Magnetic Ground States of the Rare-Earth Tripod Kagome Lattice Mg2RE3Sb3O14 (RE = Gd,Dy,Er)

We present the structural and magnetic properties of a new compound family, Mg2RE3Sb3O14 (RE = Gd, Dy, Er), with a hitherto unstudied frustrating lattice, the "tripod kagome" structure. Susceptibility (ac, dc) and specific heat exhibit features that are understood within a simple Luttinger-Tisza-type theory. For RE = Gd, we found long-ranged order (LRO) at 1.65 K, which is consistent with a 120 degrees structure, demonstrating the importance of diople interactions for this 2D Heisenberg system. For RE = Dy, LRO at 0.37 K is related to the "kagome spin ice" physics for a 2D system. This result shows that the tripod kagome structure accelerates the transition to LRO predicted for the related pyrochlore systems. For RE = Er, two transitions, at 80 mK and 2.1 K are observed, suggesting the importance of quantum fluctuations for this putative XY system.