Inverse Magnetocaloric Effect Research Articles

Inverse magnetocaloric effect and phase separation induced by giant van Hove singularity in itinerant ferromagnetic metal

Inverse magnetocaloric effect and phase separation induced by giant van Hove singularity in itinerant ferromagnetic metal

Inverse and conventional dual magnetocaloric effects in Ni substituted Y-type Sr2Zn2-xNixFe12O22 hexaferrites

The effects of Ni substitution on magnetic and magnetocaloric effect (MCE) are investigated in polycrystalline Y-type hexaferrites of Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0). With the increasing of temperature, the M-T curves indicate successive magnetic structure transitions exist in Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0), which play significant roles in MCE behaviors. As the Ni2+ doping ratio increases, the shape of −ΔSM−T curves near room temperature evolves gradually from a table-like to a peak-like form. Particularly, a significant contrast between CMCE and IMCE is observed below 100 K, whose behavior can be inherently exploited for heat sink in magnetic refrigeration applications. Among the samples in this series, Sr2Zn1.2Ni0.8Fe12O22 plays the best CMCE and IMCE performances, with the maximum magnetic entropy change (−ΔSMmax) values of 0.78 J/kg K at 354 K and −0.56 J/kg K at 16 K for ΔH=50kOe , respectively. Our work demonstrates that Sr2Zn2-xNixFe12O22 hexaferrites have great potential to be tailored for magnetic refrigeration with special needs such as different operating temperature zones, Ericsson cycle or heat sink at refrigeration.

Observation of competing interactions and field-induced ferromagnetism in noncentrosymmetric cubic Nd3Te4 lattice

Unconventional magnetism is key to advancement in a variety of spintronic applications and thus needs to be explored in new materials. Here, we report the in-depth magnetic studies of noncentrosymmetric Nd3Te4 and findings support the existence of Dzyaloshinskii-Moriya interaction in addition to symmetric exchange interaction among the moments. The large magnetic irreversibility with negative magnetization in M(T) data and associated first-order magnetic transition in isothermal magnetization data suggest the competing interactions resulting in multiple magnetic phases. The gradual evolution of magnetic texture has been probed by changes in the magnetization entropy having interesting characteristics like the inverse magnetocaloric effect. Most importantly, we have probed the existing nontrivial magnetic phase under a low applied magnetic field by ac-χ(T, H) and dc magnetization (M − H) data, having the same critical field in both measurements. The existence of multiple magnetic phases which are interconnected through first-order field-induced magnetic phase transitions have been probed at low field. The transition from paramagnetic to field-induced state for larger applied fields follows a second-order.

Quantum design of magnetic structures with enhanced magnetocaloric properties

Abstract The magnetization processes and magnetocaloric effect (MCE) of molecular magnets are studied using the quantum Heisenberg model with the goal of finding magnetic structures with optimal magnetocaloric properties. To fulfill this goal, we examine the influence of various factors such as quantum fluctuations, the magnitude and distribution of spins, the cluster size and its geometry on the conventional (cooling) and inverse (heating) MCE. We find, surprisingly, that the best cooling and heating effects are observed in the Ising limit on the smallest possible molecular clusters represented by dimers and trimers. The increasing Heisenberg interaction suppresses both the cooling as well as heating effects, but while the heating is reduced very strongly, for relatively small values of the anisotropic Heisenberg constant, the cooling effects are reduced only weakly. Since the heating effect is undesired in low-temperature refrigeration, the Heisenberg limit is also interesting from a practical point of view. Moreover, we find that spin distributions also have a significant influence on the magnetocaloric properties of molecular magnets. Specifically, configurations with large spins on the edges of the finite chain significantly enhance the cooling effect.

Stellated cuboctahedron of FeIII

AbstractThe solvothermal reaction of FeCl2 ⋅ 4H2O and H4TBC[4] in a basic dmf/EtOH solution affords an [FeIII18] Keplerate conforming to a stellated cuboctahedron. Magnetic and heat capacity measurements reveal spin frustration effects arising from the high symmetry. A crossover between inverse and direct magnetocaloric effects is observed at ~10 K for applied‐field changes lower than 3 T.

