Search

The Fe2P type Mn–Fe–P–Si alloys exhibit a giant magneto-elastic first-order transition, but the large hysteresis limits their performance. Crystal structure evolution and magnetocaloric performance were investigated by varying the Mn and Fe contents at a constant V substitution of 0.02 in Fe2P-type (Mn1.17-xFe0.73-yV0.02) (P0.5Si0.5) (where x + y = 0.02). The V substitution of Fe content shows a larger reduction of hysteresis compared with the same substitution amount of Mn content. During magnetoelastic phase transition, V-substitution reduces the volume change and the volumetric stresses, providing a superior mechanical stability. Compound with the V substitution of Fe (y = 0.02) shows the best magnetocaloric effect with a low thermal hysteresis of 0.6 K. Our developed Mn1.17-xFe0.73-yV0.02P0.5Si0.5 alloys are excellent materials for room-temperature magnetic heat-pumping applications by using a permanent magnet.

The magnetocaloric effect (MCE) in iron (Fe) nanoparticles incorporated within a titanium nitride (TiN) thin-film matrix grown using pulsed laser deposition (PLD) is investigated in this study. The study demonstrates the ability to control the entropy change across the magnetic phase transition by varying the size of the Fe nanoparticles. The structural characterization carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning transmission electron (TEM) showed that TiN films are (111) textured, while the Fe-particles are mostly spherical in shapes, are single-crystalline, and have a coherent structure with the surrounding TiN thin-film matrix. The TiN thin-film matrix was chosen as a spacer layer since it is nonmagnetic, is highly corrosion-resistive, and can serve as an excellent conduit for extracting heat due to its high thermal conductivity (11 W/m K). The magnetic properties of Fe–TiN systems were investigated using a superconducting quantum interference device (SQUID) magnetometer. In-plane magnetic fields were applied to record magnetization versus field (M–H) and magnetization versus temperature (M–T) curves. The results showed that the Fe–TiN heterostructure system exhibits a substantial isothermal entropy change (ΔS) over a wide temperature range, encompassing room temperature to the blocking temperature of the Fe nanoparticles. Using Maxwell's relation and analyzing magnetization–temperature data under different magnetic fields, quantitative insights into the isothermal entropy change (ΔS) and magnetocaloric effect (MCE) were obtained for the Fe–TiN heterostructure system. The study points out a considerable negative change in ΔS that reaches up to 0.2 J/kg K at 0.2 T and 300 K for the samples with a nanoparticle size on the order of 7 nm. Comparative analysis revealed that Fe nanoparticle samples demonstrate higher refrigeration capacity (RC) in comparison to Fe thin-film multilayer samples, with the RC increasing as the Fe particle size decreases. These findings provide valuable insights into the potential application of Fe–TiN heterostructures in solid-state cooling technologies, highlighting their enhanced magnetocaloric properties. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) in iron (Fe) nanoparticles incorporated within a titanium nitride (TiN) thin-film matrix grown using pulsed laser deposition (PLD) is investigated in this study. The study demonstrates the ability to control the entropy change across the magnetic phase transition by varying the size of the Fe nanoparticles. The structural characterization carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning transmission electron (TEM) showed that TiN films are (111) textured, while the Fe-particles are mostly spherical in shapes, are single-crystalline, and have a coherent structure with the surrounding TiN thin-film matrix. The TiN thin-film matrix was chosen as a spacer layer since it is nonmagnetic, is highly corrosion-resistive, and can serve as an excellent conduit for extracting heat due to its high thermal conductivity (11 W/m K). The magnetic properties of Fe–TiN systems were investigated using a superconducting quantum interference device (SQUID) magnetometer. In-plane magnetic fields were applied to record magnetization versus field (M–H) and magnetization versus temperature (M–T) curves. The results showed that the Fe–TiN heterostructure system exhibits a substantial isothermal entropy change (ΔS) over a wide temperature range, encompassing room temperature to the blocking temperature of the Fe nanoparticles. Using Maxwell’s relation and analyzing magnetization–temperature data under different magnetic fields, quantitative insights into the isothermal entropy change (ΔS) and magnetocaloric effect (MCE) were obtained for the Fe–TiN heterostructure system. The study points out a considerable negative change in ΔS that reaches up to 0.2 J/kg K at 0.2 T and 300 K for the samples with a nanoparticle size on the order of 7 nm. Comparative analysis revealed that Fe nanoparticle samples demonstrate higher refrigeration capacity (RC) in comparison to Fe thin-film multilayer samples, with the RC increasing as the Fe particle size decreases. These findings provide valuable insights into the potential application of Fe–TiN heterostructures in solid-state cooling technologies, highlighting their enhanced magnetocaloric properties.

