Effect of pressure and substitution for Yb on the first-order valence transition in YbInCu₄

Single-crystalline samples of YbInCu₄ and its partially substituted compounds by Y and Lu were synthesized by the flux method. The temperature dependence of the magnetic susceptibility from 2 to 320 K in the magnetic field of 0.5 T and the high-field magnetization up to 41 T under various fixed pressures were measured in order to investigate the effect of substitution, inherent chemical pressure, and external pressure on the first-order valence transition of YbInCu₄. Substitution of Yb by Y or Lu results in a small increase or decrease of the lattice parameter, while both systems show a steep decrease of transition temperature (T_v) and transition magnetic field (H_v) with substitution, resulting in suppression of the valence transition around x=0.30 for Yb_1-x Y_xInCu₄ (0≤x≤0.3) and x=0.15 for Yb_1-xLu_xInCu₄ (0≤x≤0.15). The effect of pressure on H_v of the pure and Y-substituted YbInCu₄ is reported by dH_v/dP≈-1 T/kbar, with a suppression of the valence transition of Yb_0.8Y_0.2InCu₄ at the pressure of 8 kbar. The effect of inherent chemical pressure is very small compared with the intrinsic effect of substitution. The decreasing of Kondo temperature T_K (∞1/X₀) below T_v resulting from the substitution for the Yb lattice is discussed as an important factor affecting the valence transition of YbInCu₄.