Giant Magnetic Entropy Change Research Articles

Observation of Griffiths phase and giant magnetocaloric effect in double perovskite oxide RE2FeCrO6 (RE = Gd, Tb, Dy, Er)

AbstractThe magnetic properties of double perovskite oxide RE2FeCrO6 (RE = GD, Tb, Dy, Er) were systematically studied, and the Griffiths phase evolution was observed. In Tb2FeCrO6, Dy2FeCrO6, and Er2FeCrO6, there are antiferromagnetic (AFM)‐ferromagnetic (FM) first‐order phase transition and the Griffiths phase with coexistence of FM and paramagnetic (PM) was observed by the EPR spectra. Gd2FeCrO6 has an AFM–PM second‐order phase transition, and there is no first‐order phase transition in the range of ∆H = 0–50 kOe. As the temperature decreases, all four sets of samples present χ−1 (T) deviates downwards from the Curie–Weiss linear behavior from 0.2 to 5 kOe, corresponding to the typical characteristics of Griffiths phase evolution. In addition, all four sets of samples have excellent magnetocaloric performance. Especially, the Gd2FeCrO6 oxide has giant magnetic entropy change and relative cooling power (−∆SMmax = 30.31 J/kg K and RCP = 312.8 J/kg when ∆H = 50 kOe). From the perspective of low‐temperature magnetic refrigeration application, the present work provides important candidate references for magnetic component researchers.

Dual-phase nano-glass-hydrides overcome the strength-ductility trade-off and magnetocaloric bottlenecks of rare earth based amorphous alloys

Metal-hydrogen systems have attracted intense interest for diverse energy-related applications. However, metals usually reduce their ductility after hydrogenation. Here, we show that hydrogen can take the form of nano-sized ordered hydrides (NOH) homogeneously dispersed in a stable glassy shell, leading to remarkable enhancement in both strength and ductility. The yield strength is enhanced by 44% and the plastic strain is substantially improved from almost zero to over 70%, which is attributed to the created NOH and their interplay with the glassy shell. Moreover, the hydride-glass composite GdCoAlH possesses a giant magnetic entropy change (−ΔSM) of 18.7 J kg−1K−1 under a field change of 5 T, which is 105.5% larger than the hydrogen-free sample and is the largest value among amorphous alloys and related composites. The prominent ΔSM-ductility combination overcomes the bottlenecks of amorphous alloys as magnetic refrigerants. These results provide a promising strategy for property breakthrough of structural-functional alloys.

Giant cryogenic magnetocaloric effect in mineral of gaudefroyite: Direct and indirect measurements

The magnetic and magnetocaloric properties of gaudefroyite minerals were studied. The magnetocaloric effect was investigated by direct and indirect methods in the temperature range 4.2–40 K and magnetic field up to 10 T. The magnetization was measured in a low magnetic field (200 Oe) with zero-field cooled and field cooling protocol and previous observation of typical spin glass behavior was confirmed. The giant magnetic entropy changes with anisotropic behavior and maximums |ΔSm|= 17 J kg−1 K−1 (H||c) at 18 K and |ΔSm|= 20 J kg−1 K−1 (H||ab) at 12 K at an applied magnetic field 10 T were observed. The direct measurements of the magnetocaloric effect demonstrated the maximum of adiabatic temperature changes of ΔTad = 11 K at a magnetic field change of 10 T (H||ab) at 11.5 K. Obtained values of magnetocaloric parameters for the mineral of gaudefroyite are comparable to promising materials for magnetic crycooling technologies (for example, hydrogen (LH2) liquefaction) and have an advantage for the absence of rare-earth elements in the gaudefroyite.

Effect of temperature and magnetic field induced hysteresis on reversibility of magnetocaloric effect and its minimization by optimizing the geometrical compatibility condition in Mn–Ni–Fe–Si alloy

