Magnetic and transport properties of LaCo1-xNixO3-Comparison with La1-xSrxCoO3

We have investigated magnetization, neutron scattering, resistivity, thermoelectric power and Hall effect in LaCo1-xNixO3 (x = 0.05 and 0.1) single crystals. At low temperatures, they show spin-glass behavior with a strong ferromagnetic correlation. Around 500 K, spin state transition from the intermediate spin state (S = 1) to the high spin state (S = 2) accompanied by an insulator-to-metal transition is observed as in undoped LaCoO3. These magnetic proper ties of LaCo1-xNixO3 are very similar to those previously reported for La1-xSrxCoO3. The low-temperature transport properties of both LaCo1-xNixO3 and La1-xSrxCoO3 exhibit the characteristics of an insulator near the insulator-to-metal transition. The sign of the carrier is verified to be positive in both systems from the thermoelectric power measurement. However, the sign of the Hall coefficient of LaCo1-xNixO3 is negative. These transport properties are discussed in terms of small polaron hopping mechanism.