K3Li3Gd7(BO3)9: A New Gadolinium-Rich Orthoborate for Cryogenic Magnetic Cooling.

Magnetic cooling technology based on magnetocaloric effect (MCE) has attracted great interest in obtaining extreme low temperature, e. g. for space exploration. Here we grew a new gadolinium-rich orthoborate K3Li3Gd7(BO3)9 (1) as a promising cryogenic magnetic coolant. It exhibits complicated three dimensional framework constructed from BO3 groups and gadolinium-oxygen chains. The Gd-O chain consists of two types of clusters of Gd3O20 and Gd3O19 interconncetion by Gd(4)O8 polyhydron. Thanks to its high gadolinium concentration, a large -Sm for 1 was obtained as 56.6 J kg-1 K-1 at 2 K and H = 7 T, much larger than that of commercial benchmark Gd3Ga5O12 (GGG) crystal (38.4 J kg-1 K-1), suggesting it to be an excellent MCE material.