Anomalous scaling behavior of the dynamical spin susceptibility of Ce₀.₉₂₅La₀.₀₇₅Ru₂Si₂

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Inelastic neutron scattering measurements have been performed on single crystals of the heavy fermion compound Ce₀.₉₂₅La₀.₀₇₅Ru₂Si₂ 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 Q corresponding to uncorrelated and antiferromagnetically correlated spin fluctuations, it is found that the dynamical spin susceptibility χ''(Q,E,T) is independent of temperature below a cut-off temperature TQ: the spin fluctuation amplitude saturates at low temperatures contrarily to its expected divergence at a quantum critical point. Above TQ, a Q-dependent scaling behavior of the form Tχ''(Q,E,T) = CQf[E/(aQTβQ)] with βQ<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.