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• Encapsulation of the magnetic quasi-two-dimensional system Cu(en)(H 2 O) 2 SO 4 in SBA-15. • Weakening of magnetic correlations after encapsulation. • Analysis of the EPR line shape confirmed significant magnetic dilution. In this work, we present an experimental study to find the optimal way of encapsulation of the magnetic quasi-two-dimensional system Cu(en)(H 2 O) 2 SO 4 (en = ethylenediamine = C 2 H 8 N 2) in mesoporous silica SBA-15 with hexagonal pore morphology with a pore size of 5 nm. Our main goal is to achieve the most significant possible degree of pore filling and to study the effect of encapsulation of complex Cu(en)(H 2 O) 2 SO 4 in SBA-15 silica on the magnetic properties of the studied complex by means of electron paramagnetic resonance (EPR) and magnetization measurements. It was found that the adsorption equilibrium during the adsorption of the Cu(en)(H 2 O) 2 SO 4 complex from the solution to SBA-15 was reached after only 24 h, and the samples prepared by adsorption for a longer time (72 h, 14 days) did not show an increased amount of the loaded complex. The degree of pore filling represents around 60 % of the total volume of internal pores. The analysis of temperature dependence of susceptibility, the field dependence of magnetization, and EPR spectra showed that due to the encapsulation of Cu(en)(H 2 O) 2 SO 4 complex in mesoporous silica, the magnetic correlations between Cu(II) ions are significantly weakened, yielding paramagnetic behavior in the studied system. [ABSTRACT FROM AUTHOR]

• Metal-organic framework ZIF-8 (1) and Cu-ZIF (2) were prepared as nanocrystallites. • Vibration spectra and lattice specific heat of (1) and (2) are the same. • Boson peak identified in the specific heat of (1). • Short-range correlations between surface spins manifest in specific heat below 6 K. • Short-range correlations between bulk spins manifest in susceptibility above 100 K. Applying the procedure of a rapid synthesis in the aqueous system, nanocrystalline form of ZIF-8 and Cu-ZIF was obtained. The composition of the latter was inferred from the comparison of vibration spectra and lattice specific heats of both compounds which become nearly identical. The nanocrystalline character of both compounds prevented direct comparison of powder XRD patterns and manifested by the appearance of a boson peak in the diamagnetic ZIF-8 specific heat. The low-temperature magnetic contribution in Cu-ZIF specific heat and a Curie-Weiss tail in low-temperature susceptibility may originate from the effect of surface spins while the round maximum observed in the susceptibility at 135 K indicates the presence of strong low-dimensional correlations with the exchange coupling ∼200 K. Corresponding magnetic contribution cannot be observed in the specific heat due to the huge overlap by the high-temperature lattice contribution. Negligible magnetization values at low temperatures correspond to the aforementioned strong antiferromagnetic coupling. Future experimental scenarios are discussed which should provide better understanding of the bulk and surface magnetism in this unique quantum system. [ABSTRACT FROM AUTHOR]

• Magnetization, susceptibility and specific heat experimentally investigated. • Only g -factor anisotropy is responsible for anisotropy in all data. • All data resemble main features of antiferromagnetic dimer model. • Field-induced ordered state stabilized between 6.5 T and 11 T. • Assumption of a dome shape magnetic diagram due to strong dimerization. Magnetic susceptibility, magnetization and specific heat of powder and single crystal of Cu(en) 2 SO 4 were investigated. The analysis of the data confirmed that Cu(en) 2 SO 4 can be treated as a quasi-two-dimensional array of magnetic dimers with singlet-ground state persisting up to about 6.5 T. Magnetization and susceptibility studies were performed in the singlet phase and the analysis revealed that g -factor anisotropy is the main mechanism responsible for the different behavior in the magnetic field applied along the b and c axis. The investigation of powder and single crystal specific heat in magnetic fields applied along all three crystallographic directions revealed only small anisotropy associated with the g -factor anisotropy. All mentioned data sets resemble main features of the spin 1/2 HAF dimer model with J / k B = -5.52 K. The observed deviations can be ascribed to the presence of inter-dimer interactions with the effective strength z'J' / k B = -2.7 K. In fields above 6.5 T the system passes from the singlet phase to the ordered state stable up to about 11 T. The expectation of a dome shape magnetic phase diagram is based on the strong dimerization of the magnetic lattice. Future experiments and calculations are discussed to identify the origin of the quantum phase transition associated with the gap closing. [ABSTRACT FROM AUTHOR]

