Magnetic Entropy Change Research Articles

The Influence of Sn Addition on the Magnetocaloric Effects, Magnetic and Mechanical Properties of Fe<sub>2</sub>P-Type Mn-Fe-P-Si Compounds

Mn1.25Fe0.65-xSnxP0.50Si0.50 (0, 0.02, 0.04, 0.05, 0.06, 0.08, 0.09, 0.10, 0.20) series compounds were prepared by mechanical alloying and solid-phase sintering, and their mechanical and magnetic properties were studied. The XRD measurement results show that all the compounds crystalize in Fe2P hexagonal structures, with a space group of P-62m. With the increase in Sn content, the compressive strength is significantly improved, the Curie temperature of the compound gradually decreases, and the nature of magnetic transition is tuned from a weak to strong first-order one, which is confirmed by the increase of thermal hysteresis of the compounds. The maximum magnetic entropy change of the compound increases from 9.3 J/kg·K at x = 0 to 17.2 J/kg·K at x = 0.04 under a magnetic field change of 0 - 3 T.

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.

Crystal growth and magnetocaloric effect of Li9Fe3(P2O7)3(PO4)2 with Kagome lattice

With the growing demand for low-temperature technologies, magnetic refrigeration, which is based on magnetocaloric effect (MCE) of magnetic materials, has attracted increasing attention. In this work, Li9Fe3(P2O7)3(PO4)2 (LFPP) crystals have been grown by the high-temperature flux method. The crystal structural characterization is analyzed, and its magnetocaloric effect (MCE) is in detail investigated for the first time. The maximum magnetic entropy changes (−ΔSM) of LFPP under a field change of 0–7 T are determined to be 4.6 J/kg·K (H⊥c) and 4.1 J/kg·K (H//c) at 4 K and 5 K, respectively. The slow decrease of −ΔSM around the phase transition temperature implies that LFPP has a large refrigeration temperature range.

Enhanced Magnetocaloric Properties of the (MnNi)0.6Si0.62(FeCo)0.4Ge0.38 High-Entropy Alloy Obtained by Co Substitution.

In order to improve the magnetocaloric properties of MnNiSi-based alloys, a new type of high-entropy magnetocaloric alloy was constructed. In this work, Mn0.6Ni1-xSi0.62Fe0.4CoxGe0.38 (x = 0.4, 0.45, and 0.5) are found to exhibit magnetostructural first-order phase transitions from high-temperature Ni2In-type phases to low-temperature TiNiSi-type phases so that the alloys can achieve giant magnetocaloric effects. We investigate why chexagonal/ahexagonal (chexa/ahexa) gradually increases upon Co substitution, while phase transition temperature (Ttr) and isothermal magnetic entropy change (ΔSM) tend to gradually decrease. In particular, the x = 0.4 alloy with remarkable magnetocaloric properties is obtained by tuning Co/Ni, which shows a giant entropy change of 48.5 J∙kg-1K-1 at 309 K for 5 T and an adiabatic temperature change (ΔTad) of 8.6 K at 306.5 K. Moreover, the x = 0.55 HEA shows great hardness and compressive strength with values of 552 HV2 and 267 MPa, respectively, indicating that the mechanical properties undergo an effective enhancement. The large ΔSM and ΔTad may enable the MnNiSi-based HEAs to become a potential commercialized magnetocaloric material.

Insight into the Structural and Magnetic Properties of PrZnSi and NdZnSi Compounds Featuring Large Low-Temperature Magnetocaloric Effects.

The magnetocaloric (MC) and magnetic phase transition (MPT) properties in various types of rare earth (RE)-based magnetic materials have been intensively investigated recently, which are aimed at developing suitable MC materials for low-temperature cooling applications and better elucidating their inherent physical properties. We herein provide a combined experimental and theoretical investigation into two new light RE-based magnetic materials, namely, PrZnSi and NdZnSi compounds, regarding their structural, magnetic, MPT, and low-temperature MC properties. Both of these compounds crystallize in an AlB2-type hexagonal structure with a symmetry of the crystallographic space group P6/mmm and reveal a typical second-order-type MPT with ordering temperatures (TC) at approximately 13.5 and 18.5 K for PrZnSi and NdZnSi compounds, respectively. Moreover, they all exhibit large reversible low-temperature MC effects and remarkable performances, which are identified by the parameters of maximum magnetic entropy changes, relative cooling power, and temperature-averaged entropy change (temperature lift 5 K). The deduced values of these MC parameters under a magnetic field change of 0-7 T reach 16.3 J/kgK, 294.46 J/kg, and 15.79 J/kgK for PrZnSi and 15.4 J/kgK, 284.84 J/kg, and 14.95 J/kgK for NdZnSi, respectively, which are evidently better than those of most updated light RE-based magnetic materials with remarkable low-temperature MC performances, indicating that PrZnSi and NdZnSi compounds hold potentials for practical cooling applications.

