Magnetism on the stretched diamond lattice in lanthanide orthotantalates

The magnetic Ln\(^{3+}\) 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 \(M\)-LnTaO\(_4\) (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) are synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. TbTaO\(_4\) orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with \(\vec{k}=0\), 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