Maximum Magnetic Entropy Change Research Articles

Optimizing magnetocaloric and thermoelectric performance of MnCoGe/BiSbTe composites by regulating magnetostructural transition and element diffusion

Composites consisted of MnCoGe magnetocaloric alloy and BiSbTe thermoelectric alloy were prepared to explore their potential use in all-solid-state cooling. It was found that in the composites the phase transition of MnCoGe from orthorhombic to hexagonal phase causes a large drop of magnetostructural transition temperature from room temperature to 270 K. The diffusion of Mn into BiSbTe leads to the formation of interfacial phase Mn(Bi,Sb)2Te4 and doping effect that depresses the thermoelectric performance. By adopting a low-temperature sintering strategy, the phase transition was restricted and the doping effect due to Mn diffusion was alleviated. As a result, the magnetostructural transition temperature around 300 K is maintained and the room-temperature magnetocaloric and thermoelectric properties are simultaneously optimized. The maximum magnetic entropy change of 4.3 × 10−3 J kg−1 K−1 at 2.0 T and maximum ZT value of 0.81 at 384 K have been obtained on the composite incorporated with 1 wt% MnCoGe. This work demonstrates that the control of phase transition and the doping effect of MnCoGe is crucial in optimizing the thermo-electro-magnetic properties of MnCoGe/BiSbTe composites.

Magnetic and magnetocaloric properties of R55Co30Al10Si5 (R = Ho, Dy) metallic glass ribbons

Metallic glass alloys are suitable systems for the development of magnetocaloric refrigerated materials due to the stable physical properties and the adjustable magnetic phase transition temperature. Here, the glass formation ability (GFA), magnetic properties and magnetocaloric effects of R55Co30Al10Si5 (R = Ho, Dy) amorphous ribbons prepared by the melt-spinning technique were investigated. The X-ray diffraction and DSC measurement indicated that the metallic glass alloys have a completely amorphous structure and excellent glass formation ability. The amorphous ribbons were demonstrated to undergo a second-order magnetic phase transition (ferromagnetic to paramagnetic) around Tc ∼ 18 K for Ho55Co30Al10Si5, ∼34 K for Dy55Co30Al10Si5, respectively. The maximum magnetic entropy change (-ΔSMmax) and the corresponding refrigerant capacity (RC) values are 12.7 J/kg K, 343 J/kg for Ho55Co30Al10Si5, 9.1 J/kg K, 334 J/kg for Dy55Co30Al10Si5 under a field change ΔH= 5 T. The large -ΔSMmax and high RC suggest that R55Co30Al10Si5 (R = Ho, Dy) amorphous ribbons have potential applications in low temperature magnetic refrigeration.

An Outlook into the Magnetic and Magnetocaloric Properties of Cr1.3Fe0.7O3

Herein, the magnetic and magnetocaloric properties of Cr1.3Fe0.7O3 particles are presented. The structural and oxidation states of the samples are confirmed from the X‐ray diffraction and X‐ray photoemission spectroscopy measurements. In addition, the thermomagnetization experiments reveal the coexistence of two spin reorientation, Morin transition, as well as Néel temperature below 300 K. Such complex magnetic behavior of the system can be ascribed to the metal–ligand–metal interaction caused both by Cr3+ and Fe3+ magnetic ions. The maximum magnetic entropy change estimated from the isothermal magnetization measurements is 0.056 J kg−1 K−1 at 41 K for an external magnetic‐field change of 70 kOe.

