Magnetocaloric Properties Research Articles

Magnetocaloric properties of La0.9Pr0.1Fe11.2Co0.7Si1.1 compound through direct measurements under cyclic magnetic fields up to 30 Hz

Direct measurements of the adiabatic temperature change (ΔTad) in cyclic magnetic fields with a frequency of up to 30 Hz in the La0.9Pr0.1Fe11.2Co0.7Si1.1 alloy were carried out. For this alloy, the magnetocaloric effect (MCE) under magnetic field change of 1.8 T is 2.8 K and the temperature hysteresis does not exceed 0.5 K. Under magnetic field change of 0.62 T with frequencies of up to 20 Hz, the MCE shows a weak frequency dependence (less than 5%), while under magnetic field change of 1.2 T the frequency dependence is clear pronounced. Long-term exposure to a low frequency cyclic magnetic field does not result in a change in the MCE value, while at frequencies more than 10 Hz noticeable degradation of the MCE is observed. The results of the study show that the upper limit of the operation of magnetic refrigerators can reach several tens of Hz.

Effects of composition variation and hydrogenation on magnetocaloric properties of the (Gd1-xTbx)Ni (x = 0.1; 0.9) compounds

To identify promising magnetic refrigerant materials, we have studied the influence of composition variations and hydrogenation on the magnetocaloric effect (MCE) of the (Gd1-xTbx)Ni compounds. The end compositions of the series, Gd0.9Tb0.1Ni and Gd0.1Tb0.9Ni crystallize in orthorhombic CrB-type and monoclinic TbNi-type structures, respectively. Hydrogenation boosts the unit cell volume of (Gd,Tb)Ni by more than 20 % upon absorption of 4 at.H/f.u. Hydrogen absorption changes the structure type from TbNi to the CrB-type in Gd0.1Tb0.9Ni. Decrease of the Curie temperature in hydrides reaches ∼ 60 K. The magnetocaloric effect in (Gd,Tb)NiHy (y = 0 and 4) obtained by indirect method in the vicinity of TC revealed similar values of the maximum of specific isothermal entropy change -ΔST = 20.5 J kg−1 K−1 for Gd0.9Tb0.1Ni and its hydride Gd0.9Tb0.1NiH4 at μ0ΔH = 7 T. We show that the controlled synthesis of hydrides allows us to tailor the magnetocaloric effect in the multicomponent rare earth intermetallics and obtain materials with largely different TCs but with the same MCE values that are attractive for use in low-temperature magnetic cooling applications.

Impact of sintering temperature on the structural, magnetic and magnetocaloric properties in La0.75Eu0.05Sr0.2MnO3 manganite

This work concerns a profound study on the structural, magnetic properties and the influence of gradual decrease of the sintering temperature TS on the magnetocaloric properties of La0.75Eu0.05Sr0.2MnO3 manganite elaborated by adopting sol-gel method with TS = 800 °C, 1000 °C and 1200 °C. The refinement of X-ray diffraction patterns at room temperature has shown the coexistence of both rhombohedral R3¯c and orthorhombic Pnma structural phases. The grain size of the sample sintered at 800 °C is around 56 nm. The Curie temperature TC slightly shifts from 305 K to 298 K with decreasing particle size. The magnetic behavior has been discussed based on the core-shell structure. Reducing TS induces the broadening of the magnetic transition. According to the magnetocaloric study, the maximum relative cooling power (RCP) value was recorded for the sample sintered at 800 °C (RCP = 90.11 J/kg for a magnetic field of 2 T at 298 K) suggesting that this sample represents a promising candidate for magnetic refrigeration at room temperature.

