Spin-glass and spin-fluctuation in Mo-doped Ca3Co4O9 system

Structural, magnetic, resistivity and thermal transport measurements have been performed to study the Mo-doping effect on a layered cobaltite Ca₃Co_4−xMo_xO₉(0≤x≤0.4) system. The results indicate that the low-temperature magnetic behavior of the system changes from a ferrimagnetic state to a spin-glass-like state upon Mo doping, which is due to the decrease in the average valence of Co ions. Moreover, all the Mo-doped samples have a higher resistivity and larger thermopower S compared with the Mo-free sample. The variation in the resistivity and thermopower between the Mo-doped and the Mo-free samples is dominated by the change in the carrier concentration of the samples. In the Mo-doped samples with x≥0.1, both the resistivity and thermopower decrease gradually with increasing Mo-doping level, which is suggested to mainly originate from the variation in the carrier mobility of the samples. In addition, an obvious thermopower upturn is observed in the S(T) curve of all the Mo-doped samples, which can be explained by the enhancement of spin-fluctuation induced by Mo-doping.