Magnetic properties of the quasi-XY Shastry-Sutherland magnet Er_2Be_2SiO_7

Polycrystalline and single crystal samples of the insulating Shastry-Sutherland compound Er_2Be_2SiO_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 by bulk measurement techniques, x-ray and neutron diffraction, and neutron spectroscopy. We establish that Er_2Be_2SiO_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 non-collinear 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-T phase diagrams for Er_2Be_2SiO_7 along the directions H ∥ [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 before the field-polarized phase is established in the H ∥ [001] case. This complex behavior establishes insulating Er_2Be_2SiO_7 and other isostructural family members as promising candidates for uncovering exotic magnetic properties and phenomena that can be readily compared to theoretical predictions of the exactly soluble Shastry-Sutherland model.