The analysis of specific heat, magnetic susceptibility and magnetization identified the studied compound Cu[C 6 H 2 (COO) 4 ][H 3 N–(CH 2) 2 –NH 3 ]·3H 2 O as a quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet on the rectangular lattice with the intrachain coupling J 1 /k B ≈ 7.39 K and the interaction ratio R ≈ 0.44. A phase transition to a magnetically ordered state was observed in zero magnetic field at T N = 1.28 K. The analysis of magnetic specific heat in non-zero magnetic fields revealed features characteristic of the field-induced Berezinskii-Kosterlitz-Thouless phase transition theoretically predicted for ideal two-dimensional magnets. The electron paramagnetic resonance studies of Cu[C 6 H 2 (COO) 4 ][H 3 N–(CH 2) 2 –NH 3 ]·3H 2 O revealed the increase of g x and g y and decrease of g z below 25 K due to the presence of dipolar coupling and the exchange anisotropy. The upturn of linewidth appearing below 30 K can be ascribed to the development of intralayer magnetic correlations. • The system represents S = 1/2 Heisenberg antiferromagnet on the rectangular lattice. • A phase transition to a magnetically ordered state occurs in B = 0 T at T N = 1.28 K. • The field-induced Berezinskii-Kosterlitz-Thouless phase transition was observed. [ABSTRACT FROM AUTHOR]

Gadolinium oxymolybdate, Gd2MoO6 (monoclinic, C2/c) was prepared via nonconventional mechanochemical/thermal process from powdered oxide precursors (Gd2O3 and (NH4)2MoO4). The effect of mechanical activation via high-energy ball milling on the reactivity of the stoichiometric Gd2O3 + (NH4)2MoO4 mixture was studied by thermal analysis (TG-DSC) and Fourier-transform infrared spectroscopy. While thermal treatment of nonactivated mixture leads only to decomposition of (NH4)2MoO4 and formation of Gd2O3-MoO3 system, mechanical activation provides enough energy for a chemical reaction between both reactants. The product with an average crystallite size of approximately 1 μm shows a well-faceted morphology. The investigation of magnetic properties revealed antiferromagnetic coupling, which is attributed to exchange interactions. [ABSTRACT FROM AUTHOR]

An experimental study is presented of the rotational magnetocaloric effect in a KTm(MoO 4 ) 2 single crystal at temperatures above 2 K associated with the rotation of a single crystal between the magnetic easy and hard axis in constant magnetic fields up to 5 T. The magnetocaloric properties of KTm(MoO 4 ) 2 single crystals are investigated by isothermal magnetization measurements. The maximal rotational entropy change −Δ S R  ≈ 9.8 J/(kgK) is achieved at 10 K in a magnetic field of 5 T. The adiabatic rotation of a single crystal in a field of 5 T at an initial temperature of 4.2 K causes cooling of the sample down to 0.5 K, which indicates an interesting possibility of using this material for cooling processes at low temperatures. [ABSTRACT FROM AUTHOR]

A simple one-step mechanically induced route was used for synthesis of Gd 2 MoO 6 (GMO). Single-phase with disordered structure was obtained after 12 ​h of milling. Elemental analysis revealed continuous decomposition of ammonium orthomolybdate. SEM-EDS (energy dispersive X-ray spectrometry) analysis confirmed a homogeneous distribution of Gd, Mo, and O with the atomic ratio 22.2:8.6:69.2% corresponding to Gd 1.998 Mo 0.774 O 6.228. Aside from conventional X-ray diffraction, we here paid an effort to obtain the information about the local structure of our GMO by 155Gd ​Mössbauer spectroscopy. The analysis of temperature dependence of magnetic susceptibility and field dependence of magnetization of GMO was confirmed to be similar to those of the mechano/thermally synthesized Gd 2 MoO 6 mentioned in our previous study (Tóthová et al., 2019) [1]. Small deviations suggest the presence of nonmagnetic unreacted materials in the starting mixture used in the present mechanosynthesis. We would like to emphasize that the present simplified synthesis without annealing steps leads to GMO with very good quality in the terms of magnetic properties. Mechanochemical reaction of milled mixture up to 12 ​h at 500 ​rpm. On the left: view on the grinding/milling chamber containing milled mixture together with grinding/milling balls. On the right: 155Gd ​Mössbauer spectrum of mechanosynthesized product, i.e. Gd 2 MoO 6. [Display omitted] • Preparation of nanocrystalline Gd 2 MoO 6 by one-step mechanosynthesis. • 155Gd ​Mössbauer spectra of mechanosynthesized product. • Analyzing the quality of mechanosynthesized material by magnetic measurements. [ABSTRACT FROM AUTHOR]

