Theoretical Analysis of the Reduction of Neel Temperature in La$_{2}$(Cu$_{1-x}$Zn(or Mg)$_x)$O$_{4}$

TL;DR

This paper uses theoretical calculations to analyze how nonmagnetic impurities like Zn and Mg reduce the Neel temperature in a layered antiferromagnet, explaining experimental differences through impurity effects on exchange interactions.

Contribution

It introduces a model accounting for impurity-induced reduction in intra-plane exchange couplings to explain experimental differences in Neel temperature suppression.

Findings

Zn reduces exchange coupling by 12%

Mg reduces exchange coupling by 6%

The model explains the difference in suppression rates

Abstract

Using Tyablikov's decoupling approximation, we calculate the initial suppression rate of the Neel temperature, $R_{IS}=-lim_{x-> 0} T^{-1}_{N} dT_{N}/dx$, in a quasi two-dimensional diluted Heisenberg antiferromagnet with nonmagnetic impurities of concentration $x$. In order to explain an experimental fact that $R^{(Zn)}_{IS}=3.4$ of the Zn-substitution is different from $R^{(Mg)}_{IS}=3.0$ of the Mg-substitution, we propose a model in which impurity substitution reduces the intra-plane exchange couplings surrounding impurities, as well as dilution of spin systems. The decrease of 12% in exchange coupling constants by Zn substitution and decrease of 6% by Mg substitution explain those two experimental results, when an appropriate value of the interplane coupling is used.