The advancement of magnetic materials with coupled magneto-structural phase transition (MST) to fulfill the ultimate objectives of practical solid-state cooling applications requires a better understanding of the hysteresis phenomenon linked across the phase transition region along with the large magnetocaloric parameters. For the present sample Mn0.65Ni0.65Fe0.70Si, the MST is associated with a sharp jump in magnetization along with a small thermal hysteresis of ∼13 K. A giant isothermal magnetic entropy change (|ΔSMmax|) of ∼37.6 J kg−1 K−1 at 299 K and effective refrigerant capacity (RCeffe) of ∼214.3 J kg−1 under ΔH = 30 kOe is obtained with excellent compatibility between the martensite and austenite phases. The geometrical compatibility condition, i.e., very small (∼0.55%) deviation of the middle eigenvalue (λ2) from unity justifies the observation of small hysteresis in the present material. The investigation of hysteresis behavior under different extents of the driving forces (temperature or magnetic field) reveals that both the driving forces trigger equally the phase transition and are responsible equivalently for the hysteresis phenomenon. The present study provides a pathway to understand the complexity of the hysteresis behavior, its impact on the reversibility of magnetocaloric effect, and its minimization by optimizing the geometrical compatibility condition between the austenite and martensite phases.

Itinerant ferromagnetism and room temperature giant magnetocaloric effect in (Mn0.6Fe0.4) (Ni0.5Co0.5) Si shape memory alloy

In this article, the feasibility of obtaining a magneto-structural coupling over a wide working temperature range of about 127 K (from 206.5 K to 333.5 K) with negligible thermal hysteresis in combination with the structural, microstructural, magnetic, and magnetocaloric properties of a 50 % Co-doped (at the Ni site) polycrystalline (Mn0.6Fe0.4) (Ni0.5Co0.5) Si (MFNCS-0.5) magnetic shape memory alloy (MSMA) has been thoroughly investigated. Along with leaf-like microstructure, at room temperature, the system shows a mixed phase of TiNiSi type low-temperature high-magnetic (ferromagnetic) orthorhombic martensite and Ni2In type high-temperature low-magnetic (paramagnetic) hexagonal austenite, with the dominance of the second one. To estimate the magnetocaloric effect (MCE) across the phase transition, the isothermal magnetic measurement technique has been employed. The merging of heating and cooling iso-field thermo-magnetization (M-T) curves, the presence of negligible thermal hysteresis in the MH curves, universal magnetic entropy curves, a proposed phenomenological model (across the Curie temperature), and the positive slopes of the Arrott plot (Banerjee criterion) show that the first-order structural and magnetic transition are coupled along with a second-order ferromagnetic to paramagnetic (FM → PM) phase transition (SOPT). By extrapolating the Arrott plot to the H/M = 0 axis the spontaneous magnetization value very close to 0 K, Ms(0), is found to be 71.92 emu/g (∼1.83 µB/f.u.). The linear dependency of MS2T on T2 below SOPT and the RWR (Rhodes–Wolhfarth ratio) = 4.29 > 1 indicate the long-range itinerant ferromagnetism in this alloy. A giant magnetic entropy change (ΔSm) of 25.77 J kg−1 K−1 and a refrigerant capacity (RC) of 472.83 J kg−1 are obtained at 6 T field. This observed magnetic refrigerant's key characteristics, including a giant magnetocaloric effect (MCE) near room temperature (RT), negligible thermal hysteresis loss, a wide operating temperature range of 127 K, and the use of cost-effective, non-toxic constituent elements, make it a suitable and very promising member for applications in solid-state refrigeration technology near RT.

Anisotropic magnetic property, magnetostriction, and giant magnetocaloric effect with plateau behavior in TbMn2Ge2 single crystal

The ternary RMn2Ge2 (R = rare earth) intermetallic compounds have attracted great attention due to their interesting magnetic behaviors and magnetotransport responses. Here, we reported our observation of anisotropic magnetic property, magnetostriction, and magnetocaloric effect (MCE) in TbMn2Ge2 single crystal. Below the transition temperature of Tb magnetic sublattices (T_{{text{C}}}^{{{text{Tb}}}} ~ 95 K), strong Ising-like magnetocrystalline anisotropy is observed with an out-of-plane ferromagnetic moments 5.98 μB/f.u. along the easy c axis, which is two orders of magnitude larger than that of field along a axis. Above T_{{text{C}}}^{{{text{Tb}}}}, a field-induced metamagnetic transition is observed from the spin-flip of Mn sublattices. During this transition, remarkable magnetostriction effect is observed, indicating of strong spin–lattice coupling. The responses of Tb and Mn sublattices to the magnetic field generate a giant magnetic entropy change (- Delta S_{M}) and large values of relative cooling power (RCP) and temperature-averaged entropy change (TEC). The calculated maximum magnetic entropy change (- Delta S_{M}^{max }), RCP, and TEC(10) with magnetic field change of 7 T along c axis reach 24.02 J kg−1 K−1, 378.4 J kg−1, and 21.39 J kg−1 K−1 near T_{{text{C}}}^{{{text{Tb}}}}, which is the largest among RMn2Ge2 families. More importantly, this giant MCE shows plateau behavior with wide window temperatures from 93 to 108 K, making it be an attractive candidate for magnetic refrigeration applications.