We report on single-crystal growth, and crystal structure of CuMn 3 As 2 and Cu 2 Mn 4 As 3 compounds. Magnetic properties of Cu 2 Mn 4 As 3 were studied in temperature range between 2 and 400 K. The single crystals were prepared from bismuth flux and characterized by means of single crystals diffraction, electron-microprobe analysis, magnetic and resistivity measurements. Crystal structures of CuMn 3 As 2 and Cu 2 Mn 4 As 3 were determined by synchrotron radiation x-ray diffraction experiments at 100 K. The CuMn 3 As 2 and Cu 2 Mn 4 As 3 crystallize in an orthorhombic structure with very similar lattice parameters. Magnetic and resistivity measurements on Cu 2 Mn 4 As 3 suggest existence of long range magnetic order below 315 K with another magnetic transition at 45 K. [ABSTRACT FROM AUTHOR]

• Crystal structure suggests formation of magnetic dimers between Cu(II) ions. • Good agreement of experimental data with antiferromagnetic dimer model was observed. • The intra-dimer exchange coupling was estimated J/k B = −5.52 K. • Spin gap ∼11 K is expected to vanish at the critical field 7.8 T. • Absence of phase transition to magnetic long-range order down to 0.4 K. Specific heat, magnetic susceptibility and magnetization of Cu(en) 2 SO 4 single crystal were investigated in the field applied along the b- axis. The analysis of the susceptibility within the Curie-Weiss law indicates the antiferromagnetic nature of the exchange coupling between Cu(II) ions with zJ/k B = −6.4 K. Considering the structure of this material, the formation of magnetic dimers can be expected. Very good description of susceptibility data was achieved using the Heisenberg antiferromagnetic dimer model with intra-dimer coupling J / k B = −5.52 K, effective inter-dimer coupling J ' / k B = −0.3 K and g b = 2.12. The energy gap in the spin excitation spectrum was estimated Δ/ k B ≈ 11 K and corresponding critical field B c b ≈ 7.8 T required for closing the gap. The dimerized nature of magnetic interactions was also confirmed by specific heat and isothermal magnetization data which manifest qualitatively the same behavior as the aforementioned dimer model. The possibility of further low-temperature experiments in the closed gap regime is discussed to obtain more detailed concept of magnetic interactions in this interesting compound. [ABSTRACT FROM AUTHOR]

The temperature dependence of the thermal conductivity k(T) of the AsxS100-x glass system was studied down to 1.8 K in a wide range of various (x = 20, 28.6, 40, 45, and 50) compositions. Universal glass anomalies in k(T) were revealed. The temperature dependence k(T) ∼ T2 onset at the lowest temperatures and plateau below 15 K were detected. The plateau formation is sample quality sensitive and composition-dependent. It was experimentally found that even with a slow cooling rate, several samples were cracked. Depending on the sample damage, the additional internal scattering process leads to the k(T) plateau suppression. The observed k(T) temperature dependence is similar to the glassy ceramics-like behavior. [ABSTRACT FROM AUTHOR]

[Ni(fum)(phen)] (fum = fumarato, phen = 1,10 -phenanthroline) has been identified as a system consisting of antiferromagnetic S = 1 dimers with single-ion magnetic anisotropy D comparable to the intradimer exchange coupling J , D / J ≈ 1 and D / k B = −6 K. We present reclassification of the physical model of [Ni(fum)(phen)] magnetic subsystem and the magnetocaloric investigation of a [Ni(fum)(phen)] powder sample at temperatures above 2 K in magnetic fields up to 7 T. The analysis of magnetic specific heat and magnetocaloric effect in [Ni(fum)(phen)] has shown that the temperature dependence of the isothermal entropy change under different magnetic fields is in good agreement with theoretical predictions for the S = 1 ferromagnetic dimer with D / k B = −11.5 K, E / k B = −3.4 K and intradimer exchange coupling J / k B = 2.5 K. Sizeable conventional magnetocaloric effect was found around 5.8 K leading to - ΔS max = 8.2 Jkg−1K−1 for ΔB = 7 T. • Magnetocaloric effect in [Ni(fum)(phen)] – ferromagnetic dimer. • The maximal entropy change –Δ SM ≈ 8.2 J/(Kkg) is achieved in 7 T. • The intradimer ferromagnetic coupling improves the magnetocaloric properties. [ABSTRACT FROM AUTHOR]

