The phase diagram and magnetic properties of La1-xCaxMnO3 compounds for 0 ≤ x ≤ 0.23

In this paper a detailed study of the La1-xCaxMnO3 (0 less than or equal to X less than or equal to 0.23) phase diagram using powder x-ray diffraction and magnetization measurements is presented. The lack of well characterized samples has resulted in confusion as regards the underlying physics of this complicated system. As the present study reveals, two distinct families of samples exist. The first family consists of samples prepared in an air atmosphere (designated as AP; P(O-2) = 0.2 atm). These are ferromagnetic with their Curie temperatures increasing with x. The second family of samples consists of samples prepared in air and then post-annealed under a reducing nearly zero oxygen partial pressure (designated R). These samples show a canted antiferromagnetic structure for 0 less than or equal to x less than or equal to 0.1 below T-N, while for 0.125 less than or equal to x less than or equal to 0.23 an unconventional ferromagnetic insulated phase is present below T-c. Most probably, the difference between the two families of samples, R and AP, lies in their cation stoichiometries, the AP samples being stoichiometric and the AP samples being non-stoichiometric. The most important difference between AP and R samples is the anisotropy in the exchange interactions of the R samples. This leads us to suggest the possibility that a new orbital ordered phase is responsible for the ferromagnetic insulating regime in the La1-xCaxMnO3 compounds.