Inverse Magnetocaloric Effect Research Articles

Magnetic, magnetodielectric, and magnetocaloric properties of new polar oxides RCrWO6 (R = Sm, Eu, Gd, and Tb)

We report new magnetic oxides RCrWO6 (R = Sm, Eu, Gd, and Tb) crystallizing in the polar orthorhombic structure (Space Group: Pna21), where edge-shared dimers of CrO6 and WO6 octahedra are connected by sharing corners and establish a three-dimensional framework. All these compounds exhibit antiferromagnetic ordering of Cr3+ spins at TN ∼ 28–32 K, except SmCrWO6, which shows weak ferromagnetism below TN = 32 K. Isothermal magnetization curves of RCrWO6 (R = Gd and Tb) at low temperatures show field-induced metamagnetic transition. Further, a dielectric anomaly at TN in all these compounds evidences the magnetodielectric effect. In addition, GdCrWO6 demonstrates magnetocaloric effect (MCE) with a maximum magnetic entropy change of 9.22 J kg−1K−1 at 70 kOe with relative cooling power (RCP) ∼ 101 J kg-1. On the other hand, TbCrWO6 exhibits both conventional and inverse magnetocaloric effects with significant entropy change and RCP.

Magnetothermal Properties and Magnetocaloric Effect in R3Co11B4

We present a study on the magnetic properties and magnetocaloric effect (MCE) in R3Co11B4, where R = Pr, Nd, Tb, Dy, and Ho. The two-sublattice model is used for calculating magnetization, magnetic heat capacity, isothermal entropy change ∆Sm, and adiabatic temperature change ∆Tad, for different magnetic field changes ∆H = 1.5, 3, and 5 T and at temperatures up to 600 K. Direct and inverse MCE are shown to take place in the ferrimagnetic compounds with R = Tb, Dy, and Ho. The maximum isothermal magnetic entropy change and maximum adiabatic temperature change have been calculated for ferromagnetic Nd3Co11B4 compound to be 1.85 J/K mol and 6.5 K at Tc = 432 K, for a field change ∆H = 5 T. The relative cooling power (RCP) is in the 44–161 J/mol range for the same field change. Also, the type of phase transition is investigated in the light of Arrott plots, universal curves, and the features of the temperature and field dependences of the magnetization, heat capacity, entropy, and the magnetocaloric properties. Those features confirm that the transition at the Curie temperature of these compounds is of the second order.

The Inverse and Conventional Magnetocaloric Effects in Ni0.4Cu0.2Zn0.4Fe2-xDyxO4 Nanoferrites Over an Extraordinary Temperature Range

The magnetocaloric effect (MCE) of Ni0.4Cu0.2Zn0.4Fe2-xDyxO4 (x = 0.02, 0.03, and 0.04) nanoferrites is simulated using a phenomenological model. The analysis indicates that the MCE of Ni0.4Cu0.2Zn0.4Fe2-xDyxO4 nanoferrites is strongly influenced by Dy content in both conventional and inverse MCE. For conventional MCE, the full-width at half-maximum (delta {text{T}}_{{{text{FWHM}}}}) has significant values, ranging between 200 K and 258 K for Ni0.4Cu0.2Zn0.4Fe2-xDyxO4 nanoferrites. However, for inverse MCE, delta {text{T}}_{{{text{FWHM}}}} ranges between 25 and 55 K. The MCE of the Ni0.4Cu0.2Zn0.4Fe2-xDyxO4 system covers an extensive temperature range and is a particularly interesting prospect for nitrogen and hydrogen liquefaction.

Large magnetocaloric effect in antiferromagnetic ternary carbide Dy2Cr2C3 around liquid hydrogen temperature

Field-induced magnetic transitions with large magnetization difference and mitigated thermal loss are highly desirable for the development of magnetocaloric materials used for magnetic refrigeration. Here, we report the magnetocaloric effect (MCE) in antiferromagnetic carbide Dy2Cr2C3. Both the inverse MCE (with positive magnetic entropy change ΔSM) and conventional MCE (with negative ΔSM) have been observed, which are attributed to a field-induced first-order metamagnetic transition from antiferromagnetic to ferromagnetic state and a second-order ferromagnetic to paramagnetic transition, respectively. A maximum -ΔSM of 13.5 J/kg K at 27 K for a field change of 5 T, and correspondingly a refrigerant cooling power of 315 J/kg in a wide working temperature span of 31 K have been achieved. Such a remarkable magnetocaloric response, together with the minor magnetic hysteresis of less than 0.02 T, indicate that Dy2Cr2C3 carbide could be a promising candidate refrigerant for magnetic refrigeration working at temperatures near the liquid H2.

