Ac Susceptibility and Static Magnetization Measurements of   CeRu$_2$Si$_2$ at Small Magnetic Fields and Ultra Low Temperatures
  The magnetic properties of CeRu$_2$Si$_2$ at microkelvin temperatures (down to 170 $\mu$K) and ultra small magnetic fields ($0.02\sim6.21$ mT) are investigated experimentally for the first time. The simultaneously measured ac susceptibility and static magnetization show neither evidence of the magnetic ordering, superconductivity down to the lowest temperatures nor conventional Landau Fermi-Liquid behavior. The results imply the magnetic transition temperature in undoped CeRu$_2$Si$_2$ is very close to absolute 0 K. The possibility for proximity of CeRu$_2$Si$_2$ to the quantum critical point without any doping is discussed. 
D. Takahashi (1), S. Abe (1), H. Mizuno (1), D. A. Tayurskii (1 and   2), K. Matsumoto (1), H. Suzuki (1) and Y. \'Onuki (3)...