ΔSM Values Research Articles

Anisotropy of the magnetocaloric effect in MnAs single crystal

The magnetic and magnetocaloric properties of a MnAs single crystal have been studied along different crystallographic directions in the temperature range of the first-order magnetic phase transition. The constants of magnetocrystalline anisotropy, K1 and K2, were determined below the transition temperature by the Sucksmith-Thompson method. It was found that the energy of magnetocrystalline anisotropy decreases with increasing temperature. The results highlighted the impact of shape anisotropy and the magnetic prehistory of the sample on the maximum value of −ΔSm. The anisotropy of the −ΔSm value was observed for different crystallographic directions; the −ΔSm value reaches its maximum of 35 J∙kg−1∙K−1 in the [001] direction, while 29 J∙kg−1∙K−1 in the [110] direction. The probability of overestimating the ΔSm(T) values when using Maxwell’s equation instead of the Clausius-Clapeyron formula is shown.

Achieving Magnetic Refrigerants with Large Magnetic Entropy Changes and Low Magnetic Ordering Temperatures.

Adiabatic demagnetization refrigeration (ADR) is a promising cooling technology with high efficiency and exceptional stability in achieving ultralow temperatures, playing an indispensable role at the forefront of fundamental and applied science. However, a significant challenge for ADR is that existing magnetic refrigerants struggle to concurrently achieve low magnetic ordering temperatures (T0) and substantial magnetic entropy changes (-ΔSm) at ultralow temperatures. In this work, we propose the combination of Gd3+ and Yb3+ to effectively regulate both -ΔSm and T0 in ultralow temperatures. Notably, the -ΔSm values for Gd0.1Yb0.9F3 (1) and Gd0.3Yb0.7F3 (2) in the 0.4-1.0 K range exceed those of all previously reported magnetic refrigerants within this temperature interval, positioning them as the most efficient magnetic refrigerants for the third stage to date. Although the -ΔSm values for Gd0.5Yb0.5F3 (3) in 1-4 K are less than those of the leading magnetic refrigerant Gd(OH)F2, the -ΔSm values for Gd0.7Yb0.3F3 (4) in 1-4 K at 2 T surpass those of all magnetic refrigerants previously documented within the same temperature range, making it the superior magnetic refrigerant for the fourth stage identified thus far.

Metamagnetic phase transition and corresponding magnetocaloric effect in intermetallic Ho1-xTbxCo2 alloys

A comprehensive investigation was conducted to examine the magnetic properties and magnetocaloric effect (MCE) around the phase transition temperature of the intermetallic Ho1-xTbxCo2 (x=0.05, 0.1, and 0.15) alloys. X-ray diffraction (XRD) investigations reveal that the single-phase alloys crystallize in the cubic phase (space group Fd3̅m) at room temperature and undergo a structural transition to the tetragonal phase (space group I41/amd) below their Curie temperatures. These alloys demonstrated a metamagnetic transition around their respective phase transition temperatures, accompanied by a remarkable MCE and negligible hysteresis loss. The Landau free energy study confirmed the existence of the first-order magnetic transition in the aforementioned samples. The spin reorientation occurring below the transition temperature was observed. The studied alloys displayed significant magnetic entropy change (ΔSM) values of 15.6 JKg−1K−1, 15.2 JKg−1K−1, and 13.06 JKg−1K−1 in a wide temperature span over 20 K under a magnetic field change (ΔH) of 5 T for x=0.05, 0.1, and 0.15, respectively. Furthermore, large refrigerant capacities (RC) of 323.6 Jkg−1, 311.28 Jkg−1, and 323.46 Jkg−1 were achieved under ΔH=5 T for these alloys. An unexpected asymmetric broadening of the ΔSM peak was observed as the magnetic field increased. A significant change in the adiabatic temperature (ΔTad) of 5.3–6 K was achieved under ΔH=5 T. The outstanding magnetocaloric performance of studied materials may make them promising for magnetic refrigeration applications within the 87–105 K temperature range.

