From Cuprate to Nickelate: Evolution of the Normal State Properties with Ni from La1.85Sr0.15CuO4 to La1.85Sr0.15NiO4

The influence of Ni doping on the normal-state pseudogap in La1.85Sr0.15CuO4 is studied by dc magnetic susceptibility measurements, accompanied by X-ray powder diffraction analysis and resistivity measurements. The measurements are carried out on the polycrystalline La1.85Sr0.15Cu1-yNiyO4 samples in the whole doping range from y = 0.01 up to y = 1. The temperature of pseudogap opening is found to decrease above y = 0.05 and to vanish when y exceeds 0.07. At small Ni content, up to y = 0.07, the magnetic moment induced by Ni is constant and equal to 0.7 mu(B) per Ni, while for larger y it increases abruptly and reaches about 1.6 mu(B) per Ni ion for y = 0.5. The dependence of the normal-state resistivity on temperature evolves smoothly from the metallic-like for small y, to the variable range hopping, described by the Mott law with the exponent 1/4, for samples with y > 0.15.