Effects of vacancy and Na doping on the structural, magnetic and transport properties of La0.8Pb0.1(□/Na)0.1MnO3

Study of structural, magnetic and transport properties of the polycrystalline La0.8Pb0.1□0.1MnO3 (LPMO) and La0.8Pb0.1Na0.1MnO3 (LPNMO) samples has been carried out. The X-ray diffraction shows that both samples crystallize in a rhombohedral structure with the R3¯c space group. Ferromagnetic and insulating states are found for the LPMO sample, whereas a ferromagnetic behavior below 247 K and insulator–metal transition at 180 K are observed for the LPNMO sample. The temperature dependence of magnetic susceptibility at higher temperature for both samples reveals the presence of the Griffiths phase above the Curie temperature. The thermal evolution of magnetization in the ferromagnetic phase at low temperature varies as T3/2, in accordance with Bloch’s law. The magnetization does not reach complete saturation up to a field of 6 T. Moreover, analysis of cell parameters indicates that the structure of LPMO is more distorted than LPNMO whereas additional results from the unit cell volume and the Curie temperature combined with previous results point to a lower average radius 〈rA〉 (the average ionic radius, related to the one-electron bandwidth) and higher variance σrA2 (the variance, measuring the quenched disorder) for LPMO reference to LPNMO. This result is in agreement with the enhancement of Griffiths phase characteristics and the low value of the spin stiffness constant D for LPMO. Finally, we show that the magnitude of the magnetic inhomogeneity depends on the random substitution in the A-site cations.