Anomalous scaling behavior of the dynamical spin susceptibility of Ce_(0.925)La_(0.075)Ru₂Si₂

Inelastic neutron scattering measurements have been performed on single crystals of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$ in broad energy [0.1, 9.5 meV] and temperature [40 mK, 294 K] ranges in order to address the question of scaling behavior of the dynamical spin susceptibility at the quantum critical point of an itinerant magnetic system. For two wavevectors $\mathbf{Q}$ corresponding to uncorrelated and antiferromagnetically correlated spin fluctuations, it is found that the dynamical spin susceptibility $\chi''(\mathbf{Q},E,T)$ is independent of temperature below a cut-off temperature $T_{\mathbf{Q}}$: the spin fluctuation amplitude saturates at low temperatures contrarily to its expected divergence at a quantum critical point. Above $T_{\mathbf{Q}}$, a $\mathbf{Q}$-dependent scaling behavior of the form $T\chi''(\mathbf{Q},E,T) = C_{\mathbf{Q}}f[E/(a_{\mathbf{Q}}T^{\beta_{\mathbf{Q}}})]$ with $\beta_{\mathbf{Q}}<1$ is obtained. This scaling does not enter the general framework of quantum phase transition theories, since it is obtained in a high temperature range, where Kondo spin fluctuations depend strongly on temperature.