Magnetism on the stretched diamond lattice in lanthanide orthotantalates

Abstract

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 ($P{2}_1$${}^{\prime }/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.

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