Giant room temperature magnetocaloric response in a (MnNiSi)1−x(FeNiGa)x system

The coincidence of magnetic and structural transitions near room temperature is observed in (MnNiSi)1−x(FeNiGa)x (x = 0.16 and 0.17) systems, which leads to a coupled magnetostructural transition (MST) from a high-temperature paramagnetic Ni2In-type hexagonal phase to a low-temperature ferromagnetic TiNiSi-type orthorhombic phase associated with a substantial change in magnetization and a large change in structural unit cell volume, and thus, across MST, a giant magnetocaloric effect is obtained in these systems. The alloys with x = 0.16 and 0.17 are observed to show a giant isothermal magnetic entropy change (ΔSM) of about −26.2 and −63.2 J kg−1 K−1, accompanied with a large relative cooling power of about 220.1 and 264.5 J/kg, respectively, due to a magnetic field change (μ0ΔH) of 5 T only. Moreover, the material with x = 0.16 and 0.17 shows a large temperature average magnetic entropy change of about −21.64 and −34.4 J kg−1 K−1 over a temperature span of 10 K due to μ0ΔH ∼ 5 T. Thus, these low-cost materials with giant magnetocaloric responses are highly suitable to be used as magnetic refrigerants for room temperature solid-state-based cooling technology.

Understanding of the giant magnetic entropy change around the co-occurrence point of martensitic and magnetic transitions in Ni-Mn-In Heusler alloy

Magnetic refrigeration technique based on magnetocaloric effect has attracted increasing interest due to the high energy-converting efficiency and environmental friendliness. From application aspect, a large cooling capacity with a wide working temperature span, i.e., a combination of large isothermal entropy change (|ΔS|) and large adiabatic temperature (|ΔTad|) is desired, yet these two indices are hardly achieved. In this work, we report a combination of both large |ΔS| (40 J kg−1K−1) and large |ΔTad| (15 K) under 5 T around room temperature in Ni-Mn-In Heusler alloys. This excellent combination is found to occurred near the co-occurrence point of martensitic and ferromagnetic transitions. Based on the systematic microstructure and Landau theory analysis, the magnetocaloric properties can be understood by the free energy barrier and the temperature range of field induced magnetic transition results when approaching the co-occurrence point. Our study may provide a promising strategy on designing novel magnetocaloric materials with both large cooling capacity and wide working temperature span through approaching the co-occurrence point of martensitic and magnetic transitions.

Unconventional metamagnetic phase transition in R2In (R=Nd, Pr) with lambda-like specific heat and nonhysteresis

• The field-triggered metamagnetism with lambda-like peak on the specific heat is found in Nd 2 In and Pr 2 In alloys. • Neither thermomagnetic hysteresis nor lattice changes are observable during phase transition. • Giant magnetoentropy changes of 13.2 J kg −1 K −1 and 19.5 J kg −1 K −1 are achieved with enhanced magnetoelastic coupling. • The max adiabatic temperature changes of 6.5 K and 7.4 K are obtained for Nd 2 In and Pr 2 In alloys under 7 T. • It is proposed to be from the delocalized 5 d electrons evidenced by the negative magnetoresistance. The phase transition of Nd 2 In and Pr 2 In has been studied and found to be between the first-order and second-order nature. Hardly any hysteresis nor obvious cell volume changes are presented. Concurrently the field-triggered metamagnetism is demonstrated with lambda-like peak on specific heat curve. For the field change of 7 T, giant magnetic entropy changes of 13.2 J kg −1 K −1 and 19.5 J kg −1 K −1 and adiabatic temperature changes of 6.5 K and 7.4 K have been achieved in Nd 2 In and Pr 2 In alloys respectively, which is partially contributed by strong magnetoelastic coupling represented by high saturation magnetostriction of ∼450 ppm. Such unique feature is proposed to be originated from the delocalized 5 d electrons, as evidenced by the negative magnetoresistance caused by the phase transition.

