Nested antiferromagnetic spin fluctuations and non-Fermi-liquid behavior in electron-doped CeCo1-xNixIn5

We investigate the electronic state of Ni-substituted CeCo1-xNixIn5 by nuclear quadrupole and magnetic resonance (NQR/NMR) techniques. The heavy fermion superconductivity below Tc=2.3 K for x=0 is suppressed by Ni substitutions, and Tc reaches zero for x=0.25. The In115 NQR spectra for x=0.125 and 0.25 can be explained by simulating the electrical field gradient that is calculated for a virtual supercell with density functional theory. The spin-lattice relaxation rate 1/T1 indicates that Ni substitution weakens antiferromagnetic correlations that are not localized near the substituent but instead are uniform in space. The temperature (T) dependence of (T1T)-1 for x=0.25 shows a maximum around Tg=2 K and (T1T)-1 decreases toward almost zero when temperature is further reduced as if a gap might be opening in the magnetic excitation spectrum; however, the magnetic specific heat and the static magnetic susceptibility evolve smoothly through Tg with a -lnT dependence. The peculiar T dependence of (T1T)-1 and non-Fermi-liquid specific heat and susceptibility can be interpreted in a unified way by assuming nested antiferromagnetic spin fluctuations in a quasi-two-dimensional electronic system.