Effect of substitution of magnetic rare earths for La on the structure, electric transport and magnetic properties of La 2SrFe 2O 7

Abstract

Ln 2SrFe 2O 7, (Ln=La, Nd, Gd and Dy) phases have been prepared by the ceramic method. The powder X-ray diffraction studies show that these phases crystallize with tetragonal unit cell in the space group I 4/ m m m. The unit cell dimensions decrease with substitution of Nd, Gd, and Dy for La, with more pronounced change in c which is attributed to shrinkage of the interlayer distances. Magnetic studies show that the Weiss constant ( θ) increases with substitution of the rare earths in the order Dy>Gd>Nd, which is the result of increase in the inter-layer ferromagnetic interactions due to decrease in c-axis. The Weiss constants suggest that La 2SrFe 2O 7 and Nd 2SrFe 2O 7 are antiferromagnetic, while the Gd and Dy containing phases are ferromagnetic. The increased 3D character in the rare earth substituted phases results in a decrease in the electrical resistivity in the order Dy>Gd>Nd.