Isothermal Magnetic Entropy Change Research Articles

A Metropolis study of the isothermal magnetic entropy change in spin-1/2 Ising model

Magnetic refrigeration is a sound, environment friendly alternative to conventional refrigeration techniques. Isothermal magnetic entropy change, for a magnetic substance, is an important quantity to be investigated for determining its potential for Magnetic refrigeration. We have performed extensive Monte Carlo simulations with Metropolis single spin-flip algorithm on spin-1/2 Ising model on a square Bravais lattice to study the change in the magnetic entropy, ΔSm for five values of the external magnetic field, where spin-field energies are either equal to or greater than the in-plane ferromagnetic coupling strength. Binder’s fourth order magnetization cumulant is employed for the determination of the critical point. We observe the peak of ΔSm to coincide with the critical point or the Curie point. With a gradual increase in the magnitude of the field, the peak value of ΔSm increases. The behaviour of isothermal magnetic entropy change is systematic over the entire range of temperature, under observation. This implies such materials, which obey nearest neighbour Ising interactions, are good candidates for Magnetocaloric applications.

Alternative method of helium liquification achieved by analyzing the correlation of critical exponent β and the magnetocaloric parameters

This report deals with the finding of unusually large adiabatic temperature change (ΔTad) parameter related to the magnetocaloric properties of the intermetallic compound ErIr3. The maximum isothermal magnetic entropy change (|ΔSM|) and maximum adiabatic temperature change (ΔTad) are 12 J.kg-1K-1 and 14.9 K, respectively, at a field change of 0 → 70 kOe near 5.5 K. Additionally, the system does not exhibit any thermal and field hysterias loss. The high values of the said parameters (in the vicinity of helium liquification temperature) indicate that ErIr3 can be used as a greener alternative to compressor-based He liquification technology. During analysing the origin of such high values of magnetocaloric parameters, we found a mathematical correlation between the magnetocaloric parameters and the critical exponents of the phase transition. The proposed correlation may narrow the focus of the researchers engaged in searching a material with a potential to show a good magnetocaloric merit.

Magnetocaloric effect in spin-glass-like GdCu4Mn compound

Materials based on Gd with magnetic frustration may have high magnetocaloric application potential. GdCu4Mn crystallizes in hexagonal CaCu5-type structure with space group P6/mmm (no. 191, Pearson symbol: hP6). Lattice parameters for the polycrystalline sample are equal to a = 5.114(3) Å and c = 4.151(4)Å. Due to structural disorder, namely random distribution of Cu and Mn atoms on 2c and 3g positions, a spin-glass-like behavior is observed in this material at low temperatures. In addition to the standard measurements of DC magnetization and AC magnetic susceptibility, the spin-glass state was confirmed by the memory effect and relaxation behavior. The absence of clear anomalies in the temperature dependencies of specific heat and electrical resistance suggests the lack of long-range magnetic order. For a change in magnetic field from 0 to 5 T, maximum values of the isothermal magnetic entropy change (ΔSm), temperature averaged entropy change (TEC(5)), relative cooling power (RCP), and adiabatic temperature change (ΔTad) at ∼50 K are equal to −1.3(1) J/(kg K), 1.2(1) J/(kg K), 125(1) J/kg, and 0.5(1) K, respectively.

Defect Engineering: Electron-Exchange Integral Manipulation to Generate a Large Magnetocaloric Effect in Ni41Mn43Co6Sn10 Alloys.

A promising magnetocaloric effect has been obtained in Ni-(Co)-Mn-X (X = Sn, In, Sb)-based Heusler alloys, but the low isothermal magnetic entropy change ΔSM restricts the further promotion of such materials. Defect engineering is a useful method to modulate magnetic performance and shows great potential in improving the magnetocaloric effect. In this work, dense Ni vacancies are introduced in Ni41Mn43Co6Sn10 alloys by employing high-energy electron irradiation to adjust the magnetic properties. These vacancies bring about intense lattice distortion to change the distance between adjacent magnetic atoms, leading to a significant enhancement of the average magnetic moment. As a result, the saturation magnetization of ferromagnetic austenite is accordingly improved to generate a high isothermal magnetic entropy change ΔSM of 20.0 J/(kg K) at a very low magnetic field of ∼2 T.