Conventional and inverse magnetocaloric and electrocaloric effects of a mixed spin-(1/2, 1) Heisenberg dimer

Conventional and inverse magnetocaloric and electrocaloric effects of a mixed spin-(1/2, 1) Heisenberg dimer

Cd-doping effects in Ni–Mn–Sn: experiment and ab-initio study

Martensitic transformation (MT), magnetic properties, and magnetocaloric effect (MCE) in Heusler-type Ni47Mn40Sn13−x Cd x (x= 0, 0.75, 1, 1.25 at. %) metamagnetic shape memory alloys (MetaMSMAs) are investigated, both experimentally and theoretically, as a function of doping with Cd. Ab-initio computations reveal that the ferromagnetic (FM) configuration is energetically more favorable in the cubic phase than the antiferromagnetic (AFM) state in undoped and doped alloys as well. Moreover, it is revealed that the alloys in the ground state exhibit a tetragonal structure confirming the existence of MT, in agreement with the experiments. It was indicated, both in theory and practice, that a reduction of the unit cell volume and an increase of the MT temperature as a function of the Cd doping. Indirect estimations of MCE in the vicinity of MT were carried out by using thermomagnetization curves measured under different magnetic fields up to 5 T. The results demonstrated that the doped alloys exhibit enhanced values of the inverse MCE comparable with those of Ni-Mn-based MetaMSMAs. Maximum magnetic entropy change in a field change of 2 T increases from 3.0 for the undoped alloy to 3.4 and 5.0 for the alloys doped with 0.75 and 1 at.% of Cd, respectively. The inverse and conventional MCE were explored by direct measurements of the adiabatic temperature change under the magnetic field change of 1.96 T. The Cd doping increased the maximum of inverse MCE by nearly 78% from 0.9 K to 1.6 K for the undoped and doped alloys, respectively. The results depicted that Cd doping can effectively tailor the structural, magnetic, and MCE properties of the Ni–Mn–Sn MetaMSMAs.

Magnetic glassiness and crystal field effects on thermal and electrical properties of Er5Pd2-type compounds

Magnetic properties, thermal expansion, heat capacity, and electrical resistivity of the cluster-glass compound Er4.8Pd2 and its paramagnetic isostructural counterpart Lu4.8Pd2 have been studied in the temperature range 2–300 K and in applied magnetic fields up to 140 kOe. Short-range antiferromagnetic (AFM) correlations of localized magnetic moments of Er3+ ions were found to develop in Er4.8Pd2 on cooling below T* ≈ 40 K. A cluster-glass magnetic state was observed below freezing temperature Tf ≈ 13.3 K, while Lu4.8Pd2 showed paramagnetic behavior. The crystal electric field (CEF) was found to substantially affect both the heat capacity and the thermal expansion of Er4.8Pd2. The CEF splitting of the Er3+ ion multiplet 4I15/2 was estimated to be as high as 280 K with a doublet ground state. Both the Schottky-type anomaly and short-range antiferromagnetic order contributions were found to give rise to a large volumetric heat capacity of Er4.8Pd2 at low temperatures. High direct magnetocaloric effect with −ΔSM(T)60kOe = 18.8 J mole−1 K−1 was confirmed to exist in Er4.8Pd2 while no inverse magnetocaloric effect was observed at low temperatures. Electrical resistivity of Er4.8Pd2 revealed a non-metallic behavior at low temperatures which was ascribed to an inhomogeneous electronic state due to the formation of clusters with the AFM short-range correlations.

