [100] direction, undergoes a paramagnetic to ferromagnetic transition at ∼210 K followed by a ferromagnetic to A-type antiferromagnetic transition at ∼179 K upon cooling; meanwhile, the film grown on LSAT, exhibiting anisotropic in-plane tensile strains of 0.36% along [100] and 0.50% along [ 0 1 ¯ 1 ] directions, undergoes further transition to CE-type antiferromagnetic transition at ∼145 K. NSMO/LSAT with such transitions facilitates a strong MCE over a much wider temperature range from 90 to 170 K, with the magnetic entropy change comparable to the recently reported La0.25Ca0.75MnO3 bulk. These findings suggest that control of strain in manganite films with first-order phase transition is a feasible way to broaden their MCE temperature range. [ABSTRACT FROM AUTHOR]

The isothermal entropy change of spin-1 Blume-Capel (BC) is investigated on the Bethe lattice (BL) with the variations of coordination numbers (q), crystal field (D) and external magnetic field (H) in the vicinity of critical temperatures, i.e. about the second- and first-order phase transition temperatures. The calculation is carried on the BL in terms of exact recursion relations. It is found that the peaks of the isothermal entropy variation obtained for both magnetization and quadrupole moments are observed to be increasing with increasing values of H for given D and q, decreasing with the increasing q for fixed D and H and also decreasing with the increasing values of D for constant q and H. The peaks of the curves for the quadrupole moment is less sharper then the ones obtained for the magnetization. [ABSTRACT FROM AUTHOR]

DyFe 1 − x Mn x O3 (x = 0, 0.025, 0.075, 0.15) polycrystalline samples were prepared using a traditional solid-state reaction route. The structural, magnetic and magnetocaloric properties of these samples were investigated. X-ray diffraction patterns showed that the samples exist as single-phase crystallines without peaks. The results of the Scanning Electron Microscopy (SEM) revealed that the average size of the polycrystalline particles decreased from 4.34 to 3.00  μ m as the Mn doping amount increased from 0.00 to 0.15. The magnetization versus temperature (M − T ) plots showed that the order temperature of dysprosium (Dy) ions gradually decreased and the Morin-like transition temperature moved to the high-temperature region as x increased. The T N D y gradually decreased from 13 to 10 K and the isotropic interaction of Fe 3 + -Fe 3 + was weakened as x increased from 0.00 to 0.15. The polycrystalline samples appeared as pre-formed clusters. The magnetization (M − H ) plots revealed that all the samples underwent a first-order magnetic phase transition. The maximum magnetic entropy change, occurring near the Curie temperature, obtained at a magnetic-field span of 7 T, was 18.2 J/kg K. The maximum cooling capacity of the polycrystalline DyFe 1 − x Mn x O3 (x = 0, 0.025, 0.075, 0.15) samples was 441 J/kg. [ABSTRACT FROM AUTHOR]

DyFe 1 − x Mn x O3 (x = 0, 0.025, 0.075, 0.15) polycrystalline samples were prepared using a traditional solid-state reaction route. The structural, magnetic and magnetocaloric properties of these samples were investigated. X-ray diffraction patterns showed that the samples exist as single-phase crystallines without peaks. The results of the Scanning Electron Microscopy (SEM) revealed that the average size of the polycrystalline particles decreased from 4.34 to 3.00  μ m as the Mn doping amount increased from 0.00 to 0.15. The magnetization versus temperature (M − T ) plots showed that the order temperature of dysprosium (Dy) ions gradually decreased and the Morin-like transition temperature moved to the high-temperature region as x increased. The T N D y gradually decreased from 13 to 10 K and the isotropic interaction of Fe 3 + -Fe 3 + was weakened as x increased from 0.00 to 0.15. The polycrystalline samples appeared as pre-formed clusters. The magnetization (M − H ) plots revealed that all the samples underwent a first-order magnetic phase transition. The maximum magnetic entropy change, occurring near the Curie temperature, obtained at a magnetic-field span of 7 T, was 18.2 J/kg K. The maximum cooling capacity of the polycrystalline DyFe 1 − x Mn x O3 (x = 0, 0.025, 0.075, 0.15) samples was 441 J/kg. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2MnO3 manganese oxides have been prepared by the conventional solid-state reaction. The samples crystallize in the orthorhombic structure with Pnma space group. A first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature that is found to be around 241 K. The magnetic and magnetocaloric properties have been simulated using a phenomenological model. The maximum of magnetic entropy change is of order 8.2 J/kg K for an applied magnetic field of 5 T, and the adiabatic temperature change is found to be of 4 K under a same magnetic field; this high value gives the sample the possibility of technologic application in the magnetic refrigeration area. The simulated results of magnetization and magnetic entropy change are compared with the experimental measurements. Finely, we found a good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

La0.8Ca0.2MnO3 manganese oxides have been prepared by the conventional solid-state reaction. The samples crystallize in the orthorhombic structure with Pnma space group. A first-order magnetic phase transition from ferromagnetic to paramagnetic state is observed at the Curie temperature that is found to be around 241 K. The magnetic and magnetocaloric properties have been simulated using a phenomenological model. The maximum of magnetic entropy change is of order 8.2 J/kg K for an applied magnetic field of 5 T, and the adiabatic temperature change is found to be of 4 K under a same magnetic field; this high value gives the sample the possibility of technologic application in the magnetic refrigeration area. The simulated results of magnetization and magnetic entropy change are compared with the experimental measurements. Finely, we found a good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

Recently, the all- d -metal Ni(Co)MnTi based Heusler compounds are found to have a giant magnetocaloric effect (GMCE) near room temperature and manifest different functionalities like multicaloric effects, which can be employed for solid-state refrigeration. However, in comparison to other traditional Heusler compounds, the relatively large thermal hysteresis (ΔT hys) and moderately steep ferromagnetic phase transition provides limitations for real applications. Here, we present that fast solidification (suction casting) can sufficiently tailor the GMCE performance by modifying the microstructure. Compared with the arc-melted sample, the magnetic entropy change of the suction-casted sample shows a 67% improvement from 18.4 to 29.4 Jkg−1K−1 for a field change (∆ μ 0 H) of 5 T. As the thermal hysteresis has maintained a low Δ T hys value (5.5 K) for the enhanced first-order phase transition, a very competitive reversible magnetic entropy change of 21.8 Jkg−1K−1 for ∆ μ 0 H = 5 T is obtained. Combining high-resolution transmission electron microscopy (HRTEM) and positron annihilation spectroscopy (PAS) results, the difference in lattice defect concentration is found to be responsible for the significant improvement in GMCE for the suction-cast sample, which suggests that defect engineering can be applied to control the GMCE. Our study reveals that fast solidification can effectively regulate the magnetocaloric properties of all- d -metal NiCoMnTi Heusler compounds without sacrificing Δ T hys. [Display omitted] [ABSTRACT FROM AUTHOR]