• The glasses of As x S (100-x) with x = 20, 28.6, 45, 40, 50 were prepared. • Specific heat C p / T 3 shows a nonlinear dependence of boson peak (BP) on composition. • Longitudinal elastic moduli, Raman spectroscopy and C p / T 3 depend on composition. • Correlation between type of nanocluster and C p / T 3 was found in As x S (100-x) glasses. • Ring-like and branchy-like nanoclusters are a possible origin of BP. The combination of mean coordination and concentration dependencies of elastic modules and low-frequency Raman scattering of As-S glasses brings new information about the spectroscopic boson peak (SBP) behavior. The analysis of the characteristic temperature positions of the thermometric boson peak (TBP) and the magnitude of heat capacity of As-S glasses was performed. This study was focused on the As-S compounds from the first glass-forming region with particular attention to the compositions of flexible, intermediate, and stressed-rigid phases. The origin of SBP and TBP is expected to have a structural nature. The spectral features found in the super low-frequency region of Raman spectra were assigned to quasi-localized "soft" modes. The sulfur-rich glass, g -As 2 S 5 , represents the intermediate phase with As n S m clusters containing closed ends and several "soft" nanoclusters. These soft clusters can be responsible for intrinsic quasi-localized "soft" modes, the overall rigidity of the system, and quasi-elastic light scattering. [ABSTRACT FROM AUTHOR]

Chain-like crystal structure of phenylacetato complex of Ce(III) elucidated by Rietveld method. Nona-coordinated Ce(III) ion (O 9 donor set) of muffin shape polyhedron. Field induced slow magnetic relaxation with direct and Raman relaxation processes. [Display omitted] [Ce(PAA) 3 (H 2 O)] n complex (1) (HPAA is phenylacetic acid) was synthesised and studied. The crystal structure of 1 was elucidated by the Rietveld method. Its crystal structure is polymeric and is built up of Ce(III) ions interconnected by bridging PAA− ligands. The Ce(III) ions in 1 are nona-coordinated by eight carboxylate oxygen atoms from six PAA− ligands, and one aqua ligand completes the coordination sphere yielding O 8 O donor set. The studied material displays field-induced slow magnetic relaxation. Temperature dependence of the relaxation time suggests the existence of direct and Raman relaxation processes. Similarly, as for the other Ce(III) complexes, the existence of Orbach process may be questioned due to the large discrepancy between the value of the energy gap obtained from static and dynamic measurements. [ABSTRACT FROM AUTHOR]

• Nanocluster's contribution to the low-temperatures anomalies in As-S glasses. • Raman spectroscopy revealed g (ω) ∼ ω 2 dependence at ultra-low frequencies. • Specific heat C p/ T 3 showed Boson peak about T ∼ 5 K. • Nanoclusters produce thermal conductivity plateau and boson beak. • Ring-like and branchy-like nanoclusters are responsible for boson peak. A plateau characterizes the thermal conductivity k (T) of many amorphous materials at temperatures above 1 K together with a maximum in specific heat C p , called the Boson peak at the same temperature region. It has been believed for over 50 years that those features are the universal property of glasses. Using the analogy of the keystone species concept of ecology, where one species has a disproportionately large effect on its environment relative to its abundance, we will present the impact of keystone nanocluster concentration on low-temperature k (T). Our study is focused on the As-S glassy systems, where each compound represents a different environment. It is shown that the presence of keystone S 8 nanoclusters leads to the plateau formation in the k (T) of As 2 S 3 and As 2 S 5 samples. At the same time, the Boson peak in the C p was preserved, suggesting that nanoclusters contribute to both the k (T) plateau and C p maximum. [ABSTRACT FROM AUTHOR]

