Large Magnetic Entropy Change Research Articles

Effect of Al doping on structural and magnetic properties of Ni50Mn37AlxSb13−x alloy

The Ni50Mn37AlxSb13−x (x=0, 1, 3 and 5) alloys were prepared by tri-arc melting technique. The replacement of Sb by Al increases the martensitic transformation temperature (TM) as well as ferromagnetic to paramagnetic transformation temperature (TCA) within the austenite phase. The increase in TM is found to due to the enhancement of hybridization between 3d states of Ni and Mn atoms. We also observed a large exchange bias field (HEB) of 470Oe for x=0 and it decreases with the Al concentration for field cooled (FC) magnetic hysteresis loop. A large magnetic entropy change (ΔSM) of 10J/kg-K is found for x=1 alloy under a field change (ΔH) of 50kOe and it decreased for further higher concentration of Al doping. The possible reasons for observed behaviors are discussed.

Structural, magnetic and magnetocaloric properties of La0.7Sr0.3MnO3 manganite oxide prepared by the ball milling method

Structural, magnetic and magnetocaloric properties of La0.7Sr0.3MnO3 sample have been investigated. Powder sample has been elaborated by the ball milling method. The Rietveld analysis of the powder X-ray diffraction shows that the sample crystallizes in the orthorhombic structure with Pnma space group. Magnetic measurements showed that the sample exhibits a ferromagnetic-to-paramagnetic transition at a Curie temperature close to 370 K. The magnetic entropy change (\( \Delta S_{M}\)) has been deduced by the Maxwell relation method. The maximum value of the magnetic entropy change \(| \Delta S_{M}^{\max} |\) is found to be 1.1 J/kgK for an applied magnetic field of 2T. At this value of magnetic field the relative cooling power (RCP) is 49 J/kg. At high temperature, large change in magnetic entropy has been observed in the sample. Our result on magnetocaloric properties suggests that La0.7Sr0.3MnO3 nanopowder is attractive as a possible refrigerant for high temperature magnetic refrigeration.

Theoretical Work in Magnetocaloric Effect of LaFe13−xSi x Compounds

In this paper, the magnetocaloric effect (MCE) of LaFe13−xSix compounds with 1.2 ≤ x ≤ 2.2 has been investigated. For this purpose, the magnetization dependence on the temperature and magnetic field were measured. Magnetic entropy change (−ΔSM) allowing estimation of the MCE was determined based on thermodynamic Maxwell’s relation. The experimental results show that TC increases with the Si content, whereas the magnetic entropy variation decreases. A large magnetic entropy change has been observed. The maximum \((-\Delta \mathrm {S}_{\mathrm {M}}^{\text {max}})\) of LaFe10.8Si2.2 occurring close to TC = 240 K is about 2.3 Jkg−1 K−1 for an applied field change of 0–2 T. In addition, a magnetocaloric effect of LaFe13−xSix compounds (x = 1.2 and 1.6) has been also carried out using phenomenological model. Dependence of the magnetization on temperature variation for LaFe13−xSix compounds (x = 1.2 and 1.6) in different applied magnetic fields was simulated. The values of maximum entropy change, full width at half maximum, and relative cooling power (RCP) for the LaFe11.8Si1.2 and LaFe11.4Si1.6 compounds in different applied magnetic fields were calculated.

Anisotropic magnetic properties and giant magnetocaloric effect of single-crystal PrSi

