Variation of magnetic and transport properties in magnetoresistive oxides La-ln-Pb-Mn-O (Ln=Pr, Nd, Dy, and Y)

This paper presents an investigation on the magnetic and transport properties of perovskite oxides, La/sub 0.7-x/Ln/sub x/Pb/sub 0.3/MnO/sub 3/ (Ln=Pr, Nd, Dy, and Y) in this study. The replacement of La by Pr, Nd, Dy, or Y results in a variation of the magnetization process and magnetoresistance. This fact is in agreement with the smaller ionic radii of Pr, Nd, Dy, and Y ions in contrast to La ion and the difference of electronic configuration and effective moment. The saturation magnetization M/sub S/ increases as the Pr or Nd content increases while M/sub S/ decreases as the Y content increases. Moreover, the saturation magnetization M/sub S/ increases and then decreases as the Dy content increases. These results can be explained in terms of the competition between the increase of ferromagnetically interacting spins due to the introduction of magnetic Pr, Nd, or Dy ions with f-shell electrons and suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cation into the La site. The enhancement of magnetoresistance ratio as well as the increase of resistivity is observed for all systems. The result of double-peaks temperature-dependence resistivity for Dy and Y content systems is different from the result of the rest systems. The variation of electrical property is induced by the grain boundary effect.