We report bulk magnetic properties of the monoclinic lanthanide tantalates, M ′ − L n TaO 4 ( L n = Tb, Dy, Ho, Er), where the magnetic L n 3 + ions are arranged on a distorted 2D square lattice. The heavier analog M ′ − YbTaO 4 has been investigated as a spin-orbit-coupled, quasi-two-dimensional frustrated magnet, and the properties of the other M ′ − L n TaO 4 are expected to vary depending on the electronic configuration of the L n ion, namely, Kramers vs non-Kramers behavior and different crystal electric field parameters. In this work, powder neutron diffraction is used to confirm the crystal structure for L n = Tb, Ho, Er, and to determine the magnetic structure of M ′ − TbTaO 4 , which displays long-range antiferromagnetic (AFM) order below T N = 2.1 K . The Tb 3 + moments are aligned primarily along the c axis with AFM nearest-neighbor interactions. Susceptibility data suggest that M ′ − DyTaO 4 may display short-range ordering around 2.7 K, while M ′ − HoTaO 4 and M ′ − ErTaO 4 show AFM correlations but do not order above 1.8 K. Measurements of the magnetic specific heat provide evidence for a Kramers doublet ground state in M ′ − ErTaO 4 , similar to its heavier analog M ′ − YbTaO 4 .
Kelly et al. (Tue,) studied this question.