Cool MOFs

Adv. Mater. http://doi.org/f2df2s (2013)

Credit: © 2013 WILEY

Magnetocaloric materials have latterly been the focus of intense research as the basis for efficient refrigeration technologies. By taking advantage of the thermodynamic changes associated with the varying magnetization of a material exposed to a magnetic field, the best magnetocalorics require suitable intrinsic properties that maximize the thermal response associated with the change in magnetization. In this regard, gadolinium is often used as a starting point as it has no orbital angular momentum associated with it, therefore maximizing the entropy for each spin. However, achieving a large bulk magnetocaloric effect requires a careful compromise between maximizing the density of magnetic ions present in a material, yet ensuring they are weakly coupled so that there is no magnetic order when the field is turned off. Now, Marco Evangelisti and colleagues show this can be efficiently done in gadolinium formate (Gd(HCOO)₃), a metal–organic framework (MOF) in which the Gd ions are linked by light formate ligands. The low-temperature magnetocaloric effect they uncover is enormous, and compares favourably to benchmark magnetocalorics such as Gd₃Ga₅O₁₂ (GGG). Cool things may therefore be in store for MOFs.