  Rare-earth (RE) based frustrated magnets as typical systems of combining
strong spin-orbit coupling, geometric frustration and anisotropic exchange
interactions, can give rise to diverse exotic magnetic ground states such as
quantum spin liquid (QSL). 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, Gd-Yb) compounds crystallized in a tetragonal
structure, where magnetic RE3+ ions lay out on Shastry-Sutherland lattice (SSL)
within ab-plane and are well separated by nonmagnetic GeBe2O7 polyhedrons along
c-axis. Temperature-dependent susceptibilities 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
TN~ 2.5 K and field-induced spin flop behaviors (T< TN). In addition, the
calculated magnetic entropy change from the isothermal M(H) curves reveal a
viable magnetocaloric effect (MCE) for RE2Be2GeO7 (RE =Gd, Dy) in liquid helium
temperature regimes, Gd2Be2GeO7 shows maximum Sm up to 54.8 J K-1 Kg-1 at H= 7
T and Dy2Be2GeO7 has largest value Sm=16.1 J K-1 kg-1 at H= 2 T in this family.
More excitingly, rich diversity of RE ions in this family enables an archetype
for exploring exotic quantum magnetic phenomena with large variability of spin
located on SSL lattice.
