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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]

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]