Effects on magnetocaloric and magnetoresistive properties due to nonmagnetic Zn2+ substitution at Mn-site in charge-ordered Pr0.5Ca0.5MnO3 manganite

This study of nonmagnetic Zn-substitution effect on the charge-ordered behavior of Pr0.5Ca0.5Mn1-xZnxO3 (x = 0.0, 0.1) compounds reveal the weakening of strong charge-ordered antiferromagnetic state of the parent compound (x = 0.0). Magnetocaloric effect (MCE) has been calculated using a Python package from isothermal M-H data for these samples. A prominent ferromagnetic contribution in the antiferromagnetic matrix for Mn-site doping is observed, which removes the inverse MCE observed in the pristine sample below the charge ordering temperature TCO. Development of ferromagnetism in the doped system exhibits a metal-insulator transition at TMI = 90 K under 7 T magnetic field and large magnetoresistance (> 99 %), which is not observed in parent compound. Magnetic field-dependent hysteresis at low temperature reveals the ferromagnetic metastability and first-order nature of magnetic phase transition. Random occupation of Zn at the Mn-site of the parent compound disrupts 1:1 Mn3+/Mn4+ charge-ordered superstructure of the parent compound which weakens the charge-ordered antiferromagnetic strength promoting ferromagnetism and double-exchange interaction through an enhanced 2p-3d hybridization between Mn and O ions.

Direct and inverse magnetocaloric effects in magnetostrictive GdMn2Ge2 with field-induced metamagnetic transition

Heavy rare-earth-based ternary intermetallic compounds with the formula RT2X2 have drawn great interest because of their multiple magnetic transitions and various magnetic structures. Here, anisotropic magnetic behaviors, magnetocaloric effects (MCEs), and magnetostriction effects in single-crystalline GdMn2Ge2 are studied in two different directions. Experiments show a magnetic transition characterized by a sudden decrease in magnetization for μ0H//a and a sharp increase for μ0H//c at Tt. The transition is driven by lower temperatures for μ0H//a, contrasting that for μ0H//c with an increase in the magnetic field. An inverse MCE is observed for μ0H//a with a maximum magnetic entropy change (−ΔSMmax) of −7.4 J kg−1 K−1 (μ0ΔH = 6 T), while a direct MCE is obtained for μ0H//c with an −ΔSMmax of 8.0 J kg−1 K−1 under the same magnetic field change. Moreover, a remarkable field-induced metamagnetic transition and a magnetostriction effect are observed simultaneously at Tt, indicating strong magneto-lattice coupling. The T-μ0H phase diagrams are constructed based on the magnetic properties. The coexistence of direct and inverse MCEs is discussed and is due to the spin-flop of Mn and anisotropic magnetic properties under magnetic fields in different directions.

Magnetocaloric effect in the first order antiferromagnetic phase transition compound CeMg

We report the magnetic and magnetocaloric properties of the antiferromagnetic intermetallic compound CeMg, focusing on its coupled magnetic and structural phase transition within first-order processes. Our study utilizes a model Hamiltonian incorporating interactions such as: crystalline electrical field, intra and inter sublattice exchange interactions, as well as quadrupolar and magnetoelastic to elucidate the behavior of CeMg. Through simulation, we predict and discuss both normal and inverse magnetocaloric effects, providing insights into the magnetocaloric behavior under different magnetic field directions. These findings contribute to a deeper understanding of the complex magnetism in CeMg and lay the groundwork for future experimental investigations.