A single crystal of PrSi was grown by the Czochralski method in a tetra-arc furnace. Powder x-ray diffraction of the as-grown crystal revealed that PrSi crystallizes in an FeB-type structure with space group Pnma (No. 62). The anisotropic magnetic properties were investigated by means of magnetic susceptibility, isothermal magnetization, electrical transport, and heat capacity measurements. Magnetic susceptibility data clearly indicate the ferromagnetic transition in PrSi with a ${T}_{C}$ of 52 K. The relative easy axis of magnetization was found to be the [010] direction. Heat capacity data confirm the bulk nature of the transition at 52 K and exhibit a huge anomaly at the transition. A sharp rise in the low-temperature heat capacity has been observed (below 5 K) which is attributed to the ${}^{141}$Pr nuclear Schottky heat capacity arising from the hyperfine field of the Pr moment. The estimated Pr magnetic moment 2.88 ${\ensuremath{\mu}}_{\mathrm{B}}$/Pr from the hyperfine splitting is in agreement with the saturation magnetization value obtained from the magnetization data measured at 2 K. From the crystal electric field analysis of the magnetic susceptibility, magnetization, and heat capacity data it is found that the degenerate $J=4$ Hund's rule derived state of the Pr${}^{3+}$ ion splits into nine singlets with an overall splitting of 284 K, the first excited singlet state separated by just 9 K from the ground state. The magnetic ordering in PrGe appears to be due to the exchange-generated admixture of low-lying crystal field levels. The magnetocaloric effect (MCE) has been investigated from magnetization data along all three principal crystallographic directions. The large magnetic entropy change, $\ensuremath{-}\ensuremath{\Delta}{S}_{M}=$22.2 J/kg K, and the relative cooling power, RCP = 460 J/kg, characteristic of the giant magnetocaloric effect are achieved near the transition temperature (${T}_{C}$ = 52 K) for $H=$ 70 kOe along $[010]$. Furthermore, the PrSi single crystal exhibits a giant MCE anisotropy.

The TiNiSi-to-Ni2In-type magnetostructural transitions in alloys with largely reduced Ge-concentrations

The MnNiGe-based and MnCoGe-based intermetallic compounds usually exhibit giant magnetocaloric effects at the TiNiSi-to-Ni2In-type magnetostructural transitions. However, the high concentrations of costly Ge element give rise to relatively high raw-material costs for these alloys. In this work, we realized the TiNiSi-to-Ni2In-type magnetostructural transitions in Mn16Fe16Ni34Si34−xGex system which possesses largely reduced Ge-concentrations. Large magnetic entropy changes were observed under relatively low field in a wide temperature range including room temperature.

Magnetic properties and magnetocaloric effects of Gd–Mn–Si ribbons in amorphous and crystalline states

The amorphous Gd65Mn35−xSix (x=5 and 10) ribbons were prepared by melt-spinning. The nanocrystalline Gd65Mn25Si10 alloy consisting of a main hexagonal α-Gd(Mn) phase and a small amount minor phases was also obtained by annealing the amorphous ribbons. The magnetic properties and magnetocaloric effects of these alloys were investigated. The maximum magnetic entropy changes for the amorphous alloys with x=5 and 10 are 4.6 and 4.7Jkg−1K−1, respectively, for a magnetic field change from 0 to 5T. All these amorphous alloys have a broad temperature range of the magnetic-entropy peak, resulting in large refrigeration capacities, 625 and 660J/kg for x=5 and 10, respectively. For the crystallized Gd65Mn25Si10 alloy, a relative large magnetic entropy change (∼4.6J/kg−1K−1) and refrigeration capacity (249J/kg) under a field change of 0–5T is obtained. The large refrigeration capacity and the absence of thermal/magnetic hysteresis losses indicate that the amorphous Gd65Mn35−xSix alloys are good candidates for working in active magnetic refrigeration at the temperature range of 125–275K.

Martensitic transformation and giant magnetic entropy change in Ni42.8Mn40.3Co5.7Sn11.2 alloy

The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg·K is obtained at 215 K under a magnetic field of 30 kOe (1 Oe = 79.5775 A·m−1). The effective refrigerant capacity of Ni42.8Mn40.3Co5.7Sn11.2 alloy reaches 72.1 J/kg under an applied field changing from 0 to 30 kOe. The external magnetic field shifts the martensitic transition temperature about 3–4 K/10 kOe towards low temperature, indicating that magnetic field can retard the phase transition to a certain extent. The origin of large magnetic entropy change is discussed in the paper.

