Contrasting Ni- and Zn-substitution effects on magnetic properties and superconductivity inLa2−xSrxCuO4

Both Ni- and Zn-substitution effects on superconducting and magnetic properties of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ were studied by measuring the magnetic susceptibility χ and the electronic specific heat $C_{\mathrm{el}}$ at $T\ll T_c.$ In Ni-substituted samples with $x>~0.14,$ the local nature of the spin correlation among $3d$ spins remains almost unchanged even on Ni sites at low Ni concentrations, where Ni atoms are substituted as ${\mathrm{Ni}}^{3+}$ ions. On the other hand, in Zn-substituted samples the $3d$-spin correlation is seriously disturbed on host Cu sites around each Zn site. The depression of $T_c$ and the residual γ value at $T\ll T_c$ indicate that the suppression of the superconductivity in Zn-substituted samples is much stronger than that in ${\mathrm{Ni}}^{3+}$-substituted ones. The suppression of the superconductivity in the ${\mathrm{Ni}}^{3+}$-substituted samples can be understood in the context of a potential scattering of the Cooper pairs in a d-wave superconductor. On the other hand, the strong suppression of the superconductivity in the Zn-substituted samples will occur through the local disturbance of the $3d$-spin correlation on host Cu sites around each Zn ion.