Interplay between the reversibility of the inverse magnetocaloric effect and kinetic arrest in Ni-Co-Mn-Sn Heusler alloys

The nature of martensitic phase transitions and its modification as a function of composition and application of magnetic field have been studied in detail for Ni40Co10Mn40Sn10-xGax (x=0, 0.3, 0.4 and 0.5). The phase transition temperature (TM) increases with increasing x. The kinetic arrest (KA) of the austenitic phase has been observed for x=0 and 0.3, which disappeared for x>0.3. The KA results in a decrease in the change of magnetization (ΔM) across TM. However, the isothermal entropy change ΔS varies almost linearly with [dTM/d(μ0H)]−1 (field-induced shift in TM) irrespective of the composition variation and thermal cycling. This behavior indicates that the variation of dTM/d(μ0H) is the dominant factor determining the magnitude of the ΔS rather than ΔM. Consequently, the effect of KA on ∆M has a negligible influence on ΔS in the studied Heusler alloys. The reduced field-sensitivity in TM associated with the temperature-induced decrease of magnetization in the ferromagnetic austenitic phase leads to a decrease of the thermal hysteresis and an increase of ΔS. As a result, a large reversible (|ΔSrev|=21 J/kg K for Δμ0H=5 T) has been observed for x=0.5, which exceeds previously reported values for Sn-based Heusler alloys.

Revealing contrary contributions of the magnetic and lattice entropy to the inverse magnetocaloric effect in magnetic shape memory alloy

In this work, we studied the nature and dilemma of the inverse magnetocaloric effect using Ni50Mn36In14 magnetic shape memory alloy. In this context, the inverse magnetocaloric effects of Ni50Mn36In14 magnetic shape memory alloy polycrystalline samples were investigated as a function of annealing heat treatments by the thermo-magnetometry method. Two forms of Ni49TiMn36In14 magnetic shape memory alloy were studied: one that predominantly undergoes a magnetic phase transition and the other that exhibits both a magnetic and martensitic phase transition. The magnetic behaviors and magnetocaloric properties of these alloys were analyzed to investigate the competition between magnetic and lattice contributions to the total entropy change. Finally, the mutually contradictory role of magnetic and lattice contributions was demonstrated.

Structural and magnetic properties of RE2O2SO4 (RE = Gd, Tb, Dy and Ho) oxides featuring large direct and inverse magnetocaloric effect

In this work, we fabricated the RE2O2SO4 (RE = Gd, Tb, Dy and Ho) oxides by thermal decomposition and systematically determined regarding their structural and magnetic properties, especially of the magnetic phase transition (MPT) and magnetocaloric effect (MCE). All of these RE2O2SO4 oxides are confirmed to crystallize in an orthogonal structure (space group: pmnb); the constituting elements are all distributed uniformly and presented as the RE3+, S6+, and O2− valence states, respectively. They all exhibit a typical cryogenic MPT from paramagnetic to antiferromagnetic (AFM) state together with a field-induced metamagnetic transition (first-order type MPT) from AFM to ferromagnetic state below their MPT temperatures. All of these RE2O2SO4 oxides exhibit considerable direct and inverse cryogenic MCE. The determined direct magnetocaloric parameters of present RE2O2SO4 oxides, especially of Gd2O2SO4 and Ho2O2SO4 oxides, are comparable with most of recently reported RE-based magnetic solids, making them also considerable for practical cryogenic MR applications.

Inverse Magnetocaloric Effect in Altermagnetic 2D Non‐van der Waals FeX (X = S and Se) Semiconductors

AbstractThe concept of altermagnet (AM), which is neither ferromagnet nor antiferromagnet, has recently been proposed as compensated collinear magnet. Among 2D non‐van der Waals crystals, one of the thinnest altermagnets is identified and their interesting physical phenomenon at 2D limit is investigated. According to symmetry analysis and first‐principles calculations, 2D FeX (X = S, Se) sheets with one‐unit‐cell thickness are intrinsic altermagnetic semiconductors with observable magnitude of spin splitting (103−193 meV), high magnetic transition temperature (TAM = 400 and 190 K), large out‐of‐plane magnetic anisotropy energy (0.24 and 0.74 meV per atom) and considerable metal‐like anomalous Hall conductivity (143 and 249 Ω−1 cm−1). Moreover, the spin lattices of these 2D FeX ultrathin films are formed by parallel diamond‐like chains with spin frustrated interaction through spin exchange along the b direction. Consequently, an inverse magnetocaloric effect with positive ∆Sm values of 1.7–8.2 mJ kg−1 K−1 near TAM is observed. These results enrich the database of altermagnets and provide deep insights into the spin frustration effect in 2D magnets, which paves the avenue for the next‐generation spintronics.