Hourglass-Shaped Homo- and Heteronuclear Nonanuclear Lanthanide Clusters: Structures, Magnetism, Photoluminescence, and Theoretical Analysis.

Synthesis of nonameric cationic clusters [Dy9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (1), [Dy8Tb (acac)16(μ3-OH)8(μ4-OH)2]OH·2H2O (2), and [Gd9(acac)16(μ3-OH)8(μ4-OH)2]OH·6H2O (3) (acac = acetylacetonate) is reported. The emission spectrum of 1 shows Dy(III) ion characteristic bands assignable to the 4F9/2 → 6HJ (J = 15/2 to 9/2) transitions. Emission due to both Dy(III) and Tb(III) ions is observed for 2 in the visible range, with Tb(III) specific bands appearing due to the 5D4 → 7FJ (J = 6, 4, and 3) transitions. Cluster 3 exhibits a significant magnetocaloric effect (MCE), with -ΔSm values increasing with decrease in temperature and increase in field, reaching -ΔSmmax = 20.98 J kg-1 K-1 at 2 K and 9 T. Isotropic magnetic coupling constants (Js) in 3 derived from density functional theory (DFT) calculations reveal that the exchange interactions are antiferromagnetic and weak. Compound 3 possesses S = 7/2 ground state arising from the central Gd(III) ion along with several nested excited states due to competing antiferromagnetic interactions that yield reasonably large MCE values. Utilizing computed exchange coupling interactions, we have performed ab initio CASSCF/RASSI-SO/POL_ANISO calculations on antiferromagnetic 1 and 2 to estimate the exchange interactions using the Lines model. For 2, Dy(III)···Tb(III) exchange interactions were extracted for the first time and were found to be weakly antiferromagnetically coupled.

A New Family of SO42–‐Templated 3d‐4f High‐Nuclearity Clusters: Syntheses, Structures, and Magnetic Properties†

Comprehensive SummaryThe precise syntheses of transition–rare‐earth metal clusters with desired structures remain a great challenge. Herein, by utilizing SO42– anion released by in‐situ decomposition of sodium dodecyl sulfate (SDS) as a template, a series of novel high‐nuclearity 3d‐4f clusters, formulated as [Ni24Pr22(μ3‐OH)31(pida)24(SO4)4(NO3)9(CH3COO)3]·Br4·(NO3)11·16H2O·25CH3OH (1, H2pida = N‐phenyliminodiacetic acid), [Ni24Nd22(μ3‐OH)31(pida)24(SO4)4(NO3)9(CH3COO)3]·Br4·(NO3)11·14H2O·24CH3OH (2) and [Ni24Gd22(μ3‐OH)36(bida)24(SO4)7(NO3)3(CH3COO)3]·(SO4)·Br4·(NO3)4·31H2O·32CH3OH (3, H2bida = N‐benzyliminodiacetic acid), have been successfully isolated. X‐ray crystal structure analyses reveal that all the cationic {Ni24RE22} cores in 1—3 possess a ball‐like structure with C3v symmetry, and can be viewed as consisting of an inner {RE22} core and an outer {Ni24} shell. From 1 and 2 to 3, due to the lanthanide contraction effect, the coordination numbers for rare‐earth metal centers in {RE22} are different, resulting in different number of SO42– and NO3– anions to support and stabilize the skeleton structures. Meanwhile, the magnetic properties of complexes 1—3 were also studied. The result revealed that complexes 1—3 show antiferromagnetic/ferrimagnetic interactions, and 3 exhibits magneto‐caloric effect at ultralow temperatures with a maximum –ΔSm (magnetic entropy change) value of 33.03 J·kg−1·K−1 at 3.0 K and 7 T.

Exploring the Water Oxidation Catalytic Activity of a Mn-Based Magnetic Metal-Organic Framework: The Role of Proton Conductivity and Oxygen Evolution Reaction Overpotential.