Low-temperature magnetic refrigeration in Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses

This paper focuses on the magnetocaloric effect (MCE) of Gd20Tb20Er20Al20M20 (M = Fe, Co) high-entropy metallic glasses (HE-MGs). XRD and TEM results indicate that both HE-MGs are amorphous. Magnetic studies show that both HE-MGs display spin-glass behavior, undergo a second-order phase transition from ferromagnetic to paramagnetic, and exhibit soft magnetic properties at the Curie temperature (TC). Notable large and broad table-like magnetic entropy change characteristics of Gd20Tb20Er20Al20Fe20 (Gd20Tb20Er20Al20Co20) appear near a TC of 92 (51) K. Hence, under 7 T magnetic field, |-∆SMmax|, ∆ TFWHM, and RCP are 7.83 (10.10) J·kg-1·K-1, 120.07 (71.88) K, and 1008.26 (805.70) J·kg-1, respectively. Furthermore, the modulation of the magnetic and magnetocaloric properties of the samples after substitution of Fe for Co was revealed by the intricate 3d-3d and 3d-4f exchange interactions within the system. The magnetic phase transition critical behaviors in both HE-MGs were analyzed using the scaling law to clarify the deviation of amorphous materials from the mean-field theory. Thus, this study not only highlights the potential of this material for low-temperature magnetic refrigeration applications, but also expands our understanding of its physical properties.

Magnetic phase transition and critical behavior of the chiral magnet [formula omitted]-Mn type Co7Zn7Mn6

We report a systematic study of magnetic transformation and magnetic critical behavior in the chiral magnet β-Mn type Co7Zn7Mn6. It undergoes a paramagnetic-ferromagnetic phase transition around 190 K and shows a spin glass state at 18 K. The critical exponents β= 0.685, γ= 1.385, and δ= 3.03 are obtained by the investigation of magnetic field dependence on magnetic-entropy change and the calculation with Widom scaling relation. The reliability of critical exponents is confirmed by the scaling equation. The strong reversed site disorder of β-Mn type Co7Zn7Mn6 results in the localized characterization of carriers and a slow development of ferromagnetic ordering state.

Excellent magnetocaloric effect near the hydrogen liquefaction temperature of a binary Er67.5Co32.5 metallic glass

We reported the excellent magnetocaloric effect of a binary Er67.5Co32.5 metallic glass (MG) near the hydrogen liquefaction temperature. The binary MG ribbon was fabricated by a melt-spinning method. The Er67.5Co32.5 alloy exhibits a better glass formability than most of other rare earth (RE)-Co binary alloys. The maximum magnetic entropy change (−ΔSmpeak) and refrigeration capacity (RC) of the Er67.5Co32.5 amorphous ribbon under 0–5 T reach to 17.47 J/(kg × K) near its Curie temperature (Tc, ∼ 11 K) and 472 J/kg, both of which are rather high among the RE-based MGs with a Tc around 10 K and imply the potential application perspective as magnetic refrigerants for hydrogen liquefaction. The magnetization as well as magnetocaloric behaviors of the binary MG were observed, and the mechanism involved was investigated.

Structural and Magnetic Properties of B-Site-Ordered RE2CuTiO6 (RE = Dy, Ho, and Er) Double-Perovskite Oxides with Significant Cryogenic Magnetocaloric Performance.