Enhanced magnetocaloric properties and reduced annealing time of off-stoichiometric La1.2Fe11.6Si1.4B0.75 melt-spun ribbons

The off-stoichiometric La1.2Fe11.6Si1.4B0.75 alloys with different solidification rate were prepared by the arc-melting and melt-spinning methods, and the microstructure, magnetic and magnetocaloric properties of the annealed samples were investigated. It is found that the extra La and refined microstructure (induced by rapid cooling technique) shortened the annealing time to 30 min at 1273 K. The B atoms partially dissolved in lattice interstice of 1:13 phase and brings about the lattice expansion, which improves the TC and enhances the MCE of the La1.2Fe11.6Si1.4B0.75 alloy. The high cooling rate contributes to the depression of thermal and magnetic hysteresis. In the annealed La1.2Fe11.6Si1.4B0.75 ribbon with wheel speed of 10 m/s, the mass fraction of 1:13 phase is 86.8 wt%, and a large maximum magnetic entropy change of 20.2 J·kg−1K−1 with small thermal and magnetic hysteresis can be obtained at 193 K under field change of 2 T.

Hysteresis loss and field dependence of magnetic entropy change of Zn-doped Mn5Ge3 system

In this work, a series of Mn5Ge3-xZnx samples were prepared by the arc-melting method. The Rietveld structure refinement of the powder XRD spectrum was performed using the FullProf program. The lattice parameters and cell volume increase with the doping of Zn atoms. From the magnetization curve at 5 K, the compounds show a decreased magnetic moment of the Mn atom with increasing Zn content, resulting from mixing the 3d electronic state of Mn atoms and the 3d electronic state of Zn atoms. The small hysteresis loss and soft ferromagnetism of Mn5Ge3-xZnx indicate that it is suitable for magnetic refrigeration. Thermomagnetic M(T) curves show an increase in thermal hysteresis concurrent with increasing Zn concentration, which is verified by the DSC curve. It is found that the magnetic entropy change and effective magnetic moment decrease with the increase of Zn content, which can be attributable to the doping of Zn atoms resulting in the weakening of the exchange interaction between Mn-Mn atoms and the decrease of magnetic entropy change. In addition, the specific power-law relationships between the magnetic entropy change, the maximum magnetic entropy change, the relative cooling capacity, and the magnetic field of this system were determined, which provides a tool for evaluating the performance of the magnetic refrigerant in the entire magnetic field range. Finally, the specific heat was calculated by the magnetic entropy change obtained by the experiment, and the specific heat curve proves that the sample undergoes a second-order phase transition, consistent with the results of Arrott plots. The TC obtained by the specific heat -ΔCP−T curve is in good agreement with the TC obtained by the magnetic measurement, revealing that TC obtained by the specific heat is also an effective method.

Tunable magnetic phase transition and magnetocaloric effect in the rare-earth-free Al-Mn-Fe-Co-Cr high-entropy alloys

In the present study, the structure, magnetic phase transition, and magnetocaloric performance of Al20Mn20Fe20Co14.5+xCr25.5-x (x = 0, 1, and 2), a series of typical rare-earth-free high-entropy (HE) alloys, were experimentally determined and theoretically analyzed based on first-principle calculation. Ferromagnetic behavior was established and their Curie temperature could be tuned in a wide temperature range, which correlated with Co content; specifically, it increased from 282.8 K for Co14.5Cr25.5 to 345.8 K for Co16.5Cr23.5. In addition, the electronic density of states and magnetic moments associated with each consistent element were analyzed in the HE alloys. Maximum magnetic entropy changes of 1.135, 1.150, and 1.096 J/kgK were obtained for an x of 0, 1, and 2 under a magnetic field change of 5 T. These values are comparable or superior to those of reported 3d metal-based HE alloys. Furthermore, the experimental characterizations and theoretical predications agreed well, which provided an in-depth understanding of the rare-earth-free HE Al-Mn-Co-Fe-Cr alloy system, which is expected to be expanded to other systems in the future.