The magnetic properties of the hybrid materials formed by coordination compounds and clay minerals represent one of the main challenges in material science. The investigation of the intercalation of tris (2,2′-bipyridine)nickel(II) cations [Ni(bpy) 3 ]2+ present in the solution with chloride anions into synthetic saponite (Sap) was carried out by direct exchange of the sodium ions by nickel(II) complex. The final intercalated [Ni(bpy) 3 ]2+ saponite complex was characterized by powder X-ray diffraction (XRD), infrared (IR) spectroscopy, carbon and thermal analysis, and for the first time also by magnetic measurements. The carbon analysis proved a full replacement of Na+ with [Ni(bpy) 3 ]2+ cations. Furthermore, significant increase of the d 001 value of the intercalated saponite confirmed the presence of the [Ni(bpy) 3 ]2+ in Sap interlayers. Only limited effect of the saponite layers on the ring C-H or skeletal vibrations of the [Ni(bpy) 3 ]2+ complex was observed. The thermal stability of the [Ni(bpy) 3 ]2+ increased after its intercalation into saponite. The magnetic properties of the [Ni(bpy) 3 ]2+ saponite complex revealed similar magnetic response as the starting compound [Ni(bpy) 3 ]Cl 2 · n H 2 O suggesting that the local surroundings of the Ni(II) atoms in [Ni(bpy) 3 ]2+ intercalated into saponite remained unchanged. • The intercalation of [Ni(bpy) 3 ]2+ complex into synthetic saponite was accomplished. • The increase of d-value confirmed its presence in the saponite interlayers. • Thermal stability of the complex increased after its intercalation. • Magnetic properties of [Ni(bpy) 3 ]2+ remained unchanged after intercalation into saponite. [ABSTRACT FROM AUTHOR]

• Neutron powder diffraction experiments in temperature range 20 mK–300 K. • Completing the magnetic phase diagram of NdMn 1−x Fe x O 3 substitutional system. • X-rays and neutrons used as complementary probe. The low temperature crystal and magnetic structures of NdMn 0.1 Fe 0.9 O 3 were determined on the basis of X-ray and neutron powder diffraction experiments as well as from specific heat and magnetization measurements. The compound crystallizes in the orthorhombic crystal structure, space group Pnma, in the entire temperature interval 20 mK < T < 300 K. The lattice parameters exhibit standard thermal expansion effects for T > 20 K and at lower temperatures the anomalies due to magnetostriction effect were observed. The iron sublattice orders magnetically into 3 different magnetic structures, namely into Γ 5 = (A x , F y , G z) for 130 K < T < T N (Néel temperature); Γ 1 = (G x , C y , A z) for 15 K < T < 130 K and Γ 3 = (C x , G y , F z) for 20 mK < T < 15 K. The Nd ions order at temperatures below 1.6–1.75 K into the same Γ 3 phase as the iron sublattice at these temperatures. The obtained magnetic structures fit perfectly in between the magnetic phases of closely related NdFeO 3 and NdMn 0.5 Fe 0.5 O 3 compounds. Our study, together with all previously published data, completes the entire magnetic phase diagram of NdMn 1− x Fe x O 3 (0 ≤ x ≤ 1) solid solution substitutional system. [ABSTRACT FROM AUTHOR]

In our work, we have investigated the magnetocaloric effect (MCE) of core@shell Co@Au nanoparticles by heat capacity C p measurement in temperature range 1.9–55 K under external magnetic field. After the subtraction of lattice heat capacity contribution, the maximum of isothermal magnetic entropy change ΔS m   = 3.11 J K −1 kg −1 was obtained at field change from 0 to 9 T. Adiabatic temperature change ΔT ad   =  3.31 K, refrigerant capacity power RCP = 88.9 J kg −1 and efficiency of adiabatic temperature change η  = 0.37 K/T at the same external magnetic field change were established for the investigated system. The comparison of the results to the independent magnetic measurements data revealed the accordance of fundamental magnetocaloric characteristics obtained by both methods. Thus, this work is also the first experimental confirmation of relation between magnetocaloric response of nanoparticles and the low temperature magnetic transition from superparamagnetic to blocking/freezing state. [ABSTRACT FROM AUTHOR]

The coordination polymer [Gd(PDOA)(NO 3 )(H 2 O) 2 ] n ( 1 ) (PDOA = o -phenylenedioxydiacetato) has been prepared and spectroscopically and structurally characterized. Its crystal structure is formed of a ribbon-like arrangement of Gd(III) atoms linked by bridging carboxylate groups and placed at the cusps of fused triangles with Gd⋯Gd distances of about 6.1 Å. The Gd(III) central atoms exhibit decacoordination by oxygen atoms from hexadentate PDOA ligands with chelating and bridging functions, a chelating nitrato ligand and two aqua ligands. Intra- and intermolecular hydrogen bonds of the O H⋯O and C H⋯O types contribute to the stability of the structure. The temperature dependence of the magnetic susceptibility revealed weak magnetic interactions among Gd(III) ions which may be attributed to dipolar coupling. Investigation of the magnetocaloric effect gives an estimate of the maximum value of isothermal change of magnetic entropy –ΔS m ≈ 35 J kg −1 K −1 which suggests that 1 can be a good material for magnetic cooling at low temperatures. [ABSTRACT FROM AUTHOR]