Magnetocaloric effect in the Ru-doped MnNiGe system

We investigated the magnetic properties of the Ru-doped MnNiGe system. The temperature dependence of magnetization, M(T), of Mn0.8Ru0.2NiGe shows a step-like anomaly at around Tt= 173 K (heating process) with a hysteresis of 9 K between the cooling and heating processes. The Mn0.8Ru0.2NiGe compound exhibits a first-order martensite structural change coupled with the ferromagnetic (FM) transition, as seen in the MnNiGe–CoNiGe system. Tt increases linearly with increasing the magnetic field B. The T dependence of the isothermal magnetic entropy change, ΔSM(T), peaks at around Tt, with values of −4.7, −15.1, −24.4, and −32.1 J kg−1 K−1 for ΔB=1, 3, 5, and 7 T, respectively. The three refrigerant capacities estimated from the ΔSM(T) curve show a linear dependence on ΔB. The calculated density of states, DOS, of Mn0.75Ru0.25NiGe in the paramagnetic-hexagonal austenite phase shows a peak at the Fermi energy, EF, and the Mn 3d orbitals contribute significantly to this peak. On the other hand, the DOS at the EF for the compound in the ferromagnetic-orthorhombic martensite phase is smaller than that of the compound in the austenite phase. As the total energy of the electron system, Ee, decreases with the structural change, the phase transition of this system at Tt is driven by the band-Jahn–Teller effect, where the Mn 3d orbitals play the main role.

Insight into magnetic properties and magnetocaloric effect in a Janus particle

Based on the Monte Carlo simulation, the magnetic properties and magnetocaloric effect in a ferromagnetic Janus particle with mixed-spin (1/2, 1, 3/2) were systematically explored. The effects of the exchange couplings and the external magnetic field on the magnetization, magnetic susceptibility, internal energy and magnetic specific heat were invested in detail. Besides, we presented the isothermal magnetic entropy change and adiabatic temperature change as a function of temperature for various exchange couplings and the external magnetic field. It was found that the maximum values of the isothermal magnetic entropy change and adiabatic temperature change increase with decreasing the exchange couplings or increasing the external magnetic field. Finally, the impacts of the exchange couplings and the external magnetic field on the relative cooling power were also discussed.

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.

The magnetic and the magnetocaloric properties of the binary alloy ferromagnetic and ferrimagnetic single nanoparticle

In this work, the Monte Carlo simulation has been used to study the magnetic and the magnetocaloric properties of a binary alloy ferromagnetic and ferrimagnetic single nanoparticle with radius R of the type ApB1−p. The system consists of two different species of magnetic components, namely, A and B with spins SA = 1∕2 and SB = 3∕2, respectively. The effect of the concentration p of the A atoms and the exchange interactions on the magnetization, hysteresis loops, magnetic entropy change of the system and relative cooling power (RCP) are discussed. Also, thermal variation of isothermal magnetic entropy change of the system for various magnetic fields values have been examined. It is found that the system exhibits a second order magnetic phase transition near critical temperature, the maximum value of the isothermal magnetic entropy change has been shown to take larger values as the applied magnetic field increases. It is also seen that in the ferrimagnetic state, the compensation temperature appears and the inverse magnetocaloric effect exists for some concentrations.

