Rare-Earth Ions on the Shastry-Sutherland Lattice: Determining the Magnetic Ground-States of the Rare-Earth Melilites RE2Be2GeO7 (RE = Yb, Er, Gd, Dy)

Abstract

In this manuscript, the ground-states of the Shastry-Sutherland lattice materials RE2Be2GeO7 (RE = Yb, Er, Gd, and Dy) are determined experimentally. This was achieved through measurements including SQUID magnetometry, powder X-ray and neutron diffraction, specific heat capacity, and muon spectroscopy. Point-charge crystal electric field calculations were also employed. The ground-state of Yb2Be2GeO7 is predicted to be a quantum spin liquid state. This is evidenced by a lack of long-range order to temperatures as low as 17 mK, the detection of short-range spin correlations, and the presence of persistent spin dynamics. Er2Be2GeO7 is shown to have a canted antiferromagnetic ground-state below TN = 860(10) mK. The magnetic space group was determined to be P2121’2’ (18.19). The magnetocrystalline anisotropy is Ising-like. In the ordered state, fractional magnetization plateaus are observed, which are induced via applied field and display thermal hysteresis. These occur with fractions of 1/4, 4/9, and 1/2 of the saturation magnetization. Gd2Be2GeO7 and Dy2Be2GeO7 are both antiferromagnetic with TN ∼ 1 K and exhibit meta- magnetic transitions. Gd2Be2GeO7 has a significant quadratic component to the magnetization in the ordered state, leading to a linearly increasing susceptibility in fields below ∼ 1 T. Dy2Be2GeO7 has a nearly zero susceptibility in low fields (≤ 86(1) mT at 500 mK), which we attribute to Ising anisotropy.