Néel ordering in the distorted honeycomb pyrosilicate: C-Er₂Si₂O₇

The rare-earth pyrosilicate family of compounds (RE₂Si₂O₇) hosts a variety of polymorphs, some with honeycomb-like geometries of the rare-earth sublattices, and the magnetism has yet to be deeply explored in many of the cases. Here we report on the ground state properties of C-Er₂Si₂O₇. C-Er₂Si₂O₇crystallizes in the C2/m space group and the Er³⁺atoms form a distorted honeycomb lattice in thea-bplane. We have utilized specific heat, DC susceptibility, and neutron diffraction measurements to characterize C-Er₂Si₂O₇. Our specific heat and DC susceptibility measurements show signatures of antiferromagnetic ordering at 2.3 K. Neutron powder diffraction confirms this transition temperature and the relative intensities of the magnetic Bragg peaks are consistent with a collinear Néel state in the magnetic space group C2'/m, with ordered moment of 6.61micro_Bcanted 13° away from thec-axis toward thea-axis. These results are discussed in relation to the isostructural quantum dimer magnet compound Yb₂Si₂O₇.