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]

Electrocaloric cooling is a method for flexible electronics and compact chips with a promising ability to subvert traditional vapor compression refrigeration technology. Nevertheless, most reported EC materials exhibit relatively low adiabatic temperature (ΔT) and low breakdown field strength (E b) at room temperature, limiting their further applications. Here, we develop a ferroelectric nanocomposite, composed of relaxor terpolymer poly(vinylidene fluoride-trifluoroethylen-chlorofluoroethylene) (PVTC), ceramic nanofillers [0.68(BaZr 0.2 Ti 0.8 O 3)-0.32(Ba 0.7 Ca 0.3 TiO 3)] (BCZT), boron nitride nanosheets (BNNSs), and BiFeO 3 nanofibers (BFO NFs) with different morphologies and vary components ratios. The most optimal 12BBBP nanocomposite demonstrates gigantic ECE values including an isothermal entropy change (ΔS) of 94.5 J·kg−1·K−1 and a ΔT of 13.5 K under 220 MV/m electric field at 303 K, ΔS and ΔT are 3.5 times and 2.2 times larger than PVTC under 100 MV/m. It also exhibits an excellent E b with a value of 290 MV/m. The phase-field simulation is used to simulate E b behavior of nanocomposites with fillers of different nano-morphologies under an electrostatic field. Simultaneously, the interfacial coupling and ferroelectric domain structures are also simulated based on the time-dependent Landau-Ginzburg-Devonshire (TLGD) theory through finite element analysis (FEA) to present a better explanation for ECE performance. The experimental and simulation results simultaneously denote the ferroelectric nanocomposite possesses outstanding ECE and high E b performance, laying foundation for the ferroelectrics in fields of flexible electronics and compact chip cooling. Coupled with the facile processability of terpolymer and lead-free nature of electroactive ceramics, this work paves a new way to develop a scalable, environmentally friendly and high-performance EC materials for next generation of refrigeration. [Display omitted] • Giant ECE of ΔT = 13.5 K and ΔS = 94.5 J·kg−1·K−1 are attained in 12BBBP with different morphologies. • 12BBBP nanocomposite has a large breakdown field strength (E b =290 MV/m). • Large E b due to presence of NFs that disperse electric field and hinder growth of breakdown phase. • Coexistence of tetragonal and rhombohedral phase, and strong interface coupling, lead to large ECE. • Excellent ECE and E b provide effective way for design and development of subsequent ECE devices. [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]

[Display omitted] • XRD profiles revealed the Ruddlesden-popper phase in La 1.4-x Sm x Ca 1.6 Mn 2 O 7 (0.0 ≤ x ≤ 0.4) compounds. • With increasing the Sm-concentration the unit cell volume drastically reduced from 290.51 Å3 for x = 0.0 to 290.19 Å3, 289.76 Å3 and 289.22 Å3 for x = 0.1, 0.2 and 0.3 compounds respectively. • The planer (O(3)-Mn-O(3)) and out of plane (O(3)-Mn-O(1)) bond angles have consistently decreased from 87.87°, 78.88° for parent compound up to 85.41°, 73.58° for x = 0.3 composition respectively. • Maximum entropy change obtained for x = 0.0, 0.1, 0.2, 0.3 and 0.4 samples are 2.52 J/kgK, 4.61 J/kgK, 4.2 J/kgK, 2.48 J/kgK, 1.2 J/kgK respectively upon applying 2.5 T magnetic field. • The highest values of TEC enhanced from 4.04 J/kgK (x = 0.0) up to x = 8.5 J/kgK (x = 0.1) and 7.77 J/kgK (x = 0.2) with a Δ T H - C = 5 K. Evolution in the structural, magnetic and magnetocaloric (MCE) properties for a series of samarium (Sm) doped La 1.4-x Sm x Ca 1.6 Mn 2 O 7 (0.0 ≤ x ≤ 0.4) Ruddlesden-Popper manganites prepared by using the solid-state reaction method have been investigated. Structural refinement of XRD profiles established that the MnO 6 octahedral structural units were distorted upon Sm-substitution. The effect of Sm-concentration on the microstructure was also very well observed in terms of increased average grain size and absolute density. Discrepancy in MCE parameters by implementing the conventional isothermal curve method was appeared which was resolved with a separate calorimetric method. The isothermal entropy change was enhanced from 2.52 J/kgK for x = 0.0 sample up to 4.61 J/kgK and 4.2 J/kgK for x = 0.1 and x = 0.2 samples respectively. The temperature averaged entropy change (TEC) was also remarkably improved from 4.04 J/kgK up to 8.5 J/kgK and 7.77 J/kgK for the same compounds respectively. [ABSTRACT FROM AUTHOR]

