Ferromagnetic quantum criticality in Sm1-xLaxNiC2 (x=0.85, 0.92, and 0.96)

Abstract

We report μSR experiments on the ternary compounds Sm1-xLaxNiC2 (x=0.85, 0.92, and 0.96), crossing from a ferromagnetic to a superconducting phase. Zero-field μSR measurements of the ferromagnetic sample (x=0.85) unveil a glassylike character of the ferromagnetically ordered state. At the putative quantum critical compound (x = 0.92), fluctuations of the Sm moments slow down below 2 K and remain dynamic down to 30 mK, showing persisting spin dynamics. Moreover, we find a time-field scaling (t/Hγ) of the μSR asymmetry function, evidencing quantum critical fluctuations. As to the superconducting material (x = 0.96), the muon spin-relaxation rate displays a λ-like peak at T=250 mK, indicating the coexistence of weak magnetism and filamentary superconductivity. Our results demonstrate that Sm1-xLaxNiC2 constitutes a model system for studying a ferromagnetic quantum critical point tuned by chemical pressure. © 2017 American Physical Society.