Néel Ordering in the Distorted Honeycomb Pyrosilicate: C-Er$_{2}$Si$_{2}$O$_{7}$

Abstract: The rare-earth pyrosilicate family of compounds (RE${2}$Si${2}$O${7}$) 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-Er${2}$Si${2}$O${7}$. C-Er${2}$Si${2}$O${7}$ crystallizes in the C2/m space group and the Er$^{3+}$ atoms form a distorted honeycomb lattice in the $a$-$b$ plane. We have utilized specific heat, DC susceptibility, and neutron diffraction measurements to characterize C-Er${2}$Si${2}$O${7}$. 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 N\'eel state in the magnetic space group C2'/m, with ordered moment of 6.61 $\mu_{B}$ canted 13$^{\circ}$ away from the $c$-axis toward the $a$-axis. These results are discussed in relation to the isostructural quantum dimer magnet compound Yb${2}$Si${2}$O$_{7}$.