Search for quantum criticality in a ferromagnetic system UNi1-xCoxSi2

TL;DR

This study investigates the evolution of magnetic properties in UNi1-xCoxSi2 alloys, revealing a transition from ferromagnetism to spin-glass states and identifying a critical concentration where magnetic order vanishes.

Contribution

It provides the first detailed experimental analysis of quantum criticality in UNi1-xCoxSi2 alloys, highlighting the suppression of ferromagnetism with Co doping.

Findings

Ferromagnetism is suppressed with increasing Co content.

A spin-glass-like state appears near x=0.98.

Magnetic order disappears at x=1, indicating a quantum critical point.

Abstract

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 TC(x) yields a critical concentration xc = 1, at which the magnetic ordering entirely disappears. This finding is in line with preliminary data collected for stoichiometric UCoSi2.