The magnetocaloric effect (MCE) is currently intensively investigated in various rare earths (RE)-containing magnetic solids, not only for developing appropriate magnetocaloric materials (MCMs) for cryogenic magnetic cooling but also for deepening our understanding into the inherent physical properties of these materials. Here, we provide a systematic experimental investigation into a series of new RE2CuTiO6 (RE = Dy, Ho, Er) double-perovskite (DP) oxides regarding the structural and magnetic properties, especially for their cryogenic MCE and magnetic-phase transition (MPT). All of these RE2CuTiO6 oxides crystallize in a B-site-ordered hexagonal DP-type structure with the symmetry of the crystallographic space group P6̅m2. These DP oxides exhibit magnetic ordering, with MPT temperatures of approximately 2.7, 2.2, and 2.7 K for Dy2CuTiO6, Ho2CuTiO6, and Er2CuTiO6, respectively. The magnetocaloric performances of the RE2CuTiO6 DP oxides were characterized by the peak values of magnetic entropy change, the temperature-averaged magnetic entropy change (5K-lift), and relative cooling powers. These magnetocaloric parameters were deduced to be 18.7/17.9 J/kgK and 298.2 J/kg for Dy2CuTiO6, 12.5/12.2 J/kgK and 273.9 J/kg for Ho2CuTiO6, and 13.8/12.9 J/kgK and 188.4 J/kg for Er2CuTiO6 under a magnetic field change of 0-5 T. These values are comparable to those of most reported RE-containing magnetocaloric materials, indicating that these RE2CuTiO6 DP oxides are promising candidates for cryogenic magnetic cooling applications.

Influences on the structure, magnetic, and magnetocaloric effect of La0.8Sr0.2MnO3 ceramics by Co ion doping with sol-gel method and first-principles calculations

This paper investigated the impact of Co ions doping on the structure, magnetic properties, and magnetocaloric effect for La0.8Sr0.2Mn1-xCoxO3 ceramics (LSMCO) by sol-gel method and first-principles calculations The use of first-principles calculations was provided for subsequent experiments. The sol-gel preparation of LSMCO ceramics and sintered at 950 °C for 10 h. It was shown that the samples' cell volume and lattice constants changed slightly with increasing Co2+ doping but remained a rhombohedral structure (No.167, R-3c space group) by statistics of TEM and XRD. The average particle size for the LSMCO ceramics ranged from 130 nm to 170 nm. LSMCO's chemical composition was verified by EDS and XPS and it was demonstrated that Co2+ was successfully doped. The oxidation state of La was found to be +3, Mn is a mixture of Mn3+ and Mn4+ valence states, and Co is a mixture of Co3+ and Co2+ valence states using XPS. In the vicinity of Tc, all samples presented the second-order magnetic phase transition from ferromagnetic to paramagnetic resorting to normalization and the Banerjee criterion. The Tc dropped from 292 K to 237 K with increasing Co2+ doping. The blocking temperature and the saturation magnetization were suppressed by the Co2+ substitution while the maximum magnetic entropy change of the LSMCO ceramics was observed to reduce as Co2+ increased. When the external magnetic field is 5 T, the La0.8Sr0.2Mn0.95Co0.05O3 ceramics has a Tc of 292 K and a maximum magnetic entropy change value of 3.47 J/(kg K).

Large magnetocaloric effect and negative thermal expansion of Mn-Ni-Si-Fe-Co-Ge high-entropy alloys

Magnetocaloric high-entropy alloys (HEAs) with a vast compositional space have attracted significant interest for some time due to their great potential in multifunctional application. However, magnetocaloric HEAs generally exhibit modest magnet-entropy change as their undergo second-order phase transition. This work focuses on designing MM'X (M, M′ = transition metals, X = main group elements) HEAs undergoing magnerostructural transition to achieve great magnetocaloric response. For this purpose, MnxFe1-xNi0.6Co0.4Si0.62Ge0.38 (x = 0.43, 0.45, 0.48, 0.50) with intriguingly crystallographic texture are successfully synthesized and their magnetocaloric effect and negative thermal expansion (NTE) are investigated. The substitution of Fe for Mn reduces the transition temperature (Tt) so that weakens the first-order transition of MM'X HEAs. Besides, Mn0.55Fe0.45Ni0.6Co0.4Si0.62Ge0.38 undergoing first-order transition from Ni2In-paramagnetic-austenitic phase to TiNiSi-ferromagnetic-martensitic phase exhibits a great magnetic entropy change of 16 J∙kg−1K−1 at 206 K for 2 T. Moreover, an obviously NTE is observed through phase transition with liner NTE coefficient of −6.77×10−6 K−1. In addition, Mn0.55Fe0.5Ni0.6Co0.4Si0.62Ge0.38 displays an intriguing NTE with liner NTE coefficient of −1401.7×10−6 K−1 (220–270 K) along the direction parallel to field in a temperature range from 220 K to 270 K, which is much higher than typical NTE materials. Therefore, the present work demonstrates that MM'X HEAs exhibit potential to achieve some magnetocaloric and NTE multifunctional application.

