Investigations of the Magnetocaloric and Thermal Expansion Properties of the Ln3(adipate)4.5(DMF)2 (Ln = Gd–Er) Framework Series

The development of sustainable and efficient cryogenic cooling materials is currently the subject of extensive research with the aim of relieving the dependence of current low temperature cooling methods on expensive and non-renewable liquid helium. One potential method to achieve this is the use of materials demonstrating the magnetocaloric effect where the cycling of an applied magnetic field leads to a net cooling effect due to changes in magnetic entropy upon application and removal of an external magnetic field. This study details the synthesis and characterisation of a Ln3(adipate)4.5(DMF)2 series (where Ln = Gd-Er) of Metal-Organic Framework (MOF) materials incorporating a flexible adipate ligand and their associated magnetocaloric and thermal expansion properties. The magnetocaloric performance of the Gd3(adipate)4.5(DMF)2 material was found to exhibit the highest magnetic entropy changes of the series with a peak entropy change of 36.4 J kg-1 K-1 for a 5-0 T field change at a temperature of 2 K which is suited for ultra-low temperature cooling applications. Thermal expansion properties were also investigated within these materials demonstrating modest negative and large positive thermal expansion identified along the different crystallographic axes within the MOF structures over a 100-300 K temperature range that demonstrated the novel mechanical properties of these adipate framework structures.