Magnetothermal properties and magnetocaloric effect in transition Metal-Rich Gd-Co and Gd-Fe amorphous alloys

We present a theoretical study, based on the mean-field theory, on magnetocaloric effect in both amorphous GdxCo1-x (0.16 ≤ x ≤ 0.25) and GdxFe1-x(x = 0.263 and 0.306) alloys in a temperature range up to Curie temperature and in magnetic fields up to 70 kOe.Our calculations show a fair agreement with available experimental data which confirm ferrimagnetic order in these systems.Both direct and inverse magnetocaloric effects are present. For Gd0.16Co0.84, maxima of△Smare 1.32 and 1.62 J/kg K for magnetic field changes of 40 and 70 kOe respectively. However, the peak values of ΔSmdecrease as x increases. Peak values of ΔSm are 0.64 and 0.82 J/K.kg for Gd0.263Fe0.737and Gd0.306Fe0.694respectively. The Belov-Arrott plots, the universal curve, and temperature dependence of ΔSm for Gd-Co alloys, showed that the alloys exhibit a second order phase transition at their Curie temperatures. The same conclusion is reached for Gd-Fe alloys.

Large inverse and normal magnetocaloric effects in HoBi compound with nonhysteretic first-order phase transition

HoBi single crystal and polycrystalline compounds with NaCl-type structure are successfully obtained, and their magnetic and magnetocaloric properties are studied in detail. With temperature increasing, HoBi compound undergoes two magnetic transitions at 3.7 K and 6 K, respectively. The transition temperature at 6 K is recognized as an antiferromagnetic-to-paramagnetic (AFM–PM) transition, which belongs to the first-order magnetic phase transition (FOMT). It is interesting that the HoBi compound with FOMT exhibits good thermal and magnetic reversibility. Furthermore, a large inverse and normal magnetocaloric effect (MCE) is found in HoBi single crystal in the H||[100] direction, and the positive ΔS M peak reaches 13.1 J/kg⋅K under a low field change of 2 T and the negative ΔS M peak arrives at –18 J/kg⋅K under a field change of 5 T. These excellent properties are expected to be applied to some magnetic refrigerators with special designs and functions.

Theoretical investigation of crystalline electric field influence on the magnetocaloric effect in the cubic praseodymium system PrNi2

We report a theoretical investigation of the magnetocaloric effect in paramagnetic intermetallic $\mathrm{Pr}{\mathrm{Ni}}_{2}$. We choose this particular compound because it presents high cubic symmetry, and two sets of crystalline electrical field parameters were reported, allowing a systematic study. In one of these sets, the magnetic entropy increases upon applied magnetic field in the low temperature region $(T<10\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ for $H=5\phantom{\rule{0.16em}{0ex}}\mathrm{T}$. This anomaly was investigated through a model Hamiltonian which includes the magnetic, exchange, and crystalline electric field interactions. The simulated curves of the temperature dependence of isothermal entropy variation and adiabatic temperature change present the inverse magnetocaloric effect, which is not expected for a paramagnetic system.

Sn-doping induced modification of the magnetic and magnetocaloric properties in MnNiGe alloy

Sn-doped MnNiGe alloy of nominal composition MnNiGe0.915Sn0.085 has been examined through structural and magnetic investigations. Sn-doping stabilizes the hexagonal structure (with P63/mmc space group) at room temperature. On cooling from room temperature, it first orders antiferromagnetically (with commensurate structure) around 185 K. Further cooling results in a structural change of martensitic type around 145 K. The observed structural transition is also found to be associated with a simultaneous magnetic transition from high temperature commensurate antiferromagnetic state to low temperature incommensurate antiferromagnetic state. Both conventional and inverse magnetocaloric effect (MCE), with peak values of −6.01 J/kg-K and 6.56 J/kg-K for 0 to 5 tesla of changing magnetic field, have been visible around the magnetic and structural transitions, respectively. A significant effect of external hydrostatic pressure on the magnetic and MCE behaviors has also been observed.

Inverse Magnetocaloric Effect and the Magnetostructural Transition in Pr0.15Ca0.85MnO3 Manganite

Magnetic and magnetocaloric properties of electron-doped Pr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (orthorhombic space group <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Pnma,</i> no. 62, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oP</i> 20) manganite have been studied. Low field magnetization measurements suggest that the sample orders antiferromagnetically at 147 K ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{N}$ </tex-math></inline-formula> ). Magnetocaloric effect (MCE) has been estimated in terms of isothermal magnetic entropy change ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta S_{m}$ </tex-math></inline-formula> ) and the maximum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta S_{m}$ </tex-math></inline-formula> value is about 6.4 Jkg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at 137.5 K for 70 kOe field change. Low-temperature powder X-ray diffraction studies reveal a change from orthorhombic (space group <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Pnma</i> , no. 62, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oP</i> 20) crystal structure to monoclinic (space group <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P 2_{1}/m$ </tex-math></inline-formula> , no. 11–2, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mP</i> 20) structure below 140 K. The inverse MCE shows a maximum value around the magnetostructural transition temperature. Electrical resistivity and electron paramagnetic resonance (EPR) spectroscopy results reveal hopping conduction in the paramagnetic state.

