Electrical, magnetic and magnetotransport properties of Na and Mo doped Ca3Co4O9 materials

Abstract

We report the electrical, magnetic and magnetotransport properties of Na and Mo dual doped Ca_3−2xNa_2xCo_4−xMo_xO₉ (0 ≤ x ≤ 0.15) polycrystalline samples. The results indicate that the strength of ferrimagnetic interaction decreases with increase in doping, as is evident from the observed decrease in Curie temperatures (T_C). The substitution of non-magnetic Mo⁶⁺ ions (4d⁰) in CoO₂ layers and the presence of oxygen vacancies are responsible for decrease in ligand field strength, which results in an enhanced magnetization in the low doped x = 0.025 sample due to a change from the low spin to partial high spin electron configuration. The electrical resistivity of samples exhibits a semiconducting-like behavior in the low temperature range, a strongly correlated Fermi liquid-like behavior in the intermediate temperature range, and an incoherent metal-like behavior in the temperature range 210–300 K. All the samples show a large negative magnetoresistance (MR) at low temperature with a maximum MR value of −59% for the x = 0.025 sample at 2 K and 16 T applied field. The MR values follow the observed trend in magnetization at 5 K and sharply increase below the Curie temperatures of the samples, suggesting that the ferrimagnetic interactions are mainly responsible for the decrease in electrical resistivity under an applied magnetic field.