The present work evaluates the water oxidation catalytic activity of a Mn-based metal-organic framework (MOF), which we envisioned to reduce the oxygen evolution reaction (OER) overpotential because of its high electrical conductivity, facilitated by solvent-encapsulated structural features. The presence of Mn centers induces interesting magnetic features in the MOF, which exhibits impressive cryogenic magnetic refrigeration with a ΔSM value of 29.94 J kg-1 K-1 for a field change of ΔH = 5T at 2.3 K. To the best of our knowledge, the ΔSM value of the current system ranked the highest position among the published examples. The crystal structure aligns perfectly with the thematic expectations and features as many as ten metal-coordinated water molecules, forming an extensive web of a hydrogen-bonded network while facing toward the porous channel filled with another set of much-anticipated entrapped lattice water molecules. Such structural features are expected to manifest high proton conductivity, and detailed investigation indeed yields the best value for the system at 1.57 × 10-4 S/cm at 95% humidity and 85 °C. In order to evaluate the thematic notion of a one-to-one relationship between OER and improved electrical conductivity, extensive electrocatalytic water splitting (WS) investigations were carried out. The final results show highly encouraging WS ability of the Mn-MOF, showing the electrocatalytic surface area value of the active species as 0.0686 F/g with a turnover frequency value of 0.043 [(mol. O2) (mol. Mn-MOF)-1 s-1]. Another fascinating aspect of the current communication is the excellent synergy observed between the experimental WS outcomes and the corresponding theoretical data calculated using density functional theory (DFT). Consequently, a plausible mechanism of the overall OER and the role of the Mn-MOF as a water oxidation catalyst, along with the importance of water molecules, have also been derived from the theoretical calculations using DFT.

The self-assembly of tetranuclear [Gd4] cluster: Magnetic refrigeration and efficient CO2 chemical fixation

In this paper, the self-assembly of Gd3+ ions and ligand 5-chlorine-8-hydroxylquinoline (HL) successfully generated one tetranuclear lanthanide compound [Gd4(µ3-OH)2(L)6(acac)4] (1) (L = 5-chlorine-8-hydroxylquinoline; Hacac = acetylacetone), in which four Gd3+ ions are connected into a [Gd4O2] cluster. Magnetic studies revealed that anti-ferromagnetic interactions between neighbouring Gd3+ ions were observed in 1. In addition, 1 also shows magnetocaloric effect and the −ΔSm value reaches 28.05 J kg−1 K−1 at T = 2.0 K and ΔH = 7 T. Catalytic experiments indicated that 1 and tetra-n-butylammonium bromide (TBAB) could synergistically catalyze the cycloaddition reaction of CO2 and epoxides at relatively mild condition.

Solvent-dependent Ln(III) clusters assembled by immobilization of CO2 in air: zero-field single-molecule magnets and magnetic refrigerant materials.

The automatic fixation of CO2 in air played a key role in the construction of Dy(III) single-molecule magnets (SMMs) and Gd(III) magnetic refrigeration molecular materials when Ln(III)Cl3 (Ln = Dy and Gd) was reacted with a new hydrazone Schiff base ligand {H2L = (E)-N'-(4-fluoro-2-hydroxybenzylidene)pyrimidine-4-carbohydrazide}, which is condensed from pyrimidine-4-carbohydrazide and 4-fluorosalicylaldehyde. Surprisingly, the small difference in methanol and ethanol solvents leads to dramatic changes in the structures of these Ln(III) cluster complexes. When methanol and ethanol participated in the reaction, a trapezoidal pyramid Dy(III) pentanuclear cluster [Dy5L5(OH)2(CO3)(O2COMe)(MeOH)3(H2O)]·3MeOH·3.5H2O (1) and a triangular prism Dy(III) hexanuclear cluster [Dy6L6(CO3)2(EtOH)2(H2O)2Cl2]·6EtOH (2) were obtained, respectively, and a tub-like Gd(III) octanuclear cluster [Gd8L8(CO3)4(MeOH)3(H2O)5]·12MeOH·3CH2Cl2·3.25H2O (3) and a trapezoidal pyramid Gd(III) pentanuclear cluster [Gd5L4(HL)(CO3)O(OH)(EtOH)5(H2O)2Cl]·EtOH·3H2O (4) were yielded, respectively. Notably, 1 contains not only the carbonate anion, but also the monomethyl carbonate anion as the bridging ligand, which are formed by immobilizing CO2 in air, while 2, 3 and 4 contain the carbonate bridging ligand only. Magnetic properties' investigations revealed that both 1 and 2 are zero-field SMMs, with Ueff/k values of 93.2 K and 133.5 K, respectively, while 3 and 4 show large magnetocaloric effects, with the largest -ΔSm values of 27.49 J kg-1 K-1 at 2.0 K for ΔH = 7 T for 3 and 27.58 J kg-1 K-1 at 2.5 K for ΔH = 7 T for 4.