Measurement protocols dependent giant magnetocaloric effect in MnNiSi-based system

MnNiSi-based compounds exhibit giant isothermal magnetic entropy change (ΔSM) across their induced first-order coupled magnetostructural transition (MST) in the vicinity of room temperature, though in most of the cases, the use of Maxwell relation from a very frequently used but incorrect measurement protocol provides a nonphysical spike to the calculated ΔSM. Herein, to realize the accurate measurement protocol, we explore magnetocaloric properties of a (FeCoGa)x doped (MnNiSi)1−x compound with x = 0.165 rigorously. Several methods, including the estimation of ΔSM using Maxwell relation, Clausius-Clapeyron equation, and also from the calorimetry measurement, are discussed explicitly. The studied material is observed to show a MST at 265 K and a giant ΔSM as large as about −29.3 J kg−1 K−1 due to a magnetic field change of 5 T following the Maxwell equation during discontinuous cooling and field increasing mode, which enables the material as a promising candidate for magnetic refrigeration.

Age stability of La(Fe,Si)13 hydrides with giant magnetocaloric effects

The Curie temperatures (TC) of La0.7Ce0.3Fe13-x-yMnxSiy compounds that are hydrogenated to saturation are raised to near room temperature. The age stability was investigated for the fully hydrogenated La0.7Ce0.3Fe11.5-xMnxSi1.5 compounds. This result indicates that the H content will slowly decrease in the hydrides, leading to a decrease in TC. However, no age splitting is observed after the hydrides are held at room temperature for two years, indicating the excellent age stability of the hydrides. Further structural analysis by neutron diffraction shows that Mn atoms preferentially substitute Fe in the 96i sites. The TC of La0.7Ce0.3Fe11.55-yMnySi1.45 hydrides can be adjusted to the desired working temperature by regulating Mn content based on the linear relationship between TC and Mn content. Moreover, the La0.7Ce0.3Fe11.55-yMnySi1.45 hydrides exhibit a giant magnetic entropy change of 15 J·kg−1·K−1 under a low magnetic field change of 0−1 T. As a result, the giant magnetocaloric effect, linearly adjustable TC, and excellent age stability make the La0.7Ce0.3Fe11.55-yMnySi1.45 hydrides be one of the ideal candidates for room temperature magnetic refrigerants.

Giant Magnetocaloric Response Induced by Tuning the Intrinsic Exchange Field in the Alloys With Random Magnetic Anisotropy Under a Constant Magnetic Field

The use of a limited magnetic field strength to induce a giant magnetocaloric response is desired towards the potential magnetic refrigeration applications. A method to lower the external magnetic field through taking advantage of the exchange field gradient in the alloys with different component ratios and random magnetic anisotropy under a constant magnetic field is conceived, where the conventional thermodynamic Maxwell formula is modified by replacing the external magnetic field by internal exchange field to calculate magnetic entropy change. The Ni46Co3Mn37-x CuxIn14 (x=0, 1, 2, 3, at.%) alloys are fabricated, and with increasing x, the martensitic transformation temperature increases towards room temperature, meanwhile, the ferromagnetism is weakened and the Curie temperature decreases down to room temperature. Under a constant magnetic field of 1.5 T, it is calculated that an exchange field variation of 1 T can induce a giant positive magnetic entropy change of ~14 J kg-1K-1 near the martensitic transformation and a high relative cooling power ~110 J kg-1 near the paramagnetic-to-ferromagnetic phase transition. Other features of this magnetocaloric effect include that it is weakened under stronger magnetic fields and the relative cooling power is independent of magnetic field. The Monte Carlo simulation is also performed to fit the magnetization and magnetic entropy change behaviors near the magnetic phase transition, and the exchange energy in alloys are quantified from 1.438×10-22 to 1.290×10-22 J with the x variation from 0 to 1 through fitting the linear relative cooling power results. This work not only opens a new avenue to develop a household magnetic refrigerant with low external stimuli and high signal-to-noise ratio, but also provides a method to quantify the intrinsic magnetic parameters using magnetocaloric effect.

