Magnetic properties of the quasi-XY Shastry-Sutherland magnet Er 2 Be 2 SiO 7

Polycrystalline and single-crystal samples of the insulating Shastry-Sutherland compound ${\mathrm{Er}}_{2}{\mathrm{Be}}_{2}{\mathrm{SiO}}_{7}$ were synthesized via a solid-state reaction and the floating zone method, respectively. The crystal structure, Er single-ion anisotropy, zero-field magnetic ground state, and magnetic phase diagrams along high-symmetry crystallographic directions were investigated with bulk measurement techniques, x-ray and neutron diffraction, and neutron spectroscopy. We establish that ${\mathrm{Er}}_{2}{\mathrm{Be}}_{2}{\mathrm{SiO}}_{7}$ crystallizes in a tetragonal space group with planes of orthogonal Er dimers and a strong preference for the Er moments to lie in the local plane perpendicular to each dimer bond. We also find that this system has a noncollinear ordered ground state in zero field with a transition temperature of 0.841 K consisting of antiferromagnetic dimers and in-plane moments. Finally, we mapped out the $H\text{\ensuremath{-}}T$ phase diagrams for ${\mathrm{Er}}_{2}{\mathrm{Be}}_{2}{\mathrm{SiO}}_{7}$ along the directions $H\ensuremath{\parallel}$ [001], [100], and [110]. While an increasing in-plane field simply induces a phase transition to a field-polarized phase, we identify three metamagnetic transitions in the $H\ensuremath{\parallel}$ [001] case. Single-crystal neutron diffraction results reveal that the $H\ensuremath{\parallel}$ [001] phase diagram can be explained predominantly by the expected field-induced behavior of classical, anisotropic moments, although the microscopic origin of one phase requires further investigation.