Abstract
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).
Highlights
Magnetic properties of three variants of metal-organic frameworks (MOFs)-76(Gd), {[Gd(BTC)(H2O)]·G}n (BTC = benzene1,3,5-tricarboxylate, G = guest molecules) were investigated by static susceptibility, isothermal magnetization and specific heat capacity measurements
The magnetocaloric effect (MCE) can be described as the change of the magnetic entropy and adiabatic temperature in response to a change in the applied magnetic field and can be exploited for magnetic refrigeration in a process known as adiabatic demagnetization[4,5]
Magnetic studies suggest the presence of ferromagnetic couplings between the intrachain Gd(III) ions and large magnetocaloric effects (MCEs) with −ΔSmax = 32 J.kg−1.K−1 (MOF-76(Gd)-DMF), 41 J.kg−1.K−1 (MOF-76(Gd)) and 38 J.kg−1.K−1 (MOF-76(Gd)-H2O) under 5 T applied field
Summary
Different kinds of gadolinium-based materials have attracted interest for MCE, including discrete molecules multinuclear metal clusters (molecular nanomagnets) or materials with extended structures (1D → 3D) with ΔSm values from 1.9 to 50.1 J.kg−1.K−1 under applied field change of 7 T6–11. One subgroup of materials with 3D extended structures www.nature.com/scientificreports are metal-organic frameworks (MOFs), known as porous coordination polymers These materials perform superior functional properties and application potential in gas storage, separation, heterogeneous catalysis[12,13,14,15,16,17,18,19,20,21,22], while their magnetocaloric characteristics have rarely been scrutinized[23,24,25]. This compound combines the qualities of isolated paramagnetic Gd3+ centers and the robust framework with strong covalent bond connections in the three dimensions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