A study on the magnetothermal properties and magnetocaloric effect in [formula omitted] ([formula omitted

In this study, we investigate the Gd1−xCexMn2Ge2 system with x=0.17 and x=0.33 using the mean field theory. Ab-initio based calculations are used to determine the density of states at Fermi energy, D(Ef), and Debye temperature θD for GdMn2Ge2 main compound. Our aim is to determine key properties such as magnetization, magnetic heat capacity, and the magnetocaloric effect main aspects including both isothermal entropy change and adiabatic temperature change. We examine these parameters under various conditions by applying different field changes up to 6 T and at temperatures spanning a range up to 400 K. The two systems have a Curie temperature, that is around room temperature (around 330 K). Using the trapezoidal method, the Gd1−xCexMn2Ge2 systems exhibit a maximum ΔSm value of 0.79 J/mol K for ΔH=6 T, and a ΔT value of an average 1.3 K/Tesla. In our study, the relative cooling power (RCP) was investigated and moreover, we examined the nature of phase transitions using universal curves and Arrott plots to confirm that the nature of phase transition at Tc in this system corresponds to a second-order phase transition (SOPT). The influence of high magnetic fields on the magnetization was also examined, and it showed first-order phase transition (FOPT) at low temperatures and high fields. Additionally, due to FOPT, a change in magnetic order from ferrimagnetism to ferromagnetism took place.

Gd2O3 nanoparticles prepared by spark discharge method: Structure and magnetocaloric properties

Several batches of nanoparticles of gadolinium oxide Gd2O3 were obtained by the electrophysical spark discharge (ESD) method using selected variations of the value of the energy supplied to the discharge gap. The change of the charge voltage led to a change in the energy supplied to the discharge gap in the range of 3 J to 55 J. The average size of spark discharge nanoparticles in all cases was close to 8 nm in accordance with low-temperature nitrogen adsorption data. Gd2O3 nanoparticles contained two crystalline phases (cubic and monoclinic), the amount of which varied within certain limits by changing the parameters of the spark discharge. The obtained maximum values of the magnetic entropy change ΔSM of the studied ESD Gd2O3 nanoparticles with a monoclinic phase content of less than 40 wt% are not inferior to the value of ΔSM of Gd2O3 nanoparticles obtained by chemical methods. The spark discharge technique seems to be a promising technology for manufacturing of gadolinium oxide nanoparticles applications for the magnetic cooling systems of cryogenic refrigeration.

Enhancing magnetocaloric properties of NiMnGa-based alloys via Dy micro-alloying and pseudoelastic cyclic training