In this study, the magnetic properties and the magnetocaloric effect of the spin-3/2 Blume–Capel model were explored through the Mean Field Theory, developed through a variational principle based on the Bogoliubov inequality to derive thermodynamic expressions such as free energy, magnetization and entropy. The analysis focused on magnetization, free energy and phase diagram with the presence of an external field greater than and equal to zero. The magnetocaloric effect was evaluated by observing the magnetic entropy changes due to different variations of the external magnetic field. Results were analyzed for both continuous and first-order phase transitions. To validate the magnetic entropy results, Maxwell's relations were applied in the regions with continuous magnetization variations, and the Clausius–Clapeyron equation was used in the regions with magnetization discontinuity. • Magnetic properties and the MCE of the spin-3/2 Blume-Capel model were explored. • Model developed through the Mean Field Theory using the Bogoliubov inequality. • Expressions such as free energy, magnetization and entropy were obtained. • Analysis focused on magnetization, free energy and phase diagrams with h ≥ 0. • MCE was evaluated by the magnetic entropy changes due to variation of h. • Results were analyzed for both continuous and first-order phase transitions. • Maxwell's relations were applied to regions with continuous magnetization variations. • Clausius–Clapeyron equation was used in the regions with magnetization discontinuity. [ABSTRACT FROM AUTHOR]

The current research focuses on analyzing the magnetic and magnetocaloric properties of RE H 2 (RE = Gd , Tb , Dy) in a Ca F 2 -like face-centered cubic system. Through the application of first-principles calculations and Monte Carlo simulations, the following physical parameters are determined: Adiabatic temperature change, isothermal entropy change, and relative cooling power (RCP). The magnetic moments of Gadolinium, Terbium, and Dysprosium calculated by the PWSCF method are 6.76 μ B , 5.74 μ B , and 4.65 μ B respectively, aligning well with experimental results. The compounds underwent a second-order phase transition from antiferromagnetic to paramagnetic at T N = 21.7 K , 17.6 K , and 4.3 K respectively for Gd H 2 , Tb H 2 , and Dy H 2. The isothermal entropy change (− Δ S M max) reached a maximum value of − 11.75 J / kg. K , − 12.47 J / kg. K , and − 12.87 J / kg. K for Gd H 2 , Tb H 2 , and Dy H 2 under a magnetic field of 5 T. We found also that the hydrogenation of rare earth reduces its magnetic performance while but it enhances its thermodynamic and mechanical stability. [Display omitted] • The thermodynamic and mechanical stability of RE H 2 (RE = Gd , Tb , Dy) compounds are investigated. • The RE H 2 compounds are metals with an antiferromagnetic state. • The magnetocaloric property values of RE H 2 compounds indicate that they are potential for low-temperature magnetic refrigeration applications. • Comparing the properties of Gd with RE H 2 compounds reveals the role of hydrogen in these materials. [ABSTRACT FROM AUTHOR]

Highlights • A ferromagnetic spin- S Ising model is examined. • Effective field technique is used. • Isothermal entropy change is investigated for varying values of system parameters. • Numerical data collapse onto the same universal curve for all considered values of spin components. Abstract Using effective field theory, we have investigated magnetocaloric features of the spin- S Ising model for some spin values S = 1 , 3 / 2 , 2 , 5 / 2 , 3 and 7/2 on a honeycomb lattice. Effects of the external magnetic field on the isothermal entropy change, its half-width and also cooling capacity have been determined and discussed in detail. The numerical results show that the isothermal entropy change decreases whereas its half-width and cooling capacity tends to increase when the spin magnitude of the system is increased starting from S = 1 to 7/2 for a fixed value of the external field. Finally, we have also performed some calculations to check the applicability of magnetocaloric scaling procedure for the present system. It is found that the rescaled numerical data collapse onto the same universal curve for all considered values of spin component S. [ABSTRACT FROM AUTHOR]