Behavior of the magnetocaloric effect and critical exponents in La0.67Sr0.33Mn1−xVxO3 manganite oxide

We have investigated the magnetocaloric effect along with magnetic phase transition and critical exponent analysis in mixed manganite La0.67Sr0.33Mn1−xVxO3 (0≤x≤0.15). To determine the nature of the paramagnetic to ferromagnetic phase transition, found to be of second-order, we performed a critical exponents study by dc-magnetization M(H,T) measurements around the Curie temperature TC. Modified Arrott plot method has been adopted to study the critical behavior of the compounds at their transition region, the values of critical exponents β, γ and δ are close to those expected for three-dimensional Heisenberg class with short-range interaction. A large magnetic entropy change |ΔSM| deduced from isothermal magnetization curves, has been observed in our samples with a peak centered on their respective TC. With increase in vanadium content, the temperature corresponding to the maximum entropy change as well as the magnetic transition temperature gradually shifts to low temperatures. The field dependence of the magnetic entropy change is also analyzed, which shows the power law dependence namely, ΔSM∝Hn. Relative cooling power increases from 205J/kg for x=0.00 to 258J/Kg for x=0.15 making these materials a promising candidates for magnetic refrigeration near room temperature.

Realization of small intrinsic hysteresis with large magnetic entropy change in La0.8Pr0.2(Fe0.88Si0.10Al0.02)13 by controlling itinerant-electron characteristics

Tuning of phase-transition characteristics in La(FexSi1−x)13 was conducted in view of the correlation between microscopic itinerant electron natures and macroscopic thermodynamic (magnetocaloric) quantities. To realize a small hysteresis loss QH accompanied by a large magnetic entropy change ΔSM in La(FexSi1−x)13, two types of modulation based on itinerant electron characteristics, namely, the Fermi-level shift and the magnetovolume effect were combined by complex partial substitution of Al and Pr. Ab-initio calculations predict the reduction of a transition hysteresis owing to the Fermi-level shift after partial substitution of Al. On the other hand, the chemical pressure arisen from partial substitution of Pr enhances ΔSM through magnetovolume effect. The selective enhancement of ΔSM apart from QH by the magnetovolume effect is well explained by the phenomenological Landau model. Consequently, ΔSM of La0.8Pr0.2(Fe0.88Si0.10Al0.02)13 is −18 J/kg K under a magnetic field change of 0–1.2 T, while the maximum value of QH becomes 1/6 of that for La(Fe0.88Si0.12)13.

Effect of annealing on the structure and magnetic entropy change of Mn1.1Fe0.9P0.8Ge0.2 ribbons

In this study, we report the effect of annealing temperature on the phase constitution, microstructure and magnetocaloric properties of Mn1.1Fe0.9P0.8Ge0.2 melt-spun ribbons. The secondary phases were formed upon annealing at 1073 and 1173K, whereas the pure Fe2P-typed phase was formed after a higher temperature annealing at 1273K. A huge thermal hysteresis of about 40K width was observed in the first magnetostructural transition cycle. However, during the second cycle it was drastically reduced down almost to zero. A large magnetic entropy change ΔS for ribbons annealed 1273K is estimated to be 23J/kgK for a field change of 5T.

Large Magnetocaloric Effect, Moment, and Coercivity Enhancement after Coating Ni Nanoparticles with Ag

We observe a large magnetocaloric effect in monodisperse Ni and Ni(core)Ag(shell) nanoparticles in the superparamagnetic region. The organically passivated Ni nanospheres show a large magnetic entropy change of 0.9 J kg(-1) K for a 3 T magnetic field change. In comparison to the surfactant-coated Ni nanoparticles, the Ni(core)Ag(shell) nanoparticles show an enhanced coercivity, magnetization, and magnetocaloric effect (1.3 kg K for a 3 T magnetic field change). The coercivity at 10 K increases from 360 Oe for Ni nanoparticles to nearly 610 Oe for Ni(core)Ag(shell) particles. This large enhancement is attributed to the enhanced inter-particle interaction, which is mediated by the metallic shell, over the relatively weaker dipolar interaction in the surfactant-coated Ni nanoparticles, and to modification of the surface spin structure.

