Ferromagnetism ofCeSixat ambient and high pressure

We have made detailed investigations of the structural and magnetic properties of ${\mathrm{CeSi}}_{\mathrm{x}}$ (1.0≤x≤2.0). The homogeneity region of the ${\mathrm{ThSi}}_2$-type (${\mathrm{GdSi}}_2$-type) ${\mathrm{CeSi}}_{\mathrm{x}}$ phase is limited to the Si concentrations x: 1.67≤x≤2.0 and does not extend to the concentration range 1.55≤x≤2.0, as was reported previously. A transformation from the tetragonal ${\mathrm{ThSi}}_2$-type structure to the orthorhombic ${\mathrm{GdSi}}_2$-type structure appears to occur in the ${\mathrm{CeSi}}_{\mathrm{x}}$ system in the same range (1.84<x<1.9) where ferromagnetism appears and the specific-heat coefficient γ passes through a peak. The presence of an unknown stable phase with composition intermediate to ${\mathrm{CeSi}}_{1.0}$ and ${\mathrm{Ce}}_3$ ${\mathrm{Si}}_5$ has been detected. Magnetically ordered ground states have been observed for x≤1.84 and no magnetic or superconducting ordering above 400 mK has been detected for x≥1.90. The present data indicates that magnetism in the ${\mathrm{CeSi}}_{\mathrm{x}}$ system may not be simple ferromagnetic. The experimental behavior of this system appears to be Kondo-lattice-like both at ambient and high pressure.