NONLINEAR SUSCEPTIBILITY IN HEAVY-FERMION COMPOUNDS CERU2SI2 AND CE1-XYXRU2SI2 (X-LESS-THAN-OR-EQUAL-TO-0.1)

We report linear and non-linear susceptibility measurements performed on three single crystals of the heavy fermion compound CeRu2Si2. For t he easy magnetization axis (H parallel (parallel-to) to the c-axis of tetragonal structure), the linear susceptibility, chi1(parallel-to), o f CeRu2Si2 shows the previously reported rounded maximum near 11 K. Ne w results are the existence of a non-linear susceptibility, chi3(paral lel-to), which shows a shallow dip near 25 K and a peak near 6 K. Thes e two temperatures can be related to T(K) and to the saturation of ant iferromagnetic correlation lengths, respectively. Similarly chi3(paral lel-to) is observed in Ce1-xY(x)Ru2Si2 (x = 0.015, 0.05 and 0.1). This observation of non-linear susceptibility raises the question of the p ossible existence of quadrupolar interactions in CeRu2Si2, like in oth er classical rare-earth compound.