Appearance of Griffiths phase in oxygen deficient La0.4Ca0.6MnO3−δ oxides

The crystal structure and the magnetic properties of polycrystalline La0.4Ca0.6MnO3−δ oxides were studied depending on the concentration of the oxygen vacancies. X-ray diffraction reveals that all samples (0≤δ≤0.2) crystallize in the orthorhombic structure with Pbnm space group. Although vacancies have no effect on the structure of the parent sample, they induce a great variation in the magnetic properties. The parent sample La0.4Ca0.6MnO3 show a paramagnetic behavior at high temperature and a competition between an antiferromagnetic (AFM) and charge ordering (CO) state at low temperature. When we create a deficient of oxygen a magnetic transition from paramagnetic (PM) to ferromagnetic (FM) ordering appears with the temperature decreasing. This fact is explained by the change of Mn3+ and the Mn4+ amounts in the samples. The magnetization measurements reveal features consistent with the appearance of Griffiths phase (GP) in the La0.4Ca0.6MnO2.8 sample.

► Effect of oxygen vacancies on the physical properties of La0.4Ca0.6MnO3-δ oxides. ► Lattice parameters and unit cell volume increase with oxygen deficiency increasing. ► Appearance of paramagnetic—ferromagnetic transition for deficit samples. ► Onset of the Griffiths phase for La0.4Ca0.6MnO2.8 sample.