We have investigated the changes in the magnetic properties on ${\mathrm{YbCuS}}_2$ by Lu or Se substitutions from a microscopic perspective. In general, it is expected that nonmagnetic Lu substitution dilutes the magnetic ${\mathrm{Yb}}^{3+}$ concentration and that Se substitution induces the negative pressure in ${\mathrm{YbCuS}}_2$. The ${}^{63/65}\mathrm{Cu}$-nuclear quadrupole resonance (NQR) measurements on polycrystalline ${\mathrm{Yb}}_{0.9}{\mathrm{Lu}}_{0.1}{\mathrm{CuS}}_2$ and $\mathrm{YbCu}{\left({\mathrm{S}}_{0.9}{\mathrm{Se}}_{0.1}\right)}_2$ revealed that the Se substitution leads to larger lattice expansion compared to the Lu substitution. The antiferromagnetic transition temperature $T_{\mathrm{N}}$ decreased from 0.95 K in the unsubstituted system to 0.75 K in both substituted systems. Furthermore, the $T$-linear behavior of the ${}^{63}\mathrm{Cu}$-NQR spin-lattice relaxation rate $1/T_1$, suggesting the presence of the gapless quasiparticle excitations, was observed even in the substituted systems and the value of $1/T_{1}T$ increases. These results under the chemical substitutions are opposite to those under pressure as previously reported and are consistent with the expectation. Our systematic study indicates a clear relationship between the magnetic ordered states and the quasiparticle excitations in ${\mathrm{YbCuS}}_2$.

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• Magnetic interactions
• Magnetic order
• Magnetism
• Magnetic insulators
• Nuclear magnetic resonance