Search for quantum criticality in a ferromagnetic system UNi1-xCoxSi2

Polycrystalline samples of the isostructural alloys UNi1-xCoxSi2 (0 <= x <= 1) were studied by means of x-ray powder diffraction, magnetization, electrical resistivity, and specific-heat measurements, at temperatures down to 2 K and in magnetic fields up to 5 T. The experimental data revealed an evolution from strongly anisotropic ferromagnetism with pronounced Kondo effect, observed for the alloys with x < 0.98 and being gradually suppressed with rising Co content, to spin-glass-like states with dominant spin fluctuations, seen for the sample with x = 0.98. Extrapolation of the value of T-C(x) yields a critical concentration x(c) = 1, at which the magnetic ordering entirely disappears. This finding is in line with preliminary data collected for stoichiometric UCoSi2.