Structural insights into the rare-earth modified La1.4-xSmxSr1.6Mn2O7 layered perovskites and probing their complex magnetic and magnetocaloric properties

In this work, structural characteristics upon rare-earth modification into the Ruddlesden-Popper (R-P) layered compounds La1.4-xSmxSr1.6Mn2O7 (0.00 ≤ x ≤ 0.20) were deeply investigated. The compounds were prepared through conventional ceramic-sintering method. X-ray diffraction (XRD) and Raman spectra collectively disclosed a reduction in the unit cell dimensionality and emergence of structural distortions upon Sm-modification which facilitated the separation of structural phases. Unlike the cubic manganites these distortions impart a chemical pressure mainly along c-axis of the tetragonal cell and favored a weak interbilayer exchange interaction native to layered lattice. The magnetization vs temperature (M-T) curves revealed multiple transitions that were chiefly attributed to such anisotropic exchange coupling and to a separate perovskite phase. The appearance of magnetic clusters was further confirmed in magnetization isotherms (M − H curves) and Arrott plots. The highest change in magnetic entropy (ΔSM) of 2.28 Jkg−1K−1 at 2.5 T field was obtained for pristine compound, the value slightly decreased to 1.78 Jkg−1K−1 for x = 0.05, and then increased up to 1.90 Jkg−1K−1 for x = 0.1 composition. Whereas the relative cooling power (RCP) abruptly enhanced to 100 J/kg, 110 J/kg and 92 J/kg for x = 0.05, 0.10 and x = 0.15 samples, respectively as compared to original value of 84 J/kg. It signifies an excellent magnetocaloric performance for x = 0.05 and 0.1 compositions over various categories of material systems and asserting the technological competence of these compounds for low temperature refrigeration applications.

Magnetocaloric Properties and Phenomenological Model in Amorphous Eu0.8Au0.2 Alloy

Magnetocaloric Properties and Phenomenological Model in Amorphous Eu0.8Au0.2 Alloy

Using a computationally driven screening to enhance magnetocaloric effect of metal monoborides

In most cases, substitution studies that aim to optimize magnetic properties are performed at the magnetic atomic site. However, in the case of MnB, magnetic substitutions at the Mn site significantly decrease the once promising magnetocaloric and magnetic properties. This study employs computationally directed search to optimize the magnetocaloric properties of MnB where partial substitutions of boron atoms (Mn50B50− x Si x and Mn50B50− x Ge x where x = 3.125, 6.25, and 12.5) reveal new compounds with a greater magnetocaloric effect than pure MnB at the same Curie temperature. These new compounds were obtained by arc melting the pure elements and further characterized. The computationally driven screening process is based on density functional theory calculations that do not require large databases of known compounds. This work demonstrates that using simple computational screening procedures to search for new magnetocaloric materials with improved properties can be done quickly, cost-effectively, and while maintaining reliability.

Magnetocaloric Effect in the Laves Phase of GdNi2 in Strong Magnetic Fields

Experimental studies of the magnetic and magnetocaloric properties of the Laves phase of GdNi2 have been carried out in external static up to 3 T and pulsed up to 50 T magnetic fields. It has been found that in a magnetic field of 3 T the change in the magnetic entropy of the alloy reaches its maximum value ΔSm = −8 J/(kg K) in the vicinity of the Curie temperature TC = 73.6 K. The corresponding adiabatic temperature change in this case, calculated by an indirect method, is ΔTad ≈ 3 K. The maximum value of the adiabatic temperature change measured by the direct method in a pulsed magnetic field of 50 T at T0 = 77 K, was equal to ΔTad = 15 K, which agrees well with theoretical predictions.

RNi (R = Gd and Dy) Compound-Based Magnetocaloric Materials

High-performance materials for solid-state magnetic cooling in the temperature range of 1.5–100 K were developed. The magnetic and magnetocaloric properties of the new (R, R')Ni (R = Gd and R' = Dy) compounds and their hydrides were studied in the Curie temperature region. The main regularities in the behavior of the temperature dependences of the magnetocaloric effect for different compositions were established.

