Phase diagram and magnetic properties of La$_{1-x}$Ca$_x$MnO$_3$ compound for $0\leq x \leq 0.23$

Abstract

In this article a detailed study of La$_{1-x}$Ca$_x$MnO$_3$ ($0\leq x \leq 0.23$) phase diagram using powder x-ray diffraction and magnetization measurements is presented. Unfortunately, in the related literature no properly characterized samples have been used, with consequence the smearing of the real physics in this complicated system. As the present results reveal, there are two families of samples. The first family concerns samples prepared in atmosphere ($P({\rm O}_2)=0.2$ Atm) which are all ferromagnetic with Curie temperature rising with $x$. The second family concerns samples, where a post annealing in nearly zero oxygen partial pressure is applied. These samples show a canted antiferromagnetic structure for $0\leq x \leq 0.1$ below $T_N$, while for $0.125\leq x <0.23$ an unconventional ferromagnetic insulated phase is present below $T_c$. The most important difference between nonstoichiometric and stoichiometric samples concerning the magnetic behavior, is the anisotropy in the exchange interactions, in the stoichiometric samples putting forward the idea that a new orbital ordered phase is responsible for the ferromagnetic insulating regime in the La$_{1-x}$Ca$_x$MnO$_3$ compound.