An Analytical Approach for Computing the Coefficient of Refrigeration Performance in Giant Inverse Magnetocaloric Materials

An analytical approach for computing the coefficient of refrigeration performance (CRP) was described for materials that exhibited a giant inverse magnetocaloric effect (MCE), and their governing thermodynamics were reviewed. The approach defines the magnetic work input using thermodynamic relationships rather than isothermal magnetization data discretized from the literature. The CRP was computed for only cyclically reversible temperature and entropy changes in materials that exhibited thermal hysteresis by placing a limit on their operating temperature in a thermodynamic cycle. The analytical CRP serves to link meaningful material properties in first-order MCE refrigerants to their potential work and efficiency and can be employed as a metric to compare the behaviors of dissimilar alloy compositions or for materials design. We found that an optimum in the CRP may exist that depends on the applied field level and Clausius–Clapeyron (CC) slope. Moreover, through a large literature review of NiMn-based materials, we note that NiMn(In/Sn) alloys offer the most promising materials properties for applications within the bounds of the developed framework.

Magnetic and magnetocaloric properties of Ho-=SUB=-1-x-=/SUB=-Y-=SUB=-x-=/SUB=-(Co-=SUB=-0.84-=/SUB=-Fe-=SUB=-0.16-=/SUB=-)-=SUB=-2-=/SUB=- compounds

Crystal structure, temperature and field dependences of magnetization, high-field susceptibility, and magnetocaloric effect (MCE) of Ho1-xYx(Co0.84Fe0.16)2 polycrystalline compounds (x=0-1) in magnetic fields up to 90 kOe in a temperature range of 5-400 K are investigated. An analysis of temperature dependences of magnetization (sigma) showed that, depending on the yttrium content (x), up to three "critical" temperatures can be simultaneously present in the studied samples: spin-reorientation (Tsr), magnetic compensation point (Tcomp), and Curie temperature (TC). The temperature dependence of the high-field susceptibility (chihf) of all samples with x&lt;1 has an extremum in the vicinity of 100 K, where a significant MCE is observed, associated with a sharp change in the magnetization of the rare-earth sublattice. The temperature dependences of the magnetic entropy change (Delta Sm) and the adiabatic temperature change (Delta Tad) have a complex shape and reflect all the above-mentioned "critical" temperatures observed at different x. Keywords: magnetic properties, direct and inverse magnetocaloric effect, adiabatic temperature change, magnetic moment, Laves phases, Curie temperature, compensation point, spin-reorientation transition.

In situ TEM study of phase transformations in nonstoichiometric Ni-=SUB=-46-=/SUB=-Mn-=SUB=-41-=/SUB=-In-=SUB=-13-=/SUB=- Heusler alloy

This paper presents a study of the metamagnetostructural transition of the martensitic type in the Ni46Mn41In13 alloy with magnetic shape memory and inverse magnetocaloric effect. The characteristic temperatures of the direct transition starting M_s=253 K and its finishing M_f=164 K, as well as the reverse temperatures A_s=203 K and A_f=236 K, respectively, were determined by differential scanning calorimetry. The characteristic peculiarities of the transition: a decrease of the Ms and the presence of a residual austenite phase, as well as pre-martensitic states, were studied using transmission electron microscopy. The estimated the thickness of alloy was 50 nm, when martensitic transition suppressed. Keywords: martensitic transformation, metamagnetostructural transformation, premartensitic states.

Magnetostructural features of phase transitions in the Mn-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-NiGe system Part 1. Experimental results

Experimental studies of the magnetic and structural properties of solid solutions of the Mn1-xCoxNiGe system in a wide range of Co concentrations (0.05≤ x≤ 0.8), temperatures (5 K≤ x≤600 K) and magnetic fields (0.016 T≤ x≤ 13.5 T) have revealed a number of nontrivial magnetic and magnetocaloric features of this system. The latter include: 1) a change in the nature of magnetic phase transitions from magnetostructural transitions of the 1st order paramagnetism-antiferromagnetism (0.05≤ x≤ 0.15) to isostructural transitions of the 2nd order paramagnetism-ferromagnetism (0.15≤ x≤0.8) with a change in the concentration of Co ; 2) anomalous behavior of low-temperature regions of magnetization in weak magnetic fields; 3) a change in the saturation magnetization and the appearance of irreversible magnetic field-induced transitions at helium temperatures in strong magnetic fields. Keywords: irreversible magnetostructural first-order phase transition, helimagnetism, direct and inverse magnetocaloric effects.

