Ginzburg–Landau theory for the magnetic and structural transitions in La1−y(Ca1−xSrx)yMnO3

Abstract

We present a phenomenological theory for the ferromagnetic transition temperature, the magnetic susceptibility at high temperatures, and the structural distortion in the La(CaSr)MnO 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 () for .