Electron tailoring of thermal and magnetocaloric properties in Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) metallic glasses

Transition metal (TM) elements play a key role in determining properties of magnetocaloric materials. However, the effect of TM elements on the thermodynamic behavior and magnetocaloric effect (MCE) of metallic glasses (MGs) remains elusive. In this work, ternary Tb55TM17.5Al27.5 (TM = Fe, Co, and Ni) MGs without the complexities induced by high-entropy effects were designed. It is found that both the glass transition temperature (Tg) and the initial crystallization temperature (Tx) significantly increase with decreasing 3d electron number. It leads to the low values of Trg, γ, and γm for Tb55Fe17.5Al27.5, which is consistent with its poor glass forming ability (GFA) as evidenced by the obvious lattice fringes and structural order. Despite the mediocre value of magnetic entropy change (|ΔSMpk|) for Tb55Fe17.5Al27.5, its broader magnetic transition temperature of 110.4 K associated with ∼26% evident structural order yields the maximum relative cooling power (RCP) of 546.04 J kg−1 among three MGs. Moreover, a novel weighted method for evaluating 3d electron number by consideration of the concentration and species of TM elements was adopted to reveal an inverse correlation between the 3d electron number and Tg/Tx, as well as curie temperature (Tc), |ΔSMpk|, and RCP. It is found that with the decrease of the weighted 3d electron number of TM elements, the thermal stability of rare-earth-base MGs is effectively enhanced ascribed to the strong f - d orbital hybridization effect, along with the enhanced 3d - 3d exchange interaction that induces a high Tc. This work would help us more deeply understand the role of TM elements from the perspective of electronic structure, which is crucial for designing the novel MGs with a tunable MCE and GFA applied in various cryogenic refrigeration fields.

Study of the Structure, Multiferroic, and Magnetic Order of Er0.9La0.1Cr0.8Fe0.2O3

Herein, the multiferroic perovskite Er0.9La0.1Cr0.8Fe0.2O3 was synthesized using the sol–gel method, and its structure and multiferroic properties were investigated. The magnetic order of Er0.9La0.1Cr0.8Fe0.2O3 was analyzed through magnetic entropy change curves. Furthermore, a four‐sublattice molecular field model was constructed to study the spin reorientation phenomena and explain the differences between various spin redirections through magnetic order correction. This work will provide a new perspective for studying the properties of type II multiferroic materials.

Study of magnetic, thermodynamic and transport properties of Laves phase NdRh[formula omitted]

The results of magnetic measurements, electron spin resonance, heat capacity, resistivity, and magnetocaloric effect as well as density functional theory (DFT), are presented for the compound NdRh2 (MgCu2-type structure). This compound was synthesized at a pressure of 8 GPa and a temperature of 1700 K. The magnetic properties of the material are shown to be determined by the high-temperature (over 400 K) spin polarization of the 4d Rh electrons and by the ferrimagnetic (FiM) interaction of Rh and Nd magnetic subsystems. Concurrently, the spontaneous magnetization of the spin polarization of 4d Rh electrons is ≈0.01μB/Rh, while the Nd magnetic moment is ≈1.7μB/Nd. This leads to complicated magnetic behavior with long range FiM order at TC≲7 K at zero field and with wide temperature range of spin fluctuations TC<T≲50 K. Specific heat and resistivity data provide corroboration of the spin fluctuation regime with the spin fluctuation temperature Θsf≈28.5 K. The optimal critical parameters were identified as β=1.18±0.02, γ=0.85±0.02, and TC≈40 K from modified Arrott plotting, which are distinct from any conventional universality class. The maximum magnetocaloric effect, when the magnetic field changes from 0 to 9 T, ΔH=9 T occurs at T≈11 K and the magnetic entropy change reaches −ΔSm=7.0 J (kg K)−1. In our DFT calculations, the FiM arrangement was obtained, with values of magnetic moments of Nd and Rh. Additionally, the Fermi surface was constructed.

