A Mild Chemical Route to Giant Magnetoresistance Materials: Hydrothermal Preparation and Characterization of Divalent Cations Substituted Lanthanum Manganese Oxides

Abstract

A series of giant magnetoresistance materials La_0.5A_0.5MnO₃ (A=Ba, Sr, Ca) was hydrothermally prepared at 240°C for 1∼3 days and characterized by powder X-ray diffraction, scanning electron microscope, iodometry, and DC four-terminal method. The alkalinity and molar ratio of Mn(VII)/Mn²⁺ in the initial reaction mixture, associated with hydrothermal reaction temperature, dominate the crystallization of the products. The SEM images of the as-prepared La_0.5Sr_0.5MnO₃ indicated that the product is cubic crystal about 2-5 μm, and the La_0.5Ba_0.5MnO₃ is cubic crystal about 100-500 nm. The average valence state of manganate in all the products is 3.5.