Considerable interest to improve magnetic entropy change (ΔSm) and broaden working temperature interval (WTI) of NiMnGa ferromagnetic shape memory alloys (FESMAs) was stimulated by their applications as promising candidate materials for solid-state refrigeration. In the present study, we presented an approach to enhance the magnetocaloric properties of polycrystalline NiMnGa FESMAs via combining Dy micro-alloying and pseudoelastic cyclic training. The introduction of Dy elements established stable magneto-structural coupling transformation from the paramagnetic austenite to ferromagnetic martensite, accompanied by a large ΔSm [−16.42 J/(kg K)] and a widened WTI (∼15.98 K). Fascinatingly, it was demonstrated that the internal strain fields at phase interface between matrix and DyNi4Ga precipitates could assist the phase transformation nucleation, which significantly reduced the hysteresis loss from 20.84 J/kg of Ni54Mn25Ga21 alloy to 8.14 J/kg of Ni54Mn25Ga20.7Dy0.3 alloy. More importantly, the subsequent pseudoelastic cyclic training produced a strong ⟨110⟩NM preferred crystallographic orientation, which facilitated the magnetic alignment along easy magnetization axis. Consequently, the giant ΔSm value up to −24.25 J/(kg K) and effective refrigeration capacity RCeff of 198.77 J/kg were further achieved in the trained Ni54Mn25Ga20.7Dy0.3 alloy under an external magnetic-field change of 5.0 T.

The effect of thermal post-processing treatment on laser powder bed fusion processed NiMnSn-based alloy for magnetic refrigeration

This study investigates the effects of heat treatment (HT) time (one, two, and three weeks) on the microstructure and magnetocaloric effect (MCE) of laser powder bed fusion (LPBF) NiMnSn alloys. Increasing the HT time improves chemical homogeneity, and decreases the local misorientation imparted by the LPBF process. This is also associated with an enhancement in the maximum magnetic entropy change (ΔSm) values around the martensitic transformation temperature (TM), which increases from 0.2 J kg−1 K−1 to 0.45 J kg−1 K−1 under 1 T applied magnetic field. However, the ΔSm of the one-week HTed sample around the curie temperature (Tc) (0.90 J kg−1K−1 at 315 K) is slightly lower than the two weeks and three weeks HTed samples (0.99 J kg−1K−1 at 320 K, 0.94 J kg−1K−1 at 320 K), respectively.

Some Magnetic Properties and Magnetocaloric Effects in the High-Temperature Antiferromagnet YbCoC2

The YbCoC2 compound, which crystallizes in a base-centered orthorhombic unit cell in the Amm2 space group CeNiC2 structure, is unique among Yb-based compounds due to the highest magnetic ordering temperature of TN=27 K. Magnetization measurements have made it possible to plot the H-T magnetic phase diagram and determine the magnetocaloric effect of this recently discovered high-temperature heavy-fermion compound, YbCoC2. YbCoC2 undergoes spin transformation to the spin-polarized state through a metamagnetic transition in an external magnetic field. The transition is found to be of the first order. The dependencies of magnetic entropy change ΔSm(T)—have segments with positive and negative magnetocaloric effects for ΔH≤6 T. For ΔH=9 T, the magnetocaloric effect becomes positive, with a maximum ΔSm(T) value of 4.1 J (kg K)−1 at TN and a refrigerant capacity value of 56.6 J kg−1.

Tunable structures and magnetic / optical properties of six Cd(II)-based coordination polymers by introducing different para- or dia-magnetic metal ions

One monometallic and five heterometallic coordination polymers (HCPs) based on homophthalic acid (H2HPA), [Cd2(HPA)2(H2O)2]·H2O (1), [CdMn(HPA)2(H2O)2]·H2O (2), [Cd3Co(HPA)4(H2O)4]·2H2O (3), [CdCo(HPA)2(DMSO)(H2O)2] (4), [CdNa2(HPA)2(μ2-H2O)(H2O)] (5) and [Cd2Na2(HPA)3(μ2-H2O)(H2O)2] (6), were synthesized solvothermally. Complexes 1-3 have similar two-dimensional (2D) layer structures except that all or part six-coordinated Cd(II) ions in 1 were replaced by the six-coordinated Mn(II) or Co (II) ion in 2 and 3, respectively. Complex 4 shows an 1D ladderlike structure, and 5 and 6 exhibit different 2D layer structures. The different structures of 3/4 and 5/6 could be assembled directly by controlling the different pH values with other same reaction conditions, respectively. Magnetic studies reveal that the introducing of para-magnetic Mn(II) and Co(II) ions endow antiferromagnetic interarions between the neigboring spins in 2–4, and 2 with isotropic Mn(II) ion displays a significant cryogenic magnetocaloric effect with a maximum −ΔSm value of 19.29 J K−1 kg−1 at 2 K and ΔH = 7 T. In addition, the solid-state photophysical properties of 1, 5 and 6 display blue emissions centered at ca. 453 nm, 448 nm and 428 nm, respectively.