In this paper, structural, magnetic, and magnetocaloric properties of zinc-doped nickel ferrite, ZnNiFeO ( x= 0.3 and 0.4) were investigated. The samples were prepared using solid-state reaction. X-ray diffraction (XRD) and magnetization measurements were performed to study crystallographic structure and magnetic properties. For a magnetic field changing from 0 to 5 T, the corresponding isothermal entropy change was found to be near 1.4 J/kg K for both samples. The decreasing of Ni content from x= 0.4 to 0.3, enables to shift the Curie temperature of ZnNiFeO from 450 K toward (325 K). As main results, it was found that the relative cooling power (RCP) could be significantly enhanced by changing Ni concentration in ZnNiFeO (505 J/kg (for x= 0.3) and 670 J/kg (for x= 0.4)), which is considered as a recommended parameter for a wide temperature range in magnetic refrigeration application. Our finding should inspire and open new ways for the enhancement of the magnetocaloric effect in spinel ferrite-based materials. [ABSTRACT FROM AUTHOR]

Hexagonal MnNiGe-based alloys are a series of novel functional materials with potential magnetostructural transitions (MSTs). Accordingly, it was investigated the magnetic features of bulk hexagonal MnNiGa alloy and attempted to partially substitute Mn by Co atoms to tailor its structural and magnetic properties. Nonetheless, the introduction of magnetic Co atom fails to bring about the first-order phase transition and gives rise to the emergence of second phase with cubic structure instead. For ternary MnNiGa parent alloy, the second-order nature of transition is confirmed by both the absence of thermal hysteresis and the standard Arrott plot. To the end, the values of isothermal entropy change are determined by Maxwell relation, and the maximal values follow the trend predicted by the mean-field theory. Its broad transition region (~53 K) leads to only a very small value of entropy change (~2.4 J·kg·K at a field change of 3 T). In turn, the wide transition ensures a relative large refrigerant capacity (~89.4 J·kg), which is comparable to that of MnNiGe-based systems. Although the substitution of Co for Mn site is unsuccessful, the chemically modified MnNiGa is still a promising candidate for the application of magnetocaloric effect (MCE) with merits of higher magnetization and better mechanical performance than MnNiGe-based systems. [ABSTRACT FROM AUTHOR]

The Fe-based amorphous alloys are promising candidates for magnetic refrigeration due to their large magnetocaloric effect, outstanding mechanical property and high electrical resistivity. In this paper, the influence of Co addition on the magnetocaloric effect and refrigeration capacity has been studied for Fe 82− x Co x Mn 4 Zr 8 Nb 2 B 4 ribbons. X-ray diffraction patterns indicate that the Co-doped ribbons are amorphous. The Curie temperature can be adjusted from 271 to 363 K with the Co atomic concentration changing from 2 to 8. Favorably, both isothermal entropy change (Δ S T ) and refrigeration capacity ( RC ) remain nearly the same magnitude for the Co-doped ribbons. For a field change of 3 T, the maximum −Δ S T is about 1.7 J/kgK and the RC is about 115 J/kg for a temperature span of 80 K. The stable magnetocaloric effect and refrigeration capacity near room temperature reveals that the Co-doped amorphous ribbons may be considered as refrigerants for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

• Electrocaloric effects in (SrBa)(SnTi)O 3 ceramics were investigated using direct and indirect approaches. • The largest electrocaloric strength obtained is 0.52 × 10−6 K m/V at T = 56 °C and E = 2 MV/m. • An analytic formula of electrocaloric strength (dT/dE) was firstly deduced via a thermodynamic theory. • The electrocaloric strength mainly depends on the large permittivity peak, phenomenological coefficient and polarization. The electrocaloric effect (ECE) in lead-free (Ba 1−x Sr x)(Sn 0.05 Ti 0.95)O 3 (BSSnT) (x = 0.05, 0.10, 0.15, 0.20) ceramics were investigated around room temperature using direct and indirect approaches. Results indicate that the maximum ECE occurs near the Curie temperature and slightly shifts towards high temperatures with the increasing applied electric field. The directly measured ECE is larger than that calculated using the Maxwell relation. The maximum electrocaloric strength ΔT/ΔE = 0.52 × 10−6 K m/V was obtained at T = 36 °C, with an adiabatic ΔT of 1.05 °C at 2 MV m−1. An analytic formula of electrocaloric strength (dT/dE) was deduced, via which the maximum dT/dE was estimated. The factors affecting the electrocaloric strength were discussed, and the experimental results were compared with those derived from the formula. [ABSTRACT FROM AUTHOR]