Synthesis, structure, morphology, magnetism, and magnetocaloric-effect studies of (La1−xPrx)0.7Sr0.3MnO3 nanocrystalline perovskites

Single-Phase (La1–xPrx)0.7Sr0.3MnO3 (x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) perovskites were synthesized by the sol–gel method followed by sintering at 700 °C for 5 h. Samples with x = 0.0–0.4 are found to crystallize into rhombohedral structure (R-3c space group) while the ones with x = 0.6–1.0 crystallize into orthorhombic structure (Pbnm space group). The average particle size of the samples was in the range of 21–44 nm. All samples exhibit a ferromagnetic to paramagnetic second-order magnetic phase transition at Curie temperature, which is found to decrease linearly with increasing the Pr concentration. The magnetic coercivity was found to be small (~ 10 Oe) for all the samples, at T < TC. The experimental effective paramagnetic moment (µeff) is found to increase with increasing x from 3.99 µB (x = 0.0) to 5.05 µB (x = 1.0). The magnitude of the maximum magnetic entropy change (−ΔSM)max. and the relative cooling power (RCP) for the samples having orthorhombic structure increases as x increases reaching a maximum value of 4.67 J/kg.K and 574 J/kg at ΔµoH = 9 T for x = 1.0. While the ones with the rhombohedral structure have the maximum values of (−ΔSM)max. and RCP of 4.63 J/kg.K and 472 J/kg at ΔµoH = 9 T are for x = 0.2. The large values of (−ΔSM)max. and RCP (at room temperature (RT)) and the wider temperature range of −ΔSM for the sample with x = 0.6 suggests that this compound may be considered as magnetic refrigerant material at RT, and the other compounds can be candidates in the vicinity of RT.

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.

Magnetic properties and magnetocaloric effect (MCE) in the melt-spun Tm20Ho20Gd20Ni20Al20 amorphous ribbon

We fabricated the Tm20Ho20Gd20Ni20Al20 ribbons by melt-spun technology and determined its glass forming ability (GFA), magnetic properties, magnetic phase transition (MPT) character, and magnetocaloric performance. The Tm20Ho20Gd20Ni20Al20 melt-spun ribbon exhibits fully amorphous nature and excellent GFA. A second order (SO) type MPT from ferromagnetic to paramagnetic was observed around the Curie temperature of 30.3 K. Moreover, considerable MCE and magnetocaloric performance in Tm20Ho20Gd20Ni20Al20 amorphous ribbon were realized with the maximum magnetic entropy change, temperature-averaged entropy change of 10 K lift, and relative cooling powder/refrigerant capacity of 9.4 J/kgK, 9.0 J/kgK, and 527.2/422.1 J/kg under 0–5 T field change, respectively. These magnetocaloric parameters are close to most of the recently reported magnetocaloric materials, which made the Tm20Ho20Gd20Ni20Al20 amorphous HE ribbon amorphous ribbon also of potential for practical cryogenic MR applications.

Effect of thermal treatments below devitrification temperature on the magnetic and magnetocaloric properties in mechanically alloyed Fe70Zr30 powders

In this work, the relaxation of the amorphous structure of mechanically alloyed Fe70Zr30 powders has been analyzed through interrupted heating ramps below the devitrification temperature. As a result of such thermal treatment, Curie temperature and temperature at maximum magnetic entropy change curves shift to higher temperatures as the temperature of heating treatment increases. This effect can be attributed to both the release of the stress accumulated in the amorphous powder during the milling process and to the initiation of nucleation of α-Fe crystallites, as it has been shown by Mössbauer spectroscopy.

Magnetoelastic Coupling and Cryogenic Magnetocaloric Effect in Two-Site Disordered GdSrCoFeO6 Double Perovskite