The influence of quench atomic disorder on the magnetocaloric properties of Ni–Co–Mn–In alloys

The magnetocaloric effect in Ni–Co–Mn–In alloys is studied at low magnetic field, across the first order magnetostructural transition. The Co doping at Ni site induces the large magnetic entropy change (ΔSm) above room temperature. The large ΔSm of 11J/KgK has been observed for disordered Ni1.81Co0.22Mn1.46In0.51 alloy at 337K at an applied field of 1.5Tesla. The influence of quench atomic disorder on the magnetocaloric properties of Ni–Co–Mn–In alloys has been studied. The atomic disorder significantly increases the peak value of ΔSm and decreases the peak width. The refrigeration capacity (RC) is almost unchanged with atomic disorder.

Observation of large magnetocaloric effect in HoRu2Si2

Detailed magnetic, magnetotransport, and magnetocaloric measurements on HoRu2Si2 have been performed. In this Letter, we report presence of spin reorientation transition below paramagnetic to antiferromagnetic transition temperature (TN = 19 K). Large magnetic entropy change 9.1 J/kg K and large negative magnetoresistance ∼21% in a magnetic field of 5 T has been observed around TN, which is associated with field induced spin-flip metamagnetic transition.

Large inverse magnetocaloric effect and magnetoresistance in nickel rich Ni52Mn34Sn14 Heusler alloy

Nickel rich Ni52Mn34Sn14 Heusler alloy was prepared by arc melting and subsequent homogenization by annealing. Existence of first order magneto-structural transition (FOMST) was confirmed by various measurements. In comparison to conventional Ni50−xMn36+xSn14 alloys, a larger magnetic entropy change (∆SM≈8J/kgK using Maxwell׳s thermodynamic equation and ∆SM≈18J/kgK using Clasius–Clapeyron equation) and large negative magnetoresistance (MR≈−30%) were observed in the vicinity of martensitic transition temperature due to a change of 3T and 8T magnetic fields respectively. Effect of excess Ni content was discussed by considering other nearer compositions as reported by other researchers. Irreversibility in FOMST due to kinetic arrest was also studied from MR vs magnetic fields curves taken at a single temperature in two different initial phases. The exchange bias behavior in this alloy was studied by various magnetic measurements.

Phase diagram and magnetocaloric effects in Ni50Mn35(In1−xCrx)15 and (Mn1−xCrx)NiGe1.05 alloys

The magnetocaloric and thermomagnetic properties of Ni50Mn35(In1−xCrx)15 and (Mn1−xCrx) NiGe1.05 systems for 0 ≤ x ≤ 0.105 and 0 ≤ x ≤ 0.1, respectively, have been studied by x-ray diffraction, differential scanning calorimetry, and magnetization measurements. Partial substitution of Cr for Mn in (Mn1−xCrx)NiGe1.05 results in a first order magnetostructural transition from a hexagonal paramagnetic to an orthorhombic paramagnetic phase near TM ∼ 380 K (for x = 0.07). Partial substitution of Cr for In in Ni50Mn35(In1−xCrx)15 shifts the magnetostructural transition to a higher temperature (T = TM ∼ 450 K) for x = 0.1. Large magnetic entropy changes of ΔS = −12 (J/(kgK)) and ΔS = −11 (J/(kgK)), both for a magnetic field change of 5 T, were observed in the vicinity of TM for (Mn1−xCrx)NiGe1.05 and Ni50Mn35(In1−xCrx)15, respectively.

Impact of structural disorder on the magnetic ordering and magnetocaloric response of amorphous Gd-based microwires

We have studied the impact of structural disorder on the magnetic ordering and magnetocaloric response of amorphous Gd68Ni32 and Gd53Al24Co20Zr3 microwires. We find that the presence of structural disorder significantly broadens the paramagnetic to ferromagnetic (PM-FM) transition and the temperature-dependent magnetic entropy change, while the nature of the second-order magnetic transition and long-range ferromagnetic order are not essentially affected by this effect. The large magnetic moment of Gd and the presence of the long-range ferromagnetic order are believed to result in a large magnetic entropy change, which together with the broadening of the PM-FM transition due to structural disorder contribute to a large refrigerant capacity. The excellent magnetocaloric properties of the amorphous microwires make them very promising candidates for active magnetic refrigeration.

