Anisotropy of Susceptibility and Optical investigation of the Antiferromagnetic phase Transition in U$\text{}_{1-x}$Ce$\text{}_{x}$Ru$\text{}_{2}$Si$\text{}_{2}$

Temperature dependence of magnetic susceptibility of U$\text{}_{1-x}$Ce$\text{}_{x}$Ru $\text{}_{2}$Si$\text{}_{2}$ single crystals (x=0, 0.025, 0.05, 0.075) has been studied at temperatures from 4.2 K up to room temperature and in magnetic fields applied along and perpendicular to the c-axis. The attention was paid to anomalies connected with the antiferromagnetic phase transition, which are present in crystals with x≤0.05. Far-infrared measurements of U$\text{}_{0.99}$Ce$\text{}_{0.01}$ Ru$\text{}_{2}$Si$\text{}_{2}$ single crystal have been studied for the first time. The measurements support the assumption that the origin of magnetic ordering in U$\text{}_{0.99}$Ce$\text{}_{0.01}$Ru$\text{}_{2}$Si$\text{}_{2}$ is the same as in heavy-fermion superconductor URu$\text{}_{2}$Si$\text{}_{2}$ and can be interpreted as being due to a spin-density-wave gap.