The development of new magnetic refrigerants demands an effective investigation of materials with a large magnetocaloric effect in a wide temperature range. Herein, we report on the structural, magnetic, and magnetocaloric properties of the two-site disordered double perovskite GdSrCoFeO6 prepared by the modified solid-state synthesis method. Temperature-dependent synchrotron X-ray diffraction analysis revealed that GdSrCoFeO6 crystallizes in the orthorhombic phase (Pnma), with Gd3+/Sr2+ and Co2+/3+/Fe3+/4+ ions randomly distributed on the A- and B-sites, respectively. An observed lattice parameter anomaly around 60 K indicates the occurrence of the magnetoelastic coupling, which coincides with the presence of ferro/ferrimagnetic (FM/FiM) ordering below TC ≈ 65 K from the magnetic measurements. These results match well with our first-principles calculation prediction of low-temperature magnetic (FM/FiM) and electronic (insulating/metal) transitions related to a combined effect of Co and Fe short- and long-range competitions, crossings of spin state at Co ions, and the hybridization degree between Gd-4f and Co-3d states. Additionally, a modified Arrott plot and Kouvel–Fisher analysis were used to establish the nature of the magnetic phase transition in GdSrCoFeO6, yielding the critical exponent β = 1.46(6)/1.45(6), γ = 1.48(5)/1.17(2), and δ = 2.01(3)/1.80(5), respectively. The specific heat analysis reveals two well-defined broad peaks (∼10 and ∼70 K), which match well with a Schottky anomaly (Gd-4f) and the magnetic transition of FM/FiM to paramagnetic order, respectively. The magnetocaloric effect (MCE) analysis reveals a maximum magnetic entropy change ΔSMmax ≈ 13 J kg–1 K–1 (at ∼8 K) under a field of 0–7 T. These results evidence that the Schottky anomaly and the magnetoelastic coupling seem to be key factors for driving further enhancements to the MCE in GdSrCoFeO6, making it a possible candidate for cryogenic applications.

Analysis of magnetocaloric effect in parallel Ni-Mn-Ga Heusler alloy nanowires

In this article, a magnetocaloric effect of electrodeposited Ni-Mn-Ga - based Heusler nanowires is presented using the indirect approach. The structural characterization revealed that the prepared nanowires exhibit a martensitic transformation capability above room temperature (at 350 K). The martensitic transformation results in a relatively high magnetic entropy change of> 2.5 J.kg−1. K−1. Moreover, the magnetocaloric effect analysis reveals a maximum magnetic entropy change at a moderate magnetic field of only 2 T. The presented cheap fabrication method, together with the strong magnetocaloric response of the nanowires at moderate magnetic fields, opens up new possibilities in the field of nanosized Heusler alloys operating as refrigerants, actuators, or sensors

Insight into the structural and magnetic properties of RECo12B6 (RE = Ce, Pr, Nd) compounds: A combined experimental and theoretical investigation

Rare earth (RE) based RE-TM-X (TM = transition metal elements; X = P-block elements) materials have received continuous attention due to the exhibition of various intriguing magnetic functional characteristics. In this work, a combined experimental and theoretical investigation has been conducted in detail for RECo12B6 (RE = Ce, Pr, Nd) compounds with regard to their structural and magnetic properties, particularly the magnetocaloric effect and magnetic phase transition (MPT). All of the present RECo12B6 compounds are found to crystalize in the SrNi12B6-type structure and with a ferrimagnetic ground state, which is confirmed by density functional theory calculations and magnetization measurements. The magnetic moments of RE atoms and Co atoms tend to be in antiparallel alignment, and the MPT of these materials originates primarily from the spin-polarized 3d electrons of the Co atoms, which can be greatly affected by the 4f electrons of RE atoms. Considerable magnetocaloric effects have been observed around its own TC of 130, 157, and 160 K, for CeCo12B6, PrCo12B6, and NdCo12B6, respectively, which is related to a typical second-order MPT. The corresponding maximum magnetic entropy change and relative cooling power values,with field changes of 0–70 kOe, are determined to be 2.54, 2.84, and 2.77 J/kg K and 116.8, 156.2, and 155.1 J/kg, respectively. The MPT properties of present RECo12B6 compounds were studied in further detail by critical analysis using the modified Arrott Plot and Kouvel-Fisher methods, which can be explained within the frame of the 3D Heisenberg model with short-range magnetic interaction.