Role of Ca2+ doping on the structure, magnetic, and magnetocaloric properties of La0.75Gd0.05Sr0.2−xCaxMnO3 (x = 0, 0.05, 0.075, and 0.10) perovskite manganites

Role of Ca2+ doping on the structure, magnetic, and magnetocaloric properties of La0.75Gd0.05Sr0.2−xCaxMnO3 (x = 0, 0.05, 0.075, and 0.10) perovskite manganites

Large low-field reversible magnetocaloric effect in K3Gd(PO4)2 at sub-Kelvin temperature

We synthesized a potassium gadolinium phosphate K3Gd(PO4)2 with monoclinic structure (P21/m) by the high-temperature solid–state reaction method. Its lattice constants obtained by Rietveld refinements of XRD curve are a = 0.7411 nm, b = 0.5624 nm, and c = 0.9433 nm. Magnetic and magnetocaloric properties of K3Gd(PO4)2 were investigated in detail. The magnetic phase transition temperature of K3Gd(PO4)2 was determined by ultra-low temperature testing to be 0.58 K. K3Gd(PO4)2 exhibits large magnetic entropy changes (–ΔSM). The maximum –ΔSM are 20.2 and 29.4 J/(kg·K) in the magnetic field variation (ΔH) of 1 and 2 T, respectively, which are larger than that of the commercial Gd3Ga5O12 (GGG). The maximum adiabatic temperature change (ΔTad) reaches 5.91 K under a magnetic field change (ΔH) of 1 T. K3Gd(PO4)2 is a potential magnetic refrigeration material for obtaining sub-Kelvin temperatures.

Synthesis, Characterization, and Magnetocaloric Properties of Double Perovskite BaSrNiMoO6 for Magnetic Refrigeration Applications

Synthesis, Characterization, and Magnetocaloric Properties of Double Perovskite BaSrNiMoO6 for Magnetic Refrigeration Applications

Magnetic properties, critical behaviors and magnetocaloric effect in non-stoichiometric spinel type Co1+xCrxFe2-xO4

The magnetic properties, magnetocaloric effect, and critical analysis of magnetic behavior of Co1+xCrxFe2-xO4 (x = 0.125, 0.250, 0.375, and 0.500) with a non-stoichiometric ratio are studied in detail. All the synthesized samples exhibit single-domain behavior. The Cr3+ associated with excess Co2+ led to tuning the magnetic moment, exchange interaction, magnetocrystalline anisotropy constant, and microwave frequency. The second-order magnetic phase transition has been confirmed from the Arrot and Arrot-Noakes plots for all the samples. The Cr3+ associated with excess Co2+ also tuned the magnetocaloric (MCE) properties showing the maximum relative cooling power of 156 J kg-1, which is a higher value than that of previously reported Cr3+ substituted stoichiometric cobalt ferrite. The reliability of MCE and the nature of the magnetic phase transition of the investigated samples are confirmed by analyzing the critical exponent analysis, universal curve scaling, and scaling analysis of MCE.

Theoretical investigation of direct and inverse magnetocaloric effect in La2FeMn1-xCuxO6 and Sr2RuMn1-xFexO6 using a phenomenological model

This letter presents a theoretical work on magnetocaloric properties of two series of double perovskites compounds La2FeMn1-xCuxO6 and Sr2RuMn1-xFexO6 with four different concentrations (x = 0, 0.1, 0.2 and 0.3) synthesized by solid state method. The value of the magnetocaloric effect (MCE) of both the series has been predicted by applying a phenomenological model on temperature variation magnetization data of the compounds. Along with the maximum entropy change (−ΔSm)max, specific heat and relative cooling power (RCP) were also calculated using the model. Interestingly, the simulated MCE of Fe doped Sr2RuMnO6 (Sr2RuMn1-xFexO6) showed the coexistence of direct and inverse MCE.

