Disorder effects near a magnetic instability in CePtSi1−xGex (x=0, 0.1)

Abstract

The magnetic susceptibility and nuclear magnetic resonance $(\mathrm{NMR})$ linewidth have been measured in the heavy-fermion alloys ${\mathrm{CePtSi}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$, $x=0$ and $0.1$, to study the role of disorder in the non-Fermi-liquid $(\mathrm{NFL})$ behavior of this system. The theoretical $\mathrm{NMR}$ line shape is calculated from disorder-driven $\mathrm{NFL}$ models and shows the same essential features as the observed spectra. Analysis of $^{29}\mathrm{Si}$ and $^{195}\mathrm{Pt}$ $\mathrm{NMR}$ linewidths strongly suggests the existence of locally inhomogeneous susceptibility in both materials, and agrees with the widths of the local susceptibility distributions estimated from the susceptibility fits to the disorder-driven $\mathrm{NFL}$ models. Disorder-driven mechanisms can also explain the $\mathrm{NFL}$ behavior in ${\mathrm{CePtSi}}_{0.9}{\mathrm{Ge}}_{0.1}$; the $\mathrm{NMR}$ spectra do not, however, distinguish between the Kondo-disorder and Griffiths phase models. We find that stoichiometric $\mathrm{CePtSi}$ and $\mathrm{Ge}$-doped ${\mathrm{CePtSi}}_{0.9}{\mathrm{Ge}}_{0.1}$ show similar degrees of magnetic disorder, although a narrower distribution of local susceptibilities in $\mathrm{CePtSi}$ allows Fermi-liquid behavior to appear below $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The residual resistivity reported in $\mathrm{CePtSi}$ is relatively large, which indicates a significant level of intrinsic lattice defects and seems to be consistent with the disorder observed in the $\mathrm{NMR}$ spectra.