Bulk MnFePGe alloy was prepared by mechanical milling and subsequent spark plasma sintering technique. Effect of annealing on the structure and magneto-caloric properties of the alloy was investigated. XRD results show that both sintered and annealed samples possess a hexagonal FeP-type crystal structure. After annealing, ferromagnetic impurity FeMnGe, which exists in the sintered sample, was eliminated from the alloy. Furthermore, the lattice constants a and c change noticeably, leading to a decrease in c/a ratio, while the cell volume almost remains invariable. As a result, the Curie temperature of the alloy increases from 253 K to 298 K, but the maximum magnetic entropy change decreases from 37.5 to 11.7 J·kg·K for 2 T magnetic field change. On the other hand, the thermal hysteresis of M-T curves around T upon heating and cooling is 14 and 8 K for the as-sintered and the annealed sample, respectively, showing evident change. [ABSTRACT FROM AUTHOR]

• Kinetic spin-S Ising model has been investigated. • Effects of oscillating magnetic field components on the isothermal entropy change and cooling capacity have been determined. • Dynamic phase diagrams are plotted. • Dynamic tricritical behaviors are found. By means of mean field approximation, we have investigated magnetocaloric properties of the spin- S Ising model for some spin values S = 1 , 3 / 2 , 2 , 5 / 2 , 3 and 7/2 on a simple cubic lattice. The considered system is driven by a time dependent oscillating magnetic field including a bias field. Effects of the spin magnitude, oscillating magnetic field amplitude (h 0 / J) and bias field (h b / J) on the dynamic critical behavior, isothermal entropy change (| Δ S M |) and cooling capacity (q) of the system have been elucidated in detail. Our numerical outcomes indicate that both bias and oscillating magnetic fields prominently affect the | Δ S M | and q values of the system. When h b / J is increased, both | Δ S M | and q quantities get larger for all considered spin magnitudes, in the absence of oscillating field. It is found that there is a linear relationship between q and h b / J such that it will obey the law: q ∝ γ (S) h b / J for all spin magnitudes. Moreover, the isothermal entropy change varies in such manner that it exhibits an exponential behavior, | Δ S M | ∝ e α h 0 / J for a fixed value of bias field. These results show that the magnetocaloric properties of a material can be adjusted by changing the oscillating magnetic field components as well as bias field. [ABSTRACT FROM AUTHOR]

We calculated the magnetocaloric properties of the molecular nanomagnet Cu5-NIPA, consisting of five spins S = 1 / 2 arranged in two corner-sharing triangles (hourglass-like structure without magnetic frustration). The thermodynamics of the system in question was described using the quantum Heisenberg model solved within the field ensemble (canonical ensemble) using exact numerical diagonalization. The dependence of the magnetic entropy and magnetic specific heat on the temperature and the external magnetic field was investigated. The isothermal entropy change for a wide range of initial and final magnetic fields was discussed. Due to plateau-like behavior of the isothermal entropy change as a function of the temperature, a high degree of tunability of magnetocaloric effect with the initial and final magnetic field was demonstrated. [ABSTRACT FROM AUTHOR]

• Bulk polycrystalline (Gd, Nd) 5 Si 4 compounds were studied and the influence of Gd/Nd concentration determined. • Evidence of the alignment between rare earth ions sublattices though magnetic characterization. • Magnetocaloric properties were assessed via the isothermal entropy change and the refrigerant capacity evaluated. Since the discovery of the giant magnetocaloric effect in the compound Gd 5 Si 2 Ge 2 , rare earth based intermetallics of the form R 5 (Si,Ge) 4 have been largely investigated in their structural and magnetic properties. From the parent compounds Gd 5 Si 4 and Nd 5 Si 4 , the present paper reports the magnetic and magnetocaloric properties of the series Gd 5 - x Nd x Si 4. Our results indicate that the magnetic moments of the Gd and Nd sublattices are antiparallel, where the moment of each sublattice has almost the same magnitude near x = 4. The antiparallel alignment of the sublattices is detrimental to the magnetocaloric properties of the samples. The end members of the series present larger entropy changes, while for the compound x = 4 such quantity is much lower when compared to all other samples. [ABSTRACT FROM AUTHOR]