Structure and Magnetic Properties of Melilite-Type Compounds RE2Be2GeO7 (RE = Pr, Nd, Gd–Yb) with Rare-Earth Ions on Shastry–Sutherland Lattice

Abstract

Rare-earth (RE)-based frustrated magnets, such as typical systems of combining strong spin–orbit coupling (SOC), geometric frustration, and anisotropic exchange interaction, can give rise to diverse exotic magnetic ground states such as quantum spin liquid. The discovery of new RE-based frustrated materials is crucial for exploring the exotic magnetic phases. Herein, we report the synthesis, structure, and magnetic properties of a family of melilite-type RE₂Be₂GeO₇ (RE = Pr, Nd, and Gd–Yb) compounds crystallized in a tetragonal P4̅2₁m structure, where magnetic RE³⁺ ions lay out on the Shastry–Sutherland lattice (SSL) within the ab plane and are well separated by nonmagnetic [GeBe₂O₇]^6– polyhedrons along the c-axis. Temperature (T)-dependent susceptibilities χ(T) and isothermal magnetization M(H) measurements reveal that most RE₂Be₂GeO₇ compounds except RE = Tb show no magnetic ordering down to 2 K despite the dominant antiferromagnetic (AFM) interactions, where Tb₂Be₂GeO₇ undergoes AFM transition with Néel temperature T_N ∼ 2.5 K and field-induced spin flop behaviors (T < T_N). In addition, the calculated magnetic entropy change ΔS_m from the isothermal M(H) curves reveals viable magnetocaloric effect for RE₂Be₂GeO₇ (RE = Gd and Dy) in liquid helium temperature regimes; Gd₂Be₂GeO₇ shows the maximum ΔS_m up to 54.8 J K^–1 kg^–1 at ΔH = 7 T and Dy₂Be₂GeO₇ has the largest value ΔS_m = 16.1 J K^–1 kg^–1 at ΔH = 2 T in this family. More excitingly, the rich diversity of RE ions in this family enables an archetype for exploring exotic quantum magnetic phenomena with large variability of spin located on the SSL lattice.