The effect of charge transfer on the transport and magnetic properties induced by Ca substitution in La0.3Ce0.2Sr0.5MnO3

The perovskite manganese oxides La0.3Ce0.2CaxSr0.5-xMnO3 (0 ≤ x ≤ 0.25) have been synthesized by a solid-state reaction, and their transport and magnetic properties have been systemically studied. It is found that the temperature dependent resistivity shows a maximum at Tmax below Curie temperature Tc with temperature decreasing, which is correlated to the Ce3+ spin-dependent scattering. Moreover, Tmax is almost unchanged for x ≤ 0.15, but decreases quickly and is closing on the temperature of Tc while x > 0.15, which indicates the increase of Ce ionic valence. Meanwhile, the saturation magnetic moment Ms decreases with x increasing to 0.15, and increases anomaly when x > 0.15. XANES results reveal that when x ≤ 0.15, the valence of Mn ion is almost unchanged, but when x > 0.15, it obviously shifts from tetravalence to trivalence with Ca substitution. Meanwhile, XPS spectra results indicate the similar trend of Ce valence changing from trivalence to tetravalence. It is suggested that Ca substitution changes not only the chemical pressure, but also the valence of Ce ion. There is a threshold value for the chemical pressure corresponding to Ca- substitution content at around x = 0.15 (or tv = 1.2395 Å), which is the starting point of charge transfer appearance in Ca-substituting La0.3Ce0.2Sr0.5MnO3 compound. The transport and magnetic properties of the half-doped manganties La0.3Ce0.2CaxSr0.5-xMnO3 are dominated by the competition/cooperation of Ce3+ spin-dependent scattering, interaction between Mn ions controlled by A-site ion-size, and the charge transfer from Ce ions to Mn ions.