Saturation of resistivity and Kohler's rule in Ni-dopedLa1.85Sr0.15CuO4cuprate

We present the results of electrical transport measurements of ${\mathrm{La}}_1.85{\mathrm{Sr}}_0.15{\mathrm{Cu}}_{1\ensuremath{-}y}{\mathrm{Ni}}_y{\mathrm{O}}₄$ thin single-crystal films at magnetic fields up to 9 T. Adding Ni impurity with strong Coulomb scattering potential to a slightly underdoped cuprate makes the signs of resistivity saturation at ${\ensuremath{\rho}}_{\mathrm{sat}}$ visible in the measurement temperature window up to 350 K. Employing the parallel-resistor formalism reveals that ${\ensuremath{\rho}}_{\mathrm{sat}}$ is consistent with the classical Ioffe-Regel-Mott limit and changes with carrier concentration $n$ as ${\ensuremath{\rho}}_{\mathrm{sat}}\ensuremath{\propto}1/\sqrt{n}$. Thermopower measurements show that Ni tends to localize mobile carriers, decreasing their effective concentration as $n\ensuremath{\cong}0.15\ensuremath{-}y$. The classical unmodified Kohler's rule is fulfilled for magnetoresistance in the nonsuperconducting part of the phase diagram when applied to the ideal branch in the parallel-resistor model.