The effects of Cu substitution on magnetocaloric effects of the HoCo1−xCuxSi (0 ≤ x ≤ 0.4) phases

By hetero-structural alloying ferromagnetic (FM) TiNiSi-type orthorhombic HoCoSi with antiferromagnetic (AFM) Ni2In-type hexagonal HoCuSi, the magnetic and structural evolutions have been observed in HoCo1−xCuxSi (0 ≤ x ≤ 0.4) alloys. The magnetic property is changed from ferromagnetic for x ≤ 0.3 to antiferromagnetic for x = 0.4 in HoCo1−xCuxSi system. With the field change Δμ0H = 5 T, the maximum magnetic entropy changes (−ΔSMmax) are 10.1 J kg−1 K−1, 8.6 J kg−1 K−1, 7.6 J kg−1 K−1, 10.0 J kg−1 K−1 and 13.6 J kg−1 K−1 in HoCo1−xCuxSi (x = 0, 0.1, 0.2, 0.3 and 0.4) alloys, respectively. With the enhancement of substitution amount, the −ΔSMmax is decreased for x ≤ 0.2, which is caused by magnetic moment dilution effects. But the −ΔSMmax is increased for 0.3 ≤ x ≤ 0.4, which is caused by the field-induced metamagnetic transition at the critical component.

Structural, magnetic, and magnetocaloric properties of chromium doped Gd3Fe5-xCrxO12 garnet compound

The detailed structural, magnetic, and cryogenic magneto-caloric properties of chromium-substituted gadolinium iron garnet (Gd3Fe5-xCrxO12) nanocrystalline powders were studied using the facile autocombustion method and a calcination temperature of 1100 °C. The X-ray diffraction pattern showed that all samples were single-phase with cubic Ia3d symmetry. The temperature and field-dependent magnetization data of Gd3Fe5-xCrxO12 samples revealed a ferrimagnetic ordering at low temperatures. Upon Cr3+ substitution, the Curie temperature reduced by 7% at x = 0.25 from 560 K for x = 0.00 sample. In a field up to 5 T, the maximum magnetic entropy change was observed as ΔSM ∼ 3.8 J K−1 kg−1 for x = 0.00 and −ΔSM ∼ 3.9 J K−1 kg−1 for x = 0.25 sample, while the maximum relative cooling power, RCP, value of 420 J kg−1 was measured for x = 0.25 sample, which is 10% larger than the x = 0.00 (RCP ∼ 380 J kg−1). Therefore, Cr3+ substituted Gd3Fe5-xCrxO12 samples exhibit promising magneto-caloric performance and have potential low-temperature magnetic refrigeration applications.

Structural, magnetic, and magnetocaloric characterization of NiMnSn microwires prepared by Taylor-Ulitovsky technique

We report the structural, magnetic, and magnetocaloric characterization of glass-coated Ni42.9Mn37.1Sn20.0 microwires produced by the Taylor-Ulitovsky method. Microwire samples crystallized into a single-phase austenite with the L21-type crystal structure (space group Fm3̄m, lattice parameter a ≈ 6.02 Å) and a Curie temperature of 349 K. A distinctive feature of the produced microwires is that saturation magnetization is reached at a very low magnetic field (∼0.15 T). For a magnetic field change of 3 T, the produced microwires showed a reversible maximum magnetic entropy change |ΔSM|max of 2.3 J kg−1 K−1 and a refrigerant capacity of 197 J kg−1, which are similar to the values reported by other austenitic NiMnSn alloys produced by rapid quenching techniques.

Enhanced magnetocaloric effect in the Tb2In1−xAlx (0 ≤ x ≤ 0.6) alloy by hetero-structural alloying

The evolutions of the crystallographic structure and magnetic phase transition in Tb2In1−xAlx (0 ≤ x ≤ 0.6) alloys are investigated in this work. By gradually alloying antiferromagnetic orthorhombic Tb2Al, the crystalline structure of ferromagnetic Tb2In is gradually distorted from the hexagonal type for x ≤ 0.3 to orthorhombic one for x ≥ 0.4. The ferromagnetic ground state for x ≤ 0.4 is also gradually evolved into antiferromagnetic one for x ≥ 0.5. The phase transition temperature is decreased monotonously. At the critical composition of x = 0.4, the weak field-triggered metamagnetism is realized, leading into the enhanced maximum of magnetic entropy change from 6.6 J kg−1 K−1 in Tb2In to 10.6 J kg−1 K−1 in Tb2In0.6Al0.4 for a field of 5.6 × 106 A/m. The origin is supposed to be from the lattice distortion due to the critical composition at the phase borderline.

