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

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 P (4) over bar2(1)m 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 chi(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 Neel temperature T-N similar to 2.5 K and field-induced spin flop behaviors (T < T-N). In addition, the calculated magnetic entropy change Delta S-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 Delta S-m up to 54.8 J K-1 kg(-1) at Delta H = 7 T and Dy2Be2GeO7 has the largest value Delta S-m = 16.1 J K-1 kg(-1) at Delta H = 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.