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

Abstract

Perovskite-type divalent cations substituted rare-earth metal manganese oxides with a formula of Ln_1-xA_xMnO₃ have been extensively investigated during the past forty years, due to their particular electrical and magnetic properties. Followed by the discovery of giant magnetoresistance (GMR), preparations of this class of materials attracted more attentions. However, most of the preparations are concerned to high-temperature solid-state reactions and sol-gel processes. Herein, we report a mild chemical route to these materials. Giant magnetoresistance materials La_0.5A_0.5MnO₃ (A=Ba, Sr, Ca) and La_1-xBa_xMnO₃ (x≥0.5) were hydrothermally prepared and characterized by means of XRD, TG-DTA, SEM, ICP, and iodometry. The system alkalinity and initial molar ratio of Mn(VII)/Mn(II), associated with reaction temperature, were observed dominating the crystallization of the products. Hydrothermal route exhibited obvious advantages in terms of lower synthesis temperature, short reaction time, ready chemical operation for adjusting mixed valence, and high purity and crystallinity of products.