Effect of suppression of local distortion on magnetic, electrical and thermal transport properties of Cr substituted bi-layer manganite LaSr$_{2}$Mn$_{2}$O$_{7}$

TL;DR

This study explores how Cr substitution in LaSr$_{2}$Mn$_{2}$O$_{7}$ affects its magnetic, electrical, and thermal properties, revealing suppressed local distortions and altered magnetic behaviors.

Contribution

It demonstrates that Cr doping suppresses local lattice distortions and modifies magnetic and transport properties in LaSr$_{2}$Mn$_{2}$O$_{7}$, providing new insights into impurity effects.

Findings

Cr doping induces glassy magnetic behavior.

Electrical resistivity increases with Cr content.

Thermal conductivity rises despite impurity introduction.

Abstract

We have investigated magnetic, electrical and thermal transport properties (Seebeck effect and thermal conductivity) of LaSr$_{2}$Mn$_{2-y}$Cr$_{y}$O$_{7}$ polycrystalline samples ($y$=0.1, 0.2, 0.4 and 0.6). The Cr$^{3+}$ substitution for Mn$^{3+}$ sites causes a removal of $d_{x^2-y^2}$ orbital of $e_g$-electron resulting in a volume shrinkage of 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 temperature, while it suppresses a local minimum of thermoelectric power at lower temperatures. The phonon thermal conduction gradually rises with increasing Cr content, which is contradictory 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 Cr$^{3+}$.