Tuning structural-transformation temperature toward giant magnetocaloric effect in MnCoGe alloy: A theoretical study

We propose a new model and scheme to consider the effect of structural transformation on magnetocaloric properties of Mn1-xCuxCoGe. The magnetic exchange coupling constants are estimated from first-principles calculations based on density functional theory. The magnetic phase diagram is semi-quantitatively reproduced by using mean-field approximation. The giant isothermal magnetic entropy change with the magnetostructural coupling of Mn0.89Cu0.11CoGe alloy is well reproduced by using the modified Potts model. The enhancement of magnetostructural coupling on the isothermal magnetic entropy change strongly depends on the condition of the magnetic phase transition temperature of orthorhombic and hexagonal phases.

Tuning transition temperature of magnetocaloric Mn1.8Fe0.2(P0.59Si0.41)x alloys for cryogenic magnetic refrigeration

Giant magnetocaloric effect in Mn1.8Fe0.2(P0.59Si0.41)x ( x = 1.00, 1.01, 1.02, 1.03, 1.04) alloys is assessed for cryogenic temperature applications. We found that the Curie temperature can be tuned from. 300 K to 99 K by increase of Mn/Fe and P/Si ratios. We systematically optimized metal/non-metal ratio and homogenization condition to maximize the volume fraction of the Fe2P-type phase. A giant isothermal magnetic entropy changes of 10.6 and 14.0 J/kgK under a magnetic field of 2.0 and 5.0 T is obtained at 117.0 K for Mn1.8Fe0.2(P0.59Si0.41)1.03 alloy. This work demonstrates low-cost Mn-Fe-P-Si alloys with giant MCE are competitive candidates compare to the rare-earth-containing magnetocaloric compounds for cryogenic applications.

Giant low field magnetocaloric effect near room temperature in isostructurally alloyed MnNiGe-FeCoGe systems

According to the strategy of isostructural alloying, the magnetostructural coupling was realized by doping appropriate stable hexagonal Ni2In-type FeCoGe alloy into MnNiGe systems, which results in the achievement of large magnetization difference and giant low field magnetic entropy change (ΔSm) in the isostructurally alloyed (MnNiGe)-(FeCoGe) systems. Giant ΔSm as much as −51.3 J∙kg-1K−1 at 296 K and −56.2 J∙kg-1K−1 at 275 K under 5 T magnetic field have been observed in (MnNiGe)0.91-(FeCoGe)0.09 and (MnNiGe)0.89-(FeCoGe)0.11 alloys, respectively. Moreover, the ΔSm of (MnNiGe)0.89-(FeCoGe)0.11 alloy are reached −25.6 J∙kg-1K−1 (2 T) and −43.6 J∙kg-1K−1(3 T), respectively. The observed values of -ΔSM under the magnetic field of 2 T and 3 T are larger than most of the reported MnMX(M = Co, Ni and X = Ge, Si) based systems.

Giant reversible magnetocaloric effect in MnNiGe-based materials: Minimizing thermal hysteresis via crystallographic compatibility modulation

MnMX (M = Co or Ni, X = Si or Ge) alloys with strong magnetostructural coupling exhibit giant magnetic entropy change and are currently extensively studied. However, large thermal hysteresis results in serious irreversibility of the magnetocaloric effect in this well-known system. In this work, we report a low thermal hysteresis and large reversible magnetocaloric effect in a MnNiGe-based system. The introduction of Fe into both Ni and Mn sites can establish stable magnetostructural transitions from paramagnetic hexagonal to ferromagnetic orthorhombic phases. Fascinatingly, a low thermal hysteresis of 5.2 K is achieved in Mn0.9Fe0.2Ni0.9Ge alloy with a large magnetization difference of 62.1 A m2/kg between the two phases. These optimized parameters lead to a partially reversible phase transformation under a magnetic stimulus and bring about a large reversible magnetic entropy change of −18.6 Jkg−1K−1 under the field variation of 0–5 T, which is the largest value reported in MnMX system up to now. Moreover, this low-hysteresis magnetostructural transformation and large reversible magnetocaloric effect can be tuned by doping with Si in a wide temperature range covering room temperature. We also introduce geometrically nonlinear theory to discuss the origin of low hysteresis in MnMX alloys. A strong relation is found between thermal hysteresis and the change of c axis in the orthorhombic structure during the transition. Our work greatly develops the potential of MnMX alloys as magnetocaloric materials and is meaningful to seek or design a MnMX system with low thermal hysteresis.