Magnetic properties and magnetocaloric effect of [formula omitted

We report the structural, and magnetic properties as well as magnetocaloric effect of a polycrystalline compound of Tb2Rh3Ge. This compound crystallizes with Mg2Ni3Si-type of rhombohedral Laves phases (space group R3‾m, hR18). The magnetic properties and magnetocaloric effect of Tb2Rh3Ge are explored through dc-magnetization measurements. Temperature dependence of magnetization revealed that the compound exhibits ferromagnetic behavior with TC=56 K. The field dependence of magnetization indicates that Tb2Rh3Ge is a soft ferromagnet. The obtained isothermal magnetic entropy changes (ΔSm) and refrigeration capacity (relative cooling power) for a change of magnetic field 0–9 T are 12.74 J kg−1K−1 and 497(680) J/kg respectively. The Arrott plots and universal curve of normalized ΔSm indicate that this compound undergoes a second order ferromagnetic phase transition.

Schottky-like anomaly in the heat capacity and magnetocaloric effect of charge-ordered single-crystalline (Sm, Ca, Sr)MnO[formula omitted] compound

We present a comprehensive experimental study on the magnetic and magnetocaloric properties of a charge-ordered single-crystalline Sm0.5Ca0.25Sr0.25MnO3 compound. The studies on x-ray photoelectron spectroscopy (XPS) reveals the presence of an equal distribution of Mn3+ and Mn4+ ions in the studied system. The Oxygen, O1s-core level spectra have been simulated with three binding energies curves, which correspond to the O2− ions, O1− ions, and chemically adsorbed oxygens, Ochem. The XPS analysis of the O1s-core-level spectra and magnetic characterizations indicate the proper stoichiometry of the present sample. Considering the change of volume phase fraction in the isofield magnetization measurements during the first-order magnetic phase transition from paramagnetic state to ferromagnetic state, the isothermal magnetic entropy change (ΔS) has been estimated based on the modified Clausius–Clapeyron equation. An inverse magnetocaloric effect has also been noticed in the -ΔS vs. T plot calculated by Maxwell’s thermodynamic relation, suggesting the dominant antiferromagnetic ground state supported by a charge-ordered phase of the studied system. The high-temperature zero-field heat capacity (CP) data can be well-interpreted quantitatively using the Debye model of heat capacity. With the extracted magnetic heat capacity (Cmag) data, the temperature variation of the magnetic entropy (S(0)), as well as the adiabatic temperature change (ΔTad), have been estimated. In addition to that, the low-temperature CP data displays a Schottky-like anomaly in the temperature region between 2 K and 20 K. The experimental data points are successfully fitted by considering the various contributing factors of the low-temperature heat capacity such as the lattice-phonon vibration (Clat), antiferromagnetic spin-wave (Cmag), and the two-level Schottky function (Csch) due to the energy splitting of the Sm3+ cations.

Giant magnetoresistance, magnetostrain and magnetocaloric effects in a Cu-doped-textured Ni45Co5Mn36In13.2Cu0.8 polycrystalline alloy

Ni–Mn–Z (Z = In, Sn, and, Sb) metamagnetic shape memory alloys exhibit plenty of state-of-the-art magnetoresponsive effects owing to the magnetic-field-induced reversible martensitic transformation. For this compound, achieving high magnetization difference, large transformation entropy change, strong field dependence of transformation temperature, and low thermal hysteresis is essential to obtain significant magnetoresponsive functional properties. In this work, starting from the Ni45Co5Mn36In14 alloy, the substitution of Cu for In is introduced to optimize these properties simultaneously, giving rise to the substantial improvement in the magnetoresponsive effects. By composition design, a second-phase freed Ni45Co5Mn36In13.2Cu0.8 alloy with the phase temperature just below room temperature was selected. Using the directionally solidified technique, a strong<001>-textured sample is prepared to enhance magnetoresponsive behaviors. Measurements show that the reversible magnetoresistance and magnetic-field-induced strain of the prepared sample reach −79% and 0.24%, respectively. Moreover, a maximum isothermal magnetic entropy change of 16.0 J kg−1 K−1 and the maximum adiabatic temperature change of −3.4 K are measured under a field change of 1.5 T, showing excellent low-field magnetocaloric response. The work is expected to supply a prototype alloy of NiMn-based alloy to promote the development of magnetic shape memory alloy.