Magnetic cooling: a molecular perspective.

The magnetocaloriceffect is considered as an energy-efficient and environmentally friendly technique which can take cooling technology to the next level. Apart from its commercial application at room temperature, magnetic refrigeration is an up-and-coming solution for the cryogenic regime, especially as an alternative to He3 systems. Molecular magnets reveal advantageous features for ultra-low cooling which are competitive with intermetallic and lanthanide alloys. Here, we present a guide to the current status of magnetocaloric effect research of molecular magnets with a theoretical background focused on the inverse magnetocaloric effect and an overview of recent results and developments, including the rotating magnetocaloric effect.

Magnetostructural features of phase transitions in the Mn-=SUB=-1-x-=/SUB=-Co-=SUB=-x-=/SUB=-NiGe system Part 2. Analysis

Within the framework of the model of interacting parameters of the magnetic and structural orders, taking into account the internal periodic magnetic field orthogonal to the exchange field, we analyzed the features of magnetostructural transitions in the Mn1-xCoxNiGe system. A qualitative description of changes in the nature of magnetic phase transitions from magnetostructural transitions of the 1st order paramagnetism-antiferromagnetism (x=0.05-0.1) to isostructural transitions of the 2nd order paramagnetism-ferromagnetism (x=0.15-0.8) with a change in the concentration of Co is presented. An explanation is given for the onset of irreversible magnetic-field-induced transitions at temperatures on the order of 5 K in strong magnetic fields, accompanied by a change in the saturation magnetization for samples x=0.15-0.8. The low-temperature inverse magnetocaloric effect at liquid helium temperatures is predicted for these samples. Keywords: irreversible magnetostructural first-order phase transition, helimagnetism, direct and inverse magnetocaloric effects.

In situ TEM study of phase transformations in nonstoichiometric Ni-=SUB=-46-=/SUB=-Mn-=SUB=-41-=/SUB=-In-=SUB=-13-=/SUB=- Heusler alloy

This paper presents a study of the metamagnetostructural transition of the martensitic type in the Ni46Mn41In13 alloy with magnetic shape memory and inverse magnetocaloric effect. The characteristic temperatures of the direct transition starting M_s=253 K and its finishing M_f=164 K, as well as the reverse temperatures A_s=203 K and A_f=236 K, respectively, were determined by differential scanning calorimetry. The characteristic peculiarities of the transition: a decrease of the Ms and the presence of a residual austenite phase, as well as pre-martensitic states, were studied using transmission electron microscopy. The estimated the thickness of alloy was 50 nm, when martensitic transition suppressed. Keywords: martensitic transformation, metamagnetostructural transformation, premartensitic states.

Mean-Field Modeling of Magnetocaloric Effect of Antiferromagnetic Compounds

Antiferromagnetic compounds are known in the literature to present the inverse magnetocaloric effect (MCE). This effect is characterized by the negative adiabatic temperature change, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta T_{S}$</tex-math></inline-formula> , of an antiferromagnetic material when submitted to an applied magnetic field. In an isothermal process, a positive entropy change, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Delta S_{T}$</tex-math></inline-formula> , is also expected. More recently, the anisotropic character of antiferromagnetic compounds, due to spin-flop and spin-flip transitions, has been pointed out highlighting the applicability of the antiferromagnetic compounds in a rotary magnetocaloric device. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In this work, we systematically investigated a mean-field model that describes the antiferromagnetic behaviour of materials in a multisublattice approach. Our model includes the nearest and next-nearest neighbour exchange interaction, the Zeeman effect, and a uniaxial anisotropy energy. We investigated the effect of anisotropy on the spin-flop and spin-flip transitions on the usual and anisotropic MCE. We also demonstrated and verified an area rule for —<inline-formula><tex-math notation="LaTeX">$\Delta S_{T}$</tex-math></inline-formula> vs. T curves that can be used on compounds where the saturation magnetization is magnetic field dependent.