The influence of magnetic sublattice dilution on magnetic order in CeNiGe3 and UNiSi2

Polycrystalline samples of the Y-diluted antiferromagnet CeNiGe3 (TN = 5.5 K) and Th-diluted ferromagnet UNiSi2 (TC = 95 K) were studied by means of x-ray powder diffraction, magnetization and specific heat measurements performed in a wide temperature range. The lattice parameters of the Ce1-xYxNiGe3 alloys decrease linearly with increasing Y content, while the unit cell volume of U1-xThxNiSi2 increases linearly with increasing Th content. The ordering temperatures of the systems decrease monotonically with increasing x down to about 1.2 K in Ce0.4Y0.6NiGe3 and 26 K in U0.3Th0.7NiSi2, forming a dome of long-range magnetic order on their magnetic phase diagrams. The suppression of the magnetic order is associated with distinct broadening of the anomalies at TN,C due to crystallographic disorder being a consequence of the alloying. Below the magnetic percolation threshold xc of about 0.68 and 0.75 in the Ce- and U-based alloys, respectively, the long-range magnetic order smoothly evolves into a short-range one, forming a tail on the magnetic phase diagrams. The observed behaviour of Ce1-xYxNiGe3 and U1-xThxNiSi2 is characteristic of diluted magnetic alloys. (paper)