The magnetic properties of the Zn-substituted overdoped high-$T_c$ superconductor ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{Cu}}_{1-y}{\mathrm{Zn}}_y{\mathrm{O}}_4$ have been studied by magnetization measurements and neutron scattering. Magnetization measurements reveal that for Zn-free samples with $x⩾0.22$ a Curie term is induced in the temperature dependence of the magnetic susceptibility implying the existence of local paramagnetic moments. The induced Curie constant corresponds to a moment of $0.5{\mu }_B$ per additional ${\mathrm{Sr}}^{2+}$ ion that exceeds $x=0.22$. Zn substitution in the overdoped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ also induces a Curie term that corresponds to $1.2{\mu }_B$ per ${\mathrm{Zn}}^{2+}$ ion, simultaneously suppressing $T_c$. The relationship between $T_c$ and the magnitude of the Curie term for Zn-free ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ with $x⩾0.22$ and for Zn-substituted ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ with $x=0.22$ are closely similar. This signifies a general competitive relationship between the superconductivity and the induced paramagnetic moment. Neutron scattering measurements show that Zn substitution in overdoped ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ anomalously enhances the inelastic magnetic scattering spectra around the $(\pi ,\pi )$ position, peaking at $\omega \sim 7\mathrm{meV}$. These facts are discussed on the basis of a “swiss-cheese” model of Zn-substituted systems as well as a microscopic phase separation scenario in the overdoped region indicated by muon-spin-relaxation measurements.

• Received 21 March 2005

DOI:https://doi.org/10.1103/PhysRevB.72.064521