Fluoride‐Bridged {GdIII3MIII2} (M=Cr, Fe, Ga) Molecular Magnetic Refrigerants

AbstractThe reaction of fac‐[MIIIF3(Me3tacn)]⋅x H2O with Gd(NO3)3⋅5H2O affords a series of fluoride‐bridged, trigonal bipyramidal {GdIII3MIII2} (M=Cr (1), Fe (2), Ga (3)) complexes without signs of concomitant GdF3 formation, thereby demonstrating the applicability even of labile fluoride‐complexes as precursors for 3d–4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3 J kg−1 K−1 (1) and 33.1 J kg−1 K−1 (2) for the field change 7 T→0 T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe–Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close‐lying excited states for successful design of molecular refrigerants.

Fluoride‐Bridged {GdIII3MIII2} (M=Cr, Fe, Ga) Molecular Magnetic Refrigerants

The reaction of fac-[M(III)F3(Me3tacn)]⋅x H2O with Gd(NO3)3⋅5H2O affords a series of fluoride-bridged, trigonal bipyramidal {Gd(III)3M(III)2} (M = Cr (1), Fe (2), Ga (3)) complexes without signs of concomitant GdF3 formation, thereby demonstrating the applicability even of labile fluoride-complexes as precursors for 3d-4f systems. Molecular geometry enforces weak exchange interactions, which is rationalized computationally. This, in conjunction with a lightweight ligand sphere, gives rise to large magnetic entropy changes of 38.3 J kg(-1) K(-1) (1) and 33.1 J kg(-1) K(-1) (2) for the field change 7 T→0 T. Interestingly, the entropy change, and the magnetocaloric effect, are smaller in 2 than in 1 despite the larger spin ground state of the former secured by intramolecular Fe-Gd ferromagnetic interactions. This observation underlines the necessity of controlling not only the ground state but also close-lying excited states for successful design of molecular refrigerants.

Enhanced Cryogenic Magnetocaloric Effect Induced by Small Size GdNi5 Nanoparticles

GdNi5 nanoparticles and GdNi5/Gd2O3 nanocapsules (with GdNi5 core and Gd2O3 shell) were prepared by arc-discharge technique under different hydrogen partial pressure. The GdNi5 nanoparticles show irregular spherical shape and have a size distribution of 10–50 nm with an average diameter of 15 nm. In comparison, the GdNi5/Gd2O3 nanocapsules present spherical morphology and show a size distribution of 10–100 nm with an average diameter of 60 nm. Under a magnetic field change of 50 kOe, the maximum magnetic entropy change of GdNi5 nanoparticles is 13.5 J/(kg K) at 5 K, while the corresponding value of the GdNi5/Gd2O3 nanocapsuels is only 5.7 J/(kg K) at 31 K. The origin of the large magnetic entropy change of GdNi5 nanoparticles is ascribed to its high atomic moments and small anisotropy energy barrier induced by its small particle size.

Effect of Particle Size on the Hysteretic Behavior and Magnetocaloric Effect of La0.5Pr0.5Fe11.4Si1.6 Compound

Bulk La0.5Pr0.5Fe11.4Si1.6 compound exhibits a large magnetic-entropy change ΔS m of 28.1 J/(kg K) for a magnetic-field change from 0 to 1.5 T at the Curie temperature, T C of 186 K, accompanied by a large magnetic hysteresis of 56 J/kg and a noticeable thermal hysteresis of about 1 K. If the bulk sample is ground into middle-size particles (30–60 μm), then the thermal hysteresis is almost eliminated and the magnetic hysteresis loss is decreased by 29%, while the large ΔS m maintains. Especially, fine powder with an average size of 2 μm shows the same T C as the bulk and does not lose stability. Meanwhile, a comparatively large ΔS m of 13.9 J/(kg K) and a hysteresis reduction of 70% are attained. The hysteresis reduction can be ascribed to the decrease of internal strains and to the improvement of heat transfer due to the increase of the ratio of the surface area to the volume.