ANISOTROPY OF SUSCEPTIBILITY AND OPTICAL INVESTIGATION OF THE ANTIFERROMAGNETIC PHASE-TRANSITION IN U1-XCEXRU2SI2

Temperature dependence of magnetic susceptibility of U1-xCexRu2Si2 sin gle crystals (x = 0, 0.025, 0.05, 0.075) has been studied at temperatu res from 4.2 K up to room temperature and in magnetic fields applied a long and perpendicular to the c-axis. The attention was paid to anomal ies connected with the antiferromagnetic phase transition, which are p resent in crystals with x less than or equal to 0.05. Far-infrared mea surements of U0.99Ce0.01Ru2Si2 single crystal have been studied for th e first time. The measurements support the assumption that the origin of magnetic ordering in U0.99Ce0.01Ru2Si2 is the same as in heavy-ferm ion superconductor URu2Si2 and can be interpreted as being due to a sp in-density-wave gap.