Martensitic transformation and inverse magnetocaloric effect in Ni-Mn-Ga-Co-Gd microwires

Ni–Mn-Ga-Co-Gd microwires were fabricated by the glass-coated melt spinning method, resulting in a bamboo-grained structure. In this paper, the magnetocaloric effect of Ni–Mn-Ga-Co-Gd microwires is mainly investigated, which is represented by the isothermal magnetic entropy change calculated using Maxwell equation. Specifically, Ni43Mn30Ga19.9Co7Gd0.1 microwires exhibit maximum entropy change of 11.09 J/kg·K under 5 T magnetic field, which is generally greater than that of the current Ni–Mn-Ga microwires. Additionally, Ni43Mn30Ga19.9Co7Gd0.1 microwires show the temperature corresponding to the greatest magnetic entropy change nearer to room temperature compared to other Ni–Mn-Ga microwires. Furthermore, the larger specific surface area of microwires will facilitate their application in the field of magnetic refrigeration.

Characterization of gapless topological quantum phase transition via magnetocaloric effect

It has attracted much attention on the interplay between topology and criticality in topological quantum systems, i.e., gapless topological quantum phase transition (TQPT) on critical lines. It is demonstrated that the magnetocaloric effect (MCE) is able to signal the gapless TQPT in an extended Kitaev chain, which is witnessed by the unusual critical behavior of joint effect of Grüneison ration (GR) and isothermal entropy change. We uncover the conventional TQPT between gapped phases showing high symmetry (HS) and non-HS critical points with self-duality, which is signaled by the finite value of GR as T → 0 and the largest inverse MCE with T-linear relation of isothermal entropy change. Two critical lines intersect at a multicritical point, at which there is a T−1 critical divergence of GR as well as T1/2 critical behavior of isothermal entropy change. It manifests a “weak” gapless TQPT on one critical line, demonstrated by the shifting zero-crossing of GR without the largest inverse MCE. On the other critical line, it shows a “strong” gapless TQPT, which is evidenced by the negative dip of GR together with the largest inverse MCE. Our work provides a novel thermodynamic perspective on gapless TQPT.

Transformation behavior and inverse magnetocaloric effect in Ni45Co5Mn36.7In13.3-xGex melt-spun ribbons

In the present work the influence of Ge doping on crystal structure, microstructure, martensitic transformation (MT) and magnetocaloric effect (MCE) of Heusler-type Ni45Co5Mn36.7In13.3-xGex (x = 0, 2, and 3 at. %) metamagnetic shape memory alloys (MetaMSMAs) have been studied. Melt-spinning was used to prepare ribbons of these alloys since the ribbon shape ensures a high surface-to-volume ratio favoring a high heat exchange rate in a solid-state refrigeration. Furthermore, melt-spinning can induce a specific microstructure and stabilize metastable phases at room temperature. The ribbons were examined by X-ray diffraction at different temperatures, scanning electron microscopy, calorimetry, thermomagnetization, and magnetic field induced adiabatic temperature change measurements carried out across MT. It was found that Ge doping gave rise to enhanced antiferromagnetic interactions, stabilized martensitic phase, increased the MT temperature, causing larger magnetization jumps at MT and making narrower MT hysteresis. The x = 3 ribbon exhibited an inverse MCE at 303 K characterized by the isothermal magnetic entropy change value of |26.9|J/kgK at μ0H = 5 T and an adiabatic temperature change of ǀ1.5ǀ K at μ0H = 1.96 T. These values are comparable with the previously reported data on the Ni–Mn-based metamagnetic shape memory alloys in a bulk form.

