Simultaneous suppression of ferromagnetism and superconductivity in UCoGe by Si substitution

Abstract

We investigate the effect of substituting Si for Ge in the ferromagnetic superconductor UCoGe. dc-magnetization, ac-susceptibility, and electrical resistivity measurements on polycrystalline $\mathrm{U}\mathrm{Co}{\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Si}}_{x}$ samples show that ferromagnetic order and superconductivity are progressively depressed with increasing Si content and simultaneously vanish at a critical concentration ${x}_{\mathit{cr}}\ensuremath{\simeq}0.12$. The non-Fermi-liquid temperature variation in the electrical resistivity near ${x}_{\mathit{cr}}$ and the smooth depression of the ordered moment point to a continuous ferromagnetic quantum phase transition. Superconductivity is confined to the ferromagnetic phase, which provides further evidence for magnetically mediated superconductivity.