La $_{1-y}$（Ca $_{1-x}$ Sr $_{x}$）$_{y}$ MnO $_{3}$的磁性和结构转变的Ginzburg-Landau理论
Ginzburg-Landau theory for the magnetic and structural transitions in La$_{1-y}$(Ca$_{1-x}$Sr$_{x}$)$_{y}$MnO$_{3}$
摘要：
提出了La $_{1-y}$（Ca $_{1-x}$ Sr $_{x}$）$_{y}$ MnO $_{3}$体系铁磁转变温度、高温磁化率和结构畸变的唯象理论.我们构建了一个描述磁性和结构转变的Ginzburg-Landau自由能，以及它们之间的竞争。自由能的磁性部分的参数来自于任意角动量的磁相互作用的平均场解。该理论提供了一个定性的描述所观察到的磁性和结构相变的Sr掺杂水平（$x$）为$y=0.25$的功能。
英文摘要：
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 $y=0.25$.
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