Field-sensitivity and reversibility of the inverse magnetocaloric effect at martensitic transformations

The magnetic field-sensitivity of martensitic phase transitions (MPTs) responsible for magnetocaloric effects has been examined in B-substituted Ni50Mn34.8In15.2−xBx Heusler alloys (x = 1, 2, 3, and 4). Increasing boron substitution acts as a positive chemical pressure similar to the effect of hydrostatic pressure (p) and shifts the martensitic phase transition temperature (TM) toward higher temperature. The observed structural compatibility of the MPT results in a lower thermal hysteresis (ΔThyst<5 K at low field). ΔThyst remains almost unchanged; however, the field sensitivity of TM decreases significantly with increasing B content or application of p. As a result, the reversibility of the isothermal entropy change (|ΔSrev|) reduces for higher B concentration or under hydrostatic pressure p. The experimental observation reveals that the lower field-sensitivity of the MPT with increasing B or p is associated with the simultaneous increase in the magnetocrystalline anisotropy energy (MAE) and decrease in the Zeeman energy (ZE). The relatively larger ZE and smaller MAE for x = 1 result in the improved reversibility of the entropy change (|ΔSrev| = 21.48 J/kg K for Δμ0H = 5 T), which is comparable to or even larger than the values reported for similar Heusler alloys.

Direct and inverse magnetocaloric effect in half-doped La0,5Ca0,5MnO3 and Pr0,5Sr0,5MnO3

Direct and inverse magnetocaloric effect in half-doped La0,5Ca0,5MnO3 and Pr0,5Sr0,5MnO3

Thermodynamics of resonating-valence-bond states toward the understanding of quantum spin liquid phenomena.

A quantum spin liquid (QSL) is a state of matter in which spins do not exhibit magnetic order. In contrast to paramagnets, the spins in a QSL interact strongly, similar to conventional ordered magnets; however the thermodynamic stability of QSLs is rarely studied. Here, the thermodynamic properties of centered hexagon nanoclusters were investigated using the Hubbard model, which was solved using exact numerical diagonalization. The total spin, spin-spin correlation functions, local magnetic moments, charge and spin gaps, and magnetocaloric effect were analyzed for a half-filled band as a function of the ratio between the on-site Coulomb repulsion and electronic hopping (U/t). The centered hexagon nanocluster exhibited an antiferromagnetic (AFM) behavior with exotic magnetic ordering. Resonating-valence-bond (RVB) states were observed for intermediate values of U/t, in which short-range spin-spin correlation functions were suppressed to minimize spin frustration. The AFM order was examined in terms of the Néel-like temperature derived from the temperature dependence of the magnetic susceptibility. An interesting result is that the systems under external magnetic fields exhibited an inverse magnetocaloric effect, which was remarkable for intermediate values of U/t, where the RVB state was observed. Owing to the novel discovery of exotic magnetic ordering in triangular moiré patterns in twisted bilayer graphene (TBLG) systems, these results provide insights into the onset of magnetism and the possible spin liquid states in these graphene moiré materials.

Inverse Magnetocaloric Effect in Heusler Ni44.4Mn36.2Sn14.9Cu4.5 Alloy at Low Temperatures

Direct measurements of the magnetocaloric effect were performed in a Heusler Ni44.4Mn36.2Sn14.9Cu4.5 alloy at cryogenic temperatures in magnetic fields up to 10 T. The maximum value of the inverse magnetocaloric effect in a 10 T field was ∆Tad = –2.7 K in the vicinity of the first-order magnetostructural phase transition at T0 = 117 K. Ab initio and Monte Carlo calculations were performed to discuss the effect of Cu doping into a Ni-Mn-Sn compound on the ground-state structural and magnetic properties. It is shown that with increasing Cu content the martensitic transition temperature decreases and the Curie temperature of austenite slightly increases. In general, the calculated transition temperatures and magnetization values correlated well with the experimental ones.

Inverse magnetocaloric effect and negative magnetoresistance in Ni50Mn30-xFexSn20-ySby (1 ≤ x ≤ 4 and 2 ≤ y ≤ 8) alloys

Inverse magnetocaloric effect and negative magnetoresistance in Ni50Mn30-xFexSn20-ySby (1 ≤ x ≤ 4 and 2 ≤ y ≤ 8) alloys