K3 Li3 Gd7 (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 extremely low temperatures, for example, for space exploration. Here, we grew a new gadolinium-rich orthoborate K3 Li3 Gd7 (BO3 )9 (1) as a promising cryogenic magnetic coolant. It exhibits a complicated three dimensional framework constructed from BO3 groups and gadolinium-oxygen chains. The Gd-O chain consists of two types of clusters of Gd3 O20 and Gd3 O19 interconnection by Gd(4)O8 polyhydron. Due to its high gadolinium concentration, a large -ΔSm of 56.6 J kg-1  K-1 for 1 was obtained at 2 K and ΔH=7 T, much larger than that of the commercial benchmark Gd3 Ga5 O12 (GGG) crystal (38.4 J kg-1  K-1 ), suggesting it to be an excellent MCE material.