Organo-metallic compounds Cu( en )(H 2 O) 2 SO 4 ( en =C 2 H 8 N 2 ) and Cu( tn )Cl 2 ( tn =C 3 H 10 N 2 ) representing S =1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/ k B ≈3 K, have been examined by specific heat measurements at temperatures down to nominally 50 mK and magnetic fields up to 14 T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures. A phase transition to long-range order was observed in Cu( en )(H 2 O) 2 SO 4 at T C =0.9 K while hidden in Cu( tn )Cl 2 . A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii–Kosterlitz–Thouless transition theoretically predicted for ideal two-dimensional magnets. [ABSTRACT FROM AUTHOR]

The comprehensive study reported herein provides compelling evidence that anion templates are the main driving force in the formation of two novel nanoscale lanthanide hydroxide clusters, {Gd38(ClO4)6} ( 1) and {Gd48Cl2(NO3)} ( 2), characterized by single-crystal X-ray crystallography, infrared spectroscopy, and magnetic measurements. {Gd38(ClO4)6}, encapsulating six ClO4− ions, features a cage core composed of twelve vertex-sharing {Gd4} tetrahedrons and one Gd⋅⋅⋅Gd pillar. When Cl− and NO3− were incorporated in the reaction instead of ClO4−, {Gd48Cl2(NO3)} is obtained with a barrel shape constituted by twelve vertex-sharing {Gd4} tetrahedrons and six {Gd5} pyramids. What is more, the cage-like {Gd38} can be dynamically converted into the barrel-shaped {Gd48} upon Cl− and NO3− stimulus. To our knowledge, it is the first time that the linear M-O-M′ fashion and the unique μ8-ClO4− mode have been crystallized in pure lanthanide complex, and complex 2 represents the largest gadolinium cluster. Both of the complexes display large magnetocaloric effect in units of J kg−1 K−1 and mJ cm−3 K−1 on account of the weak antiferromagnetic exchange, the high NGd/ MW ratio (magnetic density), and the relatively compact crystal lattice (mass density). [ABSTRACT FROM AUTHOR]

Two kinds of inorganic gadolinium(III)-hydroxy 'ladders', [2× n] and [3× n], were successfully trapped in succinate (suc) coordination polymers, [Gd2(OH)2(suc)2(H2O)] n ⋅ 2 n H2O ( 1) and [Gd6(OH)8(suc)5(H2O)2] n ⋅4 n H2O ( 2), respectively. Such coordination polymers could be regarded as alternating inorganic-organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (Δ H=70 kG) 42.8 J kg−1 K−1 for complex 1 and 48.0 J kg−1 K−1 for complex 2. The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm−3 K−1 for complexes 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

Magnetic properties of three variants of MOF-76(Gd), {[Gd(BTC)(H2O)]·G}n (BTC = benzene-1,3,5-tricarboxylate, G = guest molecules) were investigated by static susceptibility, isothermal magnetization and specific heat capacity measurements. In the study we used as synthesized MOF-76(Gd)-DMF (1) (G = DMF = dimethylformamide), containing DMF molecules in the cavity system, compound MOF-76(Gd) (2), activated complex without solvents in the cavities and water exchanged sample MOF-76(Gd)-H2O (3). A pronounced change in the magnetic entropy was found near the critical temperature for all three compounds. It was shown, that magnetic entropy change depends on the solvatation of the MOF. The highest value entropy change, ΔSMpk(T) was observed for compound 2 (ΔSMpk(T) = 42 J kg−1 K−1 at 1.8 K for ΔH = 5 T). The ΔSMpk(T) for the compounds 1, 2 and 3 reached 81.8, 88.4 and 100% of the theoretical values, respectively. This suggests that in compound 3 Gd3+···Gd3+ antiferromagnetic interactions are decoupled gradually, and higher fields promote a larger decoupling between the individual spin centers. The observed entropy changes of compounds were comparable with other magnetic refrigerants proposed for low-temperature applications. To study the magnetothermal effect of 2 (the sample with largest −ΔSMpk), the temperature-dependent heat capacities (C) at different fields were measured. The value of magnetic entropy S obtained from heat capacities (39.5 J kg−1 K−1 at 1.8 K for an applied magnetic field change of 5 T) was in good agreement with that derived from the magnetization data (42 J kg−1 K−1 at 1.8 K). [ABSTRACT FROM AUTHOR]