Yb ₂(Pd _1-xNi _x) ₂Sn: Interplay of geometrical frustration and Kondo effect in quantum spin system

Single crystals of Yb ₂(Pd _1-xNi _x)2Sn with × = 0, 0.1, and 0.2 were prepared to clarify the effects of pressure on Yb ₂Pd ₂Sn which is considered to reside near the quantum critical point. The magnetization and specific heat measurements revealed that their ground states are regarded as an S = 1/2 XY-like spin system. Although nondoped Yb ₂Pd ₂Sn shows no magnetic transition down to 0.5 K owing to the Kondo effect, Ni-doped Yb ₂Pd ₂Sn exhibits a distinct magnetic transition. Furthermore, the magnetic susceptibility of Ni-doped Yb ₂Pd ₂Sn exhibits a broad peak in the temperature range higher than the magnetic transition temperature, which is not explained by the S = 1/2 Coqblin-Schrieffer model, suggesting the effect of geometrical frustration arising from the characteristic structure of these compounds, i.e., the Shastry-Sutherland lattice.