Vacancy concentration dependence of magnetotransport properties of selfdoped La1-ΔMnO3+δ thin films

A study is made into self-doped, epitaxial La1-ΔMnO3+δ films prepared on LaAlO3 substrate by employing sol-gel based spin coating method, with varying Δ value from 0.02 across the vacancy solubility limit of 0.1 to 0.35. The resistivity measurements show that the ferromagnetic metallic transition begins to appear when Δ exceeds ≅ 0.045 and the transition temperature increases from 187 K for Δ = 0.045 to 250 K for vacancy solubility limit 0.104 and to the maximum value od 295 K for Δ = 0.295. The maximum magnetoresistance for these films decreases with increasing Tc, consistent with the general rule. From comparison of the Δ vs. Tc relation for these films with the vacancy solubility range from the La2O3-Mn2O3 binary phase diagram, it becomes clear that the excess Δ is necessary to achieve maximum vacancy concentration of 0.1 because of the kinetics rather than thermodynamics reason