Heterometallic Gd-Dy Formate Frameworks for Enhanced Magnetocaloric Properties.

Lanthanide-based metal-organic frameworks (MOFs) have great potential as magnetic refrigerants under cryogenic conditions and are comparable to conventional alloys and magnetic nanoparticles. In particular, MOFs with Gd3+ ions behave as excellent magnetic refrigerants because of their large spin ground states. However, the major drawback of Gd3+-based MOFs is that they are not affected by the ligand material owing to the excessively large spin-only magnetic moment; therefore, their application is limited to the cryogenic region in the magnetic cooling field. In this study, we report the magnetic properties and magnetocaloric effect (MCE) resulting from heterogenized MOFs obtained from the reaction of Gd3+ and Dy3+ ions and their varied molar composition with the formate ligand. For GdxDy1-x-(HCOO)3, where 0 ≤ x ≤ 1, the isothermal magnetic entropy change (ΔSm) increased with the increase in the fraction of Gd in the heterogenized MOFs. Meanwhile, with increasing Dy contents, the maximum peak temperature of ΔSm is shifted to a higher temperature while preserving a relatively high ΔSm value of 22.35 J·kg-1 K-1 at T = 7 K for an applied field change (ΔH) of 7 T despite the anisotropy and crystalline electric field effects. Furthermore, it was confirmed that the samples with a Dy content of 75% or more maintained the ΔSm operating temperature longer. Therefore, the current approach of including Dy3+ ions in lanthanide compounds provides the possibility of further extending the operating temperature of magnetic cooling materials from cryogenic temperatures.

Crystal structures and magnetocaloric properties of Li5ASrMB12O24(A = Mg, Zn; M = Cr, Ni)

Three new transition-metal-based borate crystals, Li5MgSrMB12O24 (M ​= ​Cr, Ni) and Li5ZnSrNiB12O24, were obtained using the high temperature solution method. Their structures were determined by the single crystal X-ray diffraction, which crystallize in the trigonal R3¯ space group. The [B3O11] groups in the structures lead to the long distance between two nearest magnetic ions, which can reduce the interaction of adjacent magnetic centers. The magnetic properties and thermal stabilities of the title compounds were also investigated. The results indicated that Li5MgSrCrB12O24 has stable chemical-physical properties and its maximum –ΔSm value of 14.33 ​J ​kg−1·K−1 at 2 ​K for Δμ0H ​= ​9 ​T reaching 88.6% of the theoretical paramagnetic limit, suggesting its potential application on the magnetic refrigeration.

Investigation on magnetic and magnetocaloric properties of Sr0.25Ca0.75Mn0.9Ti0.1O3 perovskite

Interest in magnetic refrigeration, which is based on the magnetocaloric effect (MCE), has greatly increased during the past two decades. As a less-polluting and more effective cooling technology than gas compression, magnetic refrigeration is one of the prominent and possible options. Perovskite Oxides played a major contribution for the development of magnetic refrigeration (MR). Sr0.25Ca0.75Mn1-xTixO3 (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) polycrystalline samples were synthesized by conventional solid-state reaction. Its cubic perovskite-type crystal structure is discovered to be of the Pm-3m space group. At T = 31.3 K, the alloy experiences antiferromagnetic transition for the composition of Sr0.25Ca0.75Mn0.9Ti0.1O3. It demonstrates that the greatest magnetocaloric reports are 8 J/kg K for a magnetic field of 7 Tesla and 3.2 J/kg K for 1 Tesla. These (ΔSM) value is comparable to the magnetization values of the ferromagnetic Heusler alloys and are very high in these kinds of antiferromagnetic perovskite systems. For the Sr0.25Ca0.75Mn0.9Ti0.1O3 material, this is the first report of substantial magnetic entropy changes brought on by a weak magnetic field.

