Magnetic and Transport Properties of LaCo 1-xNixO 3-Comparison with La 1-xSrxCoO 3

We have investigated magnetization, neutron scattering, resistivity, thermoelectric power and Hall effect in LaCo 1- x Ni x O 3 ( 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 LaCoO 3 . These magnetic properties of LaCo 1- x Ni x O 3 are very similar to those previously reported for La 1- x Sr x CoO 3 . The low-temperature transport properties of both LaCo 1- x Ni x O 3 and La 1- x Sr x CoO 3 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 LaCo 1- x Ni x O 3 is negative. These transport properties are discussed in terms of small polaron hopping mechanism.