Competing magnetic interactions and emergent phase diagrams in double perovskite Y2NixCo1−xMnO6

We present a comparative study of double perovskites Y2NixCo1−xMnO6 for x = 1, 0.5, and 0. The polycrystalline samples of Y2NixCo1−xMnO6 with space group P21/n were synthesized via sol-gel technique. X-ray photoelectron spectroscopy (XPS) confirms the presence of majority Ni2+/Mn4+ in Y2NiMnO6 (YNMO) and a mixed valence state Ni2+/3+/Co2+/3+/Mn4+/3+ in co-doped Y2Ni0.5Co0.5MnO6 (YNCMO). The temperature dependent magnetization results suggest homogeneous substitution of Ni ions with Co ions with minimal contribution of 3 + cationic magnetic interactions in YNCMO. The superexchange ferromagnetic (FM) interaction has a major contribution to the magnetism of YNMO. The strength of antiferromagnetic (AFM) coupling resulting from the antiphase boundaries in Y2NixCo1−xMnO6 increases with the increase in the Co concentration. The AC susceptibility (AC-χ) study further validates the presence of higher density of antiphase boundaries, which is reflected by the dynamics of domain walls in YNCMO. The isothermal magnetic entropy change (ΔSM) as functions of temperature and magnetic field is exploited to assess the stabilization of different magnetic phases. The findings of ΔSM (T,µ0H) lead to the proposed new magnetic phase diagrams for Y2NixCo1−xMnO6 for x = 1 and 0.5, in comparison with the previously established phase diagram of Y2CoMnO6.

A theoretical study of the electronic, magnetic and magnetocaloric properties of the TbMnO3 multiferroic

During the last years, a great attention has been devoted to the discovery of materials that can be used for magnetocaloric applications such as intermetallics and oxides. In this context, the multiferroic TbMnO3 appears as promising magnetocaloric material that can be used for magnetic refrigeration at low temperatures. This multiferroic presents complex electronic and magnetic structures. In this paper, different approaches are used with the aim to get more insight on the driving mechanisms behind the electronic, magnetic and magnetocaloric properties of the TbMnO3 manganite. In this way, a physical model is proposed to describe the magnetic interaction inside this material. Using the density functional theory, the electronic structure, density of states, have been evaluated. The magnetic phase stability and exchange couplings in TbMnO3 have been also investigated in order to understand and to clarify the obscured different magnetic interaction in this compound. Magnetocaloric and magnetic properties have been studied using Monte Carlo Simulation (MCS) within the Ising model. The transition temperatures, the isothermal magnetic entropy change, the adiabatic temperature change and the relative cooling power (RCP) were calculated. The highest obtained isothermal entropy change is found to be −17.8 J/Kg.K for H = 8 T. The RCP maximum value is found to be 507.06 J/Kg and the adiabatic temperature change reaches a maximum value close to 22.5 K in the field change of H = 8 T.

Gd induced modifications in the magnetocaloric properties of dysprosium manganites

We report structural, electronic, magnetic, and magnetocaloric studies of polycrystalline DyMnO3 and its A-site Gd substituents, Dy1−xGdxMnO3, where 0 ≤ x ≤ 1. Detailed comparison of various magnetocaloric parameters shows that Dy0.5Gd0.5MnO3 has the best values with a large isothermal magnetic entropy change, −∆Smmax~ 15.35 J/kg K, adiabatic temperature change, ∆Tadmax~ 6.15 K and relative cooling power, RCP ~ 307 J/kg, suggesting that rare earth mixing plays a vital role in enhancing the magnetocaloric properties. In addition, absence of magnetic and thermal hysteresis also makes it one of the best candidates for magnetic refrigeration among all known potential candidates for cryogenic temperature applications.

