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

Polycrystalline samples of the Y-diluted antiferromagnet CeNiGe(3) (T(N)?=?5.5?K) and Th-diluted ferromagnet UNiSi(2) (T(C)?=?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 Ce(1-x)Y(x)NiGe(3) alloys decrease linearly with increasing Y content, while the unit cell volume of U(1-x)Th(x)NiSi(2) increases linearly with increasing Th content. The ordering temperatures of the systems decrease monotonically with increasing x down to about 1.2?K in Ce(0.4)Y(0.6)NiGe(3) and 26?K in U(0.3)Th(0.7)NiSi(2), 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 T(N,C) due to crystallographic disorder being a consequence of the alloying. Below the magnetic percolation threshold x(c) 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 Ce(1-x)Y(x)NiGe(3) and U(1-x)Th(x)NiSi(2) is characteristic of diluted magnetic alloys.