A study of the structural, magnetic and transport properties of the polycrystalline La0.8Pb0.1□0.1MnO3 and La0.8Pb0.1Na0.1MnO3 samples was carried out. The X-ray diffraction showed that both samples crystallize in a rhombohedral structure with the R-3c space group. Ferromagnetic and insulating states were found for the La0.8Pb0.1□0.1MnO3 sample, whereas a ferromagnetic behavior below 247K and insulator–metal transition at 180K were observed for the La0.8Pb0.1Na0.1MnO3 sample. The temperature dependence of magnetic susceptibility at higher temperature for both samples revealed 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 did not reach complete saturation up to a field of 6 T. Moreover, analysis of cell parameters indicated that the structure of La0.8Pb0.1□0.1MnO3 was more distorted than La0.8Pb0.1Na0.1MnO3 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 (measuring the quenched disorder) for La0.8Pb0.1□0.1MnO3 reference to La0.8Pb0.1Na0.1MnO3. This result was in agreement with the enhancement of Griffiths phase characteristics and the low value of the spin stiffness constant D for La0.8Pb0.1□0.1MnO3. Finally, it was shown that the magnitude of the magnetic inhomogeneity depended on the random substitution in the A-site cations.

Effects of Vacancy and Na Doping on the Structural, Magnetic and Transport Properties of La0.8Pb0.1(□/Na)0.1MnO3. A.Tozri, E.Dhahri, E.K.Hlil: Journal of Magnetism and Magnetic Materials, 2010, 322[17], 2516-24