Experimental and theoretical analysis of magnetocaloric behavior ofDy1−xErxNi2intermetallics(x=0.25,0.5,0.75)and their composites for low-temperature refrigerators performing an Ericsson cycle

In the present work, the structural, magnetic, and thermodynamic properties of ${\mathrm{Dy}}_{1\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Ni}}_{2}$ $(x=0.25,\phantom{\rule{0.16em}{0ex}}0.5,\phantom{\rule{0.16em}{0ex}}0.75)$ Laves-phase intermetallics, being continuous solid solutions in the ${\mathrm{DyNi}}_{2}\text{\ensuremath{-}}{\mathrm{ErNi}}_{2}$ system, synthesized by arc melting, are experimentally studied and analyzed in accordance with mutual substitution within the rare-earth sublattice. The existence of Laves-phase superstructure (space group $F\overline{4}3m$) in the substituted ${\mathrm{Dy}}_{1\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Ni}}_{2}$ compounds was found by x-ray diffraction analysis. Low-temperature magnetic studies showed the ferromagnetic behavior of the compounds; their Curie temperatures correlate with the erbium content; namely, they decrease from 16.8 K for ${\mathrm{Dy}}_{0.75}{\mathrm{Er}}_{0.25}{\mathrm{Ni}}_{2}$ to 10.0 K for ${\mathrm{Dy}}_{0.25}{\mathrm{Er}}_{0.75}{\mathrm{Ni}}_{2}$. Heat capacity measurements performed in magnetic fields of 1 and 2 T allowed us to estimate the isothermal magnetic entropy and adiabatic temperature changes for ${\mathrm{Dy}}_{1\ensuremath{-}x}{\mathrm{Er}}_{x}{\mathrm{Ni}}_{2}$. Independently, a theoretical analysis was performed for a polycrystalline sample in the frame of a model Hamiltonian taking into account the Zeeman exchange interaction and crystal electric field anisotropy and was expanded to experimental results. Composites with optimum proportions of the individual ${\mathrm{Dy}}_{0.75}{\mathrm{Er}}_{0.25}{\mathrm{Ni}}_{2}$, ${\mathrm{Dy}}_{0.5}{\mathrm{Er}}_{0.5}{\mathrm{Ni}}_{2}$, and ${\mathrm{Dy}}_{0.25}{\mathrm{Er}}_{0.75}{\mathrm{Ni}}_{2}$ components were theoretically determined. The results indicate that the proposed composites are good candidates to be used as the refrigerant material in a magnetic refrigerator performing an Ericsson cycle at low temperatures. The relative cooling power RCP, refrigerant capacity RC, temperature averaged entropy change TEC, and the changes of emitted or absorbed quantity of heat \ensuremath{\Delta}Q were calculated for investigated samples. Direct measurements of the adiabatic temperature change in the vicinity of the magnetic transition temperature were carried out in magnetic fields up to 14 T. The regularities found are discussed in terms of Landau's theory of second-order magnetic phase transitions.

Double magnetic phase transitions and magnetotransport anomalies in a new compound Gd2AgSi3

Dc and ac–magnetic susceptibility (χ), specific heat (CP), electrical resistivity (ρ) and magnetoresistance measurements performed on the new polycrystalline compound Gd2AgSi3, crystallizing in the α–ThSi2 tetragonal structure, are reported. Two magnetic phase transitions were observed in dc and ac susceptibility, specific heat and resistivity measurements at temperatures TN1=11 K and TN2=20 K, despite a single site occupied by Gd atom, which is an indication of the complex magnetic behavior. Gd2AgSi3 turns out be one of the rare Gd compound in which a minimum is observed in the temperature dependence of resistivity in the paramagnetic state and also negative magnetoresistance over a wide temperature range (above TN2), mimicking the behavior of exotic Gd2PdSi3, in this ternary family. The isothermal magnetic entropy change, adiabatic temperature change, and refrigerant capacity reach a value of 9.5 J/kg-K, 7.5 K and 302 J/kg, respectively for the change of magnetic field 0-9 T.