Effect of x-ray irradiation on magnetocaloric materials, (MnNiSi)1-x(Fe2Ge)x and LaFe13-x-yMnxSiyHz

Abstract Understanding the behavior of magnetocaloric materials when exposed to high-energy x-ray irradiation is pivotal for advancing magnetic cooling technologies under extreme environments. This study investigates the magnetic and structural changes of two well-studied magnetocaloric materials, (MnNiSi)1−x(Fe2Ge)x composition (x = 0.34) and LaFe13-x-yMnxSiyHz composition (x = 0.30,y = 0.1.26 and z = 1.53) alloys upon irradiation. The alloys were exposed to x-ray radiation with a dosage of a continuous sweeping rate of ∼&gt;120 Gy min−1 and an absorbed dose of 35 kGy . Both the samples didn’t show any observable crystal change after irradiation. There was a considerable change in magnetization at low applied magnetic fields in magnetization versus temperature measurements from 2.72 emu g−1 to 4.01 emu g−1 in the irradiated (MnNiSi)1−x(Fe2Ge)x sample and 4.41 emu g−1 to 5.49 emu/g for the LaFe13-x-yMnxSiyHz alloys. The Magnetization versus magnetic field isotherms near transition temperature exhibited irradiation-induced magnetic hysteresis for the (MnNiSi)1−x(Fe2Ge)x (x = 0.34) while the LaFe13-x-yMnxSiyHz samples did not result in any irradiation-induced magnetic hysteresis. In both the samples the magnitude of entropy change did not change due to irradiation however, the peak entropy change shifted to different temperatures in both the samples, (MnNiSi)1−x(Fe2Ge)x (x = 0.34), showed a maximum entropy change, ΔSmag of ∼ 11.139 J/kgK at 317.5 K compared to ΔSmag of ∼ 11.349 J/kgK at Tave peak of 312.5 K for the irradiated sample. LaFe13-x-yMnxSiyHz, pristine sample exhibited a maximum magnetic entropy change, ΔSmag ∼ 18.663 J/kgK, with the corresponding peak temperature, Tave peak, of 295 K compared to ΔSmag ∼ 18.736 J/kgK, at Tave peak of 300 K. It was determined that irradiation applied to the samples did not induce any structural or magnetic phase changes in the selected compositions but rather modified the magnetic properties marginally.

The second-order magnetic transformation and magnetocaloric effect in all-d-metal Heusler ribbon Ni35Co15Mn34Ti16

The new all-d-metal Heusler alloys with good mechanical properties are candidates for magnetocaloric materials compared other famous refrigeration materials. In this work, Ni35Co15Mn34Ti16 ribbon with a second-order magnetic transformation was investigated for magnetoclaoric effect. It crystalizes pure B2 structure at room temperature and undergoes a SOMT at Curie temperature in austenite (TCA = 358 K) between paramagnetic and ferromagnetic phase. A large saturation magnetization (MS) at 5 K is 166 emu/g. The maximum values of magnetic entropy change (−ΔSM) and the temperature-averaged entropy change TEC(10 K) reach 1.62(3.42) J kg−1 K−1 and 1.64 (3.44) J kg−1 K−1 with magnetic field change (ΔH) of 20(50) kOe, respectively, which are comparable to most of other all-d-metal Heusler alloys.

Achieve outstanding refrigeration performance near ambient temperature in a Fe88Pr8B2Ce2 amorphous ribbon

A novel Fe88Pr8B2Ce2 amorphous alloy (AA) with outstanding magnetocaloric effect near 295 K was vitrified into ribbon. The Fe88Pr8B2Ce2 ribbon exhibits a typical 2nd-order magnetic transition with a peak value of magnetic entropy change (−ΔSmpeak) of ∼ 4.34 J·kg−1·K−1 near its Curie temperature (Tc, ∼ 295 K) under 5 T, which is the highest among the AAs reported in the literature with Tc = 295±10 K. The temperature averaged entropy change (TEC) for the household air conditioner (TECAC) and refrigerator (TECR) were defined to evaluate the refrigeration performance of the magnetic refrigerants in these cooling facilities. TECAC and TECR for the Fe88Pr8B2Ce2 AA reach to 4.21 J·kg−1·K−1 and 3.93 J·kg−1·K−1, both of which are also much larger than those of other AAs with Tc near 295 K and indicate the better application perspective of the Fe88Pr8B2Ce2 AA as the magnetic refrigerants working in the residential magnetic air conditionings and refrigerators.

