Magnetism on the stretched diamond lattice in lanthanide orthotantalates

TL;DR

This study investigates the magnetic properties of lanthanide orthotantalates with a stretched diamond lattice, revealing antiferromagnetic order in TbTaO$_4$ and potential for exotic magnetic states in other compounds.

Contribution

It provides the first detailed magnetic characterization of fergusonite orthotantalates with a stretched diamond lattice, highlighting TbTaO$_4$'s antiferromagnetic order and suggesting exotic states in others.

Findings

TbTaO$_4$ orders antiferromagnetically at 2.25 K

No magnetic order observed in other studied materials

Potential for exotic magnetic states at temperatures below 2 K

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 ($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.