Magnetism on the stretched diamond lattice in lanthanide orthotantalates

Abstract

The magnetic Ln3+ ions in the fergusonite and scheelite crystal structures form a distorted or stretched diamond lattice which is predicted to host exotic magnetic ground states. In this study, polycrystalline samples of the fergusonite orthotantalates M-LnTaO4 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) are synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. TbTaO4 orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with k = 0, magnetic space group 14.77 (P2_1'/c) and Tb moments parallel to the a-axis. No magnetic order was observed in the other materials studied, leaving open the possibility of exotic magnetic states at T < 2 K.