Ginzburg-Landau theory for the magnetic and structural transitions in La$_{1-y}$(Ca$_{1-x}$Sr$_{x}$)$_{y}$MnO$_{3}$

TL;DR

This paper develops a Ginzburg-Landau phenomenological model to describe magnetic and structural phase transitions in La$_{1-y}$(Ca$_{1-x}$Sr$_{x}$)$_{y}$MnO$_{3}$, capturing the effects of Sr-doping on transition behaviors.

Contribution

It introduces a new Ginzburg-Landau free energy framework that accounts for the competition between magnetic and structural transitions in the manganite system.

Findings

Qualitative agreement with observed phase transitions as a function of Sr-doping.

Derived magnetic parameters from mean-field solutions for arbitrary angular momentum.

Describes the interplay between magnetic and structural distortions.

Abstract

We present a phenomenological theory for the ferromagnetic transition temperature, the magnetic susceptibility at high temperatures, and the structural distortion in the La$_{1-y}$(Ca$_{1-x}$Sr$_{x}$)$_{y}$MnO$_{3}$ system. We construct a Ginzburg-Landau free energy that describes the magnetic and the structural transitions, and a competition between them. The parameters of the magnetic part of the free energy are derived from a mean-field solution of the magnetic interaction for arbitrary angular momentum. The theory provides a qualitative description of the observed magnetic and structural phase transitions as functions of Sr-doping level ($x$) for $y=0.25$.