Magnetocaloric effect and critical behaviour in zinc doped cobalt ferrite nanoparticles

In this report a detail investigation of magnetocaloric properties and critical behaviour of Zn0.7Co0.3Fe2O4 nanoparticles synthesized via chemical co-precipitation method has been carried out. The Rietveld analysis of the XRD patterns of ZnxCo1-xFe2O4 (x ​= ​0.5, 0.6, 0.7) nanoparticles confirm the crystal structure as Fd3¯m. The W–H plots confirm the presence of compressive micro strain inside the crystallites and a decreasing trend is observed with Zn doping. The magnetization measurements with temperature at 500 ​Oe applied field show that all the samples are superparamagnetic at room temperature. Coexistence of magnetic phases below room temperature is observed in Zn-0.6 and Zn-0.7 samples. The substitution of Zn2+ ions lead to decrease in blocking temperature (TB) as well as Curie temperature (TC). Analysis of magnetocaloric properties of the sample Zn-0.7 indicates a considerable amount of magnetic entropy change and relative cooling power. A significant inverse MCE is also expected to be observed due to anti-ferromagnetism at low temperature.

Anisotropic Metamagnetic Spin Reorientation and Rotational Magnetocaloric Effect of Single Crystal NdAlGe.

Magnetic anisotropy strongly influences the performance of the magnetocaloric effect. We investigated the magnetocaloric properties of the NdAlGe single crystal with I41md structure. The temperature-dependent magnetization revealed significant anisotropic properties; stable antiferromagnetic transition at TN = 6 K for H//a and meta-magnetic spin reorientation at low temperature (T ≤ 5 K) within an intermediate field (H = 2 T) for H//c. During the metamagnetic spin reorientation, the abrupt change of the magnetic entropy leads to a significant magnetocaloric effect with negative magnetic entropy change (∆SM) by -13.80 J kg-1 K-1 at TC = 5.5 K for H = 5 T along the H//c axis. In addition, the antiferromagnetic state for H//a shows the inverse magnetocaloric effect(I-MCE) by positive entropy change ∆SM = 2.64 J kg-1 K-1 at TN = 6 K for H = 5 T. This giant MCE accompanied by the metamagnetic transition resulted in a significantly large relative cooling power (158 J/kg at H = 5 T) for H//c. The giant MCE and I-MCE can be applied to the rotational magnetocaloric effect (R-MCE) depending on the crystal orientations. NdAlGe exhibits rotational entropy change ∆Sc-a = -12.85 J kg-1 K at Tpeak = 7.5 K, H = 5 T. With comparison to conventional MCE materials, NdAlGe is suggested as promising candidate of R-MCE, which is a novel type of magnetic refrigeration system.

Structural, magnetic and magnetocaloric properties of Laves phase (Gd,Sm)Co[formula omitted] compound

In the present work, the structural, magnetic, and magnetocaloric properties of the intermetallic Gd1−xSmxCo2 (x=0.5,0.6 and 0.7) compounds have been systematically studied. Samples were prepared by arc melting under high pure argon and homogenized at 800 K to minimize the impurity phases. X-ray diffraction (XRD) coupled with Rietveld analysis has shown that all samples crystallize in the cubic MgCu2-type structure (Space group Fd-3 m). Refinement results show that the unit cell parameter increases with increasing Sm content. The magnetic measurement reveals that the Sm content reduces the Curie temperature TC from 404 (for x=0) to 263 K (for x=0.7). The magnetic entropy change of the samples as function of temperature and applied magnetic field were calculated from the isothermal magnetization curves using Maxwell relation. The relative cooling power RCP and the temperature-averaged entropy change (TEC) have been reported. Furthermore, the magnetocaloric behavior is studied using the scaling laws and the phenomenological universal curve.

Achieving higher magnetic entropy change peak at lower temperature by minor Ti substitution for Zr in the Fe88Zr8B4 metallic glass

Fe-Zr-B-based amorphous alloys (AAs) show good magnetocaloric effect (MCE) around the ambient temperature, and their maximum magnetic entropy change ([Formula: see text] generally increases with their Curie temperature ([Formula: see text], which means the poor magnetocaloric properties near the cold end of the air conditioner. In this work, by adding 2% (at.%) Ti to replace the Zr element in a [Formula: see text] AA, we successfully fabricated the [Formula: see text] amorphous ribbon. The [Formula: see text] amorphous ribbon exhibits a slightly enhanced glass formability, improved [Formula: see text] and decreased [Formula: see text] when compared to the [Formula: see text] AA. The results are helpful for developing better MCE of the Fe-Zr-B-based metallic glasses working near the cold end of a domestic magnetic air conditioner.