Large magnetocaloric effect of RCoSn (R=Dy, Ho, Er and Tm) compounds

Materials with large magnetocaloric effect (MCE) at low temperatures under low field changes play an important role in the application of cryogenic magnetic refrigeration and attract extensive research interests of researchers. In this work, four ternary rare-earth-based RCoSn (R=Dy, Ho, Er and Tm) compounds were successfully synthesized and the crystal structure, magnetic properties, magnetic phase transition, and magnetocaloric effects were systematically studied. RCoSn (R=Dy, Ho, Er and Tm) compounds all crystallize in orthorhombic TiNiSi-type structure and undergo an antiferromagnetic (AFM) to paramagnetic (PM) transition with Neél temperature of 11.0, 7.9, 4.9 and 3.0 K, respectively. Large cryogenic MCE of RCoSn (R=Dy, Ho, Er and Tm) with the maximum magnetic entropy change (−ΔSMmax) of 10.6, 13.7, 17.1, 13.4 J/kg K for field change of 0–5 T was obtained. Furthermore, the value of −ΔSMmax for ErCoSn and TmCoSn is as high as 11.3 and 10.1 J/kg K for field change of 0–2 T, which is very competitive among low temperature magnetocaloric materials. The characteristic of second order magnetic phase transition indicates RCoSn (R=Dy, Ho, Er and Tm) compounds have good magnetic/thermal reversibility. These results show that RCoSn compounds, especially ErCoSn and TmCoSn, exhibit promising MCE and have great application potential in cryogenic magnetic refrigeration.

Influence of electron and hole doping on structural, Magnetic, and magnetocaloric properties of Ba2FeMoO6 double perovskite

The impact of Sm3+ and Ag+ doping at the Ba2+ site on the structural, magnetic, and magnetocaloric properties of Ba2FeMoO6 (BFMO) double perovskite was compared. Samples were synthesized using the sol–gel method. Rietveld refinement patterns of samples Ba2-xAxFeMoO6 (A=Sm, Ag, x = 0.0, 0.025) showed all samples had cubic structures with Fm-3 m space group and no impurity. The lattice parameters and unit cell of the Ba1.975Sm0.025FeMoO6 (BSFMO), and Ba1.975Ag0.025FeMoO6 (BAFMO) samples decreased compared to the parent sample. X-ray photoelectron spectroscopy confirmed that Fe and Mo ions were mixed valence for all samples. The results of magnetization versus temperature (M−T) showed an increase for BSFMO and a decrease for BAFMO samples under an external magnetic field of 0.05 T. The magnetic study indicated a decrease in the transition temperature for BSFMO (∼303 K) and an increase for BAFMO (∼321 K) to compare with the parent sample (∼310 K). The maximum value of magnetic entropy changes (ΔSMmax)of the BFMO, BSFMO, and BAFMO samples at H=3 T obtained 0.92 Jkg-1K−1, 0.75 Jkg-1K−1, and 0.39 Jkg-1K−1, respectively, and the second-order magnetic phase occurred around the transition temperature. For BFMO, BSFMO, and BAFMO, the relative cooling power (RCP) is 34.48 J/kg, 32.25 J/kg, and 21.97 J/kg, respectively. The second-order magnetic phase transition occurred around the transition temperature for all samples using the energy criterion as well as the universal curve method. In addition, we used Widom’s law to determine the critical exponent of the samples, which provides a new thermodynamic method to determine the magnetic phase transition. The results of the magnetocaloric effect indicate that although the maximum entropy changes and relative cooling decrease with doping Ag and Sm ions, they have a wide temperature range of magnetic entropy changes compared to the pristine sample, which can be candidates for magnetic cooling.

Comparison of two methods for achieving table-like magnetic entropy change in Eu-Ga-Ge clathrates

A novel method has been developed to efficiently produce composites of Eu-Ga-Ge clathrates through the process of spark plasma sintering (SPS) under varying pressures, temperatures, and times. This technique enables the adjustment of the α and β phase ratios, thereby allowing for the fine-tuning of material properties. The resulting composite exhibits a cohesive growth of both phases rather than a mere mechanical mixture, making it suitable not only for enhancing magnetic applications but also for improving various other physical properties including thermoelectric characteristics. The article focuses on the investigation of magnetocaloric properties in composites with different phase ratios. Remarkably, it was observed that an appropriately balanced ratio between the two phases yields a distinct table-like curve depicting magnetic entropy change, consequently leading to a enhanced refrigeration capacity (RC). Additionally, a hybrid sample was obtained through the mechanical mixing of several Eu-Ga-Ge β phases with different Tc values. The hybrid also exhibits a magnetic entropy change curve with a table-like shape. A comparative analysis between these two methods was conducted.