Giant reversible magnetocaloric effect in orthorhombic GdScO3

Abstract The magnetic and magnetocaloric properties were studied in orthorhombic polycrystalline GdScO3. GdScO3 possesses an antiferromagnetic ordering below the Neel temperature ∼2.8 K. Negligible thermal and magnetic hystereses were both observed in GdScO3, indicating a second-order feature of phase transition and a reversible magnetocaloric effect (MCE). In the magnetic field changes of 0–50 kOe and 0–70 kOe, giant maximum magnetic entropy changes of 39.39 J/kg K and 50.77 J/kg K were obtained near the liquid helium temperature, respectively. The giant reversible MCE indicates the polycrystalline GdScO3 is a very promising refrigerant candidate for the low-temperature magnetic refrigeration.

Enhanced magnetocaloric effect in Ni-Mn-Sn-Co alloys with two successive magnetostructural transformations

High magnetocaloric refrigeration performance requires large magnetic entropy change ΔSM and broad working temperature span ΔTFWHM. A fourth element doping of Co in ternary Ni-Mn-Sn alloy may significantly enhance the saturation magnetization of the alloy and thus enhance the ΔSM. Here, the effects of Co-doping on the martensite transformation, magnetic properties and magnetocaloric effects (MCE) of quaternary Ni47−xMn43Sn10Cox (x = 0, 6, 11) alloys were investigated. The martensite transformation temperatures decrease while austenite Curie point increases with Co content increasing to x = 6 and 11, thus broadening the temperature window for a high magnetization austenite (13.5, 91.7 and 109.1 A·m2/kg for x = 0, 6 and 11, respectively). Two successive magnetostructural transformations (A → 10 M and A → 10 M + 6 M) occur in the alloy x = 6, which are responsible for the giant magnetic entropy change ΔSM = 29.5 J/kg·K, wide working temperature span ΔTFWHM = 14 K and large effective refrigeration capacity RCeff = 232 J/kg under a magnetic field of 5.0 T. These results suggest that Ni40.6Mn43.3Sn10.0Co6.1 alloy may act as a potential solid-state magnetic refrigerant working at room temperature.

Thickness as a control parameter for magnetocaloric effect in Cr75−xFe25+x (x = 0, 5) thin films

The results of a detailed investigation of the magnetocaloric effect (negative isothermal magnetic entropy change, -ΔSM(T,H)) in Cr70Fe30 and Cr75Fe25 thin films are presented. The generalized magnetic scaling equation of state in nonlinear scaling variables, which makes use of the previously reported critical exponents, not only reproduces the observed -ΔSM(T) at constant magnetic fields (1kOe⩽H⩽70kOe) over a wide temperature range around the ferromagnetic-paramagnetic phase transition temperature, T=Tc, but also describes correctly the functional dependence of -ΔSM on H at T=Tc. Reasonably large relative cooling power (RCP) and magnetic refrigerant capacity (RC), primarily due to the unusually large (130 K–180 K) full-width at half-maximum (FWHM) of the -ΔSM(T)|H curve, is observed for the magnetic field change ranging between 20 kOe and 70 kOe. This work clearly bears out that the film thickness can be used as a control parameter to tune both the peak value of -ΔSM as well as the FWHM, and hence RCP and RC. Another important result is the observation of giant isothermal magnetic entropy change at T = 2 K within the reentrant regime (where long-range ferromagnetic order coexists with cluster spin glass order) when the film thickness is reduced to ≃20nm.

Giant magnetic entropy change in gadolinium orthoferrite near liquid hydrogen temperature

The magnetic properties and giant magnetic entropy change in gadolinium orthoferrite have been investigated for their potential application as magnetic refrigeration working media. We found GdFeO3 polycrystalline sample exhibits a large magnetic entropy change value (–ΔSM = 50.2 J/kg K at 70 kOe) near the liquid hydrogen temperature, which is much larger than those of other oxide magnetic refrigerators. The large magnetocaloric effect is related to the half-filled 4f electronic state in rare earth-transition oxides. The large values of these parameters, together with negligible hysteresis, suggest that GdFeO3 multiferroic ferrite could be potential materials for magnetic refrigeration in low-temperature region.