Effect of suppression of local distortion on the magnetic, electrical, and thermal transport properties of the Cr-substituted bilayer manganite LaSr2Mn2O7

Abstract

We have investigated magnetic, electrical, and thermal transport properties (Seebeck effect and thermal conductivity) of LaSr2Mn2-yCryO7 polycrystalline samples (y=0.1, 0.2, 0.4, and 0.6). The Cr3+ substitution for Mn3+ sites causes a removal of dx2-y2 orbital of eg electron, resulting in a volume shrinkage of the lattice. Magnetic measurements reveal the appearance of a glassy behavior for Cr-doped samples, accompanied by both a collapse of the A-type antiferromagnetic structure and the growth of ferromagnetic clusters. Cr-doping effect on electrical transport strongly enhances an insulating behavior over a wide range of temperatures, while it suppresses a local minimum of thermoelectric power at lower temperatures. For all polycrystalline samples with Cr substitution, the variable-range-hopping conduction model gives a reasonable fit to both resistivities and Seebeck coefficients. The phonon thermal conduction gradually rises with increasing Cr content, which is in contrast to a typical impurity effect on thermal conductivity. We attribute this to a suppression of local lattice distortion through the introduction of Jahn-Teller inactive ions of Cr3+. © 2005 The American Physical Society.