Magnetic properties of double perovskite oxide Gd1.8Ce0.2NiMnO6

In this paper, a double perovskite oxide Gd1.8Ce0.2NiMnO6 polycrystalline sample was prepared using a conventional high temperature and solid-state reaction method. The phase formation of sample was examined using X-ray diffractometry, and the magnetic properties were measured using a PPMS. The results showed that the sample was monophase and had a space group of monoclinic P21/n. At T > TG the sample was purely paramagnetic. At TC < T < TG paramagnetic and ferromagnetic states coexisted, and Griffiths-like phase appeared in the sample. In the lower temperature region (T < TN) there was competition between ferromagnetic and antiferromagnetic states, and cluster spin-glass behavior appeared. When a magnetic field of 7 T was applied, the double perovskite oxide Gd1.8Ce0.2NiMnO6 showed a maximum −ΔSM value of 3.12296 J · kg−1 · K−1 near Curie temperature with an RCP (Refrigeration Cooling Performance) of 231.09904 J/kg. Analysis of the Arrott, recalibration and Loop curves all proved that the sample underwent a second-order phase transition.

The Stepwise Formation of {Gd4} Clusters with Magnetocaloric Effect, Accompanied by In Situ Condensation Cyclization Reactions

Accompanied by condensation cyclization reactions in solvothermal conditions, three Gd(III) tetranuclear clusters {[Gd4(Lx)2(μ3-OH)2(NO3)2(Ac)6]} (x = 1, 2, and 3 for 1, 2, and 3, respectively) were isolated and characterized, wherein, L1–3 were in situ synthesized from bis[3-(pyridin-2-yl)-1H-1,2,4-triazole-5-yl]methane (bptm), 5-bptm (bis[3-(5-methylpyridin-2-yl)-1H-1,2,4-triazole-5-yl]methane), and 4-bptm (bis[3-(4-methylpyridin-2-yl)-1H-1,2,4-triazole-5-yl]methane) in the presence of GdIII ions, respectively. The step-by-step formation process (bptm → L1 → Gd1(L1)1 → Gd2(L1)1 → Gd2(L1)2 → Gd3(L1)2 → Gd4(L1)2) of the tetranuclear clusters in 1 was tracked by mass spectrometry technology. The study of their magnetic properties showed that 1–3 displayed significant magnetocaloric effects with the −ΔSm values of 29.25–29.64 J K–1 kg–1.

Large magnetocaloric effect in the frustrated antiferromagnet EuIr[formula omitted]P[formula omitted

We present a theoretical analysis of the magnetocaloric effect in the frustrated antiferromagnet EuIr2P2. Monte Carlo simulations indicate a large magnetic entropy change ΔSMmax∼5 J kg−1 K−1 at T=2.45 K for a moderate change in the external magnetic field ΔB=1.2 Tesla. The highest value of ΔSM seems to be associated with the presence of a multicritical point in the magnetic field versus temperature phase diagram (at Bm∼1.2 Tesla and Tm∼2.2 K) but it persists with similar large values for a broad range of temperatures T≲Tm. Single crystal EuIr2P2 magnetization vs magnetic field experiments allowed us to obtain the magnetocaloric effect for T>2 K. The results are consistent with the theoretical analysis and show a large magnetocaloric effect for T∼2.5 K. Finally, we present a phenomenological Landau functional analysis that provides a simplified description of the phase diagram and of the magnetocaloric effect. Although the magnetic frustration in this system leads to a rich phase diagram, we found no clear indication that it plays a significant role enhancing the magneticaloric effect, other than by reducing the transition temperatures and fields.