Effect of configuration entropy on magnetocaloric effect of rare earth high-entropy alloy

In this work, the relationship between configuration entropy and isothermal magnetic entropy change (ΔSM) of rare earth high-entropy alloys (HEAs) was studied. The results show that the matrix of rare earth HEAs GdTbHoEr exhibits the largest refrigerant capacity up to now (about 924.48 J kg−1 at a 5 T magnetic field). With the addition of non-magnetic elements La and Y, the configuration entropy increases, but the values of ΔSM and the refrigerant capacity decrease from 8.64 to 5.85 J kg−1K−1, 924.48–245.70 J kg−1, respectively. Further, the magnetic element Pr was added to GdTbHoEr, which also increased the configuration entropy and provided magnetism, but the ΔSM of the HEAs GdTbHoErPr (6.92 J kg−1K−1) still decreased. The analysis shows that the magnetocaloric effect of HEAs just depend on the intrinsic magnetic characteristics of rare earth elements with 4 f electrons and are independent of configuration entropy.

Magnetocaloric effect of high-entropy rare-earth alloy GdTbHoErY

Magnetocaloric effect of a single-phase high-entropy rare-earth alloy GdTbHoErY with the hexagonal close-packed (HCP) structure was studied. As the external field increases, the peak isothermal magnetic entropy change (ΔSM) of the alloy is accompanied by a hump, which widens the ΔSM peak and thus increases the refrigerant capacity (RC) value. Under a magnetic field of 5 T, the RC and the ΔSM reach 453 J kg−1 and 5.4 J kg−1 K−1, respectively. The high RC for the high-entropy alloy is mainly attributed to the wider working temperature range. Moreover, the random distribution of atoms in the lattice leads to a complex magnetic structure and exchange coupling in this alloy. This feature of high-entropy alloy GdTbHoErY makes a gradual change in the magnetic sequence, which leads to an enhanced magnetocaloric effect.

The impact of Pr and Nd substitution on structure, hysteresis and magnetocaloric properties of La1−x (Pr,Nd) x Fe11.6Si1.4

In this study, a combination of induction melting and suction casting methods were used to produce a series of high-purity samples of system with R = Pr and Nd for x = 0.1, 0.2, 0.3 and 0.4. The Curie temperature () is lowered for all the substituted compositions compared to , while the hysteresis area shows a small increase for higher amounts of substitution element. The estimated isothermal magnetic entropy change () of all samples are in the same range with a maximum of 25 . The , under the cyclic conditions for all compositions decreases compared to the first application of the magnetic field due to the thermal hysteresis. Applying the Bean–Rodbell model to the isothermal magnetization data, the temperature dependence of the critical field was found. Excluding the phase transition region, the model accurately describes the temperature and field dependence of magnetization above and below the magnetic transition, highlighting the magnetic moment change of the system due to the structural transformation.

Direct and Inverse Magnetocaloric Effects in FeRh Alloy: A Theoretical Study

There are two types of magnetocaloric effects that are the so-called direct and inverse effects originating from ferromagnetic-paramagnetic (FM-PM) and antiferromagnetic--ferromagnetic (AFM-FM) phase transitions, respectively. Here, the magnetocaloric effects of FeRh alloy, which exhibit both the direct and inverse effects, have been studied by combining first-principles calculations and Monte-Carlo simulations. The magnetic exchange coupling constants in the AFM and FM phases are evaluated by first-principles calculations based on the Liechtenstein formula. The Monte-Carlo calculations considering the two-phase mixtures of AFM and FM well reproduce the experimental magnetization curves at zero external magnetic field. It is also shown that the isothermal magnetic entropy changes near the AFM-FM transition temperature under magnetic fields are successfully reproduced based on the Maxwell relation. The entropy changes in a wide range of the magnetic fields near the AFM-FM and FM-PM transition temperatures are investigated and the direct and inverse magnetocaloric effects of FeRh are discussed. The giant relative cooling power of FeRh alloy is achieved due to the large saturation magnetizations and the first-order AFM-FM phase transition.