Dilution of 2D antiferromagnetism by Mn site substitution in La{_1}Sr{_2}Mn{_{2-x}}Al{_x}O{_7}

TL;DR

This study investigates how substituting Al for Mn in La{_1}Sr{_2}Mn{_2-x}Al{_x}O{_7} weakens 2D antiferromagnetic order, alters magnetic and electronic properties, and fits experimental data to theoretical models.

Contribution

It provides new insights into the effects of Al substitution on magnetic interactions and electronic conduction in bilayered manganites, highlighting the short-range Heisenberg behavior.

Findings

Antiferromagnetic transition temperature decreases with Al substitution.

Resistivity increases due to weakened double exchange.

Magnetic specific heat fits a gapped Fermi surface model.

Abstract

We report the effect of Al substitution on the Mn site of the bilayered half doped manganite La{_1}Sr{_2}Mn{_2}O{_7}. This substitution dilutes the magnetically active Mn-O-Mn network without introducing an appreciable distortion in the lattice and ionic considerations leads to a predominant reduction of Mn{^{4+}} with increasing Al. The rate of fall of the long range antiferromagnetic transition temperature as a function of substitution is seen to match well with established quasi 2D Heisenberg systems indicating that the nature of magnetic interactions in this quasi 2-D system is of the short range Heisenberg type. The magnetic contribution of the specific heat estimated using Fisher's relation could be fitted with a function incorporating the presence of a gapped Fermi surface appropriate for this type of systems. The resistivity was seen to increase as a function of substitution due to the weakening of the double exchange within the ferromagnetic layers of these A type of antiferromagnets and justifiably, in the paramagnetic region the data could be fitted to Mott's equation for the variable range hopping of polarons in 2 dimensions.