Magnetic field dependent metal insulator transition by monovalent doping (Na+) in PrMnO3: Investigation through structural, magnetic and transport properties

A detailed study on the structural, magnetic, and transport properties of a monovalent (Na+) doped Pr0.75Na0·25MnO3 (PNMO) compound has been carried out. Temperature (T) and magnetic field (H) dependent magnetization (M), and resistivity (ρ) measurements have been carried out which reveal a second-order magnetic phase transition around TC = 60 K accompanied by a metal-insulator transition around TMI = 138 K. Magnetization measurements also confirm the coexistence of antiferromagnetic (AFM) and ferromagnetic (FM) components in the low-temperature regime. M − H has been used to calculate the magnetocaloric behavior and the system is found to show a maximum magnetic entropy change i.e. –ΔSmax as 2.54 J kg −1.K −1 for the field change of 5 T. Temperature dependence resistivity has been measured under the applied magnetic field and the system exhibits a colossal magnetoresistance (≅ 81%). Spin-polarized tunneling (SPT) model is applied to explain magnetoresistance (MR) phenomenon under applied magnetic field. Analysis of zero-field resistivity data signifies that a transition from Mott-VRH to Efros-Shklovskii-VRH (ES-VRH) conduction occurs in the low-temperature region in this present PNMO system.

Preparation and magnetocaloric performance of La(Fe,Co,Si)13 alloys with wide transition temperature range

NaZn13-type La(Fe,Si)13 alloys are one of the most promising magnetocaloric materials for room-temperature magnetic refrigeration. However, the narrow ferromagnetic-to-paramagnetic transition temperature range of La(Fe,Si)13 alloys severely limited their magnetic refrigeration application. Herein, a series of La1.4Fe11.8-xCoxSi1.2 (x = 0.88, 0.94, 0.98, 1.02, 1.06) alloys were designed and prepared by high-energy ball milling and annealing. It is discovered that all the samples are composed of La(Fe,Co,Si)13 main phase and a small amount of α-Fe phase. The Curie temperature of the ferromagnetic-to-paramagnetic transition was well adjusted to room temperature by optimizing the x. A maximum magnetic entropy change (-ΔSM) of 4.0 J kg−1 K−1 for the sample with x = 0.98 was obtained at a magnetic field of 2 T. Meanwhile, all the samples exhibit a significant increase in the half-height width of -ΔSM reaching approximately 35 K, increased by more than 41% compared with that of the reference sample prepared by arc melting. The broadened temperature range originates from the lattice distortion induced by the ball milling process. Our work indicates that La(Fe,Si)13 alloys with relatively large -ΔSM and wide transition temperature range can be simultaneously obtained around room temperature by optimizing the composition and the ball milling process.

Magnetic critical behavior and room temperature magnetocaloric effect in Ba1.9Pr0.1FeMoO6 double perovskite compound

In this paper, we report the critical behavior related to the magnetocaloric effect of Ba1.9Pr0.1FeMoO6 double perovskite. A maximum magnetic entropy change, |ΔSMmax| ∼ 0.68 Jkg−1K−1 and relative cooling power, RCP ∼ 62 Jkg−1 were observed under applied field of H = 2.5 T. The critical exponents were evaluated by using modified Arrott plots, Kouvel-Fisher, critical isotherm analysis and Widom scaling relation methods. A second order phase transition (paramagnetic to ferromagnetic) was observed at Curie temperature, TC = 319.73 K with critical exponents β = 0.45, γ = 0.84, and δ = 2.91. The value of these critical exponents shows that this sample obeys mean field model and Widom scaling relation. Also, we observed that the different isothermal magnetization data are able to collapse into the two branches below and above TC based on the single scaling equationM(H,ε)=εβf±(H/εβ+γ) that affirms the authenticity of the critical exponents.