Physicochemical insight into the metal atom effect on magnetocaloric behavior of paramagnetic metalloporphyrins

To reveal the effect of coordinated organic and inorganic σπ-ligands on the magnetocaloric properties of metal ions at room temperature, we have synthesized paramagnetic (5,10,15,20-tetraphenylporphinato)cobalt(II), (chloro)(2,3,7,8,12,13,17,18-octaethylporphinato))manganese(III), their coordination complexes with 1-methyl-2-(pyridin-4′-yl)-3,4-fullero[60]pyrrolidine (1:3 and 1:2, respectively), and (ethoxy)(oxo)(5,10,15,20-tetraphenylporphinato)molybdenum(V) and have fully characterized their chemical structure by UV–vis, IR, 1H NMR, MALDI TOF spectral methods. Using the direct microcalorimetric method and DSC we have obtained, respectively, magnetocaloric effect, heat, change of enthalpy/entropy during the magnetization over the temperature range of 285 – 338 K in magnetic fields from zero to 1 T and the specific heat capacities in the temperature range from 270 to 400 К in zero fields for paramagnets synthesized. Involving the results of DFT calculations, we have shown that the electron structure of a central metal atom is the determining factor in the positive magnetocaloric effect in the complexes studied. The decrease in the MCE value is observed in the case of the intramolecular antiferromagnetic interactions in external magnetic fields (manganese(III) complexes) and additional axial bonding of the bulk fullerene-containing base.

Magnetocaloric effect and critical behavior of the Mn5Ge3−xZnx alloys

In this paper, the magnetocaloric properties, phase transition and critical behavior of Mn5Ge3−xZnx (x = 0.1, 0.2 and 0.3) compounds fabricated by the arc-melting method were investigated. The Curie temperature and the magnetic entropy change of Mn5Ge3−xZnx alloys decrease with doping of Zn. The normalized curves of universal behavior further demonstrate the feature of second-order transition in the Mn5Ge3−xZnx alloys, consistent with the results of the Landau coefficient and Banerjee criterion analysis. To explore the properties near the phase transition, we investigated the critical behavior of this series using modified Arrott plots, Kouvel-Fisher method and critical isotherm curves. The critical exponents β, γ and δ were calculated in accordance with the Widom scaling relation, and magnetic state equation, demonstrating the experimentally obtained exponents are accurate. The spontaneous magnetization derived from the isothermal entropy change calculated from Maxwell equation, is in agreement with the spontaneous magnetization calculated from the curves, proving the validity of calculating the spontaneous magnetization from the curves.

Magnetic and Transport Anomalies and Large Magnetocaloric Effect in Cubic R4PtAl (R = Ho and Er)

We report the electronic properties of R4PtAl (R = Ho, and Er), which contains three sites for R, by the measurements of magnetization (ac and dc), heat-capacity, transport, and magnetoresistance (MR). Dc magnetization data reveal antiferromagnetic order below 19 K and 12 K in Ho and Er compounds, respectively. Additional features observed at lower temperatures (12 K for Ho4PtAl and 5 K for Er4PtAl) are akin to the cluster spin-glass phase. Resistivity data exhibit a weak minimum at a temperature marginally higher than their respective Néel temperature (TN), which is unusual for such rare-earths with well-localized 4f states. Isothermal magnetization and magnetoresistance data well below TN exhibit signatures of a subtle field-induced magnetic transition for a small magnetic field (<10 kOe). Notably, the isothermal entropy change at TN has the largest peak value within this rare-earth family; for a field change from zero to 50 kOe, the entropy change is ~14.5 J/kg K (Ho4PtAl) and ~21.5 J/kg K (Er4PtAl) suggesting a role of anisotropy of 4f orbital in determining this large value. The results provide some clues for the advancement of the field of magnetocaloric effect. The magnetocaloric property of Er4PtAl is nonhysteretic, meeting a challenge to find materials with reversible magnetocaloric effect.