The family of derivatives with formula [GdIII4TMII8(OH)8(L)8-(O2CR)8(MeOH)y] (ClO4)4 - where TM = Zn, Cu, Ni, Co - offers an excellent playground for probing the physical phenomenon at the basis of the magnetic refrigeration, known as the magnetocaloric effect (MCE). From magneto-thermal experiments at low temperature, we show how the MCE evolves by introducing either antiferromagnetic or ferromagnetic interactions, or magnetic anisotropy, that is, by replacing the nonmagnetic ZnII with CuII, NiII or CoII, respectively. Counter intuitively, Gd4Cu8 and Gd4Co8 have an overall smaller MCE than Gd4Zn8. In spite of increasing the magnetic density and hence entropy, the inclusion of CuII or CoII ions brings in antiferromagnetic interactions or magnetic anisotropy, which ultimately inhibit the MCE. It turns out that, under the proper experimental conditions, the predominant antiferromagnetic interactions in Gd4Cu8 yield an inverse MCE that is, the temperature increases on lowering the applied magnetic field. The ferromagnetically coupled Gd4Ni8 has the largest MCE, reaching –ΔSm = 23.0 J kg-1 K-1 at T = 3.8 K, for an applied field change ΔB = (7−0) T.

Resumen del trabajo presentado a la 4th EuChemMS Inorganic Chemistry Conference (EICC), celebrada en Copenhague (Dinamarca) del 2 al 7 de julio de 2017.

Peer Reviewed